Back end knock
Thread Starter
Instructor
Joined: Dec 2016
Posts: 190
Likes: 30
From: Wollongong Great Southern Land
Back end knock
Hey All,
happy new year!
weve got a knock coming from the back, you can feel it as well as here it. Sounds like its behind the seats and from the middle. Happens only when you take off, and feels like a light tap with a hammer from below. Doesnt happen all the time. The snubber appears to be in good condition, was replaced 5 years ago and only done 1500miles since. Ive heard it could be the quasi in the diff, have replaced the oil. Maybe the diff needs a rebuild?
happy new year!
weve got a knock coming from the back, you can feel it as well as here it. Sounds like its behind the seats and from the middle. Happens only when you take off, and feels like a light tap with a hammer from below. Doesnt happen all the time. The snubber appears to be in good condition, was replaced 5 years ago and only done 1500miles since. Ive heard it could be the quasi in the diff, have replaced the oil. Maybe the diff needs a rebuild?
Race Director
Joined: Nov 2006
Posts: 13,228
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
Maybe?? I'd double check that snubber.
And while under there, check all the other bushings. Trailing arm, strut rod, etc.
Also closely inspect all 6 U joints. A worn U joint can also clunk on take off. I recently did mine. 4 out of 6 were bad. And it certainly wasn't the first time.
And while under there, check all the other bushings. Trailing arm, strut rod, etc.
Also closely inspect all 6 U joints. A worn U joint can also clunk on take off. I recently did mine. 4 out of 6 were bad. And it certainly wasn't the first time.
Melting Slicks
Joined: Nov 2006
Posts: 3,410
Likes: 1,821
From: Apple Valley, MN
Start with the basics - is the snubber rubber or poly? If poly, replace it.
Check the side play on the stub axles. If a c-clip fell off, you could have a large amount of movement there.
Check all of the u-joints.
If the noise occurs only in a straight line, the posi is not likely a problem.
Check the side play on the stub axles. If a c-clip fell off, you could have a large amount of movement there.
Check all of the u-joints.
If the noise occurs only in a straight line, the posi is not likely a problem.
Race Director
Joined: Apr 2011
Posts: 11,183
Likes: 3,335
From: North of Toronto - Ontario
If the snubber is good, it's hard to see but check the condition of the rear driveshaft u-joint if you can give it a shake to see if there's any movement there as well. Also grab the driveshaft and see if it'll slide fore/aft at all just in case
Trailing arm front bushing also but that should make noises going over bumps and whatnot not just taking off
Posi clutches usually chatter and complain making corners not going straight.
M
Trailing arm front bushing also but that should make noises going over bumps and whatnot not just taking off
Posi clutches usually chatter and complain making corners not going straight.
M
Team Owner
Joined: May 2001
Posts: 87,364
Likes: 1,592
From: Western NY
Happened to a '79, that used to be my wife's. The inner edges of the side yolks in the diff wore down, and allowed the yolks to move in and out, as the slack was taken up under acceleration. The wear wasn't enough that it caused the "C"clips to fall out, but it did allow the pinion shaft to slightly elongate the holes in the carrier, that the shaft rode in, and this, too, added to the noise.
