ID: nht74-2.13

DATE: 09/30/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Nabors Trailers, Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your August 21, 1974, question whether a "logging pole trailer", which consists of a beam to which an axle-mounted bolster can be clamped at different points to accomodate different log lengths, qualifies as a heavy hauler trailer as that term is defined in Standard No. 121, Air brake systems:

"Heavy hauler trailer" means a trailer with one or more of the following characteristics:

(1) Its brake lines are designed to adapt to separation or extension of the vehicle frame; or

(2) Its body consists only of a platform whose primary cargo-carrying surface is not more than 40 inches above the ground in an unloaded condition, except that it may include sides that are designed to be easily removable and a permanent "front-end structure" as that term is used in @ 393.106 of this title.

This also acknowledges receipt of your September 5 and September 17, 1974, letters on the same subject.

The logging pole trailer you describe is a heavy hauler trailer, and as such, Standard No. 121 does not apply to this trailer until September 1, 1976. The beam or "reach", together with the bolster, constitutes the frame of the trailer, and the brake lines are designed to adapt to extension of the bolster element along the beam.

This arrangement differs from the standard highway van which has a one-piece frame with an adjustable tandem axle. The purpose of this sliding arrangement is unrelated to an extension of the frame itself to accomodate the transportation of heavy or oversize loads.

Yours truly,

ATTACH.

NABORS TRAILERS, INC.

Sept. 17, 1974

Sidney Williams -- National Highway Traffic Safety Administration

Dear Mr. Williams:

It should be of interest and concern to the National Highway Traffic Safety Administration that we have not had the sight nor the specifications nor the price of a brake equipped axle assembly that can be certified to meet the requirements of Federal Motor Vehicle Safety Standard 121. We are wholly dependent upon the one source for our brake axle assemblies. From that source we have been told that they have encountered one delay after another in their program to develop and test brakes that will meet the new requirements. Their best hope now is that by the end of October they will be able to give us technical information and sometime in November they will be able to begin shipping certifiable brakes.

The same situation prevails with respect to wheel and drum assemblies. Our supplier of drums have told us that they are conducting tests now and that they should be able to tell us in November what drums will be required for compliance with the new Safety Standard.

You can guess from this information the predicament in which we find ourselves when trailers that we put into production in December scheduled for completion in January will be required by law to be in compliance with SS 121. We are certain that there are many other trailer manufacturers who are dependent upon the same sources of supply that we are who are in the same predicament. There may be other sources of supply for brake axle assemblies and for wheels and drums who are ready to describe and certify their products to meet the new Safety Standard, but we, for one, could not at this time get in schedule with new suppliers.

Sincerely yours, B. H. Smith -- President

NABORS TRAILERS, INC.

Sept. 5, 1974

Sidney Williams -- National Highway Traffic Safety Administration

Dear Mr. Williams:

On November 15, 1973 I sent a collection of our pole trailer catalogs and of photographs of logging pole trailers in service to the Truck Trailers Manufacturers Association in Washington. I thought that these had been sent over to your offices. Perhaps they never did get there. My letter went to Mr. M. L. Higgins who at that time was handling these matters for TTMA, and very shortly after that he resigned and Mr. Burt Weller took his place.

With this letter I am sending you two each of our Catalog 196 and our Form 198 describing our standard types of pole trailers.

The logging pole trailers described in Catalog 196 are those about which we are primarily concerned with respect to MVSS 121. Those trailers are designed and used exclusively in logging operations and move logs from the woods to the saw mills or to storage areas. Logging pole trailers are subjected to unbelievably difficult conditions, or at least unbelievable to those who have never witnessed difficult logging operations. Maintaining brakes and lights on logging pole trailers when the very minimum of equipment is used is difficult and often impossible. When the hardware that is required for compliance with MVSS 121 is added to braking equipment as now being used, the difficulties of maintenance will be multiplied and the likelihood that the brakes will be kept operational is reduced.

On the inside of Catalog 196 you will see good views of the rear assembly of our two popular models, the Logmaster and the SPR. These two trailers are identical in capacity and in usage, and the two models are built simply because some loggers like one type and some like the other. In both models you will see that the rear bolster sits on a frame that sits on the two-spring suspension that sits on the axles. A pole or drawbar connects the front bolster assembly to the rear assembly. The rear assembly can slide along the pole to change the distance between the front and rear bolsters to accommodate various log lengths. If you look closely you will see that the rear assembly is locked into place on the pole by means of clamping collors around the coupling pole ahead of and behind the rear assembly. Also, for safety purposes a pin is dropped through the pole at the rear to avoid the possibility that the trailer might slide off the pole.

You will see in the illustrations that the two hoses for the brakes and the cable for the lighting on the rear assembly are connected to the truck or to the front bolster assembly at the front and are connected to the rear assembly at the rear with quick detachable couplings. You will see that when the distance between the bolsters is relatively short these brake and light lines must be coiled up and supported by the pole. If the trailer should be extended in length, the full length of these lines would be required. It is a characteristic of these trailers that the brake lines are designed to adapt to permitting the distance between the front and rear bolsters to contract and to expand.

