Mike,
Since you said you're coasting, I'll ignore halfshafts and differential (it
*could* be any of these components and/or u-joints in between, but you'd be
more likely to hear these in power on/off transition) for now.
Grab the top of each rear wheel (one at a time...) and rock back and forth.
Do you hear the clunk? If yes, your bearings are very worn (this is the
problem I'd most suspect). Have your ears gotten accustomed to a low rumble
coming from the rear end? Bearing wear occurs slowly (ideally, anyway) and
you might not have noticed it before now. You don't want to try to rebuild
the hubs yourself if the bearings have perished. If there's a reputable
shop in your area that has done them before and has the right tools, pay
them. TRF will rebuild them, but it's not cheap.
Pull the lever shocks off (very simple job) and check for freeplay. You
should feel relatively strong resitance under compression, relatively little
resistance on rebound. This is a good time to refill the shocks with fluid.
Check for loose/broken bolts from trailing arm brackets to frame and
brackets to trailing arms. Has the rubber in the bushings perished? This
is primarily a visual inspection, because all of these bolts are loaded by
the road springs, unless you remove them first, so you won't be able to feel
any play by hand.
Speaking of road springs, are they firmly seated in the frame and trailing
arms?
Still haven't found the problem?
Jack the car, remove the rear wheels, remove the screws holding the brake
drum to the hub (screws missing? New ones are pennies from TRF), pull the
drum and look for broken brake shoes, gravel, warped/scored drums, broken
springs, dead rats, etc.
If you still haven't found it, suspect the drivetrain.
Jack the rear of the car as high as you can and support it on strong, well
positioned jack stands; scoot under the car and see if you can move the
differential. This is extremely dangerous, because if the car is not
securely supported by strong, high-quality jack stands, it could fall on
your head (I don't have to tell you how little ground clearance the car has
in the rear). If you're not comfortable with this, don't do it. Take it to
a shop that does wheel alignments. Anyway, what you're looking for is a
broken frame where the differential mounts to it, worn bushings at these
mounts, or broken/loose bolts. If you suspect any of the above, at least
buy the rebushing kit from TRF. If the frame is broken (common TR6
problem), prepare to pay considerable $$ to have it fixed. This is probably
not the problem, though, or you should be hearing a good, solid thunk when
you get on or off the throttle.
Still haven't found it? It's probably universal joints or the bolts holding
them to the half-shafts. Parts are cheap, but plenty of labor to get to
them. You can fix them yourself with the aid of a large, solid vice and
several large, solid sockets. (Is there a FAQ on this?) It would be a good
time to rebush the differential, install a new exhaust system,
replace/refill shocks, install new brake shoes and brake lines, maybe
replace worn springs with stock or competition springs. Spring for
rebuilding the hubs if you've got some spare cash that you don't know what
else to do with.
These are all the major systems at the rear end. I don't know anything
about the insides of the differential, so I won't even hazard guesses about
that.
Good luck!
Kevin Riggs
rkriggs@ingr.com
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