The Stovebolt Site Forums The Shop Area General Truck Talk Need help with my Brakes...'57 Chevy 3100, brakes slowly locking up

Hello -

Finished converting my '57 Chevy 3100 from a TH400 to a 4spd and took it on it's inaugural ride. Everything seemed to be working fine, although it truck seemed a bit sluggish. Whatever, I though, I'm not used to the gearing yet, and I have 2.73s in the rear.

But it kept getting worse...like I was pulling a heavy trailer.

Then I started to smelled something burning.

Uh oh.

Got out of the truck, and ALL 4 brakes were smoking, and the brake lights were stuck on. Pedal seemed a bit firmer than usual.

Limped the truck home, and got it up in the air. Came in this morning, all the wheels spun freely, so I pulled the tires, got under the truck, and inpected all the lines, thinking maybe I damaged one when I was getting the tranny in place. No kinks anywhere that I could find. MC full of fluid. Parking brake wasn't engaged. Brakes lights worked like they should. Pumped the brakes for a minute with the car up in the air. Brakes released as they should, and the brake light worked as it should.

Here's the setup I've got: The PO installed a dual well MC with front discs, looks like a Speedway kit. The MC is still under the floor and uses the factor pedal and linkage. Both lines from the MC feed into a non-adjustable proportioning valve, and the brakes lights are actuated by a pressure switch that's plumbed into the lines feeding the front brakes. Rear end is stock with drums from a 72 - 73 full size Pontiac. When I got the truck, the brakes were shot, so I did a full brake job including cutting the front rotors, new front pads, complete new hardware on the rear, new shoes, cut the drums, and a new wheel cyl on the pass side (leaking). Brakes bled out fine and worked as they should. Previous owner did not have any of the e-brake hardware installed, so I reinstalled the complete ebrake system, including all new cables and hardware. Ebrake works as it should, holds the truck on a hill and disengages smoothly.

Before I did any of the work, the brakes did work, but the pedal sank to the floor because of the leaky wheel cyl. Other than the parts mentioned, I did not touch the MC linkage or pedal.

The only thing that I can think of that's bad is the proportioning valve. This one one of those solid units that you can get on Ebay that has a provision for a pressure switch. Can proportioning valve go bad and cause the brakes to lock up?

When I did the brake job, the MC well feeding the rears was empty because of the leaking wheel cylinder. Any chance some moisture could have gotten in there are corroded the inside of the proportioning valve?

I took the truck for another ride this morning, and the same thing started to happen, and it got worse the more I drove the truck.

If not, any ideas what would cause all 4 brakes to lock up? Everything seems to be in order, so I'm stumped.

Thanks...

Chris

Its like the MC is not returning and staying applied, how old is it? Could be something acting like a check valve.

Do have free play between the brake pedal rod and the master cylinder? If not, maybe the piston isn't returning in the master cylinder all the way. It would be like driving with the brakes on and creating heat, and making everything expand and get worse with more heat. Then when it cools down, everything is normal again till it heats back up. Just a WAG.

Truck, 55 - I don't know how old the MC is. The truck is an older frame off, but I don't know when it was done.

There's 1/8" play between the pedal linkage and the MC pushrod, meaning I can push the pedal in about 1/8" before I feel any resistance.

Chris

have you changed all the rubber lines?

Bill

Red - I have not replaced the lines, although they are not original and were replaced at some point in time. They're not cracked, still pliable, and appear to be intact.

Chris

wouldn't cost much to replace them, the rubber can break down and swell internally throttling the return flow

Bill

I don't know about 1/8", that seems kind of close. You want a lot more free play than that. It sounds like the MC rod is not coming back far enough to allow all the fluid to return. Your symptoms would fit that case.

Trucker -

1/8 is what the manual says, so I'm not going to 2nd guess the General. I crawled under the truck and pulled the brake lever down manually and released it several time. Everything moves as it should, and no matter how many times I pulled, the linkage didn't bind up or show any sign of not returning as it should. The return spring is also in place an intact.

The 2nd time the brakes started to seize and the brake lights stuck on, I got the brake lights to go out by cracking the bleeders on one of the front calipers.

I took another look at the proportioning valve, and it's NOT brass, it's starting to rust, so it's steel or cast. Posted this on the HAMB, and someone commented that the p. valve was from the 60s or 70s, so it's suspect as far as I'm concerned.

Next step would be to replace the MC if I can ID it.

I'll post pics in the morning.

Chris

Might I inquire as to where in the manual you saw the 1/8" spec for brake pedal freeplay? I've checked the manual, and cannot find any spec for 1/8" freeplay, only a 5" pedal to toeboard w/75 pound force on the pedal and an 11/16" clearance from the lower pedal to seal clearnce at full return.
I checked mine just for reference, I get about 3/4" freeplay with a properly adjusted stock system.

With a dual master cylinder installed your freeplay may be different from stock. As mentioned above, the plunger has to move into position to relieve the pressure. I'd think 1/8" is too tight even with a stock MC.