Another common practice in the use of logging pole trailers is to load the rear frame assembly on the back end of the truck when the trailer and truck are being carried unloaded back into the woods. This practice is for both economic and safety reasons. When the rear assembly is loaded on the truck the brake lines must be disconnected. Also, no part of the brake system can extend below the bottom of the axles because the axles must rest on the truck frame or on the runners that are put on the truck frame to carry the trailer.

When you look closely at these pictures of these logging pole trailers you will observe that the space between the axles and the load-carrying bolster is limited and is filled with equipment with current types of brakes. The trailers shown have only one air reservoir. In order to comply with MVSS 121 another larger air reservoir will have to be added. There simply is no place to put it on these logging pole trailers without interfering severely with their intended usage. If in addition to this other air reservoir we must add spring-loaded power chambers and the valves and logic boxes and electrical connections required for the anti-skid brake system, it is up to now inconceivable to us how to add that hardware in such a way that it could reasonably be expected to stay on the trailers when they are used in the log woods.

The Models TP and TPC Pole Trailers illustrated in our Form 198 are designed and used primarily for hauling pipe and poles and reinforcing rods and long steel beams and other, long and self-supporting objects. The same difficulties in adding the anti-skid brake equipment and the spring loaded power chambers apply to these trailers as to the logging pole trailers. However, since these two models are used primarily on improved roads the difficulties of maintaining the equipment would not be as great. Trailers of these two models constitute no more than perhaps 50 units a year for us. They do have the same characteristic of logging pole trailers in that the brake lines are designed to be adapted to permitting the distance between the front and rear bolsters to change. There would be the same difficulties on these trailers in getting the speed of brake application and release that there would be on other pole trailers.

I can understand the difficulty of writing an exemption for any one class or category of trailers without letting the exemption be subject to unintended interpretations. However, it has seemed to me since we first became concerned with the problems of MVSS 121 that pole trailers as defined in Part 371.3 of the Federal Motor Vehicle Safety Standards could be exempted without any reasonable misunderstandings. Pole trailers as defined in Part 371.3 were exempted from the requirements of MVSS 108 and have been exempted from certification requirements. I have not understood why they could no also be exempted from MVSS 121, and I think that their categorical exemption would be beneficial rather than detrimental to the highway safety program. I have made all of these statements previously in letters to the National Highway Traffic Safety Administration and to the Truck Trailer Manufacturers Association.

We appreciate very much your consideration of our problems and I thank you again for your telephone call on September 3rd in response to our letter of August 21st.

If it might be helpful to giving you and others concerned a better understanding of our problems, which we think are shared by many others, I would be willing to come to Washington for a conference.

Sincerely yours, B. H. Smith -- President

Enclosures

NABORS TRAILERS, INC.

August 21, 1974

Sidney Williams -- National Highway Traffic Safety Administration

Subject: FMVSS 121 - Air Brake Systems, Docket #74-10, Notice 5

Dear Mr. Williams:

We are unable to determine from the subject Notice 5 and from the discussions and considerations that preceded it whether or not it is the intention of NHTSA that Logging Pole Trailers be considered "Heavy Hauler Trailers" within the definition of that category.

In one way of looking at it nearly all Logging Pole Trailers come within Characteristic (1) of the definition because the brake lines are designed to adapt to permitting the rear frame assembly of the pole trailer to slide on the pole or drawbar and thereby to adapt to extension or contraction of the effective length between the load bearing members. In another way of looking at it, pole trailers would not come within Characteristic (1) because there is no actual separation or extension of the vehicle frame. Actually, in pole trailers there is no frame as such connecting the front and rear load bearing members.

The one consistent and definitive characteristic of pole trailers, as we understand them, is that they consist of a front bolster that rests on the towing tractor and a rear bolster that rests on the trailer suspension and axles with the two connected with a pole on which the rear assembly can slide forward and backward.

In some logging operations the length between the front and rear bolsters is changed frequently, maybe daily. In some operations the length between the bolsters is changed only as the species or types of logs being hauled change. In some operations, on every unloaded trip the rear assembly is moved forward on the pole and is loaded on the truck to be hauled back into the woods. Since logging conditions and practices require different effective lengths between the front and rear bolsters and different problems with respect to the brake lines, practically all of our Logging Pole Trailers are rigged out with quick disconnectors for the brake and light lines at the rear assembly, and to that extent the rigging is similar to that on extendable platform trailers. The difficulties of maintaining good air line connections and unrestricted flow of air are certainly as great on pole trailers as on extendable frame trailers.

There are other inherent problems in applying and maintaining brakes on Logging Pole Trailers that in our opinion should be considered before there is a requirement upon trailer manufacturers to add anti-skid devices, spring loaded power chambers, dual or triple air reservoirs, and the other hardware that goes with the system. For example, up to now we have not been able to devise a way to put spring loaded power chambers on the axles of Logging Pole Trailers without swinging them under the axles. We definitely do not have sufficient clearance for putting the spring loaded power chambers over the axles with the suspensions and construction that we are using now. To put the (Illegible Word) chambers under the axles on pole trailers that are destined for the logging woods is, in our opinion, impracticable. The operators will not be able to keep the power chambers in place. The net result will be that they will knock them off or take them off the trailers and run the trailers without brakes. We run into similar but not insoluble problems with respect to installing additional air reservoirs and all of the other wiring and hardware required in an anti-skid system, but the trailers will have to be redesigned, they will be made substantially more expensive, and they will be less suited to their purpose.

