The Stovebolt Site Forums The Parking Lot Big Bolts BRAKES

I've been having a time with the brakes on my 2 ton. The back ones were not releasing. I put a new wheel cyl. on one side, Bleed it and that was fine but they would not retract. even with a c clamp on the wheel cyl. pistons. so I loosened the line coming out of the master. And pistons still would go back in the wheel cyl. with the c clamp. When I bleed it the fluid comes out freely. This thing is driving me crazy. Any ideas

Is the hose to the rear axle new or in very good shape? Hoses can deteriorate inside and act like check valves.

But if you loosened the line at the master cylinder, that says that the master cylinder is the issue. It may not be retracting far enough to release the brakes. Try adjusting the pedal linkage so that it's shorter.

But I removed the brake line from the master cyl.. The fluid should flow with the c clamp pressure on the wheel cyl. I put all new lines on it 15 years ago and you see threw the brake fluid in the master. Could it be the hoses?

Here's the way I'd approach it...

Lock the brakes up again and then open a rear wheel cylinder bleeder to see if shoes release (check both rear wheels after opening only one bleeder). If that doesn't release them than you have bad wheel cylinders, broken return springs or trash in the cylinder not allowing the piston to retract. If that does releases the brakes, do it again and this time open the bleeder on the Hydrovac...if they stay locked up then it's the rubber hose acting like a check valve.

Hope this helps,

Mike B

I read your post understanding that you were able to get the brakes retracted after cracking the master cylinder connection. But if they still didn't release, then my money's on a bad brake hose.

Here's the way I'd approach it...

Lock the brakes up again and then crack open a rear wheel cylinder bleeder to release the pressure (check both rear wheels after opening only one bleeder)...did that release the shoes? If that releases the brakes, do it again and this time crack open the bleeder on the Hydrovac...if they stay locked up then it's the rubber hose acting like a check valve.

If all of the above does nothing them than you have bad wheel cylinders, broken return springs or trash in the cylinder not allowing the piston to retract.

Hope this helps,

Mike B

Why waste brake fluid? When I'm trying to diagnose a problem such as this, I adapt an air hose and a blow gun to the brake lines, and operate the brakes with compressed air instead of fluid. It's cleaner and more convenient, and once the brakes are functioning on air pressure, I reconnect the lines, fill the master cylinder with clean fluid, and bleed the system. I leaned that trick when we were fabricating disc brake systems for race cars, using air pressure to clamp the calipers to the rotors while we built custom caliper brackets.
Jerry

I'm retiring in 1 month so Hopefully I'll be able to stay on this thing and get it back on the road! I can't get to the other side because the truck is in a 12' wide building and no room to remove the axle, but I'm thinking it's the rear hose because both rear brakes were not releasing about equally. I could tell from the temp. of them. They bleed great, but my next step is to remove that rear hose. Every brake line was new 15 years ago but the hoses might have been Chinese. Thanks for the input

It was the rear hose. I've never heard of of a hose plugging up, but it does kind of make sense. Because you have Hyd. pressure pushing one way and a 75 year old spring pushing the other!

Hoses fail from the inside out. There are multiple layers of rubber and fabric, and as the hose delaminates the inner layers collapse and prevent the fluid from returning to the master cylinder quickly- - - -it seeps back slowly after a few minutes and the cycle starts over.
Jerry