1976 Rear End Noise

[twamd80driver]

My 1976 C-3 rear end developes a rubbing (friction) noise AFTER it has been driven and comes up to temperature. It is noticable when turning corners (aka turning in the driveway) at slow speeds or from a dead stop. I just had the whole rear end rebuilt, and I am waiting for a slot to get back in but the summer is wasting away. Any help would be greatly appreciated!
Chris

 

[Chas]

My 1976 C-3 rear end developes a rubbing (friction) noise AFTER it has been driven and comes up to temperature. It is noticable when turning corners (aka turning in the driveway) at slow speeds or from a dead stop. I just had the whole rear end rebuilt, and I am waiting for a slot to get back in but the summer is wasting away. Any help would be greatly appreciated!
Chris

did you do the breakin stuff after the rebuild? doing figure 8's and such?

 

[L48]

Could this be the e-brake hanging up slightly? When the parts (edit->) heat up they expand increasing the friction.

Have you looked around under there to see if you can see anything rubbing?

I could also guess a caliper is hanging up a little when it gets warmed up.

 

[twamd80driver]

did you do the breakin stuff after the rebuild? doing figure 8's and such?

I was not told about this....what does that do? I am thinking of adding another 4 oz posi fluid....What do you think?

 

[twamd80driver]

Could this be the e-brake hanging up slightly? When the parts hang up they expand increasing the friction.

Have you looked around under there to see if you can see anything rubbing?

I could also guess a caliper is hanging up a little when it gets warmed up.

Thanks L-48....I had some brake work done too.......I guess it is either or!

 

[Chas]

I was not told about this....what does that do? I am thinking of adding another 4 oz posi fluid....What do you think?

by doing figure 8's it works the fluid into it and works the clutch packs, its all about getting the lube into tight places...i would be sure about the posi fluid, im not the expert, but i think it has a mixture ratio ...i would not use it until i found out from the installer or manufacturer about the break in period.
it took me about 2 weeks of manuvers and such to break in my new rear end.
mine was totally ruined and i had to replace the entire unit...maybe mine was diffrent than yours and your dont require it...but i did it and mine is working good.
check into it and be sure your doing the right thing before you do it....
Good luck, Chas

 

[waterboy1976]

Sounds kinda like a caliper hanging slightly. Working at a car dealer for as long as I have with "lot rot" aka rust build up on the rotors we hear a lot of "friction" at slow speeds... Good luck TWA

Rob

 

[GTR1999]

Differential should not require breaking in other then new gear sets. In this case drive the car about 20 miles but nnot longer then 30 minutes until the differential is warm. Stop and let it cool for an hour. Repeat 3-4 times and change the gear oil at 500 miles. No heavy starts. If the posi was rebuilt like stock with the springs and you're getting posi hammer you can try adding additive to get it into the clutches. If this was an exchange rebuild then all bets are off as to how it was built. Good luck hopefully it's nothing serious.

 

[Dave Z]

by doing figure 8's it works the fluid into it and works the clutch packs, its all about getting the lube into tight places...i would be sure about the posi fluid, im not the expert, but i think it has a mixture ratio ...i would not use it until i found out from the installer or manufacturer about the break in period.
it took me about 2 weeks of manuvers and such to break in my new rear end.
mine was totally ruined and i had to replace the entire unit...maybe mine was diffrent than yours and your dont require it...but i did it and mine is working good.
check into it and be sure your doing the right thing before you do it....
Good luck, Chas

Have had the entire rear (all components) replaced (bushings too), and my '75 still thumps and bumps and clanks around corners. Today the u-joints were replaced. The drive shaft u in the rear was binding. The fliud was replaced along with the proper 2 cans of GM additive and it's still doing it!
Does it really take time for the fluid to work it's way through the clutch plates? I'm at my whits end. Coming home from the shop after the u-joint repalcement today I thought the rear was going to fall out when hanging a left from a traffic light. Then, it just smoothed right out. This is the first I've read in the forums about a "breaking in" period. Could it actually be I just need to drive it around more? I put about 100 miles a week on it.

 

[crause]

Slow down on all of the mechanic work and try adding another bottle of anti-slip positrac additive and only use the GM brand. This took care of the exact problem on my 75. Use only GM diff. fluid with the proper additive and you shouldn't have anymore problem. The first time I changed the diff. fluid I used a synthetic and the problem continued. If you did this then suck it all out and put in the correct type.
Good luck

 

[BADWILLIE]

check the half shafts going into the rear if there pulling away its a shim problem . bring the car back to who did the rear for you . that is part of the rebuild good luck

 

[Dave Z]

Slow down on all of the mechanic work and try adding another bottle of anti-slip positrac additive and only use the GM brand. This took care of the exact problem on my 75. Use only GM diff. fluid with the proper additive and you shouldn't have anymore problem. The first time I changed the diff. fluid I used a synthetic and the problem continued. If you did this then suck it all out and put in the correct type.
Good luck

All of the rear needed replacing anyhow, it's taken 2+ years for that to happen. I had thought that after all of the work, this problem shouldn't exist anymore.
So, are you suggesting I add a third container of GM posi additive to the rear?