Opinions have been expressed that we should simply assume that the definition of Heavy Hauler Trailers does embrace Logging Pole Trailers and that we should bother ourselves and our customers no more about the problem. We are not willing to leave it there because we cannot afford to be found in violation of the law and to be required to go back and add equipment which we did not furnish when the trailers were built. If we must put the anti-skid equipment on Logging Pole Trailers we must be getting ready for it in our designs and in our production methods, and we must be preparing our customers for the added cost and for the maintenance problems that will be inevitable.

Pole Trailers make up hardly more than 1% of the truck trailers that are manufactured. According to the Bureau of the Census Industrial Report for May, 1974, 189 pole trailers were shipped in May 1974, 214 in April 1974, and 177 in May 1973. For ourselves, the total volume in pole trailers is less than 300 units per year, but that is a substantial portion of our total volume and we are one of the largest suppliers of such trailers to the Southern lumber industry. Could you tell me exactly where we stand with respect to Logging Pole Trailers and MVSS 121?

Sincerely yours, B. H. Smith -- President

ID: nht74-2.14

DATE: 09/30/74

FROM: R. B. Dyson; NHTSA

TO: Royal Industries

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your August 28, 1974, question whether a "logging pole trailer", which consists of a beam to which an exle-mounted bolster can be clamped at different points to accommodate different log lengths, qualifies as a heavy hauler trailer as that term is defined in Standard No. 121, Air brake systems:

"Heavy hauler trailer" means a trailer with one or more of the following characteristics:

(1) its brake lines are designed to adapt to separation or extension of the vehicle frame; or

(2) Its body consists only of a platform whose primary cargo-carrying surface is not more than 40 inches above the ground in an unloaded condition, except that it may include sides that are designed to be easily removable and a permanent "front-end structure" as that term is used in @@393.106 of this title.

The logging pole trailer you describe is a heavy hauler trailer, and as such, Standard No. 121 does not apply to this trailer until September 1, 1976. The beam or "reach", together with the bolster, constitutes the frame of the trailer, and the brake lines are designed to adapt to extension of the bolster element along the beam.

ID: nht74-2.15

DATE: 03/20/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Kelsey-Hayes Company

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your February 1, 1974, request for interpretation of the language "maximum temperature of 500 +/- 50 degrees F" appearing in S6.1.8.1 of Standard No. 121, Air brake systems, 49 CFR 571.121.

The language is intended to specify a temperature range within which to conduct the burnishing procedure in the event brake applications cause the hottest brake on a vehicle to reach 500 degrees F. The word "maximum" is inappropriate and will be deleted in an upcoming notice responding to petitions that raised the same point.

Yours truly,

ATTACH.

KELSEY-HAYES COMPANY

February 1, 1974

National Highway Traffic Safety Administration, U. S. Department of Transportation,

Attention: Lawrence Schneider -- Chief Counsel

RE: Request for Interpretation FMVSS-121; Air Brake Systems Docket 73-13; Notice 3 @ 6.1.8.1 Brake Burnish Procedure

Gentlemen:

We would appreciate an interpretation of the following sentence which appears in the above cited section of Standard 121:

"If during any of the brake applications specified in Table IV, the hottest brake reaches 500 degrees F, make the remainder of the 500 applications from that speed except that a higher or lower speed shall be used as necessary to maintain a maximum temperature of 500 degrees F +/- 50 degrees F."

We believe the meaning of this sentence to be that the temperature of a brake may not exceed 550 degrees F at any time during a brake application and that the speed limitations specified in Table IV may be waived to maintain the temperature below 550 degrees F only if the temperature of the hottest brake reaches 500 degrees during any stop.

We are puzzled by the words ". . . maintain a maximum of 500 degrees F +/- 50 degrees F", as the tolerance appears to be inappropriate if our interpretation is correct. Conversely, if the intent is to limit the temperature range to 500 degrees F +/- 50 degrees F once a temperature of 500 degrees F is reached, the word "maximum" is inappropriate.

A prompt reply would be very much appreciated.

Very truly yours,

John F. McCuen -- Attorney

cc: W. T. Birge; D. Renner

ID: nht74-2.16

DATE: 11/14/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Hall and Myers

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your October 23, 1974, question whether the language of S5.3.1(b) and S5.3.2(b) in Standard No. 121, Air brake systems, exempts all liftable, nonsteerable axles from the "no lockup" requirements of the standard. You specifically ask whether a liftable, nonsteerable "tag" axle and "pusher" axle would be exempt if they were both mounted on a vehicle equipped with a single nonliftable, nonsteerable axle or with tandem nonliftable, nonsteerable axles.

The sections in question permit "lockup of wheels on nonsteerable axles other than the two rearmost nonliftable, nonsteerable axles on a vehicle with more than two nonsteerable axles." This language is limited to vehicles which have more than two nonsteerable axles and therefore a liftable axle on a vehicle with only one other nonsteerable axle would not be exempt. Such combination can be found on some intercity buses.

