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Old 07-19-2005, 05:26 AM
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Rearend clunk

Greetings folks, my first time on here.
Hope someone can help me out here, Iím just about pulling whats left of my hair out.
I just got my 59 El Camino finished; (350/th350, 10 bolt posi rearend from 72 chevelle)
After you drive it about 4 miles, a loud CLUNK starts coming from the rearend. Its not a regular clunk but it is quite frequent. Most noticeable at low speeds going dead straight. Severe enough to jar the vehicle.

The rearend has been apart, and all seems OK. I did not take the pinion assembly out, but it spins freely and there is no play. There is a small amount of gear backlash, but not excessive, and there is a little backlash in the spider gears. The posi clutches are new. The crosspin fits snugly. Wheel bearings seem fine.

The odd thing is that with the rearend up on jackstands and running in drive, it does not happen, even with the parking brake partially engaged to provide some load.

When it first started to happen , I assumed it was the driveshaft center bearing, but It was fine. (I replaced it anyway) all the universals are fine and no amount of experimenting with shimming pinion angles etc makes any difference.

Any ideas?

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Old 07-19-2005, 11:41 AM
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Generally if there is a "clunk" in the drivetrain it will show up when you put the car in gear..that is there are worn u-joints or excessive slop in the rear end..Sinc this only happens when you are driving I woudl look at shock mounts or shocks..maybe worn bushings in the suspension or something in that area..

My truck "clunks" but I have traced it to the shocks rattaling when I hit a bump..Remember these ole cars are not as smooth as we are used to in new cars..

And aboard the board so to speak..

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Old 07-19-2005, 01:47 PM
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You'll want to get after your U joints pretty quick, you don't want one failing on you on the road.... especially the front one!!!
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Old 07-19-2005, 03:30 PM
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Since this is a factory posi, did you add the GM limited slip differential lube? if you didn`t the rear will make all kinds of pop and clunking noises, usually the noise doesn`t show up until the rear diff gets hot. If you used standard gear lube you`ve found the problem. You can get about a 4 oz bottle from any GM dealer, or you can upgrade to a synthetic lube like royal purple which doesn`t require any anti chatter additive. Most factory posi`s had a tag on them that said "use GM limited slip differential fluid only" most people don`t know what the term "limited slip" means, so they add standard fluid. I`ve seen people in the past have the rear replaced because of the chatter, not knowing all they had to do was add the fluid. I had a 79 Z28 with a posi, the car sat 9 years and the rear chattered like crazy, I added the parts store additive that said it elimated chatter, it did no good, I added the GM additive, problem solved. In my Cutlass that I have now, I installed a posi diff, added royal purple lube alone, no chatter problems.
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Old 07-19-2005, 04:54 PM
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Thanks for your suggestions, guys, but I've got all those things covered, (I think...)
As I said, all the U-joints are in good shape, All the suspension bushes are new- this car has been completely restored.
You can bounce up and down on it all you like and it makes no noise from the suspension.
I used Kendall posi additive in the oil this last time, but when first assembled, I used the GM stuff ( a little hard to get here sometimes). The posi clutches do make some noise on turns, but what I'm experiencing is a worse clunk which happens when driving dead straight, which kind of rules out posi problems, I would have thought.
The clunk has a kind of 'snatching' quality to it. It certainly seems to cause the wheels to judder, and seems to be mostly coming from the passenger side- I sat in the bed and listened while the missus drove it.
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Old 07-21-2005, 08:08 AM
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My Z28`s rear would clunk going straight forward, but I don`t recall ever being able to feel it. Was the tranny rebuilt? The tranny has a anti clunk spring as we call it that must be reinstalled or it`ll clunk also. Since you say the rear does chatter in turns, I would look further into the additive, the kendall additive may not work. Even so your in england, I don`t see why you can`t order royal purple gear lube or have access to another Synthetic gear lube, I`d say it`s worth a shot, ever since I tried parts store anti chatter additive and it didn`t do away with the problem I don`t trust them. If the clunk is still present I would Investigate further into the rear again or the tranny. If the clunk is in the tranny the noise can travel down the drive shaft and make you think it`s coming from the rear.
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Old 07-21-2005, 03:44 PM
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Quote:
Originally Posted by briz
Thanks for your suggestions, guys, but I've got all those things covered, (I think...)
As I said, all the U-joints are in good shape, All the suspension bushes are new- this car has been completely restored.
You can bounce up and down on it all you like and it makes no noise from the suspension.
I used Kendall posi additive in the oil this last time, but when first assembled, I used the GM stuff ( a little hard to get here sometimes). The posi clutches do make some noise on turns, but what I'm experiencing is a worse clunk which happens when driving dead straight, which kind of rules out posi problems, I would have thought.
The clunk has a kind of 'snatching' quality to it. It certainly seems to cause the wheels to judder, and seems to be mostly coming from the passenger side- I sat in the bed and listened while the missus drove it.
i was fixin to put hat it could have been a u-joint to, i had the noise that you are talkin about and it was my u-joint
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Old 09-11-2005, 04:39 PM
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well i was just wondering if because i have posi the rear end would make a clunking while i'm turning are extremely low speeds, like it makes a clunk and shakes the whole car, it does it in reverse too, and after coming off the highway but only when turning slow
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Old 09-11-2005, 07:14 PM
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check wheel bearings, my 61 bearings try to lock up with me, i caught,them just in time
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