Been hearing some strange sounds coming out of the back of my newly acquired '76. So started with the brakes and had them checked today. Everthing in real good shape except the cost-cutter pads previous owner installed......lucky the rotors not harmed any. Anyhow, most of problems went away....for a while. Got to my mom's house and turned into the driveway which slopes upward. Immediately the groaning & creaking sound returns as before plus a couple of popping sounds. Started home later and all continued just as bad - especially when starting from a stop and turning. The more incline upward after a turn, the worse it sounds. So, I am still a rookie with a Vette. I desperately need the experts to guide to the next area of focus. Would it be the springs? Maybe not a big deal but it is bugging the stew out of me....especially since I just bought it and honeymoon beginning to wear off way too fast!! Sincere thanks for any & all advice & assistance!!

 

I can't answer your question exactly except to say that my 76 makes some of the noises that you described. I think some noise is the nature of these cars, although yours does sound excesive. good luck

 

I think you are correct that some is to be expected. That much I did know going into shopping for one about a year ago. This is excessive though. It almost could be described as sounding like metal stretching or bending. I don't think there are any rods or the like in the rear except of course the axle. The brake mechanic did not notice any thing else though this morning that looked wrong outside the pads. I have had one other piece of advice that the springs may be misaligned and causing the trouble.....don't know or how I could know except by riding under there while someone else is at the wheel.....and I am a bit too plump and old for that experiment! Thanks for your reply. Any light at this point is better than no light. I just don't want to tear up anything or end up sitting in the road somewhere after losing part of the rear end!

 

There are soem common areas for noise in the rear suspension,brakes and differential on C2 & C3 vettes.

If you're getting a hammering sound like something is moving very hard while turning most likely it's the posi clutches in the rear end. They stick and people use differnt oils in them. If this sounds like it then get the oil warm and drain it out. The only way to that is pump it out with a hand pump. I add drain plugs to them but the factory never did. Use 2 bottles of GM limited slip additive, available from any GM dealership part counter. I use 90 wt gear oil.

If you heard a ticking noise coming from the wheels it could be the parking brake springs or shoes hanging up or broken. It could also be rear bearings-lets hope not.

If you get thud sound on movement it could be a bad U-Joint in a 1/2 shaft.It could also be worn bushings in the strut rods, front differential mount, or T arm. It would help to know what work was done on the car
recently.

Finding a good early vette mechanic can be almost as hard as finding the noise. A lot of the people here do their own work so if you're gaem you'll get a lot of help here. Although a lot of the experienced guys have left there are still a few who know these cars.
Gary

 

I agree with above.....sounds like problem I had. Get all (if any left) fluid sucked out of rear put in container of GM Posi Additive and top off with 90 W. If noise is mostly in turns thats it. PS- After fluid change run car in tight figure 8's in a empty parking lot to distribute lube good. Noise should subside rather quickly.

 

While your under there changing the rear diff fluid, look at all the u-joints close, it sounds like its one or the other. If it's one of the u-joints and it sounds as bad as you say, you should be able to tell by looking at it.

 

Sounds like you have a positrac problem. There is a special lubricant which MUST be used in the dif. Have the lube changed and add the proper amount of this 'special' positrac lube purchased from GM. If this is not added the 'clutches' in the rear end will stick and chatter and cause all kinds of noice and vibrations when you make low speed turns.

 

You quote is sooooo true!

 

Yep, 100% accurate. Bad news is that I tried the posi lube and the figure 8s. No joy. Still worth a go as its an easy fix (IF it works). I have decided to do the whole rear end - diff trailing arms etc. Might as well get it all done properly

 

You might give Van Steel a call (Corvette Forum sponsor) and ask what they think. Their link is on the left side of this page under Accessories.

If you decide to do the work yourself, the Van Steel suspension video is very useful.

 

Changing the spring is one of the most cost effective changes. There cheap and the ride will be so much better. While changing it you can check the control arm condition and strut bar bushing. If your strut bar bushings are bad they will also pop.

The fluid change as discribed is also a good option. I know when my posi started to fail, if you would launch hard it would head for the ditch. I almost hit the guard rail at the track and I knew it was time.

 

I think you have the right idea here. Once you start taking the rear apart, you might as well go all the way.

 

BINGO. when i 1st got my vette had terrible sounds from the rear, thought something tragic was wrong. friend told me to put this additive in there and my probs would be gone. i was so shocked a little additive cured that rearend racket.

