Technical Master Cylinder question

I have a Speedway Motors Corvette style master cylinder, small dual booster, and their hanging pedal. Using stock Lincoln 47 drum brakes up front and stock 66-67 Fairlane drum brakes on the rear. Car stops great. But, the pedal never seems to return to the same place? I'm using a 67 Chevy push type brake light switch [off when pedal arm is against it] mounted to the steering column, that hits a flat bracket welded to the brake pedal arm. I also have a lightweight spring pulling the pedal back toward the switch. I started out with the switch just barely through the mount, now it's all the way forward. Sometimes, the pedal will return and cut off the brake lights like it's supposed to, other times it only returns to barely touch the switch, if it gets back that far at all. Seems like there is too much free play from the arm to the master cylinder, but not all the time. Sometimes it works like it's supposed to.

Are the cups sticking in the master, not letting it return fully? Maybe a wheel cylinder not retracting properly? Or do I just need a stronger pull back spring on the pedal?

I don't remember it doing this before it was parked 5 years ago, but it might have. I do good to remember what I had for breakfast sometimes....

Thanks in advance.

 

Had a similar situation, i didn't tighten the lock nut on the adjustable length pushrod, so the rod threaded into the clevis. Is you freeplay still the same?

 

I had something weird like that happen with my Chevy II on my recent trip. I didn't find anything else to explain what was happening, so I replaced the MC, and it's been fine since.

 

That's what's odd, the free play seems to change as well. That's why I can't figure it out. Squirrel may have my solution.....

 

master cyl rubbers probably swollen up, making it stick in different positions

 

Possibly rubber brake hose(s) internal swelling inhibiting return flow of fluid.when brakes are released. It may be variable depending on brake application…..i.e. light application for slow down vs stronger application for full stop or more abrupt application. Heve the brakes been adjusted recently?

Ray

 

I don't think it's the hoses, they are all braided lines from Speedway, but I guess it could be. They are all adjusted up. Guess I'll tear it all down in a few weeks and see what I find. With the quality of rubber products anymore, it could be any of it.

All brake components are about 6 or 7 years old, were new when I put them on. I'm sure sitting in the shop 5 years didn't help anything.

 

Mine was 7 years old, and I never flushed the fluid like I planned to...

 

The pedal needs a positive stop and a spring strong enough to ensure full returns, including any brake switch resistance, which may be the main cause of your problem.

 

I use the same master cylinder I think it's inch and 1/8 I used it on the disc brake disc brake car my model A

 

I recommend flushing the brake fluid out mine was given to me and I had it rebuilt and they said it had some Oddball parts inside so I have them put it all standard

 

If the car sat for 5 years, replace the master cylinder, and pull back the rubbers on each end of the wheel cylinders and look for Leakes. You may have to replace them also. Sitting is very hard on wheel cylinders and master cylinders.

 

Haven't updated this tread in a while. Finally got around to replacing the master cylinder, found the problem. Was leaking out at the booster, the reason I never saw anything. Once I got it off it was apparent where it was coming from. That explains why sometimes it had good brakes, other times it took a pump to get the pedal up to normal. Back like it's supposed to be now.