I'll agree with that. You might need to contact the manufacturer of the dual circuit conversion kit to see what spec they give.
In the meantime, just for giggles, I did check my later model truck ('85 S10 Blazer) which has a dual master cylinder and a disk/drum brake system for free play. Got a dimension of about 1/2" freeplay.

I'll share my experience - perhaps it will help. I had a similar issue when I switched out the front rotors and calipers on my truck. Front disc brakes would tighten up after a few blocks. Had me and couple of good mechanics stumped !
It turned out to be a combination of problems. The rear drums need to be adjusted properly as they activate first ( piston in M/C opens rear circuit first ). Getting the rears right, allows you to fine tune the travel on the push rod from the booster to the M/C. Piston needs to return to correct position when pedal released in order for fluid to flow back into the M/C, and take pressure off front brake lines. You should also have a residual pressure valve installed on the rear line, as well as proportioning valve. If you are concerned with your proportioning valve, I'd replace it. ( Not too expensive )

So then its the linkage holding the brakes on. No brake pedal ever has just 1/8 inch free travel. That is so slight that you are feeling free travel of the MC piston, and like the last post says.

Ok, I'll open up the clearance between the rod and the MC and see what happens.

In the meantime, part II of the saga is the MC. I have no idea what it's out of.

Pic links below. Can anyone ID it for me?

Thanks...

Chris

http://i904.photobucket.com/albums/ac248/barsteel/001_zps5662e0cc.jpg

http://i904.photobucket.com/albums/ac248/barsteel/002_zpsb7dba35e.jpg

http://i904.photobucket.com/albums/ac248/barsteel/003_zpsaff4684e.jpg

http://i904.photobucket.com/albums/ac248/barsteel/007_zpsba654076.jpg

Hy Barsteel, there is not enough distinctive information in the pictures to identify a particular master cylinder. The rectangular cover is typical of GM master cylinders. we need to know the cylinder bore, the size and thread pitch of the ports, and the mounting stud spacing. You said your brake light switch is mounted in the proportioning valve, is it mounted or teed into a delivery port, or is it in the center of the valve?

Should be a casting number on it. Find a grey beard at an auto parts store that can operate a catalog. In the back of the catalog there are casting numbers that should cross to the part number you need. That's the way it used to be years ago. Maybe that information isn't available any more.

Do you have a good return spring for the brake pedal? I have seen a weak spring used and that can cause the master cylinder to be pumped as your driving, especially if the clearance on the rod is not enough. Good luck.

Don, et. al. -

Return spring is strong.

Did some digging on Rockauto.com and Raybestos.com, and found that the most likely match is their part #MC36317, a manual disc/drum MC with a 1 1/8" bore, used on '69 Camaros and 69 - 74 Novas. It matches visually and has the same center to center measurement for the mounting bolts (3 3/8 as I measured it, 3.4" according to NAPA's tech line).

I could also use Raybestos MC36376, what the tri-five guys call the "C3" MC, used from '69 - '76, with a 1" bore.

I'm aware that I have to match bore size, mounting bolt spacing and post thread size, but at least I have 2 possibilities now. The final call will come when I remove the old MC and get the specific specs.

There's actually a really good thread on Master Cylinders on trifive.com http://www.trifive.com/forums/showthread.php?t=33201

I know that a smaller bore MC is supposed to be better with manual brakes at the expense of pedal travel, but I'm going to wait until I pull the MC to see what was on there before I order a new one. I was going to see if the problem was fixed with a new proportioning valve, but since a new MC is only $30 or so and I don't know how old my existing one is, I might as well replace it while I'm under there and dirty.

Chris

Yeah, just throw more money at it. You'll eventually find the problem.

Cletis -

I guess you could look at it that way. But since the truck is a 20-30 y/o frame off that sat for a while, I'd rather spend the extra $50 or so to replace the older parts to make sure that I know what I have. Not spending the $50 would look pretty foolish if I ran the truck into a tree because the brakes failed.

As far as diagnosing the parts, I do plan on doing that, first to the proportioning valve (as best I can, it's not like you can disassemble it), and second to the MC. However, doing so will call for me to either replace the MC or buy a rebuild kit, which wouldn't make that much sense since you can buy a new one for almost the same cost.

I dislike spending money as much as the next person, but in this case, I don't feel that it's a waste given that the brakes are a vital part of the truck's safety equipment.

If I spend the money and I still have the problem, shame on me...

Chris

It's probably a good idea to replace it all if it sat a while.

ALL 4 SMOKING

Fluids not returning to M/C which means the piston is not returning all the way to open up the return.

A- it's got crud in it and needs to be rebuilt / replaced

B - you've got the brake pedal adjusted wrong.

When the Dual Master is installed it is moved slightly from the original location. You may be getting heat from the Exhaust pipe heating the brakeline.

I had this same issue when I was sorting out my 59. It turns out the pedal/MC system did not have a return spring, so the MC piston was not returning all the way. Also, the manual specifies 11/16 clearance between the seal in the floor and the pedal link. You will find an eccentric bolt with a cotter pin nut that makes a pretty slick adjustment method under there.