As always, diagnosing issues via e-mail is problematic. I can
offer some suggestions, and things
Since the problem occurs in any forward gear, it is unlikely to
be the gearbox particularly since it is shifting smoothly, not jumping
out of gear, etc. But let me ask this question: Does the pitch of the
grinding noise follow the car speed or the engine speed? That is, in
second gear at 20 MPH is the grinding the same pitch as it is at 20 MPH
in third gear? If the pitch is the same, the primary suspect is between
the drive shaft and rear wheels. While it is still possible that the
gearbox is the culprit, I would suggest moving it down the list of
possible culprits for now.
If the pitch is different depending on which gear is engaged,
the suspect is the gearbox.
Assuming that it is in the driveline or rear axle, a good first
guess is a u-joint. This will give the thumping you describe, and means
that it is on the verge of failure. I am mystified by the fact that it
only happens under deceleration, but anything is possible I suppose.
Jack up one rear wheel, and put the tranny in neutral. Rotate
the wheel by hand in both directions. As much as possible, keep your
hands on the wheel while rotating the tire several turns in each
direction. Feel any grinding or "thumps"? Let down that wheel and repeat
on the other side. Feel any grinding or thumps?
YES - I feel grinding on one wheel but not the other - suspect u
joints on the side the that grinds.
YES - I feel grinding on both sides - suspect u joints on drive
line or perhaps the differential.
No - I feel no grinding or thumps - Send Email to Vance thanking
him for his worthless advice.
Some other random thoughts: Have you checked your diff fluid?
Does it have any swarf or metal lumps? Yes - Kiss your diff goodbye. Is
it at the correct level? No - top off and take car for test drive (not
likely to solve problem, but worth a shot).
From: email@example.com [mailto:firstname.lastname@example.org] On
Behalf Of RJSmalling@aol.com
Sent: July 04, 2005 9:38 AM
Subject: Gear Box or Diff?
Dear 6-pack Listers,
I am getting a serious grinding noise and random thump from the
when I come off the accelerator in any gear. Under cruise or
car is smooth and you would not know anything is wrong. Push in the
and it goes away. I thought is was coming from the rear passenger hub
had alot of play in it so I replaced that HUB along with all 4 half
joints. Still grinding. So now I need to figure out if the problem is
Diff or the gear box or somewhere else. Diff was professionally
15,000 miles ago. Gear box shifts smoothly in all 4 gears and reverse.
thoughts on where the problem lies?
75 TR6 Carmine Red