In both of the examples you described the vehicle has more than two nonsteerable axles, and therefore the language of S5.3.1(b) and S5.3.2(b) would exempt the tag and pusher axles from the "no lockup" requirements of the standard. I would like to emphasize, however, that our language is intended to require "no lockup" performance on not less than two nonsteerable axles of any vehicle with at least two nonsteerable axles. We did not contemplate the unlikely configuration of a single fixed axle and two liftable axles which you cite as an example. If a safety problem arises with this configuration, we would consider an amendment of the standard to require "no lockup" performance of two of these axles.

Yours truly,

ATTACH.

ID: nht74-2.17

DATE: 08/12/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Walter Case

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your June 13, 1974, request for approval of your "park-lock" device under the parking brake system requirements of Standard No. 121, Air brake systems, 49 CFR @ 571.121. After a trailer's emergency air supply applies the brakes through the service brake chamber in response to a low service brake air supply, your device locks the brakes in the applied position.

The relevant provision of the standard states:

S5.6.3 Application and holding. The parking brakes shall be applied by an energy source that is not affected by loss of air pressure or brake fluid pressure in the service brake system. Once applied, the parking brakes shall be held in the applied position solely by mechanical means.

The arrangement described would not meet this requirement because the energy source to apply the brakes (the emergency air supply) would be affected by loss of air pressure in the service brake system. For example, any failure in the service brake piston diaphragm would cause a loss of air pressure that would in turn "affect" the energy source that applies the parking brake. The brake chamber housing assembly is an element which is not considered to be part of the service brake system for this requirement.

Standard No. 121 does not specify the design of brake system components. Therefore we neither approve nor disapprove the use of particular components like the "park-lock" device. It may be used in any parking brake system which meets the requirements of the standard.

I would like to point out that the standard becomes effective January 1, 1975, for trailers, and that it does not regulate air brake systems on trailers manufactured before that date.

Yours truly,

ATTACH.

June 13, 1974

Larry Schneider -- Chief Counsel National Highway Admn.

Dear Mr. Schneider:

This is being written at the suggestion of Mr. Sid Williams, made to me during a telephone conversation only a few minutes ago.

I am the inventor of a brake locking device for air brake system equipped trailers. This device which weighs barely two pounds has been pronounced by leaders of the Motor Freight industry as the greatest safety device offered the industry in thirty-five years.

Some eight or so weeks ago, B. F. Goodrich Company examined and tested this brake lock and informed us of their intention to use it on their new safety systems, these being readied for market. This followed careful examination of the requirements for complying with NVSS 121 by both B. F. Goodrich and ourselves.

Our device does not alter the regular braking system in any manner. This brake lock works in conunction with the long required and approved Reserve Emergency Valve and trailer emergency air supply system. With the improved (modulated) RE 4 Valve plus our (Park-Lock) brake holding device, safety involving trailers has been increased many fold whether on the highway, parking lot or at the loading dock.

Should the service brake air supply be broken intentionally or by accident the trailer emergency air supply would take over and bring the vehicle to a stop. In such an instance, the Park-Lock would lock the set brakes automatically when the air pressure dropped to 20 lbs.

We submit that our brake locking device meets all requirements of NVSS 121 and of particular reference to (e) paragraph of Div. 12-369-26508 which prompted B. F. Goodrich's bringing to our attention they had been informed there was some question about Park-Lock meeting one requirement. The question concerns a brake chamber diaphragm failure.

Conversations with two large Motor Freight Companies (Transcon - E.T.M.F.) answered our inquiry this way: Concerning failure or malfunction of a diaphragm was, according to their records the rarest of their problems. The only maintenance reports are that of slow leaks reported by the driver. Neither Company could recall a burst diaphragm. In the event of such leak there is a warning device in the cab calling such to the driver's attention.

Particular care was given to explain to us that should the service system fail, the trailers system would be activated by the RE 4 Valve and the vehicles would be brought to a stop, even with a leak in a diaphragm.

Should the trailer system malfunction, the tractor system, protected by the tractor protection valve, would provide the necessary braking power to bring the vehicles to a safe stop. Either way, they emphasize, adequate braking is there to bring vehicles to a stop and all that is really needed for safety is a satisfactory brake lock to fit the tried and proven system now in use.

The Park-Lock brake lock has been proven in regular service for over a year. It is small enough to hold in your hand. The device is simple of construction, has three moving parts making for little wear, or requirement of maintenance.

We will appreciate your careful examination and checking out of our claims. The same, we are confident, can be said for the industry who has hailed our safety device.

Sincerely yours, Walter Case -- PARK-LOCK, INC.

ID: nht74-2.18

DATE: 06/07/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Certain-Teed Products Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your April 5, 1974, question whether S5.6.1 or S5.6.2 of Standard No. 121, Air brake systems, requires parking brakes on all axles other than front steerable axles.

S5.6.1 requires "parking brakes on an axle other than a steerable front axle" to have certain static retardation force values. "An axle" refers to any axle other than steerable front axles and therefore S5.6.1 requires parking brakes on all axles other than steerable front axles. A tandem axle consists of two separate axles for purposes of this requirement.

