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Old 07-10-2015, 09:49 PM   #1
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Mystery Clunk Of The Night

175,000 miles, I guess it's time for the drivetrain to start showing its age.

I was driving home from work today, stopped at two places, last of which being just around the corner from my house. I pulled out of the parking lot "with spirit" and started hearing this clunking sound. It was consistent with hitting a bolt or some piece of metal on the road, but kept clunking about once per wheel rotation.

I didn't know what it was so I let off the gas, and it was still clunking just less loud. I then put the (auto) transmission in neutral and the sound stopped. Fortunately it was downhill to my driveway so I coasted. When I got in the driveway I carefully put it back into gear (not that there's an.. un-careful way with an automatic) before the vehicle came to a stop, and eased it up the rest of the driveway and into the garage. The clunk returned, at a slower pace.

Did something break loose in my transmission?? After dinner I went back out and visually inspected, can't see anything underneath the car that doesn't look right. I fired it back up, no clunk. Backed out to the end of the driveway (about 25'), no clunk. Moved forward in gear, clunk returned. Again in neutral there's no sound. After doing this a few times, I feel like it's hitting whatever 1x per rotation of the driveshaft. I'm not familiar with the internals of transmissions, only engines, so could anyone point me in the right diagnostic direction?

Edit: Camaro is a 1995 3.4l with automatic transmission

Last edited by FoaRyan; 07-10-2015 at 09:56 PM. Reason: Adding vehicle info.
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Old 07-11-2015, 10:40 AM   #2
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I've been reading through the Drive Train section in my Chilton manual this morning, just familiarizing myself with all the parts and where they are, how they're connected, etc.

When I got to the U-Joint section, there's an introductory paragraph that reads: "Bad U-joints, requiring replacement, will produce a clunking sound when the car is put into gear. This is due to worn needle bearings or a scored trunnion end possibly caused by improper lubrication during assembly. U-joints require no periodic maintenance and therefore have no lubrication fittings."

Some extra info in there, but the clunking sound in gear rang a bell. Or clunked a drive train, if you prefer.

Again -- my problem is not that there's a clunk when I shift into gear. My problem is that when I move in gear the clunking sound happens as things rotate. I'll be jacking up the car to get underneath so I can check transmission mounts, the U-joint, rear end, and so forth today. It didn't sound like the clunk was from the rear of the vehicle, more of the center, but that's with me sitting inside so it could really be anywhere.
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Old 07-11-2015, 11:12 AM   #3
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Oi! So guess what? I got one wheel jacked, and took a look underneath before getting to the other side. Found my problem, the 2-piece drive shaft is broken at the joint. I got pics, the thing just flops around. Coffee first, then pics, and I'll figure out what has to be replaced.
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Old 07-11-2015, 11:19 AM   #4
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Change that two piece into a one piece.


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Old 07-11-2015, 11:59 AM   #5
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Quote:
Originally Posted by BK047 View Post
Change that two piece into a one piece.
LOL! I'm sitting here looking at the diagrams, and asking myself, WhyTF do I have the one on the *bottom*?!



Here's a look at the shaft, I'm guessing whatever mounting hardware is involved broke loose, shaft itself may be okay.



I'll have to get under there again with it lifted properly and higher to see exactly what's broken. It moves around freely with my hand, which explains why the 1 clunk per rotation was happening (especially at low speed). It was a metallic rubbing sound when I inched forward in the driveway.

Now, why didn't it make a sound in reverse? Simple -- physics! Confused? I'll explain:
  • In reverse, torsion would be pulling the shaft outward in both directions. <----===---->
  • Whereas in forward gears, the stress causes it to go inward. ---->===<----
  • (Think about it - rear wheels lunge forward, and as they surge the equal and opposite reaction of the mass of the car (channeled through the drive train) presses back against it. In reverse the opposite is happening, and effectively stretches the components.)
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Old 07-11-2015, 12:04 PM   #6
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Direct Replacement?

So, BK047, this looks like a direct replacement from the diagrams. I may give American Camaro and Firebird a call (if they're open today) and see what they have in stock.

This shop is a junk collector in Bethany, Oklahoma that specializes in F-bodies. They have never done me wrong over the last 9 years since I've lived here. The owner knows his parts and can usually tell me offhand what he has in stock, from door lock switches to salad shooter wheels to t-top headliner panels. I think they ship, too, if anybody needs to look them up sometime.
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Old 07-11-2015, 01:00 PM   #7
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Further update, called AM C&F, they've got a direct replacement (98 or 99+) 1-piece shaft I can get for $125. If I can get there before noon I can finish this project this weekend. Otherwise It'll be a Monday off work.

