I have something going on with our 77. There is a shudder for lack of a better word upon acceleration, it also appears to be a little laggy. I put it up on jack stands last night and while I was under it had my wife accerate slightly and it was difficult to see what the problem was as everything was sort of shaking. Checked the rear diff seems to have enough lube, but I am going to change it out anyway. The brakes don't seem to be an issue as I was able to turn the wheels when in neutral. Possibly u-joints? Any ideas? Thanks for the anticipated advice.

 

The pinion mount or trans mount will give you a wiggle or rubble under your seat and make the car seem lagging in power ...

Take a pry bar or big screwdriver and see if you can get up and down movement in those areas.

 

Could be half-shaft u-joints but you would see that with the wheels jacked up and turning. Trailing arm pivot bushings that are shot can give you weird sensations and eratic handling.

 

You have a limited slip differential surronding your rear gears. This means clutches. If your *** end is dry, your vette will exhibit bad behaviors, over/under steer......... unstabile arround corners. GM makes a special rear end grease for corvette diff's SAE 80W-90 [GM numbers..... lifted off the bottle...... "1#1052271 petroleum oil [gear oil]...... CAS X 64742-65-0

 

how are your tires? I had a rear side to side wobble at acceleration and slow speeds and it was my old unevenly worn tires

 

I have had something similar happen a long time ago on a 1972 El Camino when the transmission mount dry cracked and broke. made the under body shake a bit till I replaced it. I also agree on the U Joints have had to replace them also in the past.

When you had the rear of the car in the air did you feel for rear wheel bearing play? My 1977 has it and I need to take it in for a rear bearing adjustment or replacement. I can move the rear wheels a little while it is off the ground and hear than feel a click when I do it. So I know they need adjusting or even replacing.

 

Tires will shake at a certain speed and is not constant most will vibrate between 50 to 70 MPH in about 5 MPH increments from start to stop

Flat spots in tires from sitting too long on the ground show up between 60 and 70 MPH than quick cure is pump them up to 40 psi and run them a few hundred miles. Tires out of balance will also show up after 50 MPH and can vibe for a long or short time depending how far they are out of balance they are.

Bent or out of round rims will cause vibrations at different speeds also depending on how bent the rim is. The only fix for a bent rim is replacement but balancing them helps after the tires wear into the bend.

My bearing problem shows up at around 55 MPH and does not go away until after I pass 70 MPH. I am not driving the car much until they are replaced because I could fry a spindle on the rear.


I used to be a tire guy 20 + years ago

 

Rear Clutches.

 

Are you suggesting that the rear limited slip differential needs to be rebuilt?

They do sell them rebuilt in increments of different ratios these days from 3.08 to 3.73 for limited slip rear ends differentials. Here are a few.


http://www.ecklerscorvette.com/catal...tials&cat=1388

 

Well, It is a 77, which is notorious for grinding up stub axles and depositing all of that metal in the rear end. If you determine that is occurring, it would be advisable to go ahead and repair the unit. Otherwise first try to change the fluid and additive.

 

Thanks for all the advice. I don't think it is the tires as they are fairly new, when I get under there again will change the fluid, check the u-joints and trans mount. Is it possible I could have a parking brake hanging up? Thanks again and I will keep you posted.

 

If the parking brake was hanging up the rear hub would be really hot so it is not very likely this is happening.

Heck I still need to inspect the parking brake on my 1977 since it does not work at all. I think it really needs adjusting but not going to adjust the cables until I pull the hub to inspect the pads. Since the rear has 2 separate brake systems for parking and stopping on them and my disk brakes only looked about 10 % worn I also need to inspect mine further. Front brakes are only 50 % worn and all the calipers look fairly new. Fronts calipers are painted black and rear is just a little rusted. I will paint them black soon enough. Brake fluid on mine needs to bled out because it is really dirty. I will use a full synthetic Valvoline DOT 3/4 Fluid when I bleed them out.

My rear bearings need adjusting or replacement I can feel them loose when I put the car up in the air a few weeks ago. I know the rear diff oil needs replacement since I do not think it has ever been done. Going with Valvoline 75w90Full Synthetic since it is a Limited Slip DIfferential gear lube.