S5.6.2 has no specific axle-by-axle requirements. Its performance standard may be met by any means which hold the vehicle stationary and conform to S5.6.3 and S5.6.4. It should be emphasized that this requirement cannot be met simply be equipping the vehicle with parking brakes which hold to the limit of tractive ability but permit vehicle movement.

Yours truly,

ATTACH.

CERTAIN-TEED PRODUCTS CORPORATION

April 5, 1974

Chief Council -- National Highway Traffic Safety Adm., U.S. Department of Transportation

RE: Federal Vehicle Motor Safety Standards No. 121-Air Brake System Docket No. 74-10; Notice 1

Dear Sir:

We are requesting clearification of Paragraph S. 5.6.1 and S. 5.6.2.

Is the intent of Paragraph S. 5.6.1 to require parking brakes on all axles other than a steerable front axle, and is a tandum axle from the viewpoint of this regulation considered to be made up of two (2) separate axles?

In Paragraph S. 5.6.2, is it necessary to have parking brakes on each axle of the vehicle, or would a vehicle be acceptable if parking brakes mounted on only a portion of the axle were adequate to meet the grade holding requirements.

There appears to be questions in the minds of vehicle manufacturers, who are our customers, as to whether a trailer or a truck and bus with a modulated emergency system would require parking brakes on all non-steerable axles or whether only a portion of the axle requires parking brakes. We would appreciate an early reply to this inquiry.

Yours very truly,

B. D. Sibley -- Chief Product Engineer, Brake Products

ID: nht74-2.19

DATE: 10/22/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Truck Trailer Manufacturers Assoc.

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of September 4, 1974, in which you ask several questions regarding the possible manufacture of semitrailers designed to transport people. You state the semitrailers would be pulled by conventional tractors, would have air-operated bus-type side doors, a rear door for emergency exit, seats, handrails for passengers who stand, and windows that open and close. Communication between the passenger compartment and driver would be limited to a horn that the driver can blow and a blinking red light operable by either a passenger or the driver. You ask whether this type of vehicle is legal, whether it is legal to transport passengers in this fashion, and what specific requirements would be required to be built into the trailer.

We would consider the vehicles in question to be trailers under the Motor Vehicle Safety Standards, and consequently subject to the standards applicable to trailers. These standards are Standard No. 108, "Lamps, reflective devices, and associated equipment," Standard No. 106, "Brake hoses" (eff. as to trailers on September 1, 1975), and Standard No. 121, "Air brake systems" (eff. as to trailers on January 1, 1975), at this time. The trailers would, of course, have to be certified as conforming to all applicable standards, in accordance with the Certification Regulations (49 CFR Parts 567, 568).

Many States prohibit the transportation of passengers in trailers, and as a consequence NHTSA requirements for crashworthiness and occupant protection have not been made applicable to trailers. These requirements include those for restraint and seating systems, glazing materials, head restraints, and emergency exits. Whether or not State laws prohibiting the transportation of passengers in trailers would apply to semitrailers of this type would depend upon each State's interpretation of its law, and that information should be obtained from the various states. However, should it become a commonly permitted practice for persons to be transported in trailers, this agency would very likely expand its occupant protection and crashworthiness requirements through rulemaking to apply to these vehicles.

The transportation in interstate commerce of passengers for hire also falls within the regulatory authority of the Bureau of Motor Carrier Safety, in the Federal Highway Administration. We have forwarded your letter to that agency, requesting that it respond directly to you regarding the effect of regulations it administers on vehicles of this type.

Yours truly,

ATTACH.

Truck Trailer Manufacturers Association

September 4, 1974

James B. Gregory -- National Highway Traffic Safety Administration, Department of Transportation

Dear Dr. Gregory:

A member company is currently evaluating the possibility of manufacturing semitrailers which are detachable from the tractor, that are specifically designed to transport people or personnel. These trailers would be pulled over the Federal highways and would be pulled by a detachable conventional tractor. The trailers would be more or less conventional construction with the following basic specifications:

(1) The trailer would have an air operated bus type side door operated off the tractor air brake system.

(2) The trailer would have a rear door for emergency exit that could be operated from the inside.

(3) The trailer would be equipped with seats and handrails for those passengers standing up.

(4) The trailer would be equipped with windows that could be opened and closed.

(5) There would be no communication between the passenger compartment and driver compartment other than a horn that the driver can blow and a blinking red light that can be operated from either the interior of the trailer or the interior of the tractor.

Specifically, is this type of vehicle legal or is it legal to haul passengers over the highway with a detachable semitrailer of this type, and if it is legal what are the specific requirements that have to be built into the trailer?

We would appreciate receiving your thoughts on this matter.

Sincerely yours,

Burt Weller -- Engineering Manager

ID: nht74-2.2

DATE: 03/08/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Certain-Teed Products Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your January 25, 1974, question whether failure of a "common" clampband assembly on the "Camtite" emergency and parking spring brake, which would cause complete loss of air to the service brake system and failure of the emergency/parking brake portion of one unit, would be in violation of paragraph S5.7.2.2 of Standard 121.