Upon LED-lighted inspection, I can see it looks like just the middle rubber bearing or bushing, or whichever it is, is the only thing that's broken. That would be much cheaper, but it does look like this center support has to be replaced as a unit with the whole shaft. Looks like I've got me a project, now I need a ride... bbl!
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Old 07-11-2015, 01:30 PM   #8
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Quote:
Originally Posted by BK047 View Post
Change that two piece into a one piece.
This!!
Quote:
Originally Posted by FoaRyan View Post
LOL! I'm sitting here looking at the diagrams, and asking myself, WhyTF do I have the one on the *bottom*?!
Cause your car is a v6?

Quote:
Originally Posted by BK047 View Post
Here's a look at the shaft, I'm guessing whatever mounting hardware is involved broke loose, shaft itself may be okay.
Still, Get a 1 piece

I'll have to get under there again with it lifted properly and higher to see exactly what's broken. It moves around freely with my hand, which explains why the 1 clunk per rotation was happening (especially at low speed). It was a metallic rubbing sound when I inched forward in the driveway.

Now, why didn't it make a sound in reverse? Simple -- physics! Confused? I'll explain:
  • In reverse, torsion would be pulling the shaft outward in both directions. <----===---->
  • Whereas in forward gears, the stress causes it to go inward. ---->===<----
  • (Think about it - rear wheels lunge forward, and as they surge the equal and opposite reaction of the mass of the car (channeled through the drive train) presses back against it. In reverse the opposite is happening, and effectively stretches the components.)
[/QUOTE]

Quote:
Originally Posted by FoaRyan View Post
So, BK047, this looks like a direct replacement from the diagrams. I may give American Camaro and Firebird a call (if they're open today) and see what they have in stock.

This shop is a junk collector in Bethany, Oklahoma that specializes in F-bodies. They have never done me wrong over the last 9 years since I've lived here. The owner knows his parts and can usually tell me offhand what he has in stock, from door lock switches to salad shooter wheels to t-top headliner panels. I think they ship, too, if anybody needs to look them up sometime.
Quote:
Originally Posted by FoaRyan View Post
Further update, called AM C&F, they've got a direct replacement (98 or 99+) 1-piece shaft I can get for $125. If I can get there before noon I can finish this project this weekend. Otherwise It'll be a Monday off work.

Upon LED-lighted inspection, I can see it looks like just the middle rubber bearing or bushing, or whichever it is, is the only thing that's broken. That would be much cheaper, but it does look like this center support has to be replaced as a unit with the whole shaft. Looks like I've got me a project, now I need a ride... bbl!
A 1 piece would still be better. Not ever have to worry about that happening again.
An aluminum 1 piece from a z28/SS or Trans Am/WS.6 will also work.
I had a '92 3.1L v6 Camaro that had a 1 piece drive shaft, I thought it was really weird, I expected to see a 2 piece when I looked under it, but there it was,a 1 piece. Also had a 9 bolt differential.
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Last edited by Ercmann; 07-11-2015 at 01:36 PM.
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Old 07-11-2015, 02:25 PM   #9
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Got the 1-piece, steel not aluminum. If I had time to hunt around I might try to find the lighter aluminum, but this one is good, U-joint is good, and I should have it installed this afternoon.
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Old 07-11-2015, 06:21 PM   #10
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It's installed. That took less time than I thought it would, even with cleaning up some gunk. Old shaft required a little finagling to get out, which should be expected with a two-piece propeller shaft.



Side by side, you can see the yoke on the newer 1-piece shaft is longer. I thought this might be an issue on install, but it just slid right in and there was plenty of room on the back side.



There are 2 caps and 4 bolts to hold the u-joint/spider onto the rear end. My manual said to tighten to 16 ft lbs., which is about the lowest torque setting I have. That doesn't seem very tight, but these are only 11mm bolts, and the spider just needs to be held in place, like a rod cap on the crankshaft.

Test drive went well! I didn't have any issues, later today or tomorrow I should be able to see how everything feels on the highway.

Review of the procedure. Removal:
  1. Remove center support bearing screws (18mm and 13mm)
  2. Remove spider/u-joint caps (4 bolts, 11mm)
  3. Slide drive shaft forward (best to place a milk crate or something underneath to catch it in the next step)
  4. Lower the u-joint side out of its housing.
  5. Slide shaft rearward and carefully work out. Try not to bump your head.
Installation of the new shaft:
  1. Clean up the yoke seal as necessary, and apply chassis lube on the outer ring.
  2. Slide the 1-piece shaft yoke into the transmission extension case.
  3. Move back to the rear end, and carefully lift the shaft as you slide the spider back into its housing.
  4. Install the caps and torque bolts to 16 ft lbs.
One last look at the broken old shaft. I thought I could reuse the bracket, but it's basically welded into place and wont slide over the ends of the shaft. Anyway, it isn't necessary on the new one.


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