 

Well, the last thing I wanted to hear - total rear end job.....fluid & fluid level OK but axle seals leaking, metal & trash in the rear end housing. Took it to an old pro with Vettes in my area who has owned & driven them for 30 years. He's getting up in age so don't fool with them much on mechanical side now....just manages a local tire & maintenance shop. They don't do heavy stuff like this. He said a lot of work had been done underneath and good work at that...but, someone did not go far enough and finish the job and now here I am stuck with it! Just part of the game and the risk with old stuff though. Should have thought more before jumping back into nostalgic reminiscing in the 70s! Live & Learn! The guy said I should check around and find someone good to do it with a garage and time to do it right...or, find a used one in good condition at a yard. Where would you guys advise me to start? Or, would it be better to let it go and find something else? I am somwhat mechanically inclined but not to the extent that I could do this job I am afraid..or the facilities to do it within. The old guy who diagnosed it has a '92 he wants to sell for $15K....30,000 miles, almost new & untouched. He said it was a 'deal' if I wanted to sell mine and buy his sometime in the future. I must admit the thought is now crossing my mind!

 

15k seems high for a C4 to me.

How is the rest of the car and do you like it? How much have you got into it would you recoup your money? 74+ vettes aren't going to be gold mines in the near future.

If you're going to keep it and think about doing it yourself I can send you the procedures I use to rebuild them. If you're going to farm it out it wouldn't hurt to know what questions to ask.Different places use different procedures when rebuilding them.

You can get a general rebuild for $500. Add in shipping, HD rear cover, yokes, gears and you're up to $1,000 not including labor to remove and install. It cost me about $650-700 in parts to do one, no labor. I'd put it up against anyones in the business though.

Think about it before you write anymore checks.

Good luck,
Gary

 

You have helped guide me back into the light I think. I went and picked it back up and drove it home. Figured I would leave it parked until deciding what to do. I figured already I could save a lot doing it myself but just been so long since I done anything (near as complicated as this sounds), but maybe not hugely complicated. I would alsolutely welcome with open arms your procedures/instructions. I called the Chevy dealership just to get some idea from them and of course they tell you little or nothing over the phone....only that the parts would come from Ecklers because they are out of production at GM. Any & all help to get me started would be great. This is great therapy and enjoyable for me once the ball gets rollinng....part of the reason I bought the car. I just did not anticipate this big of a bite right now....but got to stay positive and welcome it as a learning experience. I appreciate your offer more than you know and anyone else out there as well. Years ago I messed around with engines and nothing from the rear main seal back. So, that explains my ignorance with my problem. I'm so dumb with it that I do not even know what parts encompass the 'rear end' and other necessary items for success with it. As for the '92 for $15K, I have not given it serious consideration. Just wanted to go get the 76 back home and think about it a few days before 'writing any more checks' as you say. The only hint the service manager gave me was anywhere from $2000-3000 total cost for this job from a competent mechanic. I had this sinking feeling in my gut. I had been wondering all afternoon what it could be done for at home....and, how long does it take on average working alone on it? Well, enough questions and thoughts for now. Let me know how to get to square 1 and beyond and maybe there is light at the end of the tunnel. I have a 76 Vetter with nearly $8K in the car at present. It has 82K original miles, matching numbers on engine, everything original in & out and I hate to think about throwing up the white flag at the first crisis. So, what is another grand or so. I should be able to get my money back out in a few years. Of course, by then I will have probably rebuilt the engine and tranny as well. Thanks again.

 

With the exception of rear bearings and axles, you should be able do do anything on the rear end yourself. Change the spring, rebuild the diff, shocks, strut rods, u-joints - Get an assembly manual (AIM) and a haynes or chilton's and go to town.

spring: 300.00
bushings: 30-45
shock mounts (optional) 40 each
shocks - 45-100 each
Ujoints - 25 each

most stuff is not too expensive.

 

Thanks for the good words of encouragement. I had already ordered the manuals so as soon as they get here I am going for it. I will probably get most of stuff online - Ecklers or elsewhere...not many places around here I would trust for the right parts. You have done a fantastic job on yours - WOW! Wish I could afford a '73 or back, but had to grab what I could while the fever was high. Of course, you get what you pay for and now I got a little work in front of me but there have been many in front of me. Thanks again.

 

No problem. I PM'd you the procedures. For some reason the file wouldn't copy on the format used so I just copied the opened version. I'm going to PM you my phone number in case you have a question,maybe I can help you with. Take your time,maybe invest in some good tools,and you can do it.If you don't have the tools required at least you know what should be done if you bring it to someone.
Gary

 

I think all previous replys have covered what is likely to be the case. But one more you might later check is the swaybar bushings - those that are used to mount the swaybar to the frame. Mine need some lubrication (didn´t lobricate them good enough when installed the new swaybarkit)