I got my 78 Vette last year, but just in time to put it away for the winter. My first Vette. It has been quite a learning experience.

I posted this message at the Corvette Action Center forums, but I will post it here also.

I am experiencing a "binding" type of noise that sounds like it is coming from the left rear. So far I have replaced both rear calipers (and disks), the left front caliper, rear steel and flexible brake lines. I have had the left rear wheel bearings and u-joints replaced. I removed all the parking brake hardware from the left rear rotor.

The weird thing is the noise doesn't show up until I have driven it a bit (about 10 miles or so). Then it comes and gets worse until I get home.

I step on the brakes and get a binding type noise. Then, as I pull away, you can hear the "pulsing" of the binding until it goes away (till the next stop). It is like the pads won't quite release from the rotor.

I noticed that the rubber in the MC is loose, in that the plunger for the rear cup is always down when I open it, while the front one is up. Could it be causing enough resistence to prohibit the caliper pistons from returning in a timely fashion?

I have got to get this fixed before I wind up sleeping in ka-ching.

If you know of any good Vette mechanics in SE Minnesota, let me know.

 

Just so you know, the brake pads should always be touching the rotors on Corvettes. This is by design and allows for a firmer pedal feel since there is no extra pressure required before the pads start touching the rotors. There are springs inside each piston which push the pad to the rotor.

The rubber in the MC wouldn't have any effect on the brakes, but if one side is always "down" for the rear, it might be because that side is leaking. Do you have to fill it? Even with this sound, does the car stop OK? Could the sound be coming from the drive shaft or something else?

I'd jack up the car and spin the wheels by hand. If they turn OK and you don't see or hear anything else wrong, they are probably fine.

Good luck -

 

I'd replace the rubber lines to the back calipers just to rule them out. A collapsing line might be slow in disengaging - holding pressure on the pads.

 

Are you using a Corvette-specific master cylinder? Some other master cylinders will physically fit the Corvette, but won't work properly.

It's also possible that your brake pushrod is not properly adjusted and holding pressure to the brakes.

These would affect both brakes in that circuit, though.

Have you put the car up on jacks, hit the brakes and tried to see if there is in fact something holding the brakes?

I noticed in your writing that you've replaced just about everything in the hydraulics, like the flex lines, so you can rule out that part of the system.

I also wouldn't rule out a very worn differential clutch pack. This can do the same thing under the right circumstances.

 

The brakes work just fine. Nice and firm. No discernible leaks anywhere. The only time I have to put in brake fluid is when I am bleeding the brakes. Maybe that rubber bit just "falls down" when I take the top off.

My fear is that this is going to be an expensive thing. I just paid $500+ for the wheel bearings and u-joint replacement. The boss will not be happy.

 

Again, everything is as it should be, until I put a few miles on 'er. Then...

 

You mentioned the rear, how does your rear's cushion (bushing) look. I too went thru the mystery sound thiunking it was brakes and it turned out it was the cushion. Have you tried emptying your ashtray?

 

When you are braking fast, do you get a vibration, like a warped rotor?

 

I had similar problem. Convinced the brakes were all ok after all that work, I put in NEW gear oil with additive and no more problem. Done that first sure would have saved me alot of work.

 

The bushings need to be replaced. They look not good. No vibration, like a warped rotor. I talked to a guy from a local brake shop last night. He appears to know a bit about Vettes. He, too, suggested that I change the diff fluid. So, I will go to the GM dealer today and get some new juice. If I read the forums correctly, I need 2 bottles of posi additive and 2 bottles of diff gear lube. Does that sound correct? I haven't crawled under the beast yet. Is there a drain plug at the bottom, or do I need to get a suction device to get the old fluid out (it's a 78).

I know I haven't changed it, and I seriously doubt that the previous 2 owners did either. Maybe this is finally it and I can move on to the next project. Thanks for all the advice guys (and gals?)

 

That's correct. It takes 2 bottles of gear oil and 2 of the additive. One bottle of additive works, but I'd recommend 2.

 

One other thought... What would be the effect if only the inner caliper was bled (and not the outer)?

 

Songy pedel depending on how much air might me in that caliper half. No way it would drag the pad. That ain't it.

 

That's kinda what i thought. The barkes are as hard as Chinese arithmetic.

 

I had the same kind of noise in the back end of my '78. I found that it happens when you are stopping and starting while turning (right on red style). I posted to the forum and was told that it was more than likely the posi-clutch catching. You may feel a slight jerking in the back end too, or it may sound like grinding of gears (you can imagine the metal flake when you hear it). Additive fixed this and after talking to some people it seems that this is a very common occurance on our older vettes.

I also thought it was brakes at first because I had just replaced the E-brake cables when it started happening. But not the brakes...

Good luck.
Hope this helps.

 

I got the posi additive and the gear lube at lunch. Hopefully I can get around to it this weekend.

 

I like that one - gonna file it with my favorite:
"It's tighter than a crabs azz (and that's watertight)".

Good luck - and post your results.
My 75 always acted like this - now with a frame-up resto, it should be fixed.

 

I bought a syphon gun at Auto-Zone ($10) and replaced the fkuids in the diff. Two bottles posi additive and 2 bottles diff lube.

You guys called it. It took me about 2 hours to do the job. I removed the Right Rear tire and all the spare tire garbage. Probably a good thing because I found out that the spare tire was flat. It took longer for me to find a wrench to fit the fill plug than anything else. I, too , noticed that I couldn't remove the rear cover on the diff. What was that mechanic thinking?

I took it for a spin after I buttoned it back up and the noise only occurred once. That was when I stopped to open the garage door. Then I did a hard left into the driveway (from a dead stop). I got the noise, a bit, then it went away. Before It would have made your teeth hurt and it would 'grind' until I came to a stop in the garage.

I don't want to jinx myself, but I think I may finally have it solved.

Thanks a bunch for all your advice.

 

Go to a parking lot or other big space and do a bunch of figure 8s to work the additive in quicker. My friend had the same problem after changing the dif fluid and adding the additive. When the noise didnt stop right away he was about ready to destroy the car but the figure eights worked it in in about 15 mins and all has been good since then.

 

You need to do circles or figure 8's to work the new oil + additive in quicker.