# Odd chunking noise in driveshaft...



## mstyles0927 (Nov 30, 2000)

My truck is now a 77, 2WD Chevy 1/2 ton with LB and 350 + auto. I have noticed an odd chunking noise when beginning to move from a dead stop or when moving slowly and then turning and accelarating. It feels like it is happenning somewhere under the cab but past the engine and transmission. My first thought was U-joint, but find no play in any of the joints that would indicate any looseness there.

The only thing I can think of now is that this truck has the 2-piece drive shaft with the odd-looking driveshaft-bearing along about the middle. This looks like a bearing in a rubber mount inside of the clamp that holds it to the frame. Is it possible that this is wobbling from the increased torque when applying the gas?


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## wyldman (Jan 18, 2001)

It could be that carrier bearing,but usually they will cause more of a vibration than a clunk.

I'd check for a loose slip yoke,broken or loose leaf springs,loose u-bolts etc.Check the pinion bearing,it may be loose,or there may be too much backlash in the rearend.

Also look for a broken or separated trans mount,or possible the exhaust hitting the frame somewhere ?


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## 84406 (Apr 27, 2003)

It is probably the slip spline just after the centre driveshaft bearing. It gets dirty and get bind as the rear rocks when coming to a stop. Then when you start off it unbinds with a little clunk or thunk. Dissassemble, clean splines, grease and the problem should be gone. Hope it works for you


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## wyldman (Jan 18, 2001)

84406 - your probably right,that is a common problem.It can affect the slip yoke at the trans too.GM has a special grease to help rectify the problem.


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## TomatoRedGMC (Apr 29, 2003)

If I'm experiencing the same problem with my 4WD, could it be a slip slpine or rear end play as well? the drive train and mounting all seem to be tight, and can't see any visual abnormalities at all.


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## jimfulco (May 1, 2003)

My 69 swb c-10 with 2pc. drive shaft eats the rubber swing bearing insulator, causing clunking but not vibration. The rubber tears up in about 3000 miles. I have yet to figure out why.


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## wyldman (Jan 18, 2001)

TomatoRedGMC - the slips yokes\splines and rear end play can cause a clunk.

jimfulco - if your eating up a carrier bearing every 3000,then something is drastically wrong.You must have a driveshaft that is way out of line,too short,out of balance,bad u-joints,out of phase,etc.Something is way out in the drivetrain.


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## jimfulco (May 1, 2003)

Thanks wyldman. It actually only messes up the rubber part, the bearing itself is fine. After I fix it, it runs smooth as silk, but the rubber just tears up again. I replaced all 3 U-joints (the rear one was bad), but it made no difference. The only thing I can think of is that I don't drive the thing but once in a while, and maybe the rubber takes a set or something. I think maybe I'll put a one-piece shaft in it next time. Thanks again. JF


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## Pelican (Nov 16, 2001)

I had a clunk in one of my older trucks that I had trouble locating. It would only sound when changing direction, from forward to reverse & vice versa. It ended up being one of the rear end carrier bearings was worn and allowed excessive backlash like wyldman suggested.

Chock the wheels and put the truck in neutral, then try to move the driveshaft back and forth. The amount of play in the rear end should be unnoticeable, if you can see or feel the driveshaft move more than a minute amount, there's too much play.

Now I have a question along the same line. My Chevy 3500 has a driveline whine and vibration above 30 mph. I rode in the back and the noise is most intense where the body and cab meet. I suspect either the driveshaft carrier bearing or transmission tailshaft bearing, but can't find play in either one.

I don't want to just change parts, is there a way to test either of these parts?


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## wyldman (Jan 18, 2001)

Pelican - the trans output shaft bushing will not usually make much noise,but will vibrate if it's loose.You said there is no play in it,so it's probably fine.The carrier bearing may cause it,you should be able to unbolt it and feel for any roughness when turning.Another thing it could be is a dry u-joint.Sometimes one cup will go dry,and get stiff,and it will whine and vibrate,but you won't feel any noticable play.I would drop the entire drive shaft out,and feel everything (u-joints and carrier bearing) by hand and see if you find anything.Also make sure you pinion bearings aren't loose.If it's a 4WD you could drive it with the rear shaft out,and see if the noise disappears,just to verify it's in the rear driveline.


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## wyldman (Jan 18, 2001)

jimfulco - if your u-joints are new,double check to make sure they aren't to tight or binding.Smacking the driveshaft ears will help seat the cups and loosen up the joints.

Next thing I would check is that the driveshaft is in line.It should be in a perfectly straight line from the trans,to the diff,from side to side.If this is out,then the trans or diff is not centered properly.The short shaft from the trans to carrier bearing should also be perfectly straigt exiting the trans.If not,you trans mount may be toast,the crossmember is bent or improperly installed,or the carrier bearing needs shimming.

The angle of the two rear joints must also match.You can measure this with an angle meter.You can shim the leafs\diff,or shim the carrier bearing to get these in line,but whatever you do may require going back and getting the front level again.You can also shim under the trans mount to help as well if neccesary.


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## wyldman (Jan 18, 2001)

Here is a quick drawing of what the driveline angles should look like,looking from the side of the truck..They are exaggerated and not necessarily to scale.

From underneath,everything should be in a straight line.

Remember,I'm not an artist or anything.


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