The Stovebolt Site Forums The Parking Lot Tons 'o Fun Brakes, brakes and more brakes

I have a 52 3/4 ton truck. I added a 8in power booster and dual reservoir master cylinder.

Link to exact kit:
http://www.classicperform.com/Store/1947_59_Trucks/4754BBD.htm

Then my front shoes went in the dumper - I mean they are only 50+ years old and likely hadn't been replaced. Started doing some math and figured it would cost less to upgrade to disc brakes (not to mention off the shelf parts). Made some brackets, bought some calipers, rotors, pads and carriers from a 2010 3500 Express van. Bolted it all on, bled the lines/caliper/master cylinder and well...

No front brakes.

The pistons don't move at all. They have fluid but it doesn't spray out like the rears do. Thinking that the 1/4 in line wasn't supplying enough pressure, I swapped the fronts to 3/16 in line and the line to the front is on the back fitting of the reservoir. The brake line from the master cylinder T's off and has the exact length of line going to each caliper.

It doesn't matter if only the fronts are connected to the master cylinder, both lines or which port the lines are connected to. It's like there just isn't enough pressure.

Do I need something else to make this work or what am I missing?

Help please, its the only thing holding me back from driving this truck again.

Hy 52 Cheese, did you order the booster/master cylinder kit for a drum drum system before you decided to do the disc brake conversion? Did you bench bleed both sides of your new master cylinder? Does your new system have a proportioning valve? Was a residual pressure valve for the rear brakes supplied in the kit? If you do have a proportining valve, check to see if there is continuity between the electrical connection terminal and the main metal body of the valve, if there is continuity, then the valve has been shuttled one way and is severely limitng flow to one half of the brake hydraulic system. In your case it sounds like the fronts are shut off.

The booster kit has been on the truck for 5+ years and it was never a thought to go to disc brakes until I read a few threads on here about it. So it is a drum drum master cylinder.

Master cylinder has been bench bled and is known good.

The rear drums are working as they are supposed to. I can have the rear of the truck on jack stands with the wheels turning, step on the pedal and the wheels will stop quickly (not just free wheeling to a halt).

No proportioning valve or residual pressure valve.

It doesn't matter which port on the master cylinder the front lines are connected to, the fluid just dribbles out and doesn't spray like the rears do.

Thanks for the help.

When I did my studebaker, I replaced all the lines and master and wheel cylinders. I couldn't get any fluid out the rears. I took it all apart again and found a tee fitting was plugged. Just a thought.

Hy 52 Cheese, Okay firstly disc brake master cylinders do not have residual pressure valves built into them, drum brake master cylinders do. Disc brakes do not use or require residual pressure valves, under normal installation circumstances, however in some master cylinder below the level of the caliper installations a low p.s.i. resisdual pressure valve is recommended. If a proportioning valve is not used in a disc/drum system, then rear brake lockup on hard braking is commonly experienced. Builder may have a good thought about something restricting flow to the front brakes, so check your lines up to where they tee for kinks, and take the tee apart to make sure nothing is restricting it. If it were my truck I would do the following:
Install a disc/drum master cylinder, or a disc/disc master cylinder with a drum appropriate residual pressure valve in the rear brake circuit
Install a proportioning valve to deal with the rear brake lockup problem (also gives you the system failure warning if you hook up a light to the electrical connection), hope that helps.

Thanks for the help and suggestions.

I ripped the old master cylinder off and went to a local auto parts store (not a chain place like NAPA, Advance etc) and the hot rod guys got me a master cylinder that would work.

Best part is that they had one sitting on the shelf from a 76 Chevy ton truck. Has huge (like 3x the reservoir) size of what I had and was already set up for disc/drum brakes. Its a tight fit mounted on the frame rail between the floor but it fits and doesn't hit anything.

No proportioning valves or residual valve. Bench bled the master, bolted on, bled the lines and drove it. Stops straight and the pedal feel is great - almost like a newer vehicle.

There is a new issue though. Sometimes the calipers seem to stick and not completely release. I lubed all the caliper slide pin bolts with the special grease or whatever it is that they come with and they move better but not quite right.

Any ideas for that?

Thanks again for the help and suggestions - I was out of ideas.

Possibly something not quite lined up, on dimension, or incorrect about the brackets you fabricated?

Grigg

Nope, brackets are spot on exactly where they need to be. Rotors roll straight and true in the caliper bracket openings.

Anyways, sticking caliper issue is fixed and wasn't even that. The push rod from the booster to the master was just a hair bit too long and left more pressure on the lines and calipers not allowing them to completely relax.

Problem solved and about 100 trouble free miles on the truck today. I'm excited.

Thanks for the help and ideas.