Split Window vibration (a bit long)

[Frank D.]

So, last June my bone stock 63 coupe started shuddering right under my backside after the car had been driven a while; the right rear brake (all stock drum on all 4 corners) was heating up (like 35*-40* different than the left rear) and you can smell the hot linings. Once the shuddering starts it continues even when not braking and once the car sits a while is fine again.

So - I replaced the wheel cylinders, all parking brake cables (they were seized but not the issue), rubber hoses in the back and bought new high-end drums (all around as mine were getting thin) and replaced all of the shoes. Problem remains (see picture of rear drums) right rear is tinted gold. I even put washers between the master cylinder and power brake booster to ensure the brakes weren't dragging (which I think would affect both sides).

So, then I think maybe I have a bad bearing heating things up and this turns into a complete rear suspension rebuild, which was due anyway.
* Trailing arms (including NEW spindles) and half-shafts rebuilt by Van Steel
* Replaced 63 inner body cushions, snubber, sombrero, NOS leaf spring cushions and strut rod bushings.
* Driveshaft balanced and Spicer U-joints installed
* New shocks
* I didn't mess with the posi differential as stub yoke play was 0.025" on the left and 0.027" on the right - which isn't much and I don't see how that woul cause this issue anyway.

Eight months go by after this work (due to health issues) and I can finally start driving the cara again.

It appears I have the SAME issue now, very frustrating., just got back from a drive and everything was glass-smooth for 15 minutes. After some traffic the shuddering starts and the hot brake lining smell - I get home and the left side hub is 85* and the right side is 117*.

I'm stymied, I can replace (once again) all the brake parts on each end of the rear axle, but now I'm wondering if a master cylinder or booster issue may be the culprit. I'm seldom completely stumped on an issue but this one has done it.

[John L.]

Re: Split Window vibration (a bit long)

Frank
A thought.......bad internal delaminated rubber brake line on that wheel.... which can keep some pressure on that brake, especially as the brake fluid heats up

[Larry M.]

Re: Split Window vibration (a bit long)

Frankie:

As I recall, you added power brakes to the car.......correct?? If so, did you MEASURE the depth in the MC for the push rod and then MEASURE the extended length of the rod from the booster?? CSSB, Inc, Zip and others have a nice and cheap little tool to do this job. I just bought one and used it to help a friend. We found the booster rebuilder (very well known person) had set the rod about 3/32 inch too long.

You should have maybe 1/32 to 1/16 inch gap between rod end and MC internal surface to allow for heat up. Check it out if you haven't done so. You mentioned using washers as spacers to obtain clearance, but maybe they were not thick enough.

You also have a "residual valve" in the MC to hold a few psi on the drum brake shoes. Perhaps this valve is also acting up and holding more back pressure. Difference in drum temps may be just the way some shoes are set up a bit tighter (or arced slightly different) than the others. Checkout the wear pattern on the shoes to see how they are contacting the drums. YEARS AGO, there was a special AAMCO machine for doing this shoe arcing.

Larry

[Frank D.]

Re: Split Window vibration (a bit long)

When this drill started i replaced the rear rubber hoses and wheel cylinders with some NAPA parts that I've used in the past and things didn't improve, I also ran with the added power brake setup way back before judging in 2016 (Somebody here has a good memory) so I don't think the pushrod length is the issue but I'll revisit it - now the master cylinder residual valve is interesting but I would have thought it would affect both rear brakes but maybe not. I'll sure look into that as its something new I haven't investigated - thanks for the thought.

I also ordered the booster pin adjustment tool - that is a long shot IMO, but I'll try anything at this point

[Richard M.]

Re: Split Window vibration (a bit long)

Frank just reaching here but I'd completely disconnect the park brake cable at the rear junction to rule that out.

Rich

[Tim S.]

Re: Split Window vibration (a bit long)

It sounds like you are pretty handy and know your way around a Corvette. It does certainly sound as though you have either a hydraulic issue or a cable issue. As mentioned loosen up your cables. Also, if one were to crack the bleeders and see where you have residual pressure built up in the system. If I understand it correctly, you still continue to have issue with the same wheel in terms of drum temp?

Tim

[Tom E.]

[Frank D.]

Re: Split Window vibration (a bit long)

It sounds like you are pretty handy and know your way around a Corvette. It does certainly sound as though you have either a hydraulic issue or a cable issue. As mentioned loosen up your cables. Also, if one were to crack the bleeders and see where you have residual pressure built up in the system. If I understand it correctly, you still continue to have issue with the same wheel in terms of drum temp?

