Rear end noise - Help
Thread Starter
4th Gear
Joined: Dec 2003
Posts: 4
Likes: 0
From: Garden City South Ny
Rear end noise - Help
My dad purchased a 1976 Corvette with an L48, 4 speed a little over a year ago. The car is pretty much stock except for the interior and a new true dual exhaust. The previous owner did work on the suspension and replaced the shocks and bushings. One problem is the shifter will pop out of 2nd gear when decaccelerating, i was wondeirng if anyone else has had this problem, and if they know how to fix it. And the second more serious problem is there is a noise comming from the rear of the car sometimes but quite often when making turns and sometimes while accelerating straight. Its kinda like a thump thump thump, and it is quite loud and doesn't sound to pleasent. I hope someone has an idea of whats causing this becuase we have no clue. Thanks for the advice.
Melting Slicks
Joined: Jul 2002
Posts: 3,128
Likes: 3
From: Deltona (son of Deland and DAYTONA) FL
Originally Posted by Jclgodale3
try draining and replacing your differential oil and remember to add the posi additive...this is a cheap start but amy solve your rearend noise problems...
The posi additive is available at a GM dealer.
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
Originally Posted by LilRed76
My dad purchased a 1976 Corvette with an L48, 4 speed a little over a year ago. The car is pretty much stock except for the interior and a new true dual exhaust. The previous owner did work on the suspension and replaced the shocks and bushings. One problem is the shifter will pop out of 2nd gear when decaccelerating, i was wondeirng if anyone else has had this problem, and if they know how to fix it.
Originally Posted by LilRed76
And the second more serious problem is there is a noise comming from the rear of the car sometimes but quite often when making turns and sometimes while accelerating straight. Its kinda like a thump thump thump, and it is quite loud and doesn't sound to pleasent. I hope someone has an idea of whats causing this becuase we have no clue. Thanks for the advice.
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
Originally Posted by LilRed76
My dad purchased a 1976 Corvette with an L48, 4 speed a little over a year ago. The car is pretty much stock except for the interior and a new true dual exhaust. The previous owner did work on the suspension and replaced the shocks and bushings. One problem is the shifter will pop out of 2nd gear when decaccelerating, i was wondeirng if anyone else has had this problem, and if they know how to fix it.
Originally Posted by LilRed76
And the second more serious problem is there is a noise comming from the rear of the car sometimes but quite often when making turns and sometimes while accelerating straight. Its kinda like a thump thump thump, and it is quite loud and doesn't sound to pleasent. I hope someone has an idea of whats causing this becuase we have no clue. Thanks for the advice.
Drifting
Joined: Mar 2003
Posts: 1,608
Likes: 3
From: Canberra AUSTRALIA
St. Jude Donor '05-'06
Originally Posted by LilRed76
My dad purchased a 1976 Corvette with an L48, 4 speed a little over a year ago. The car is pretty much stock except for the interior and a new true dual exhaust. The previous owner did work on the suspension and replaced the shocks and bushings. One problem is the shifter will pop out of 2nd gear when decaccelerating, i was wondeirng if anyone else has had this problem, and if they know how to fix it. And the second more serious problem is there is a noise comming from the rear of the car sometimes but quite often when making turns and sometimes while accelerating straight. Its kinda like a thump thump thump, and it is quite loud and doesn't sound to pleasent. I hope someone has an idea of whats causing this becuase we have no clue. Thanks for the advice.
The rear end could also be internal so do the fluid change and add posi like the other guys suggested. If it is high mileage then it may be worn yokes and worn out U-joints, or the more common rear bearings. Get it up in the air and start pulling and pushing on the car.
What moves? Because most of it should not by more then .010".
Good luck. It may get expensive....
Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,987
From: Connecticut, USA
As said you can check the shifter, but chances are 2nd was banged a few times and both the syncro and 2nd teeth may be worn. Slider may also be worn. Will require removal most likely.
Rear end- Try the oil and additive change, but you real;ly have to look at the rear suspension. Again if the car has been beat on then you may a few items that ned attention. Look at the U-Joints, front diff snub bushings, change the oil and see where you are. Sounds like you have a very used vette- not uncommon to find on the market these days.
If you just got this car and do indeed need to make some major repairs you might want to think things over before spending a lot of money on it. If you can do most of the work I can walk you through a lot, but if you are not equiped with tools, room, or experience you're facing a big bill if you farm out the work.
Good Luck.
Gary
Rear end- Try the oil and additive change, but you real;ly have to look at the rear suspension. Again if the car has been beat on then you may a few items that ned attention. Look at the U-Joints, front diff snub bushings, change the oil and see where you are. Sounds like you have a very used vette- not uncommon to find on the market these days.
If you just got this car and do indeed need to make some major repairs you might want to think things over before spending a lot of money on it. If you can do most of the work I can walk you through a lot, but if you are not equiped with tools, room, or experience you're facing a big bill if you farm out the work.
Good Luck.
Gary
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Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Popping out of gear on decel is a very common problem when you break a syncro key. If not that then most likely a worn blocker ring. But do check the adjustment first since that costs nothing.
Safety Car
Joined: Dec 2001
Posts: 4,832
Likes: 0
From: Florida
Originally Posted by pws69
Sounds like you have worn synchros which, unfortunately, means you are due for a requild. It will only get worse - eventually, you won't be able to apply ANY power when in 2nd without it jumping out.