The answer is no. S5.7.2.2 requires that failure of components common to the service and emergency braking systems shall not result in a loss of air that causes the parking brake to be inoperable. We interpret "parking brake" to mean the entire parking brake system. The failure you describe would not render the entire system inoperable, because all parking brakes other than the affected unit would remain operable.

This letter will be placed in the public file for the information of other interested persons.

Yours truly,

ATTACH.

CERTAIN-TEED PRODUCTS CORPORATION

January 25, 1974

Administrator -- National Highway Traffic Safety Administration, U. S. Department of Transportation

Re: Federal Motor Vehicle Safety Standard No. 121 - Air Brake Systems

Dear Sir:

We have been questioned by a customer for an interpretation as to the conformance of our CAMTITE emergency and parking spring brake design, as described in the attached brochure, to Paragraph S5.7.2.2., EMERGENCY BRAKING SYSTEM FAILURE, of FMVSS 121. This paragraph states:

"In the event of a failure of a valve, manifold, brake fluid housing, or brake chamber housing that is common to the service brake and emergency braking systems, loss of air shall not cause the parking brake system to be inoperable."

The service brake portion of our Camtite is "sectioned" in white and the emergency or parking spring brake portion in black on the Dimensional Drawing page of the enclosed brochure (SB-102). The clampband (Item #12 on the Parts List page) is common to both the service and emergency/parking brake portion of the unit.

We would appreciate a reply to the question: "Would failure of the "common" clampband assembly during a service brake application which could cause both loss of air and the complete "disengagement" of the service brake pressure side, as well as the total emergency/parking spring brake portion of the unit, be in violation of the intent of paragraph S5.7.2.2. of FMVSS 121?".

Very truly yours,

C. W. Mohr -- Vice President-Marketing

[Graphics omitted]

[Graphics omitted] REPLACEMENT PARTS NUMBER ITEM DESCRIPTION QTY. TYPE 24 TYPE 30 TYPE 36 1 Cylinder Assembly 1 47-31737-9 -- 47-40108-9 2 Piston Assembly 1 47-31797-9 -- 47-40093-9 3 Felt Wiper Ring 1 47-31805-9 -- -- 4 Piston Seal Ring 1 47-31799-9 -- -- 5 Seal Ring 1 36-524615 -- -- 6 Nylon Bushing 1 47-31745-9 -- -- 7 Bulkhead Seal Ring 1 47-31800-9 -- -- 8 Retaining Ring 1 47-31804-9 -- -- 9 Bulkhead 1 47-31747-9 47-31738-9 47-40095-9 10 Machine Screw 1 47-36161-9 -- -- 11 Follower 1 47-31785-9 -- -- 12 Clamp Band Assembly 1 40-31061-9 40-31062-9 40-31063-9 13 Self Tapping Screw 2 47-40012-9 -- -- 14 Diaphragm 1 40-31251-9 40-31165-9 40-31252-9 15 Return Spring 1 47-31258-9 -- -- 16 Non Pressure Plate 1 47-31364-9 47-31267-9 47-40098-9 17 Filter 1 47-31971-9 -- -- 18 Stop Washer 1 47-31974-9 -- -- 19 Snap Plug 1 47-31975-9 -- -- 20 Release Bolt 1 47-31970-9 - 47-40105-9 21 Capscrew 8 46-31656-9 -- -- 22 Spring (Light) 1 41-31920-9 -- -- Spring (Medium) 1 41-31921-9 -- -- Spring (Heavy) 1 41-31922-9 -- -- Spring (Booster) 1 47-40112-9 -- -40101 Push Rod (8.00 Proj.) 1 47-36034-9 47-31986-9 47-40102-9 Spring Locator 1 47-40191-9 -- --

NOTE: The symbol -*- indicates part is identical to part number listed in first column. Parts that differ are listed under appropriate type number. Parts shown are for complete units.

DIMENSIONAL DRAWING REFERENCES

A. AIR INLET ORIENTATION STANDARD 22 1/2 degrees +/- 3 degrees

B. CLAMP BAND ORIENTATION STANDARD 45 degrees +/- 3 degrees C. PUSH ROD PROJECTION (See back page)

D. YOKE CENTER PROJECTION (See back page)

CAMTITE

NOMINAL SPRING FORCES (OUTPUT OF COMPLETE UNIT)

[Graphics omitted]

CAMTITE

SPRING RELEASE PRESSURE NOMINAL RELEASE SPRING TYPE PRESSURE +/- 10% BOOSTER 30 LIGHT (40) 40 MEDIUM (50) 51 HEAVY (60) 62 MEDIUM PLUS 81 BOOSTER HEAVY PLUS 91 BOOSTER

NOTE: FOR EASE OF INSTALLATION ALL UNITS ARE SHIPPED IN MECHANICALLY RELEASED POSITION.

[Graphics omitted]

PUSH ROD AND YOKE SIZES

PUSH ROD PROJECTION:

Push Rod Projection is the Distance the Push Rod Extends Out from the Mounting Face of the CAMTITE Chamber. When Replacing Service Brakes with CAMTITE Chambers, the Push Rod Projection Length will Remain the Same. CAMTITE Standard Projection Length is 1-3/4" TYPE OF PROJECTIONS PART CHAMBER AVAILABLE NUMBER 24 1-3/4" (Std.) 47-31512-9 24 8" 47-36034-9 30 1-3/4" (Std.) 47-31511-9 30 8" 47-31986-9 36 1-3/4" (Std.) 47-40101-9 36 8" 47-40102-9

Other projections available upon special request.

