Rear clunking vibration?
Thread Starter
Instructor
Joined: Jul 2001
Posts: 189
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From: Berkeley Heights New Jersey
Rear clunking vibration?
Can anyone share their experience with a clunking vibration when I turn into my garage at a very low speed. Maybe 2-3 mph. THe car has a posi rear. I don't know if or when the prior owner may have replaced the lubricant in the differential. When driving on a straight road or taking off from a stop light it does not do it. I recently replaced all the u joints in the half shafts. I was reading about the posi additive by GM that may help solve this problem. Has anyone tried it with any success? How do I drain out the old lubricant. I have a vaccuum siphon pump but don't know if I could use this or take it to a garage.
Melting Slicks
Joined: Mar 1999
Posts: 2,845
Likes: 2
From: Apex NC
Re: Rear clunking vibration? (bl75vette)
It may be the posi clutches in the rear end. You can easily siphon out the old lube and add new along with the posi additive. Is the car a 4 speed or auto trans? My car had a wicked clunk in the rear due to a bad mount at the front of the differential. Odds are that yours hasn't been replaced. It's not too hard to do and it made a huge difference in my case.
Shannon
Shannon
Thread Starter
Instructor
Joined: Jul 2001
Posts: 189
Likes: 0
From: Berkeley Heights New Jersey
Re: Rear clunking vibration? (sb69coupe)
Hi Shannon, Thanks for your input. Car is an automatic. Should I siphon out all the fluid and add the posi lubricant plus the additive before trying to replace the mount your talking about.
Racer
Joined: Aug 2000
Posts: 255
Likes: 0
From: Dixon, CA, USA
Re: Rear clunking vibration? (bl75vette)
I didn't have a clunking, but I did have a "moan" from the rear when backing out of the driveway. I changed my fluid yesterday, picked up two bottles of the gear oil and one bottle of the additive from my GM dealer. I backed onto my rhino ramps and wrestled with getting the bolt out. It's a strange size and I had a hard time finding a socket to fit it and it was on there very tight. I found a 3/4 inch socket that fit it and with a long extension and my 1/2 inch ratchet I was able to break it loose. I siphoned the old stuff out and used a hose attachment to put the new fluid in. 30 minute job with 20 minutes taking the bolt out. Put the additive in first and then fill up until the gear oil runs out the hole. I went out afterwards and did a few figure 8's in a parking lot and then moan is gone for now. Good luck.
Advanced
Joined: Sep 2001
Posts: 83
Likes: 1
Re: Rear clunking vibration? (bl75vette)
I would check the mount. It is under the pinion flange to driveshaft u joint. You can check your diff fluid by removing the fill hole cap nut and stick your finger in and smell it. If it smells like rotten eggs, your cool, if it smells like grease, change it.
Good luck!
Good luck!
Melting Slicks
Joined: Mar 1999
Posts: 2,845
Likes: 2
From: Apex NC
Re: Rear clunking vibration? (bl75vette)
Yes, I'd try replacing the fluid and additive first. The post below mine outlines it well. Do the figure-8's in a parking lot or cul-de-sac to distribute the fluid to the clutch plates.
On the bushing, it can be deceiving. The lower bushing usually looks fine. It's the top half that sits above the mount on the frame that gets squished and worn out. It's a little tricky to replace, but the bushing doesn't cost much and it makes a big difference.
Shannon
On the bushing, it can be deceiving. The lower bushing usually looks fine. It's the top half that sits above the mount on the frame that gets squished and worn out. It's a little tricky to replace, but the bushing doesn't cost much and it makes a big difference.
Shannon
Advanced
Joined: Apr 2000
Posts: 90
Likes: 0
From: Hobart, Tasmania, Australia
Re: Rear clunking vibration? (bl75vette)
BL75Vette, I had exactly the same symptons!
Started adding up the numbers for a new diff etc etc......
Didnt believe that replacing the diff fluid would fix it but guess what, IT DID :D
Before you do anything I would suck all the old juice out of the diff and replace it with nice fresh stuff. I siphoned mine out, took hours to drain :mad
Get a pump thingi, after I did mine I found one in a hardware store, too late!
The stuff you get out will be very black and very thick in comparison to the new stuff.
If this dont fix your problem, then you have a more expensive one! :smash:
Started adding up the numbers for a new diff etc etc......
Didnt believe that replacing the diff fluid would fix it but guess what, IT DID :D
Before you do anything I would suck all the old juice out of the diff and replace it with nice fresh stuff. I siphoned mine out, took hours to drain :mad
Get a pump thingi, after I did mine I found one in a hardware store, too late!
The stuff you get out will be very black and very thick in comparison to the new stuff.
If this dont fix your problem, then you have a more expensive one! :smash:
Melting Slicks
Joined: Oct 2000
Posts: 3,023
Likes: 2
From: TEXASTEXASTEXASTEXAS TEXASTEXASTEXASTEXAS
St. Jude Contributor
Re: Rear clunking vibration? (OzVette75)
Yup, me too. A moaning, groaning, clunking sort of noise on low speed turns. New fluid & two bottles of GM posi lube cured it completely. However, since I'd heard it's a pretty nasty job, I dropped the spare tire carrier so the plug was accessible and paid the $18 to the quick lube place down the strret to have them suck the old out and put the new in.
JB
'78SA
JB
'78SA
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Joined: Feb 2001
Posts: 7,226
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From: Northern CA
Re: Rear clunking vibration? (bl75vette)
The best 25 bucks I've spent on this car...was the day I took it down to the local tranny shop to pump out the rear end and add new gear lubricant and GM rear-end additive. The "clicking, clunking and popping" I had in reverse turns went away immediately. I never spilled a drop and the guy did the job in five minutes.
Melting Slicks
Joined: May 1999
Posts: 2,897
Likes: 0
From: Moon Township PA
Re: Rear clunking vibration? (bl75vette)
Clunking while turning could well be u-joints. To the best of my knowledge there is only one way to test u-joints and that requires pulling them. If you are going to go to the effort of pulling them, you should replace them, IMHO. The stuff in the differential I will leave to others. If you were getting a clunking sound when you accelerate or let of the gas I would suggest a rear differential mount had failed. I am talking about the rubber doughnut between the front mount of the diff. and the cross member.
Gary
Gary