Navyt

Cutting to the chase, I have no front brakes and minimal rear at the end of pedal stroke. First, I dont know how that is possible because brakes are plumbed LF-RR and RF-LR. I bleed the brakes and everything returns for a SHORT trip, 5 miles or so and less when using the brakes in traffic or at lights. I know the rear brakes are engaging at the end of the pedals stroke, i.e. the floor board, because at low speed I feel the *** end of the car drop when the brakes are really stood on. I have gone through all proper brake bleeding procedures, but problem persists. There is no moisture around any calipers or the master cyliner. Could a caliper be bringing in air somehow? I hope someone has some suggestions! This thing is not safe for the road and Spring is quickly approaching. Thank you in advance! Oh, by the way, this is a '67.

wmf62

2 things..

are you getting air out when you bleed each time after a failure?

when was the master cylinder rebuilt?
Bill

Mr D.

Not sure what you’re saying there. The brakes on a 67 should be isolated between the front and rear based on the dual MC reservoir.

wombvette

Yea that's nutty.

It is obviously a severe run out problem causing the calipers to suck air. Very common problem with cars that have had brake work by amateurs. Check the ones that have air when you bleed, and look for run out on the rotors. The rotors should run true, not wobble.

wmf62

yep, that's the major shortcoming of fixed calipers...; floating calipers are more forgiving
Bill

Navyt

Thank you for the fast response. Yes, each time I am getting air out of the system. There is noticably more air coming from the RF than the others. I have owned the car since '97 and there has not been a rebuild on the MC.

Navyt

I wasn't aware that they plummed the brakes in this manner. On all other cars and trucks I have owned/built they have been cross isolated as a redundency to maintain equal braking in case half of the MC ceases working

Navyt

In a pinch last year it did have to go into a shop when out of state, where partial disassembly of the brakes would have been necessary. The problem did not happen before this, but did not begin immediately afterwards, so I wasn't really thinking of it. So runout in the rotors can cause air to be brought in from the calipers? When they do work, there is no shake or wobble while braking.

Allcoupedup

Had this problem recently. Turns out that one of my calipers was leaking ever so slightly and air was being introduced into the system. Changed the caliper and problem was solved.

Brian

Navyt

That is what I was leaning towards. Thank you for the response!

Allcoupedup

Note that the leak was so minor I didn't notice it so I ended up replacing bearings because I did have unacceptable run out. Still had the issue so when I removed the caliper again I noticed some dampness on the back side of one of the pads and the rest was history.

brian

Navyt

Great, I will rip that apart this weeked to see what I'm working with on the inside of that caliper. Thank you again, I'll update with what I find

mikem350

There are plenty of writeups in both the C2 and C3 forums on measuring and fixing runout and diagnosing brake problems.

wmf62

note how the caliper moves... this is a floating caliper and cannot be felt in the brake pedal and short term has no effect on the brakes or braking (but i fixed it...).

this movement would be noticeable in a C2 with a fixed caliper and would definitely suck air into the caliper at some point.
Bill

Chuck Gongloff

If your rotors had been removed previously, i.e. the rivets drilled out, and were reinstalled in the same position, you would not have introduced runout.

Just maybe the shop didn't orient the rotors on the same studs when they reinstalled them.

AND, just maybe, you had little to no runout when they were in the first position, but after they were changed, runout was introduced.

"Back in the day" they used to sell shim kits to shim the rotors to eliminate runout. You need a dial indicator to accurately measure the runout.

Chuck

Mr D.

Well it's been a long time but I think that would be true on front wheel drive vehicles that use a diagonal brake line system, a rear wheel drive vehicle would use conventional piping with the tandem MC.

Hey I could be wrong, been many moons since I turned wrenches for a living back in the day. I'm also a 65-66 master cly knid of guy these days.

wombvette

Leaking calipers do not introduce air in the calipers, unless the fluid gives out. You can pretty much forget that. You obviously have a run out problem. The rotors and hubs were final machined as a unit. Chevy didn't even recommend servicing them them. They figured we didn't have enough sense to do it right, so they recommended changing them as a unit. If the person doing the job is not knowledgeable about this, he removes the rotors and turns them on a brake lathe, and re installs them. Now that sounds like a smart thing to do, but, because the surfaces were not necessarily true in relation to the assembly, error is introduced. And that's when all of these sucking air brake problems crop up. You need to check the run out on the rotors.

Sky65

I had the same problem on the HRPT last year. Take a look here.
https://www.corvetteforum.com/c1-and...holy-crap.html

JohnZ

The second-design calipers and pistons (no guides) entered production just after the start of the 1967 model year.

I'd guess that less than 1% of the Corvettes originally built with the '65-'66-only 1st-design calipers and guided pistons still have them, as the caliper rebuilders routinely machined-out the guides in the 1st-design caliper bores when they were sleeved and used the 2nd-design pistons in everything.

Sky65

I never did figure out the root cause of the severe tapered pad wear. I did however change to wildwood calipers do to the more modern design. Not saying there is anything wrong with the stock design, just saying I like the newer design better.