•Contains additives to assist in protecting gear teeth
•Maintains excellent low temperature fluid protection down to -50°F (-46°C)
•Provides outstanding thermal stability for cleanliness and longer service life
•Contains special additives to reduce chattering in limited-slip differentials
•Recommended for (conventional and limited slip) manual transmissions where an API GL-5 or MT-1 fluid is specified
•Protects parts from rust and corrosion
•Compatible with conventional gear lubricants


I have some rear suspension problems and need some of it replaced. All the adjustment bolts are frozen and the alignment shop did not adjust it because they were afraid of breaking some bolts. When cornering hard under hard throttle I have a scrubbing sound and not sure what that is yet. Could be the rear diff or just bushings worn out on the rear suspension. My 1977 sat for long periods of time before I bought it and appears to have only about 144,000 original miles on the car. Still has the original blue paint on the engine and very clean. Wish it was the Chevy Orange liked that engine color a lot more

 

Well tonight got the car up on the jack stands again had a good look, there is a bit of a strange noise from the transmission, it leaks a bit and I have been putting of a rebuild as fluid is cheaper, we just call the car spot. The real problem I believe is that the driver rear tire can be moved in at least an inch at the top, well outside the acceptable movement, the passenger is practically nil. So my thoughts are the rear wheel bearing is shot, and I will have to get a shop to do it as it looks like I may need some special tools. Any thoughts on this?

 

Yes the rear wheel bearing on that side could be shot and it may require rear spindle replacement if that is what is causing your shuddering in the rear. Gotta love old cars their is always something to replace on them.

My rear bearings also need to be replaced I can move both of the rear the wheels and hear a click when doing so. They are not bad yet and it is on the list of things to do in the near future. I have inspected mine top to bottom in the 9 weeks I have owned it and know now most of my problems with the car I have. Knew it would be a money pit the first 2 years I own it. I fully expected to dump about $4000.00 into any classic car when I bought one again. I am half way there

 

Well have an appointment for Friday morning with a shop I really trust, so here's hoping, kinda rips me that I don't have the tools or the time to try and tackle this thing myself, but sometimes you need to go with experience! Mako you kinda sound like my dear wife, she expects we need to put some work into it. And at 38 years and all original things just wear out. And some things like the transmission leak we have chose to live with, about 500ml of fluid leaks a season, that's about 1/2 quart for my American friends. I will let you all know what I find out on Friday.

 

What kills me is I cannot do all the work myself and sometimes I have to pay others to do it for me. I perform all work up to the point I do not feel comforatable doing. I always will buy more tools if I think I can tackle the job.

 

Movement of 1 inch is not a bearing. If it was it would make a awful noise. Most likely the stub axle is worn and your tailing arm bushing are worn. You can see this when under the car while someone moves the tire at 12 and 6 oclock. The stub axle should move very little in and out in the rear end. You will also notice the trailing arm twist. If it's a bearing you would only notice the wheel moving without the stub axle or tailing arm twisting.

 

Possibly "shuttering on accelleration" from the U-joint rubbing on the tunnel when the rear end goes squat. My '64 did this when I replaced the rubber bushing with an aluminum Guldstrand piece and plenty of other people have also experienced this as the bodies sag. The easy solution is to remove the nut and use a big screwdriver to pry the two pieces apart, install a couple fender washers, and replace the nut.

The only evidence of this would be what looks like a pencil line in the fiberglass where the U-joint would rub.

 

Well got it back from the shop and the trailing arm bushing is shot! He says it is a huge job to replace and hasn't got time right now. Maybe as a winter project. He had it on the lift and saw the problem and the front bushing is screwed. How much work to replace this? And can an average to above average mechanical guy tackle this? Thanks.

 

From what I can tell it is not the easiest job to perform because this also requires a rear wheel alignment after the bushing is replaced. If you choose to perform the work yourself you will still need to bring it into a shop for a rear end alignment because the trailing arm at the bushing is also where they adjust the rear Toe in/out settings.

You should probably do both sides so your suspension travel is the same on both sides of the rear end. Probably about 2 to 3 hours labor for a mechanic to perform on each side would be my guess. If one bushing is shot the other is not far behind the first one that went bad.



Here are some diagrams of the rear end.

http://www.autozone.com/autozone/rep...00c1528008379b

Here are some of the parts required.

http://www.ecklerscorvette.com/suspe...ling-arms.html