My brakes (4 wheel drum) other than grab and pull to the left every once and a while (very intermittent) they also stay partly engaged once hot. I haven't jacked the car up and confirmed this, but when I pull in the garage and see the reflection of my brake lights in the garage door, I know they are not completely returning.

This only happens after about 20 minutes of driving or more. I don't think it happens if I am on the highway for 20 minutes, but if I drive around town and have to stop for lights or stop signs, it will start to hang up. On the road I can tell this is going on because when I stop for stop sign or light, my car doesn't roll on a slight incline like it should if the brakes are disengaged.

Here is something else I just noticed. If I step on the brakes a couple of times once the car is shut off the pedal comes back up to rest against my brake light switch. But as long as the car is still hot from driving I can start the car and the pedal will stick again.

If the car is cold, like when I first get in it, it works fine and always returns to the top of it's stroke.

I posted about this before and the advise that I went with was to pull the clevis off the brake pedal and see if it is in the pedal assembly or the booster/master.

I can barely touch the clip to release the clevis without making the pedal move back to the top, so I haven't been able to see what the rod feels like when stuck, without the pedal attached. However once it is disconnected the pedal is free and there is no binding at all, so it has to be either the booster or the master cylinder.

The booster and master are chromed and they get very hot under the hood. This might have been the same with the old system, but I never had a reason to check.

I have the old master in a box, but it was manual and I don't know if the new master has a plug that can be removed and installed in the old one so that they are compatible. I want to know if anyone has any suggestions before I go through the trouble of pulling everything apart and risking my paint again with messing with brake fluid.

 

That is truly wierd. As I read your post, I think I have an idea then the next paragraph makes that idea improbable. It sounds like something that is heat sensitive is acting like a check valve, but I can't imagine what that would be. Flush the system first. There is an old rule in aviation: when things go wrong, count to 10 then undo what you did last. Put plastic on your paint and tape it on the edges with painters masking tape. It will give you time to get to the paper towels. Good luck with the repairs.

Here's a bump for ya.

 

Neither the booster nor master cylinder look like stock GM components for any year Corvette- do you know what they are?

 

That master cylinder looks suspiciously like the one I recently put into my 56 Chevy when I converted to FRONT only disc brakes.

I went the non power route. I looked around quite a bit before I bought the front disc brake kit for my 56, and don't recall seeing a dual master cylinder for 4 wheel drums.

My point? Wonder if you have the wrong MC, and that's holding residual pressure in the system?

Chuck

 

Here's a pic.

 

hopefully your system only has the newer silicone based brake fluid. if older brake fluid was in lines the two brake fluids under use might have a expanding effect. also, in putting in a different master cylinder did you make sure that the master cylinder push rod had a small amount of free play. a push rod with no play will have also have noticeable effects on the brakes after a short ride.

 

I think you will find that your problem is the wrong combination of components or their proper adjustment. A miss-adjusted master cylinder pushrod will cause the brakes to apply hot and apply harder the hotter they get, usually with a rock hard pedal. I lived this nightmare after rebuilding a 389 in a 62 Bonneville. In an attempt to improve the pedal we monkied with the pushrod adjustment, and sailing down the interstate with a fresh build I overheated the motor with the brakes on & cooked a rod bearing (according to the machine shop, naturally).

Anyway, it is real important for you to be using the right master cylinder that is appropriate for your application; that the geometry of the pedal throw vs. the master you are using vs. the requirements of the wheel cylinders are important considerations.



Dan

 

I'll answer each suggestion individually so that we can all know what I've tried and what I didn't. It's too late to do more than this one tonight though, I'll respond to the others tomorrow.

Vogie, The entire system is new, and the fluid comes out clean and hard when I bleed the brakes. It took quite a while for me to notice the pedal wasn't coming all the way up.

Check this out, I was on another forum and there is someone with the same problem. I sent him a message and want to see what he has tried.

 

With a stock booster, the pedal return function is handled by a return spring that's internal to the booster (not by the stock manual brake return spring around the pedal pivot shaft, which is omitted with power brakes), with an adjustable clevis rod to ensure adequate free play; don't know how your aftermarket booster is set up. If you don't have adequate pedal free play at the top of travel, it doesn't take much pressure on the booster-to-pedal rod to activate the booster just enough to apply the brakes lightly so they drag (and eventually lock up).

 

To check if your brakes are draging when hot release bleeders with out touching the pedal if fliud comes out under pressure you have a risdule line valve in the master cylinder or no free play in pushrod at the rear of master cylinder.I have same setup on my 59 and it works great.

 

Grabbing and pulling to one side would indicate a rear axle leak, this can be intermittent if it is a small leak.

My '37 Ford pickup streetrod seems to have a non internal spring booster, as I had to install a fairly stout pedal return spring to make the pedal go to top.

Doug

 

replace the brake hoses. One is collapsing from the inside

 

I don't believe that would hold his brake lights on.

 

Mike, very few things on my car are stock and I have no idea who the manufacturer is.

Chuck, I had to add residual valves to front and back lines because the Master didn't have any. I think this one has a plug in the back of the Master to allow it to be used with power brakes and can be removed to be used for manual.

scopeli, I'm using DOT3 and have never used silicone, so I know there is no contamination. I left the master connected to the booster as it came that way and never checked to see if there is the correct about of free play there. I do have the correct amount of play at the pedal end of the linkage.

Dan, the M/C and booster came as a unit, so I have to trust they do go together, but as I said above, I have not taken the unit apart to see if the pushrod from the master to the booster has any play. The pedal does not get hard when the pedal starts to stick. The Master is for 4 wheel drums and the angle of the booster to the fire wall and then to the pedal is right where the clevis attached before. I had to make a bracket to attach the booster to the firewall, and I made sure I duplicated the angle.

John Z, I let the spring move the pedal to the top of it's travel until it hit the stop/bumper. Then I adjusted the rod so that the pin would slide in without having to touch the pedal or the rod. Did I make the rod too long? Should I make it so that I have to depress the pedal slightly (.25"-.50") in order to get the pin in, so that the pedal spring has more preload? The pedal spring is much lighter than I thought it would be, though it appears to be fairly new.

steanpunk, I do have residual valves in the line, because they were not present in the master. I'm not sure if your method would tell me anything since I know there are residual valves in play. I do have to check the rod between the master and booster though.

Doug, I don't see any leaks. I also wonder if I were to install a stiffer spring on the pedal, it that would solve the brake dragging problem. But I do have a few things to check before I go that route.

Thank you all for taking the time to help me figure this out. I'm going inside to split the master from the booster and see if I can tell if I have a little clearance for the rod. Not sure how I'll approach that until it's apart. I figure if I take out the bolts and the master doesn't push away from the booster, there is some play there.

 

Yes. You should adjust the clevis connection so you have 1/8" to 1/4" of free pedal travel before actuating the booster, as shown in the Assembly Manual.