 

[GTR1999]

If the stock posi setup is used( as in most cases) you may find you can add a gallon of additive and still have a problem. You have a late model C3 which uses what I call snowflake clutches. They are close to junk, the new fiber clutches are junk. I've rebuild and custom tuned many posi's and the stock units hammer because of the sloppy tolerances from day one and the loading pressure from the 4 springs against the clutches. Depending on how tight the spider gear backlash is set to will determine how much hammer you'll get. That is if the cluthces haven't broken yet. If you go over to that other forum and look up my is gtr1999 you'll find a lot of pictures on this subject and how to fix it.
Good luck, try the additive first it may still work but keep in mind what I said.

Gary

 

[RUSS O'BLENES]

My 1976 C-3 rear end developes a rubbing (friction) noise AFTER it has been driven and comes up to temperature. It is noticable when turning corners (aka turning in the driveway) at slow speeds or from a dead stop. I just had the whole rear end rebuilt, and I am waiting for a slot to get back in but the summer is wasting away. Any help would be greatly appreciated!
Chris

I HAVE REBUILT MANY OF THESE REARENDS AND FOUND THAT SOME ARE WORSE THAN OTHERS WHEN IT COMES TO THE CLUTCH CHATTER WHEN TURNING. I DON'T KNOW WHAT IS IN THE GM POSI ADDITIVE, BUT IT IS THE ONLY ADDITIVE THAT SEEMS TO CURE THE PROBLEM. I KNOW THAT SOMETIMES IT SEEMS THE REAREND IS FALLING OUT, BUT I HAVE HAD SOME THAT HAVE TAKEN 500 MI TO HEAL ITSELF, AND I HAVE PUT UP TO THREE OF THE SMALL BOTTLES IN THE REAREND. HOPE IT WORKS OUT FOR YOU. RUSS

 

[Dave Z]

I know this is an old thread, but I finally have resolution for the rear end problem on my Vette. Here's the story: After all the rear end work I had done (including a new rear) the only thing really left to chance was the new rear itself. Odds were not in my favor that the new rear was bad. The shop I use has been baffled by the ongoing problem too. One day the shop owner happened to be talking to a rear end specialist. He told this specialist about all the symptoms my car was having and said, "Oh yeah, if a rebuilt / new rear sits without lubricant on the shelf as inventory for any length of time, the clutch packs will ruin no amount of additive will cure it". The shop pulled the rear and all of the plates were burnt and scored, and after less than only 2K miles from the install date. He replaced the plates, and ever since the rear has been smooth as silk. I haven't seen this particular scenario posted, so I just thought I'd add my story to all the other cures.

 

[THORIN]

Mine was doing that, all it was, was a cotter pin that had bent up and was rubbing on the wheel. It was on the outside of the brake shoe caliper. Sniped a little off. No more rubbing.

 

[Evolution1980]

He told this specialist about all the symptoms my car was having and said, "Oh yeah, if a rebuilt / new rear sits without lubricant on the shelf as inventory for any length of time, the clutch packs will ruin no amount of additive will cure it". The shop pulled the rear and all of the plates were burnt and scored, and after less than only 2K miles from the install date. He replaced the plates, and ever since the rear has been smooth as silk.

Definitely good info to know! Thanks for posting the update! You can almost guarantee that at sometime in the future, your find will come back around to help someone else with your same situation!

 

[Tepot]

Hi twamd80driver,

Just wondering if you got this problem solved? I've just had my rear end rebuild. when I say rebuild I mean new Motive Gear 3:55 ring an pinion plus brand new posi clutch.

since then after driving a few miles and the diff temp get's warm. It's making noise like crazy when making a turn. It's just like the complete rear end was ready to fall in pieces.

The mecanic checked everything again and everything is tight. He said he added additive but the noise is still there. Didn't know anything about the figure 8 breaking so I will try that tomorrow for sure.

Can you tell me if you were able to get yours fix and how did you do it?

 

[GTR1999]

If the noise you're getting is from cornering from a stop that sounds like clutches. If the posi was built with the 4 springs then you may be getting hammer from that setup. Clutch type is also important as you have a choice of fiber or solid clutches. Also check to see if the side yokes are not hitting the housing- this shouldn't be the case if the unit was just rebuilt- it shows up with very worn side yokes.
If the GM additive doesn't help then it's not going to get better and will require checking. If it's the clutches you can live with it or tune the posi to eliminate the hammering.

 

[JimVette]

I had the same problem on my '66 years ago and the only thing that fixed it was 2 bottles of additive. I don't know if it made any difference but mine was an original and never rebuilt. Back then the additive was whale oil and GM changed some time later.