The Stovebolt Site Forums The Shop Area Driveline Brakes - no pressure

Hi everyone. I need a little help with the brakes please.

There is no pressure at all when the pedal is pressed. The master cylinder was dry so I filled it up with fluid, and tried to bleed the brakes, but still no pressure. Hardly any fluid comes out of the open bleeder valves. Any guesses on the trouble? This seems like a master cylinder to me.

I installed a master cylinder kit about 12 years ago and adjusted the brakes and they worked fine. And it seems to me there was even a little pressure after pumping as recent as 3 years ago. Also, the rear right slave cylinder is leaking. And the truck has been sitting since all this time.

Thanks.

1. The fluid had to go somewhere. Fix the wheel cyl and any other known leaks before going any further.

2. With a lot of air in a system, use a power bleeder. It can be a long haul to get it done manually.

3. A single pump of the pedal on a dry master cyl can damage the piston. Be sure to test for leak by and pull back the dust cover and look for seeping after the system is bled.

Good advice. If the lines were as empty as the MC it might be worth the time to disconnect them at the wheel cylinders and flush them. It can be done when the MC is working. That will clear any crud before it can get to the wheel cylinders. You will also know if the MC is working. Let us know how it goes.

Thanks guys. After sleeping on it, I'm thinking that the master cylinder works because I burst two brake lines yesterday while trying to bleed the brakes.

The leaky wheek cylinder was siezed, so I loosened it up and put it back together. Maybe I'll check and adjust each of the wheels and then proceed.

Line burst? Ridged or flex? If you had a flex line fail, I would replace all three of them. They can collapse and no brakes is a very bad thing. If you burst a ridged line it was compromised. RUST is not your friend. Might have to look at all of them.

I wouldn't even look at the brake lines. I would replace all hard lines, soft lines, wheel cylinders, and master cylinder (if there is significant fluid showing under the rubber boot). These trucks don't stop real well when everything is perfect and new, let alone when something isn't right. But then I'm getting less daring than I used to be.
Carl

If the lines burst from putting that much pressure in the lines, then yea, examine and replace all of em would be my suggestion... saftey first! Dont wanna be going 55mph with no brakes down the road!!!

And with that, if your burst the lines, but weren't getting anything out of the bleeder screws... I would assume failed flex lines (thats exactly what happened to me)

All soft lines are replaced, and all but 1 or 2 hard lines are also replaced. Each wheel cylinder and the master cylinder had a kit put in about 12 years ago.

The master cylinder just isn't pumping any fluid. I removed it and the piston and all the seals look good to me. I forgot to check the outlet, I suppose the outlet could be plugged.

There is no pressure when the pedal is depressed and no fluid is moving. Could the linkage cause this if it were not asjusted correctly? Maybe the pushrod has to be shorter.

Bench bleed the MC first. If you don't get fluid into the bottom of the MC, its not going to work. Try that (proper bleeding procedures from scratch) before assessing the situation further.

Stove,

Do you have an original style master cylinder?
Or, do you have a newer-style, dual-chamber master cylinder?

I have never bench bled an original-style Master cylinder and I have never had a problem (I follow the Shop Manual bleeding procedure).

If you are using a newer-style, dual-chamber master cylinder, I bench bleed is appropriate.

The master cylinder is the original, it is a single piston with one outlet directly into a junction block. The last time I put this on I did not bleed it and did not have problem.

OK, I removed the master cylinder and bench bled it. It does pump and after a dozen strokes the bubbles were clear. BUT, the spring was very slow to return the piston, it seemed to be getting stuck, until the air was clear.

I put it back on the vehicle and the piston is not returning properly. What would be the cause of this. Maybe I need a new kit.

It would appear that there were more than one MC for the 1/2 ton truck in 1952? Is there a difference with GMC? When did the MC change? One listed for 47-50 with a 1 inch bore. Another listed for 51 with a 1 and 1/8th inch bore and another listed for 52 to 55 early. It could be you have the wrong kit. Just to make things more confusing, there is also an MC kit listed for get this, 1937 to 1959...? How would one kit fit all three MC's? Now I am confused. This is just one catalog page and it ain't helping.

http://www.oldchevytrucks.com/

Any thoughts out there?

The 37-59 kit fits same bore MCs - 1 1/4" bore for 1-ton and larger trucks.

The 1/2 truck brake system design changed in 1951.

What are JC's more than one MC part numbers for a 1952 1/2 ton?

The rebuild kit should match the bore.

One reason for different MCs with the same bore is the difference in the size of the brake line diameter that connects to the MC.

Thanks! With a simple measurement it can be sorted.
1, Early Huck type 1 inch ( 1/2 and 3/4 ton) to 51
2, Later Bendix type 1 and 1/8 inch (1/2 and 3/4 ton)51 and later
3, 1 and 1/4 for big bolts ( 1 ton and up)37 to 59
Have I got it right this time? I can still mess it up you know.

Turns out it was the master cylinder. I used a brake hone to clean it up and installed a new kit, it seems to work OK. Maybe the valve got crudded up after sitting for so long. Thanks!

if you haven't looked at the brake system in 12 years, and you are breaking lines. I would really be for going through the entire system. It is kind of a pain in the neck, but so is stacking your truck up into the back of a semi.