Tim

I haven't done that yet and I should, I just hate DOT3 spraying around (maybe this is my chance to switch to DOT 5); I will try that and am also looking at the rear crossover brakeline and junction boxes - SOMEthing is making those shoes stay engaged. I may disconnect the parkinb brake and back way off the adjusters and take a drive. This is really driving me bonkers...

I should have added that the temps I recorded above were after the car sat a few minutes, but I've checked them before right after the issue and recorded higher temps with the same left-to-right disparity.

After all the rear end work I'm gonna do a REAL good physical inspection on the lift and make sure I didn't munge the rear crossover line or something equally stupid.

[Robert P.]

Re: Split Window vibration (a bit long)

Frank , i would try switching the drums in the rear from side to side and then take a test ride , its an easy and no cost check
Bob

[Michael D.]

Re: Split Window vibration (a bit long)

I owned a Norton Commando motorcycle with hydraulic rear disc brake and it had the same problem. The short of it was that there was sludge in the line. Fluid would be pushed in and actuate the brake fine but it would release pressure VERY slowly. Like 5 minutes. In your case, any potential blockage would be isolated to the leg going to the rear brake in question. Certainly not saying this is the case here, but you have definitely had a time with this and I only offer another long shot you may want to investigate.

[Larry M.]

Re: Split Window vibration (a bit long)

Frankie:

I would also check linings for grease/oil and brake fluid............and then lightly sand them with 80 grit if found to be clean.

Any fluid or grease on the linings will cause them to stick or behave erratically. Ask me how I know this.........I blew out both rear axle seals on my 65 Plymouth during a large burnout. Driving the car on the street after this was VERY problematic. .

Larry

[Harry S.]

Re: Split Window vibration (a bit long)

Frank, I was having a brake problem, no associated shimmy. One at a time I opened the wheel cylinder and attached a tube into a large ice tea container, then I blew the line out with my compressor.

Flush.jpg

That did not fix the problem, here is the goop in the wheel cylinder.

Cylinder.jpg

I replaced both cross over lines, all rubber lines, the four short lines and all the blocks as well as the wheel cylinders and went with DOT 4. The only lines I did not replace was the long line and the line from the MC to the block. If you are changing the front cross over line, pull the center bumper bracket. That will make it much easier.

Brake problem fixed. That goop will screw the system.

[Frank D.]

Re: Split Window vibration (a bit long)

Thanks Harry, I'm looking at the whole rear brake setup (AGAIN)... I've been dealing with drum brakes (non-Corvette) since the mid-60's and never had this much trouble - mystifying. I'll pull the master cylinder next week and wash out the lines with some air and alcohol and make sure I get flow to all four corners...

[Dan D.]

Re: Split Window vibration (a bit long)

When this drill started i replaced the rear rubber hoses and wheel cylinders with some NAPA parts that I've used in the past and things didn't improve, I also ran with the added power brake setup way back before judging in 2016 (Somebody here has a good memory) so I don't think the pushrod length is the issue but I'll revisit it - now the master cylinder residual valve is interesting but I would have thought it would affect both rear brakes but maybe not. I'll sure look into that as its something new I haven't investigated - thanks for the thought.

I also ordered the booster pin adjustment tool - that is a long shot IMO, but I'll try anything at this point

Frank, I would look seriously at your master cylinder. I have run into this before whereby the residual valve gets plugged up or something and doesn't let the fluid return to the cylinder. And yes, it can affect only one side. The fact that it will go away in time indicates that the fluid is slowly bleeding off. To check for this you can loosen the wheel cylinder bleeder valve and see if fluid squirts out with pressure.

Also you have changed out about everything else, so the master is about the only thing left.

-Dan-

[Frank D.]

Re: Split Window vibration (a bit long)

Frank, I would look seriously at your master cylinder. I have run into this before whereby the residual valve gets plugged up or something and doesn't let the fluid return to the cylinder. And yes, it can affect only one side. The fact that it will go away in time indicates that the fluid is slowly bleeding off. To check for this you can loosen the wheel cylinder bleeder valve and see if fluid squirts out with pressure.

Also you have changed out about everything else, so the master is about the only thing left.

-Dan-

Yeah - and on top of that its a repro master cylinder (without casting number)...so who knows about the quality....
I've already ordered a better repro for a power brake 63 (with the casting number) and will swap it in when it arrives.