In a message dated 10/06/2000 8:21:43 AM Eastern Daylight Time,
SadekCH@NSWC.NAVY.MIL writes:
<< More seriously, what is Grey Rock? The special metallics of the
60's are the ones for my drum brakes. Is Grey Rock the same thing. or real
asbestos? >>
Grey Rock is (was?) a division of Raybestos Manhattan Crop.
They manufactured two racing compounds.
5262 is a full metallic lining (meaning it does not have any organic
material, such as asbestos). 5262 was developed for superspeedway Grand
National stock cars (drum brakes). It has extremely constant holding with no
wheel lock-up or pull.
5191 is also full metallic. It holds better than 5262 and withstands heat
better. 5191 was developed for tracks like Riverside and Martinsville where
brake fade was more a problem. 5191 swells under high heat, so more drum
clearance when cold is required.
The other material that you might find in an old shop is Velvetouch
manufactured by S.K. Wellman Corp. It is more likely that you might find some
velvetouch than Grey Rock. The one drawback of Velvetouch is that it must be
bonded rather than riveted to the shoe. Actually, with modern adhesives that
shouldn't be a problem. Velvetouch was also sold as a truck lining at
Chevrolet dealers under part #3830635.
Success with drum brakes relies on some basic procedures that are critical.
1. The drum finish should be perfect.
2. After machining the drums should be washed with soapy water to remove all
particles and oil.
3. The linings should be ground to match the drums. They should be cut .030"
under the drum diameter.
4. The lining should have .008 to .010 clearance at the toe and heal when the
center contacts the drum. This will give a slight rocking effect which is
desirable. Never let the heal and toe to contact the drum with clearance at
the middle, otherwise the pedal will have "feel", but the car won't stop.
5. Proper seating-in is a must. Several moderate laps, cool down, repeated at
least twice. There will be a different "feel" when they are seated, but this
may be difficult to detect on a disc/drum car, because the front brakes may
mask it.
Good luck.
Jack Woehrle
4.
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