low speed clunk in rear end

[L48]

My first thought was "this is a u-joint". At speeds below 5 mph there is a ryhtmic clunk. I hear about 2 or three clunks when the car starts moving. It reminded me of sounds of a bad cv joint on GM front wheel drive cars.

The problem is I could not locate a loose u-joint. I jacked up the car and tried turning the wheels and saw no play in the u-joints. I also tried moving the half-shafts by hand to see if there was any play but could not feel any.

Any thoughts?

 

[gmjunkie]

It's a u-joint or WB. a little dry!! Prob is! Its hard to find!! LOOK for rust powder around U-joint cap's at seal!! If you dont find any, then take out Drive shaft theas joint's move less and have a tend. to ware more in one spot on u-joint spindle!! junk!!P.S. Check Rubber mount at front of Diff housing!!

 

[Chas]

i had a clunking sound...but this seemed to change the motion of the car when i heard it.turns out , the ring bolts in the rear end had loosened and were bouncing off of things...i have heard its not uncommon for this to happen in a vette.the repair cost me over $2000 needing a new rear end ,housing and all...the core was worthless for return...including labor out the door....my opinion is that you find a person that knows this rearend and u-joints.....have them look it over before you have a problem like i did....on the bright side, i did go from a 3:08 to a 3:55 ratio and it is much better out of the hole!
Chas

My first thought was "this is a u-joint". At speeds below 5 mph there is a ryhtmic clunk. I hear about 2 or three clunks when the car starts moving. It reminded me of sounds of a bad cv joint on GM front wheel drive cars.

The problem is I could not locate a loose u-joint. I jacked up the car and tried turning the wheels and saw no play in the u-joints. I also tried moving the half-shafts by hand to see if there was any play but could not feel any.

Any thoughts?

 

[brumbach]

My clunking sound came from missing trailing arm shims. Periodically, when turning a corner at low speed, the trailing arm would move causing the noise. Dicovered the problem, had the trailing arms realigned with required shims and all is well. Hopefully, your problem will be so simple.

 

[L48]

It's a u-joint or WB. a little dry!! Prob is! Its hard to find!! LOOK for rust powder around U-joint cap's at seal!! If you dont find any, then take out Drive shaft theas joint's move less and have a tend. to ware more in one spot on u-joint spindle!! junk!!P.S. Check Rubber mount at front of Diff housing!!

The u-joints on the main drive shaft have been replaced. They have grease fittings. I can't tell you why I did not grease them when I was looking at them! I will try this and see if it helps, and look closely for rust under the caps on the half shafts. If not then I'll have to figure out where to go next.

I am not sure it is the trailing arm since it clunks when I am going straight, but I am not ruling anything out yet.

Loose ring gear? Yikes! Sorry to hear about that one. Has anyone else had this problem?

 

[John Kuzman]

Had the same clunking problem last year. Side yoke clip fell off. Ended up re-building rear suspension.

Jack up rear end and have someone move the rear wheels in and out from the 12 o'clock and 6 o'clock position while you watch the side yokes where they enter the rear diff. You should see only minimal movement. I do not remember the tolerence, but in my case, I saw over 1/2" movement.

The good news is I did not damage the rear diff. I pulled the rear end and trailing arms and delivered them to Bairs up in northwest PA, just over the Ohio border. Bairs is probably a 1 1/2 - 2 hour drive for you. Great people and always available by phone for follow up questions.

 

[L48]

Had the same clunking problem last year. Side yoke clip fell off.

Thanks - this is also a possibility I will check into.

 

[Billybeau1]

I had that problem last year with my 74. I know this is hard to believe but I had bad brake calipers on the rear. When I renewed the calipers, the clunk disappeared. Strange but true.

 

[gmjunkie]

I had that problem last year with my 74. I know this is hard to believe but I had bad brake calipers on the rear. When I renewed the calipers, the clunk disappeared. Strange but true.

Not hard for me to Believe!! If it will happen it will happen Here!! junk!!

 

[74bigblock]

Does it make the sound when you are moving at a constant speed? How about when turning? How about in Reverse? Is it only when you accelerate from a stop?

