Power Brake pedal ret not good Brake light On

[jackbird60]

Hi,

I replaced the master cylinder on my 60 Tbird w/A/C , and power booster is inside the engine compartment. (not under the dash)

The problem is the pedal was low and I checked everything. I changed out the brake cylinders, I checked the hoses for bends , ballooning, or kinks etc. New Brake shoes, newer drums you name it. Yes, bled the brakes several times.


Now, I might have adj the master cylinder to high to get a higher brake pedal, but sometimes, after I turn off the car, the brake lights will stay on unless I kick the pedal and kinda of hand force it up a bit. Even then, it will go off, then come back on sometimes.

Also, I had a 60 Tbird before, and there doesn't seem to be much brake pedal return at all. My neighbor, who is a pretty good backyard mechanic, says it's most likely the return spring or something like that in the brake booster. Does that sound correct?

If so, is that a big job to replace the booster. ?

Thahks Jack

[DKheld]

That's unusual to have the engine compartment mounted booster and A/C - would have been a dealer add on (or possibly a PO)

The repair manual says slow return or fail to release could be:
Clogged air cleaner (top outside of booster)
Improper master cyl pushrod adjustment
Internally to the booster - (restricted air passage, sticky valve plunger, broken return spring, atmosphere popet valve stuck closed)

If you had to replace the master cyl and it was leaking to the inside of the booster the leaking fluid may have clogged the air passages. Doesn't say you need any special tools to remove the front of the booster and check the spring although it says to mark the end plate and piston vac cyl to make sure they are replaced in the same orientation. Looks like the rest of the "guts" will fall out.... also says not to oil the internal valve plunger but use only crocus cloth and clean it. Pretty easy to take the booster out but you have to stand on your head inside the car to get the pedal rod bolt out - lots of fun. (you can just take the pedal rod loose from the brake bracket under the hood but it is just as much fun removing and re-installing that lever pin)

I couldn't find a kit for the Bendix booster when I wanted to rebuild mine so I finally sent it off to Power Brake Booster Exchange and had it done. Glad I did - was well worth it. Works flawlessly and had a 1 year warranty (that was 8 years ago).

Rebuilt the original system and ran that for a few years then converted to discs. I've never had any trouble with pedal return on mine either way - just lucky I guess. Power Brake Exchange sent a modified pedal rod when I converted.

There is a procedure in the manual to set the master cyl rod height but it mentions that once set at the factory it should be good and not need adjustment again. The pedal height adjustment is done by moving the offset bolt securing the pedal to the pedal rod.

Hope some of this helps,
Eric

http://boosterdeweyexchange.com/

[jackbird60]

Thanks it does , and I do remember reseting that brake pedal. I have been doing work on the car the last couple of weeks, but in the midst of selling my home and I am by myself, so I might just buy the booster (rebuilt) for $185, and have someone install it. I'll have to pay a core charge though of $150. I would love to fool with it, but can do that with possible buyers walking in and out. Wish I could.

Thanks again,

Jack

[simplyconnected]

I think Eric pretty much covered all the bases for just about anything that could possibly go wrong. (Good job, Eric.) He also speaks from experience AND the Shop Manual. It doesn't get any better than that.

I hope you check out these suggestions before buying any parts. This could save you some money whether you or your mechanic do the work. You cite three distinct problems:

...The problem is the pedal was low and I checked everything...

...after I turn off the car, the brake lights will stay on unless I kick the pedal and kinda of hand force it up a bit...

...there doesn't seem to be much brake pedal return at all...

The key to this is your brake light switch. It operates with very little pressure. That tells me that your brakes are always applied, that the M/C spool never returns, and your brake system never 'resets' itself.

First of all, did you bench bleed your new M/C?

There are two distinctly different adjustments; one between the booster and the M/C, and your pedal bolt (which has an offset shoulder).

Let's start at the pedal. Can you lift it? Is there any 'jiggle' room (or is it solid)? I'll wait for your answer on this.

Remember, every M/C is slightly different. If you unbolt your M/C off without cracking brake lines, see if your brake lights go off. Look in the back of your M/C and notice if the spool returns all the way back to the snap ring. <--This is important.

At rest, the spool should return completely and on it's own, which opens the reservoir port to the brake lines. This resets the system, allowing the wheel cylinders to return, and it sets up for the next brake cycle. If the M/C piston cannot come back to the snap ring by itself, the spool is internally stuck which keeps pressure on the brake lines.

Another cause for the M/C to not return is if the booster output shaft is extended too far. Your booster and brake pedal should retract on their own without the M/C. If they don't, find out if the spring inside the booster (that returns the brake pedal) is broken.

The booster should have an output screw with a jamb nut arrangement. Stick a piece of clay (PlayDough, plumber's putty) between the M/C and booster, and bolt them together. Then unbolt them and look at the clay. If the clay is squashed out, the jack screw must be backed off just enough to let it jiggle. - Dave

[Guest]

I had a bad master cyl. when my brake lights would come on and run the bat. down