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Notes From Dave's
Garage
Last Updated: January 20, 2002
This is the first in a series of
Corvette technical notes
created by David Herlinger, owner of Herlinger's Corvette Repair in
Mountain View, California. I will be be creating an index and other
helpful web gadgets, along with some pictures as Dave adds to this
document. - Allen Woolley C1, C2... indicates the generation of Corvettes each note is
applicable to. [C3]
Diagnosing
rear wheel bearing & yolk endplay problems START FROM THE
BEGINING
1. Put the rear of your Corvette securely
on frame stands so both rear wheels are off the ground
2. Grab the tire with both hands
perpendicular to the ground. With one hand at the top and one hand at the bottom
apply a substantial amount of force. You will feel some movement. This
movement is differential yoke endplay.
3, Grab the tire parallel to the
ground with both hands, apply force very lightly, just enough to feel a little
movement. This movement is rear spindle bearing endplay.
ENDPLAY
When I rebuild a differential it will go
out the door with zero yoke endplay. I would like to think the yokes would
stay at zero endplay, however, they don't. First of all, The
main cause for the differential yokes loosening up is the posi clutch
pack. The side yoke is installed in such a way that it passes through the outer
case, through the posi clutch pack and through the side gear. A snap ring holds
the yoke in place. The posi unit is made up of metal discs similar to a
motorcycle clutch. The posi discs are made of metal and submerged in gear
oil. As soon as a new posi clutch pack breaks in, because they are metal on
metal, they will loosen up slightly. This causes
endplay.
The second cause of a loose yoke is the
yoke itself. From about 1978 to around 1981 G.M. had a problem with one of
their outside venders. The vender did not properly heat treat the side
yokes. I replaced hundreds of 78 and 79 side yokes at 35,000 miles or
less. Some yokes would be worn down as much as 1/4 of and inch to where the snap
ring groove and snap ring were gone. Usually the snap ring went through
the gears without causing too much damage. Sometimes the outer case seal
and case would be destroyed. The yoke would wear down so much
that it would cut into the side of the differential case. I would guess
that by now most 78 to 82 Corvettes with defective side yokes have probably been
replaced.
HOW MUCH ENDPLAY
How much is too much endplay. I would
say a Corvette differential, assuming the clutch pack is shimmed properly, should
not have over about .050 endplay. Most Corvette's that come into my shop
have between .060" and .125" endplay. If the end play is from a very loose
clutch pack the differential might chatter when making a sharp turn. If the
differential chatters add some G.M. posi additive and hope it
works.
WHEEL BEARING
ENDPLAY
When I rebuild a rear torque arm assembly I
try to set the endplay as close to .001" as possible, never over
.002". When you check rear wheel bearing endplay, if the bearings
are set up properly, you will barely be able to feel the movement. This is
good. The factory allows up too .008" rear wheel bearing endplay.
.008" is way too much endplay and the rear wheel will feel very
loose.
CONCLUSION
Check the yoke endplay, check the rear
wheel bearing endplay, determine which is at fault and proceed ahead. If the
yoke is very loose, pull the differential, shim the clutch pack, replace the the
yoke and reassemble. Rebuild the complete differential if it makes you
feel better. If the rear wheel bearings are loose, pull the rear torque
arm assemblies and replace the bearings and shim them to .001".
Herlinger's
Corvette Repair |