Rear Clunk
Thread Starter
Racer
Joined: Jul 2006
Posts: 478
Likes: 56
From: Woodstock Georgia
Rear Clunk
I just bought this `75 and there is a clunk that is heard and felt when creeping forward or backwards at a few MPH. I initially thought it to be a u-joint, but this morning I checked them out and visually they look ok. I greased the half shaft's u-joints. I also put it in drive while it was on jack stands and heard nothing - probably because there was little load on the drive train. I noticed that it doesn't do it in neutral while rolling either.....again, little load on the rear. Does this sound like a u-joint or do I have other major problems looming such as rear end?
Burning Brakes
Joined: Nov 2005
Posts: 832
Likes: 1
From: Breckenridge Colorado
Try the easiest thing first. I see threads like this all the time and what is always suggested is a flush and refill of the rear differential and especially important to add a bottle of the GM Differential addative which is like $7. I had the same type of sounds comming from the rear of my 76 under the same conditions and I just flushed and refilled mine the other night and added a bottle and MAN does it make a difference. My rear end noise went away almost completely. I have seen others here spend thousands trying to track down a rear end sound like yours and some never try the simpliest solution. Try the GM addative....they will have it at your local GM dealership.
Racer
Joined: Dec 2005
Posts: 344
Likes: 0
From: Washington DC
Originally Posted by MartyW
Try the easiest thing first. I see threads like this all the time and what is always suggested is a flush and refill of the rear differential and especially important to add a bottle of the GM Differential addative which is like $7. I had the same type of sounds comming from the rear of my 76 under the same conditions and I just flushed and refilled mine the other night and added a bottle and MAN does it make a difference. My rear end noise went away almost completely. I have seen others here spend thousands trying to track down a rear end sound like yours and some never try the simpliest solution. Try the GM addative....they will have it at your local GM dealership.
I had a similar problem and this took care of it.
Instructor
Joined: Sep 2005
Posts: 194
Likes: 0
From: Hamilton Ontario
Follow that advice and you should be fixed up. Just one word of advice. Don't put your vehicle in gear while on jackstands or you will be replacing Ujoints, among other things. Real bad for the car.
Racer
Joined: Jan 2005
Posts: 365
Likes: 1
From: Glenview IL
Originally Posted by corvette_maniac
I just bought this `75 and there is a clunk that is heard and felt when creeping forward or backwards at a few MPH. I initially thought it to be a u-joint, but this morning I checked them out and visually they look ok. I greased the half shaft's u-joints. I also put it in drive while it was on jack stands and heard nothing - probably because there was little load on the drive train. I noticed that it doesn't do it in neutral while rolling either.....again, little load on the rear. Does this sound like a u-joint or do I have other major problems looming such as rear end?
with replacing the fluid. Also, check the front diff mount. They tend to get pretty flat and make some noise.~Rich
Instructor
Joined: Mar 2003
Posts: 195
Likes: 0
From: Eagle Wi
Originally Posted by Chev-Hell
my car is doing the same feels like someone kicking the floor under braking and when taking off
They rot out and need to be replaced. That was the clunk on my car.
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Advanced
Joined: Apr 2005
Posts: 96
Likes: 0
From: Ogden Iowa
I had a knock that i thought was the front diff bushing, turned out to be loose passenger door striker, hinge springs. For months I was sure that was were it was coming from (sound). Till a passenger said she could feel the door moving with the bumping noise. She held the door down, noise stoped. I could have swore it was underneath car.
Thread Starter
Racer
Joined: Jul 2006
Posts: 478
Likes: 56
From: Woodstock Georgia
Tomorrow I am planning on changing the diff fluid and add the additive. Me being a Firebird guy and being able to get on all 12 bolts with ease makes me wonder what I'm getting into. Is it very straight forward or will I have to remove a lot to take the cover off of the differential?
Pro
Joined: Nov 2001
Posts: 534
Likes: 6
From: Cave Creek AZ
There is a plug on the passenger side, you'll need a vacuum pump to suck the old stuff out. To remove the differential cover requires lots more work, removing the spare tire tub, the leaf spring, the crossmember... You'll want to eyeball the spring mount on the diff cover, it is common for these to crack and cause a clunk when moving from standstill.
Thread Starter
Racer
Joined: Jul 2006
Posts: 478
Likes: 56
From: Woodstock Georgia
Well I drained and replaced the diff fluid (adding the GM additive first). I did some figure 8s and drove it 10 miles or so and it is still clunking at low speeds. ...so it's time to look at those bushings.
On a lighter note, I stopped all of my power steering leaks by rebuilding the control valve yesterday. I woke up this morning to find a puddle under the car! Turns out it was a combination of the control valve and power steering return hose. I just went ahead and replaced all hoses and now I'm pretty sure I'm leak free.
On a lighter note, I stopped all of my power steering leaks by rebuilding the control valve yesterday. I woke up this morning to find a puddle under the car! Turns out it was a combination of the control valve and power steering return hose. I just went ahead and replaced all hoses and now I'm pretty sure I'm leak free.