(Illegible Word) ASSEMBLIES:

CAMTITE Yoke Assemblies are Available and may be Ordered as Complete Assemblies Containing Yoke, Yoke Pin, and Cotter Pin, or the Assembly Components May be Ordered Separately.

For Special Applications Requiring the Yoke to be Applied at Factory the Dimension from the Mounting Surface of the CAMTITE Chamber to Center Line of the Yoke Pin Should Be Specified.

[Graphics omitted] ASSEMBLY DIMENSIONS PART NUMBER 1 2 3 4 D 1-3/ 40360479 1-27/32" 1/2" 9/16" 8" 3" 1-3/ 40360489 1-3/4" 5/8" 9/16" 8" 3" 13/ 1-3/ 40360499 1-7/8" 3/4" 16" 8" 3"

**Figures for "O" Represent Standard Dimension Using Push Rods with 1-5/4" Projection.

ID: nht74-2.20

DATE: 05/13/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: American Trailers, Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your April 12, 1974, question whether a permanently attached steerable axle on a trailer is required (1) to meet the S5.3.2 stopping distance requirement with no uncontrolled lockup of any wheel above 10 mi/h, and (2) to meet the parking brake requirements for trailer converter dollies or for all other vehicles.

The answer to your first question is yes. The steerable axle(s) of any trailer must meet the stopping distance requirements of S5.3.2 with no uncontrolled lockup of wheels above 10 mi/h.

In answer to your second question, the permanently attached steerable axle you describe is not a separate vehicle which would qualify as a trailer converter dolly. Therefore the axle is simply part of a trailer which must meet the parking brake requirements of either S5.6.1 or S5.6.2. Neither of these options specifies that there be parking brakes on steerable axles, although in satisfaction of S5.6.2 (grade holding), the manufacturer could utilize parking brakes on the steerable axle.

Yours truly,

ATTACH.

April 12, 1974

James B. Gregory -- Administrator, National Highway Traffic Safety Administration

Dear Sir:

We manufacture a complete line of semi-trailers. Among these is a doubles grain trailer setup. In this doubles grain setup the lead trailer is a 24 foot, single axle semi-trailer which connects to the truck-tractor by means of a standard kingpin. The second trailer is a two axle, four wheel type of trailer, 21 foot long, which is connected to the lead trailer by means of a pintle hook-lunette eye attachment. The front axle on the second trailer is part of a dolly, which is steerable, and is permanently attached to the trailer by means of a bolted 360 degrees turntable.

Our question is one of interpretation. Is the front axle dolly a "converter dolly" in the sense that it would be exempt from having "antilock" and spring brakes as outlined in S5.8 of standard 121? Or is it to be classed so that it will require anti-lock and spring brakes? Your expeditious answer as to interpretation is appreciated.

Sincerely, Al Zajic -- Project Engineer, AMERICAN TRAILERS, INC.

Encl:

(Graphics omitted)

LEAD TRAILER

SECOND TRAILER

PERMANENT 360 DEGREES TURNTABLE

ID: nht74-2.21

DATE: 08/12/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: B. F. Goodrich Aerospace and Defense Products

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your June 4 and June 20, 1974, letters asking if a parking brake system which locks mechanically after the brake is applied by any emergency air supply acting through the service air brake chamber would comply with Standard No. 121, Air brake systems. The parking brake provisions require in part:

S5.6.3 Application and holding. The parking brake shall be applied by an energy source that is not affected by loss of air pressure or brake fluid pressure in the service brake system. Once applied, the parking brakes shall be held in the applied position solely by mechanical means.

The arrangement described would not meet this requirement because the energy source to apply the brakes (the emergency air supply) would be affected by loss of air pressure in the service brake system. For example, any failure in the service brake piston diaphragm would cause a loss of air pressure that would in turn "affect" the energy source that applies the parking brakes. The brake chamber housing assembly is an element which is not considered to be part of the service brake system for this requirement.

I would like to point out that the provisions of Standard No. 121 do not apply to trailers manufactured before January 1, 1975.

Your truly,

ATTACH.

June 4, 1974

CHIEF COUNCIL -- U. S. Department of Transportation National Highway Traffic Safety Administration

Dear Sirs:

The following inquiry is submitted to you with regards to telephone conversations with Mr. S. F. Williams on Friday afternoon, May 31, 1974, and Monday morning June 3, 1974.

Will MVSS 121 permit actuation of a mechanically locking parking and/or emergency brake, using air that is applied to the service brake diaphragm?

The air is supplied, of course, from an isolated emergency source.

