Interpretation 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.