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Receding Brake Pedal

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SteveHall64Healey

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Over the summer driving season, I noticed that the brake pedal began to sit lower and lower as the weeks progressed. At the end of the season in November it sat about 1” lower than the gas pedal that it had been aligned to a year ago.

I have no fluid leaks anywhere in the system.

I am able to adjust the brake pedal back to the same level as the gas pedal, but would like to understand why it has apparently receded.

Thanks,
Steve
 
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Re: Receding brake pedal ?

Disc brakes are self-adjusting, but the drum brakes require adjusting. that is probably why.
 
Re: Receding brake pedal ?

If you say you can adjust it back to level, how are you doing that? If the rod going into the master cylinder is threaded, maybe the lock nut loosened and the rod rotated.
 
Re: Receding brake pedal ?

Hi John, I have adjusted the rea brakes and it had no impact on pedal position. I've had the front calipers off and given them a good cleaning. Neither had any impact on pedal position.
 
Re: Receding brake pedal ?

The brake pedal has an adjustment mechanism allowing you to bring it up or down by an inch or so in each direction when the pedal is at rest. It is held in place by a nut at the end closest to the pedal. That nut has been on firmly all the time...
 
You might check you master cyl it may have fluid on the other side of the piston. Is the peddle still hard and does the peddle go down if you hold pressure for a time?? Madflyer
 
I checked the master cylinder this morning and there is no fluid between the cylinder and the pedal - no leaking whatsoever. I can pump the pedal up rock hard and hold it for several minutes, with considerable leg pressure, and the pedal remains very firm.
 
Can you pull the master cylinder rod so the pedal resumes it's original position. Maybe the return spring is broken or simply worn out.
 
Steve,

By your name it looks like you have a '64 BJ8?
Check your servo for leaks. both vacuum and fluid.

Rick
 
RTaillieu said:
Steve,

By your name it looks like you have a '64 BJ8?
Check your servo for leaks. both vacuum and fluid.

Rick
Click to expand...

IIRC quite a while ago on the email list some folks talked about the servo diaphragm leaking, causing it to 'eat' brake fluid. Rick's idea sounds like the best one so far.
 
There are no visible leaks or traces of old leaks anywhere in the system. The level of fluid in the reservoir has not dropped. I replace the servo last August with a new one, and the system does not appear to have any leaks.
 
Steve,
If the level in the reservoir isn't dropping at all, then fluid must be passing by the seal in the master cylinder, allowing it to gradually settle down.

Have you replaced or rebuilt the MC?

A Healey friend tried to use a Wilwood .7 MC on his 4-wheel disc-braked 100-6 and had a similar problem - he had to pump the brakes to get them to work. He bought a .7 Girling MC from Pegasus, installed it, and hasn't had any problems since. There was something wrong with the Wilwood and he returned it.
 
Did you ever have the rear drums cut? They could have high spots. Find an old codger shop that can actually do mechanical work.
 
Steve,

Disconnect the vacuum line from the manifold and cap off/plug the manifold fitting. See if you notice any difference in the brake pedal.
If you're not noticing any fluid drop in the reservoir then the hydraulic side isn't leaking.
You could still have a problem in the master cylinder like the other Steve mentioned.
 
The brake pedal should have a pretty substantial return spring; I can't think of anything that could overcome this spring and 'suck' the pedal down. Even if the system is devoid of fluid the spring will return the pedal to its normal resting height. Is the spring installed and not broken? Am I missing something?

What usually fails in a servo is the 'gland' seal; which seals the hydraulic part of the servo from the air/vacuum part. When it fails, the air/vacuum part sucks fluid, which can work its way back to the intake manifold, causing white smoke from the tailpipe (not indicating your car has a new pope).
 
Hi Bob,

There has been no loss of fluid - the reservoir has remained at the full level. If this were the case, I should see some drop on the reservoir...?
 
I had the opportunity to look at the master cylinder:
1) there is no fluid leakage at the MC
2) the cylinder fully returns when you take foot off the brake - ie return spring appears to be working
3) there is very little slack (1/8") between touching of brake pedal and initial movement of the cylinder

And, there is no drop in the reservoir level....

Also, the servo is the Lockheed type (I gave up on trying to rebuild Girling units after two units, two attempts by me and two professional rebuilds) with about one month of use on it before being laid up for the winter. At the end of the driving season, I had the recessed pedal issue, but had very good brake boost - just as good as my 2016 Wrangler.
 
Thanking outside the box: Are you sure it was the brake pedal lowering and not the gas pedal rising? Your original description compared the brake pedal to the gas pedal. I could see slippage in the linkage for the latter causing it to rise, but we're not coming up with an explanation for the brake pedal slipping down.
 
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