C2 brake saga_revisited

[Steve D.]

63 convertible_drum brakes

After many trials and tribulations of bleeding and re-bleeding ad nauseam, I think I have narrowed my excessive pedal travel down to a geometry problem. The spec for pedal free travel in the AIM (Sect 5, Sheet 4 note at bottom) is 0.6" to 0.25", but I measure free travel to be 1.25". I have the clevis and rod assembly adjusted out to maximum length and mounted in the proper (upper) hole of the pedal arm. The pedal hanger assembly is mounted directly against the firewall, so no extra distance has been introduced there. What else can affect free travel?

The 1.25" free travel of the pedal results in approximately 0.5" travel of the clevis/rod. It appears that a longer rod (0.5" to 1") would solve the problem. In the catalogs, only one rod is offered for 63-67. I may have asked this question before, but are there other (ie, non Corvette) GM rods that might be used? Or perhaps (God forbid) Ford or MoPar? As a last resort, I could get a rod of proper diameter and length and thread one end and round off the other. Comments appreciated.

Steve

[Michael H.]

Re: C2 brake saga_revisited

ette) GM rods that might be used? Or perhaps (God forbid) Ford or MoPar? As a last resort, I could get a rod of proper diameter and length and thread one end and round off the other. Comments appreciated.

Steve

I made a rod from a long 3/8" bolt a few years (decades) ago. (or is it 7/16"?)I removed the head and ground/polished the end into a round shape, as the original. Not exactly a precision part but it worked.

Are you sure the main cyl piston is returning all the way to the back of the bore? I've seen these bind/stick and create the exact problem you describe.

[Steve D.]

Re: C2 brake saga_revisited

I'm reasonably sure. The MC is new and when I bench bled it the return was very positive.

[Bill I.]

Re: C2 brake saga_revisited

Steve, maybe a silly question, but if you put on new shoes, did you adjust them before beginning the bleeding? Bill

[Steve D.]

Re: C2 brake saga_revisited

Bill

Yes, adjusting the shoes has been a part of the saga.

[John D.]

Re: C2 brake saga_revisited

Steve, Sounds like a master cylinder issue like Hanson said.
ARe you using silicon brake fluid? JD

[Bill C.]

Re: C2 brake saga_revisited

Steve,
Do you have power brakes? If so, the 63 only booster has an adjustable push rod. There is an adjustment procedure inthe service manual if needed.
If you have manuals, do you have the rod clevis mounted in the correct position on the pedal? Should be in the upper hole for manual.

You should be able to look down thru the vent hole in the bottom of the m/c resevior to be sure the piston is returning to its seated position, every time. I have seen them hang up often and will creat your problem.

Same thing will also happen if the rod is to long, preventing the piston from seating back all the way and not uncovering the vent hole, that will limit the cylinders ability to draw in more fluid.
Good Luck

[Chris D.]

Re: C2 brake saga_revisited

Long shot...Is the new MC dimensionally correct for the car? In your particular case, is the piston push rod seat to mounting flange dimension the same as on the original MC? Mistaken assembly (wrong piston) would not be surprising for a limited use item like this that has only a two year application

If you still have the original, I'd be more inclined to get it sleeved. The new ones aren't even that close in appearance to the '64 model they try to copy.

[Steve D.]

Re: C2 brake saga_revisited

Michael

You are right, 3/8" - 24 thread.
I checked the MC plunger and it is retracting all the way back in the MC.
I will pick up a bolt tommorrow and see what happens.

Steve

[Steve D.]

Re: C2 brake saga_revisited

Chris

Unfortunately, I don't have the original MC, but that's the one part of the geometric picture that I hadn't considered.

Steve

[Michael H.]

Re: C2 brake saga_revisited

Chris

Unfortunately, I don't have the original MC, but that's the one part of the geometric picture that I hadn't considered.

Steve

I can't think of any other part that could cause the problem. It almost has to be the MC piston design.

[Steve D.]

Re: C2 brake saga_revisited

For research purposes, I will start another thread and ask if someone has (for a 63 MC) the measurement for the distance from the MC face that abutts the firewall to the recess of the piston where the rod seats. I will make the same measurement on mine and compare.