63_ Stopping distance PART 2

[Steve D.]

I did a lot of aggressive stops as suggested and found that with more effort on the pedal, the distance is much shorter. It stops straight without any pulling. However, after the third or fourth stop I heard and felt a "clunk". I couldn't tell what it was, but it occurred again after a few more deliberate stops from about 50 mph. It didn't clunk while stopping, but shortly after being stopped. No problems moving out again and going thru the gears after experiencing the sound. Does this make sense to anyone? The only thing I could think of was that something (what, I don't know) locked up whlie braking and released (causing the clunk) after being stopped. Suggestions on how to investigate?

Steve

[Paul J.]

Re: 63_ Stopping distance PART 2

I did a lot of aggressive stops as suggested and found that with more effort on the pedal, the distance is much shorter. It stops straight without any pulling. However, after the third or fourth stop I heard and felt a "clunk". I couldn't tell what it was, but it occurred again after a few more deliberate stops from about 50 mph. It didn't clunk while stopping, but shortly after being stopped. No problems moving out again and going thru the gears after experiencing the sound. Does this make sense to anyone? The only thing I could think of was that something (what, I don't know) locked up whlie braking and released (causing the clunk) after being stopped. Suggestions on how to investigate?

Steve

Steve, I've had some clunks before, mostly with discs. The reason would be the same for either discs or drums. It can be casued by one of two things. Either the brake line is collapsing and briefly holding pressure before releasing, or the piston is sticking in the bore briefly, holding the shoes/pads out for a second after the pressure is released. The "clunk" is the pressure releasing and the springs pulling the shoe back into position. The deterioration of the brake line occurs inside, so it will look fine on the outside. However, this is usually accompanied by pulling to one side, as it also restricts all of the pressure getting to the cylinder. Since your braking is straight, this may not be your problem. If the piston is sticking, it is most commonly caused by a loss of pressure due to leakage past the seal, although it can sometimes be caused by dirt deposits (ridges). Drive the car and try to isolate which wheel it is, or just inspect all of them. Pull your dust boots and look for seepage. They are easy to rebuild and you'll find it a lot easier than doing a disc brake conversion. If you replace them, keep your old parts.

Paul

[Edward J.]

Re: 63_ Stopping distance PART 2

Steve, I think Paul has the right idea, moving a 3000lb car and hitting the brakes hard at 50MPH will certainly make some funning noises, When the car does come to a stop and the brakes finally release they may release with some nosie. I would say its kind of unwinding.

[Joe M.]

Re: 63_ Stopping distance PART 2

If the brakes are funcrioning correctly check out all components of the IRS.
Something may have loosened/ crossmember cushions/bolts. Pull a rear drum and check components. Old weak brake return springs?

for what it's worth, the 1963 road test in Road and Track has the 30-0 braking distance at 30'
60-0 @ 134'

[Steve D.]

Re: 63_ Stopping distance PART 2

What is the IRS (he asked sheepishly)?

[Duke W.]

Re: 63_ Stopping distance PART 2

Independent Rear Suspension

When was the last time you did a complete brake fluid flush? When was the last time any work was done on the brake system like new shoes?

Duke

[Steve D.]

Re: 63_ Stopping distance PART 2

Fresh brake fluid 18 mos ago. Brake shoes are several years old but only have a few hundred miles on them. Wheel cylinders, springs and shoes are all the same age. Brake areas on all four wheels are nice and clean: no brake fluid leaks or bearing grease.

[Michael W.]

Re: 63_ Stopping distance PART 2

Have a peek to make sure all your alignment shims are present and accounted for on the upper A-arms.

[Duke W.]

Re: 63_ Stopping distance PART 2

It could be something in the brakes or suspension. Intermittent noises like this can be tough to find. Since it only occurred during your "brake test" you will likely never hear it in normal driving, and it's probably not a serious safety threat.

Duke