Still making noise....

[pasvorto]

Well, Ka-ching is still at it. I was (am) experiencing a 'binding - release (best way I can describe it)" noise coming from the left rear. So far I have:

1. Replaced both rear calipers and pads
2. Replaced left front caliper (in case I was mishearing where it was coming from)
3. Replaced wheel bearings and u-joints in left rear
4. Gutted all the parking brake stuff from left rear rotor

Thought I had it yesterday (after replacing LF caliper). Then, last night, I drove it for 10 miles and it was back again!!!

It seems to happen when I put on the brakes lightly (like slowing down). Or, I will stop firmly, and then, when I try to go, it will be there (like the caliper won't release). But the weird part is that it doesn't happen until I have driven it for 10 miles or so. I fix something, drive it around the neighborhood and no noise. I think I have if fixed, finally. Then, the next trip of 10 miles or more, it is back.

I am trying logically to think of what the connection could be, but I am running out of things to replace. I don't know of a good Corvette mechanic in SE Minnesota or around the LaCrosse Wisconsin area, so I am kinda stuck with myself, you guys, or (shudder) the local Chevy dealer.

Anything else I should look at? This is driving me crazy (and broke).

Anyone want to buy a 78 Vette?

 

[Vettehead Mikey]

Could be the rubber brake line connecting the trailing arm to the frame. They frequently collapse internally keeping fluid pressure inside the caliper.

No, I don't have stats to prove it.

 

[pasvorto]

Actually I have a new set of rubber hoses. I can try that. But, I can't see how driving for a few miles would cause the problem. But, it's worth a try. I'm getting desperate.

 

[pasvorto1]

Well, I changed the hose in the Left Rear. That seems to be where the noise is coming from. I drove the same route I went yesterday. Instead of the loud, dare I say 'scarey', noise, I just got a fairly light version. That is until i was actually pulling into the garage and had the brakes on 'half-mast'. Then I started hearing the noise again. Not as loud, mind you, but still there.

So, tomorrow I am going to replace the hose in the Right Rear just to keep both rear brake lines the same age. Then see if that helps any.

I am beginning to wonder if I have a slightly warped rotor in the left rear. I don't seem to get the noise when the brakes are applied "crisply". It seems to be at the worst when I am creeping to a stop. I always thought I would feel a 'throb' in the brake pedal if the rotor is warped. Am I wrong?

 

[yellow77]

When I had excess runout on the rear rotors, the only indication I had was air being drawn into the system via the caliper piston seals, no pulsing pedal or anything.

 

[pasvorto]

I think the next step is to take the rotor in and have it checked to make sure it is not bogus. Ka-chinbg certainly is living up to 'er name.

 

[Vettehead Mikey]

I think the next step is to take the rotor in and have it checked to make sure it is not bogus. Ka-chinbg certainly is living up to 'er name.

Rotors must be checked in situ installed on the hub or spindle, not on a bench or a lathe.

What's a 'bogus' rotor anyway?

 

[pasvorto1]

A 'bogus' rotor is one that is just not right...I always thought that I could just take the rotor in and have it checked. Evidently not. So, per this project, a small $$ bill will now become larger as I have to pay them to take off the tires, etc.

After work, I replaced the flexible hose on the right rear caliper. The grabbing is still there (after I drove it about 10 miles). I am stumped. There are no Corvette shops (or mechanics for that matter) in this area. Maybe this is not a Corvette problem, but just a brake problem.

I am quickly coming to the point where there is nothing left. I have replaced everything but the rotors. I'm glad the seats are comfortable because it won't be long before I am going to have sleep in the money pit.

Now I am going to just think out loud... When I took the master cylinder cover off to put in brake fluid (for the 3rd bleeding this week), I noticed that the rubber gasket in the cover is not in real good shape. Each time I take it off, the "plunger" for the rear cup is out, while the one for the front is not. Could that have any effect? I mean, could it be creating back pressure such that the caliper pistons are fighting it? Or am I just grabbing at straws.

 

[AKRAY4PLAY]

have you checked your wheel bearings, trailing arm bushings, u-joints and yoke play in the rear end?? i am will to bet that the wheel bearing is loose and when you hit the brakes it "snaps" the tire into alignment. also check that your camber rods are tight and the bushings in good order. the stock rubber on these cars are known for withstanding the elements over time. it's something simple, don't loose hope, you'll find it.

 

[pasvorto]

The wheel bearings and u-joints have been changed recently. The rubber looks original. The part that bugs me is the time thing/distance thing. When I first start out, everything works just fine. But, give me 10 miles of open road or the equivalent in town mileage, and it starts acting up. it's like something has to heat up before it starts acting up.

 

[jdp6000]

Sounds like a brake problem. Did you have the exact same problem before you replaced the calipers and pads?? if that was the case then the problem is obviously in something you didn't replace. Change that rubber gasket.

It could be the combination valve but if that was the case both rear brakes would bind.

Did you bleed in the proper sequence? always make sure there is enough fluid in the master cylinder. book says bleed in the following order,left rear inner, left rear outer,right rear inner, right rear outer, left front and right front. Proceedure, open valve, attach bleeder tube to valve and run into a jar, fully depress brake and close valve, repeat steps for all. make sure master has fluid after each proceedure.

Jim

 

[pasvorto1]

I met with a guy tonight who appears to know his way around a Vette. He suggested that I drain the rear end and put in some new posi fluid and half synthetic rear end oil. His feeling was that the noise could be the differential clutches. His experience is that replacing the fluid can quiet down a myriad of noises. I have never changed the diff fluids and I doubt that the previous owner did either. I couldn't speculate on the owner before him. Anyway, it is a cheap thing to try. It needs it anyway. I can probably get around to doing it this weekend if I can find the right fluids at AutoZone. I will post the results.

 

[jdp6000]

Make sure you get the right fluid. No margin for error here. Hopefull that solves your problem.

Jim

 

[JohnZ]

I met with a guy tonight who appears to know his way around a Vette. He suggested that I drain the rear end and put in some new posi fluid and half synthetic rear end oil. His feeling was that the noise could be the differential clutches. His experience is that replacing the fluid can quiet down a myriad of noises. I have never changed the diff fluids and I doubt that the previous owner did either. I couldn't speculate on the owner before him. Anyway, it is a cheap thing to try. It needs it anyway. I can probably get around to doing it this weekend if I can find the right fluids at AutoZone. I will post the results.

If the noise you've been having is predominantly at low speed, like when turning a corner from a stop, he may be right; if it occurs only while going straight ahead, it probably isn't. Go to your Chevy dealer and get the GM Diff Lube and the GM Posi additive - that's what the diff was designed to use.

 

[pasvorto1]

I bought a syphon gun at Auto-Zone ($10) and replaced the fluids 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 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 for all the advice.

 

[Whiplash]

I had a very similar problem with my left rear after a complete TA, Diff, rotor, caliper, etc rebuild. When I put the rear back together I used the bolts that came with the caliper kits without looking at them closely. There were two length bolts in the kit longer ones for the front calipers and shorter ones for the back. Needless to say I put one of the longer bolts in the left rear caliper. The net effect is that the bold hits the inside of the rear rotor where you cannot see it when everything is together. After a few miles it grinds a groove in the inside of the rotor. Then the noise comes and goes depending upon how hot the rotors get and how hard a turn you make.

The noise doesn't make sense for the actual problem. It did sound like a rear diff to me at the time. I hope this is not the case for you but it's worth checking if the noise doesn't go away.

Good luck,

Whiplash

I bought a syphon gun at Auto-Zone ($10) and replaced the fluids 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 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 for all the advice.