 

[glen242]

i had a clunking sound...but this seemed to change the motion of the car when i heard it.turns out , the ring bolts in the rear end had loosened and were bouncing off of things...i have heard its not uncommon for this to happen in a vette.the repair cost me over $2000 needing a new rear end ,housing and all...the core was worthless for return...including labor out the door....my opinion is that you find a person that knows this rearend and u-joints.....have them look it over before you have a problem like i did....on the bright side, i did go from a 3:08 to a 3:55 ratio and it is much better out of the hole!
Chas

Had the same thing happen on my '76. Rear end guy told me that it is very common on '74 - '77 'vettes. He claims the GM workers did not always use Loctite on the bolts as they were supposed to. A loose bolt was thrown into the cover making a hole as if shot with a rifle. When we took the rear end apart we found 2 bolts completely out and the others were very loose. Good excuse to buy a HD cover.

BTW, had the rear end completely rebuilt, yokes, bearings, posi clutches, everything new but the ring and pinion. Cost me about $800, parts + labor. I did deliver the rear end to him.

 

[steelblue75]

Suck out the diff. lube from the rear end, add new stuff with posi. additive.

the clutch plates are sticking, not sliding like they should.

 

[wishuwerehere82]

Suck out the diff. lube from the rear end, add new stuff with posi. additive.

the clutch plates are sticking, not sliding like they should.

I second that.

 

[L48]

Does it make the sound when you are moving at a constant speed? How about when turning? How about in Reverse? Is it only when you accelerate from a stop?

Does not happen at constant speeds. Does not happen after the first few feet of movement. I have only noticed it accelerating forward from a stop. I have not noticed it when backing up or turning.

As far as the calipers, I have tried slowing without the brakes, then starting again and the sound is there, so I don't think that's it.

Suck out the diff. lube from the rear end, add new stuff with posi. additive.
the clutch plates are sticking, not sliding like they should.

Would this happen going in a straight line?

 

[jdp6000]

Don't know if this will help. I had a clunking sound for a while. I did the usual...replaced U joints...yokes etc. A local mechanic found the problem. I was missing a rubber bushing just above and to the front of the differential.

Jim

 

[steelblue75]

Does not happen at constant speeds. Does not happen after the first few feet of movement.


Would this happen going in a straight line?

I had the Same problem on my 75 loud banging noise, comming from
under the car, happened when starting out going real slow. could feel
it. changed diff. fluid and possi. additive. it solved my problem.

 

[DPF]

I had the same clunk that you describe. Turns out that a common problem with the rear is the stub axles wearing against the spyder pin. My rear tires were leaning in at the top, that's the first sign. Now that I have gone thru the diff, and put in hardened axles and spyder pin, the tires are back up straight and no more noise. I went thru the entire diff, and changed bearings and seals and all. It may have been cheaper just to get an exchange unit.

 

[L48]

Update:

I removed the half-shafts from the car today with the intention of replacing the inner u-joints. The half-shafts came out really easy - all I had to do was unbolt them from each end and they came out.

The driver side yoke has about 3/8" play in it, meaning it will slide in and out 3/8 of an inch. This is considerably more than the passenger side and will need to be addressed. In the near term I am probably not going to do anything about this.

It is clear that the yoke is hitting the half-shaft on both sides. So I suspect that the parts I have are somehow not matching up - the yoke and the halfshafts. The driver side half-shaft says "Spicer A3N69" on the end near the differential. The passenger side says "Spicer A3R98" in the same place.
Can anyone tell me if these are OEM parts - or if they came from a 75 Corvette?

My plan is to replace the u-joints and grind the high spots off the axle yoke on each side so the clunking stops. It looks like about a 1/8" high narrow strip on each side of the yoke that is causing the contact.

 

[rscanlon69]

68stinger

ok I took my 68 out last eve for the second ride of this year. After warm up I found this clunking noise when I started out from a stop turning left, just a easy let the clutch out n clunk... not a good feeling! happened again pulling out from a stop, no issues in 3rd or 4th gears or higher speed (45-55 mph) or upon deceleration. I did hear/feel the clunk when letting clutch out (moving) backed her into the garage. car has 54k original miles n has sat in garage with less than a hundred miles traveled each year past 25yrs. all original excluding braking system was gone over. From what I read here, my first thought is to maintenance the rear differential and check for universal joint failure and the front bushing. Any suggestions? thanks, I don't like when my baby is not feeling good

 

[Tom Bryant]

First I'd change the differential lube and add the posi additive. It sounds like posi clutch chatter to me.

Tom