As others have said, sounds like it's lacking in the Posi Additive department. Suck the old stuff out, put in a bottle of the GM Posi Additive (I actually found some at a CAP once), then fill with your favorite gear lube (mine's Mobil1). Drive it in several figure 8's in each direction and you should be all set.
As others have said, sounds like it's lacking in the Posi Additive department. Suck the old stuff out, put in a bottle of the GM Posi Additive (I actually found some at a CAP once), then fill with your favorite gear lube (mine's Mobil1). Drive it in several figure 8's in each direction and you should be all set.
I had the same problems. I had the tranny and diff rebuild by Van Steel.
They did a great job. Try changing the diff fluid first. If that does'nt fix the problem have it rebuilt. The tranny will only get worse over time. You dont want it getting to the point were you need a new tranny. That will cost you big bucks vs. a rebuild.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
At best it is a tranny linkage adjustment (free) and a fluid change in the rear (about 30 bucks). At worst it is a tranny rebuild and rear rebuild. As was said earlier it depends on your skills on how much this will cost. If you farm it out hold on it will cost some $$$. Not as bad if you remove the transmission and rear yourself and have someone rebuild it for you.
Drifting
Joined: Jan 2005
Posts: 1,389
Likes: 9
From: Seabrook Texas
St. Jude Donor '05
What is considered Big $$$ just a ball park? I have heard the rear end is somthing the average joe would not want to mess with. So if I were to drop it off at a shop and want new bearings, u joints bushings, trailer arms etc. what would be a resonable price?
Premium Supporting Vendor
Joined: May 2000
Posts: 4,312
Likes: 70
From: Clearwater FL
Originally Posted by swtato
What is considered Big $$$ just a ball park? I have heard the rear end is somthing the average joe would not want to mess with. So if I were to drop it off at a shop and want new bearings, u joints bushings, trailer arms etc. what would be a resonable price?
Diff rebuild is $545
T-Arm $300-$400 depending on how your parts are it could be more
1/2 Shafts $80 - $85 each
Tranny rebuild is $425. plus parts if needed
Premium Supporting Vendor
Joined: May 2000
Posts: 4,312
Likes: 70
From: Clearwater FL
What the other have stated is true. Change the diff fluid 1st. 2 bottle of fluid 1 bottle of posi fluid. Put the posi fluid in 1 st and than do figure 8's in a parking lot.
If your tranny poppin, I would think it's the 1/2 slider also.
If your tranny poppin, I would think it's the 1/2 slider also.
Melting Slicks
Joined: Dec 2004
Posts: 2,161
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From: pr, frederick md.
they all speak the truth, but i thought the synchros were to help get into the gear? old trannys didnt have them! the first place i would look would be the linkage and then the fork and slider. wouldnt be too concerned with the synchros. but check the stops on your shifter and linkage adjustment, that outa fix it 
Burning Brakes
Joined: Apr 2003
Posts: 844
Likes: 0
From: Central KY
I would agree that you double-check the shifter adjustment on the tranny first. Get that little metal guage from CC (sold under their C2 parts only!) that locks your shifter into neutral with all the pieces aligned... Adjust the rods and see what happens. With mine it wouldn't go into 2nd gear at all. It ended up needing a rebuild - forks, synchros were bad...
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
The transmission is due for a rebuild.
On the rear end, these cars had a bad problem in the rears. They were defective from the factory. The hardening on the end of the half shaft yoke was not good and the yokes wear off. That lets the yoke recede into the rear end and grinds up metal inside. Naturally this aint too good. It causes a variety of maladies one of which is wearing gears and posi clutches which causes the noises, another is alignment of the rear wheels. You should check for this condition by looking at the yokes and seeing if they are rubbing the main housing and or are not out where they are supposed to be. Symptoms will be excessive negative camber, rubbing on the rear housing, noises, clips off of the shafts.
On the rear end, these cars had a bad problem in the rears. They were defective from the factory. The hardening on the end of the half shaft yoke was not good and the yokes wear off. That lets the yoke recede into the rear end and grinds up metal inside. Naturally this aint too good. It causes a variety of maladies one of which is wearing gears and posi clutches which causes the noises, another is alignment of the rear wheels. You should check for this condition by looking at the yokes and seeing if they are rubbing the main housing and or are not out where they are supposed to be. Symptoms will be excessive negative camber, rubbing on the rear housing, noises, clips off of the shafts.
Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,987
From: Connecticut, USA
Originally Posted by wombvette
The transmission is due for a rebuild.
On the rear end, these cars had a bad problem in the rears. They were defective from the factory. The hardening on the end of the half shaft yoke was not good and the yokes wear off. That lets the yoke recede into the rear end and grinds up metal inside. Naturally this aint too good. It causes a variety of maladies one of which is wearing gears and posi clutches which causes the noises, another is alignment of the rear wheels. You should check for this condition by looking at the yokes and seeing if they are rubbing the main housing and or are not out where they are supposed to be. Symptoms will be excessive negative camber, rubbing on the rear housing, noises, clips off of the shafts.
On the rear end, these cars had a bad problem in the rears. They were defective from the factory. The hardening on the end of the half shaft yoke was not good and the yokes wear off. That lets the yoke recede into the rear end and grinds up metal inside. Naturally this aint too good. It causes a variety of maladies one of which is wearing gears and posi clutches which causes the noises, another is alignment of the rear wheels. You should check for this condition by looking at the yokes and seeing if they are rubbing the main housing and or are not out where they are supposed to be. Symptoms will be excessive negative camber, rubbing on the rear housing, noises, clips off of the shafts.
You probably have several things going on back there.
