No free brake pedal clearance afer a few stops ?

Discussions related to braking systems.
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Joined: Sun Jan 17, 2010 5:40 pm

No free brake pedal clearance afer a few stops ?

Post by 42Formal » Sun Jan 17, 2010 6:27 pm

I have had the master cylinder rebuilt by AP and on first drive the brakes locked up when the pedal clearance disappeared .
I had no choice but to continue driving for 25 miles home . I reached under to open a bleeder and so I was able to drive into the garage. I first cooled down each smoking wheel with the garden hose. During the next year I replaced all wheel bearings , grease seals , wheel cylinders, brake shoes w bonded lining and rebuilt the master cylinder . Bleed the system with a vacuum pump. Using DOT 3 brake fluid. Adjusted the brakes to .015 feeler gauge spec Pedal had 1/2 inch free play .
First road test I lost the pedal free play and the left front brake locked up .
I as before replaced the front brake shoes , properly cleaned all parts , yada , yada as above. This story gets better
I have no emergency brake as I adjusted the shoes with much more clearance that .015 . Now the right rear wheel is locking up after a few stops. Yes no pedal play again . This gets even better . I backed the car out of the garage to wash it , let it run with a fast idle to charge the battery while I washed it .....The brake lights came on after 15 minutes ....checked the pedal free play none... hand pushed the pedal and pressure relieved only enough to release stop light switch. Hey guys what is your advise short of calling GHOST BUSTERS ?

John Harley
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Joined: Mon Jul 06, 2009 3:44 pm
Location: Dumont, NJ

Re: No free brake pedal clearance afer a few stops ?

Post by John Harley » Sun Jan 17, 2010 7:08 pm


I forget the name right now, but there is a relief port in the master cylinder to return the fluid to the master cylinder when the brakes are released.
It's plugged somehow. The fluid cannot return to the master cylinder and the shoes cannot retract, i.e. the brakes are remaining on after you take your foot off the pedal.

The most common causes are that either

the parts in the master cylinder piston are assembled out of sequence,

or more likely, the threaded rod is out of adjustment and not allowing the piston to uncover the port. Give yourself some more free play in the pedal using the threaded rod coming out of the master cylinder.

Clear as mud?


John Harley

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Joined: Sun Jan 17, 2010 5:40 pm

Re: No free brake pedal clearance afer a few stops ?

Post by 42Formal » Mon Jan 18, 2010 3:57 am

John , Thanks for the reply . I at first thought that this was the problem but the master cylinder is OK and works well . The problem is when any heat in the brakes ( normal ) transfers to the brake fluid There is reverse pressure in the master cylinder. This pressure then applies the brakes at all 4 wheels generating even more heat
The brakes applied themselves while the car was stationary on fast idle with nobody in the car after about 15 minutes .
I can release the pressure by simply opening a bleeder valve for a second and then I have pedal clearance .
I have ordered a set of new flex brake lines and hope that the old ones are the problem by expanding under pressure and then contracting giving the sense of an additional "master cylinder" pushing the wheel and master cylinders the opposite way.
I am open to any help that you can give . I also need to bone - up on the Minor adjustment to the shoes.

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Re: No free brake pedal clearance afer a few stops ?

Post by Adam » Mon Jan 18, 2010 5:42 am

My first thought is to agree with John about the master cyl not allowing the fluid pressure to release (there is always a small amount of line pressure held in the system by a valve at the end of the master cyl, to keep the wheel cylinders full of fluid). Therefore, I wonder if the master cyl has been rebuilt using the wrong kit of seals, which may well cause this problem. It would be worth ordering a new Master cylinder seal kit and asking your friendly motor factor to verify that the kit is correct from the bore size and casting numbers.

I also like your idea of internally collapsing flexible hoses. Unless you know the hoses to be good (and not too old) I would certainly change them as a first measure. This could well be your problem, as it would have the same effect that I described above.

Do let us know how things progress.

"Do not underestimate the English cousin.....they are not as stupid as they look!" - Signor Altabani in The Italian Job.

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Re: No free brake pedal clearance afer a few stops ?

Post by 42Formal » Mon Jan 18, 2010 6:37 am

Adam & John ,
Thanks for the reply . To will give you more background on this situation..I had the Master Cylinder resleeved and rebuil by Apple Hyd. and after the first brake no pedal clearance I had AH send me another rebuild kit which I meticoulusly installed and tested . I have given it more than sufficient threaded M C push rod adjustment so I have half a pedal play. I will however remove the MC again when I receive the new flex lines and again reassure myself that it is OK.
This car had fabulous brakes with only one problem which was a leaking MC which I had as noted above , rebuilt. I had the MC installed by someone that did not adjust the pedal play and cost me a total rebuild of all 4 corners from the axles out to the hubcaps , et al .
I now do all the work myself so I know what was done and especially by who . hehe :oops:

Dave Czirr
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Joined: Tue Jun 16, 2009 5:30 am
Location: New Jersey

Re: No free brake pedal clearance afer a few stops ?

Post by Dave Czirr » Mon Jan 18, 2010 7:39 am

A bit of a wild guess, but perhaps the company that sleeved the MC forgot to drill the compensator port, or did it incorrectly so there is no way to relieve the build-up of hydraulic pressure resulting from heat expansion. You didn't say what year or model car this is (or did you and I missed it?) but for many you can buy brand new MCs and avoid the issues like sleeving, etc.

I'd remove the MC and check the opening and clearance for the compensator port.

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