Slack in rear end
Thread Starter
Intermediate
Joined: Jul 2009
Posts: 38
Likes: 0
From: Bracebridge Ontario
Slack in rear end
Before any one thinks I'm asking a personal question, I'm inquiring about my 87 convertible. I just had the suspension and drivetrain updated. All new bushings, all new u-joints, brake lines and hoses, fuel lines, shocks, exhaust system. It is as tight as the day it rolled off the assembly line, but I still have this feeling that something is lose. It is most noticeable slowing down and at lower speeds. It feels like the rear end is shifting forward. Is there something that could be slack in the differrential? That is my next project to change the fluid, but apart from that, I wouldn't know what to do.
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
You don't mention miles or if it's an A4 or a 4+ transmission so one doesn't know if it's a D36 or D44 BUT I'd guess and it's just that maybe that the differential needs serviced and I can't imagine why it wasn't done when you did all of the maintenance you just mentioned.
You could maybe determine this by very rapid change of direction movement of the wheel CW then CCW and see what you feel, just quick jerks by hand CW and CCW and then do the same at the pinion flange. See what you feel. You missed the best opportunity to do it while everything else was being done.
That was then but now you're faced with whatever it is. Can you feel the slack when maybe feathering the throttle rapidly at a very slow speed in a lower gear?
How many miles? A4 or 4+?
You could maybe determine this by very rapid change of direction movement of the wheel CW then CCW and see what you feel, just quick jerks by hand CW and CCW and then do the same at the pinion flange. See what you feel. You missed the best opportunity to do it while everything else was being done.
That was then but now you're faced with whatever it is. Can you feel the slack when maybe feathering the throttle rapidly at a very slow speed in a lower gear?
How many miles? A4 or 4+?
Thread Starter
Intermediate
Joined: Jul 2009
Posts: 38
Likes: 0
From: Bracebridge Ontario
You don't mention miles or if it's an A4 or a 4+ transmission so one doesn't know if it's a D36 or D44 BUT I'd guess and it's just that maybe that the differential needs serviced and I can't imagine why it wasn't done when you did all of the maintenance you just mentioned.
You could maybe determine this by very rapid change of direction movement of the wheel CW then CCW and see what you feel, just quick jerks by hand CW and CCW and then do the same at the pinion flange. See what you feel. You missed the best opportunity to do it while everything else was being done.
That was then but now you're faced with whatever it is. Can you feel the slack when maybe feathering the throttle rapidly at a very slow speed in a lower gear?
How many miles? A4 or 4+?
You could maybe determine this by very rapid change of direction movement of the wheel CW then CCW and see what you feel, just quick jerks by hand CW and CCW and then do the same at the pinion flange. See what you feel. You missed the best opportunity to do it while everything else was being done.
That was then but now you're faced with whatever it is. Can you feel the slack when maybe feathering the throttle rapidly at a very slow speed in a lower gear?
How many miles? A4 or 4+?
Thread Starter
Intermediate
Joined: Jul 2009
Posts: 38
Likes: 0
From: Bracebridge Ontario
Melting Slicks
Joined: Nov 2010
Posts: 2,216
Likes: 113
From: Michigan
Drifting
Joined: Jul 2009
Posts: 1,258
Likes: 98
From: Ashland PA
2021 C4 of the Year - Modified Finalist
Same Problem
Before any one thinks I'm asking a personal question, I'm inquiring about my 87 convertible. I just had the suspension and drivetrain updated. All new bushings, all new u-joints, brake lines and hoses, fuel lines, shocks, exhaust system. It is as tight as the day it rolled off the assembly line, but I still have this feeling that something is lose. It is most noticeable slowing down and at lower speeds. It feels like the rear end is shifting forward. Is there something that could be slack in the differential, That is my next project to change the fluid, but apart from that, I wouldn't know what to do.
Thread Starter
Intermediate
Joined: Jul 2009
Posts: 38
Likes: 0
From: Bracebridge Ontario
I have the same problem, I thought it was the bushings because they were starting to fall apart so I replaced all the bushings in the rear, U-Joints, and replaced all the seals and bearings in the differential. I also made sure everything was torqued to spec's including the C-Beam, I still have that clunking noise. Some times it does it some times it does not.
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Drifting
Joined: Jul 2009
Posts: 1,258
Likes: 98
From: Ashland PA
2021 C4 of the Year - Modified Finalist
I just had the fluid changed in the rear diff and we think we have the problem. The noise is caused by the clearance gap between the gears in the diff. They refer to it a "lash". The bigger the gap the louder the noise. Next time you brake, put the car in neutraul before applying the brakes. You should not hear any clunks. It can be corrected but it requires you to drop the diff. Something I don't want to do in prime cruising weather. I'm going to do it this winter.
Thread Starter
Intermediate
Joined: Jul 2009
Posts: 38
Likes: 0
From: Bracebridge Ontario
When I replaced the seals and bearings I adjusted and checked backlash in the gears, they are in factory specs. I tried the coasting and braking method you described several times and I got no clunks. One day I am going to stick a camera under the back and drive around to see if it shows anything.
Drifting
Joined: Jul 2009
Posts: 1,258
Likes: 98
From: Ashland PA
2021 C4 of the Year - Modified Finalist
Oh, that's not good news. If your's is to spec that almost rules out the backlash unless we are talking two different things. My mechanic mentioned some shims may need to be repalced or adjusted. I think it definitely is in the differrential somewhere because it doesn't happen when you pop the car in neutral. If it was bolts or bushings etc., it should still happen. Anyway winter project for me. I'll update everyone next spring.............