Yours truly, B. F. GOODRICH ENGINEERED SYSTEMS COMPANY A Division of The B. F. Goodrich Company;

A. J. Burt -- Sales Engineer

CC: S. F. Williams, D.O.T.; R. D. Buehler, B. F. Goodrich, Washington D. C.; C. R. Collins, B. F. Goodrich, Springfield, Virginia

B. F. Goodrich Aerospace and Defense Products

June 20, 1974

S. F. WILLIAMS -- U. S. Department of Transportation, National Highway Traffic Safety Administration

Dear Sid:

Relative to our phone conversation this afternoon, attached is a copy of all the technical information we have concerning the Park-Lock brake.

The Park-Lock people that we talked to in February of this year were Mr. Joe D'Angelo and Mr. Paul Mantle.

I should note that my inquiry to the Chief Council dated June 4, 1974 and copied to you, is meant to be interpreted as a generalized question concerning the use of a service brake diaphragm. The "mechanically locking parking and/or emergency brake" was not meant to refer specifically to the "Park Lock" device, but any general device which would require actuation by emergency air applied to a service brake diaphragm, and then mechanically locking once the actuation stroke is completed.

Yours truly,

A. J. Burt -- Sales Engineer, Highway Products

CC: R. D. Buehler -- B. F. Goodrich, Washington, D.C.; C. R. Collins -- B. F. Goodrich, Springfield, Virginia

Park-Lock

(Illegible Word) PARK LOCK?

Park Lock is an Automatic Brake Holding Device that holds your brakes, once applied . . . A New Friend to the Trucks.

WHAT DOES PARK LOCK DO?

Park Lock prevents trailer roll offs; climinates wheel chocking; prevents release of brakes when service system air pressure is below safe operating level.

HOW IS PARK LOCK APPLIED?

In emergency conditions, such as loss of air, the Relay Emergency Valve applies your brakes. . . As the air leaks off, Park Lock gently applies, automatically, and holds your brakes by mechanical means.

HOW IS PARK LOCK RELEASED?

There are two ways to release Park Lock.

1. With the application of air, Park Lock releases automatically.

2. By mechanical means. No special wrench is required. Pliers, screw-driver or coin can be used.

IS PARK LOCK SAFE?

Park Lock is a true safety device. Any child can dismantle it without danger (no explosion hazard).

DOES PARK LOCK WORK ON EQUIPMENT PRESENTLY IN USE?

(Units in service prior to S-121 and September 1, 1974)

Park Lock can be installed on all trailers, new and used. The Relay Emergency Value and air tank, currently on all trailers, applies your brakes. Park Lock holds your brakes mechanically, thus preventing trailer roll-offs.

IS PARK LOCK DURABLE?

The Park Lock casting is made of especially treated aluminum, for long, tough wear. Park Lock has four movable parts that include a special brake rod. Park Lock is mounted on your present brake chamber and plumbed into the Relay Emergency Value. Installation is easy and simple. The Park Lock weighs about two pounds.

PARK LOCK AND S-121 (After September 1, 1974)

Park Lock passes all requirements under S-121, pertaining to both parking brakes and emergency brakes for your trailers. It is used in conjunction with a Relay Emergency Value and air tank (same tank used under S-121 to release the spring brake).

Park Lock works in conjunction with your New Anti-Skid Braking System and allows you to come to a complete anti-skid stop. This is accomplished by plumbing the air (emergency mode) back through the anti-skid computer valve.

Park Lock can be released from the tractor cab by the same method used to release the spring brake. As required by S-121, Park Lock has a manual release that can be released from the unit.

HOW DOES PARK LOCK SAVE YOU MONEY?

Park Lock eliminates trailer roll-off accidents. This will reduce insurance claims. . . thus reduce insurance premiums.

Park Lock virtually eliminates replacement costs. There are few moving parts.

The sole function of Park Lock is to hold your brakes, once applied; therefore there is virtually no wear on the units.

Park Lock requires very little maintenance, which eliminates down time.

Park Lock eliminates wheel-chocking and need for expensive chocks, chains, and locks.

Park Lock protects your landing gears. No more damage to the landing gear caused by hooking the tractor to the trailer, running fork lifts into the trailer while loading, etc.

(Illegible Words) FIND OUT MORE ABOUT PARK LOCK?

For more information about Park Lock write or call

PARK LOCK, INC. 8240 C Moberly Dallas, Texas 75272 (214) 381-2237

(Illegible Text)

(Graphics omitted)

INVENTORS

Woller Case William F. Benefield to and communicating with said first bore, the said brake actuating red having a series of rack teeth transversely thereof and operatively extending through said first bore and connected at one end to said power element and connected at its opposite end through a linkage to said brake crank and a spring biased pawl rod in said second bore and a salenoid coil connected into the electrical system of said vehicle and embracing said pawl rod whereby, which said salenoid coil is energized, the pawl rod is operated to (Illegible Word) the rack teeth on said brake actuating rod and restrain the same in position to set the brakes.

2. In a brake getting mechanism, as described in claim 1, the said spring actually biasing the pawl rod in retracted position to (Illegible Words) said pawl rod being extended to engage said brake actuating rod by said solenoid against the tension of said spring.

3. In a device as described in claim 1, and a collar on said pawl rod for adjusting the tension of said compression spring.

(Illegible Line)

UNITED STATES PATENTS

(Illegible Table)

GEORGE E. A. HALVOSA, Primary Examiner

UR Ct. XR 74-503; 192-3; 188-163