I have a 73 f100 but the back want work. I put on a new wheel and master cylinder but can't get any fluid to the back.I tried blleeding them but still nothig.The front workes ok. Thanks for any help.

 

Time for a new master cylinder?(Sometimes new ones are faulty cause they're rebuilds) Or blowing out the lines with a little compressed air?
-Chris

 

I have delt with similar problems with new master cylinders. It is like there is more air in the system than the master cylinder can compress or the mastercylinder is airlocked.
Or thats what i call it. When there is air in the piston area they don't pump for crap, It is not primed.

I use a Mighty-Vac hand operated vacuum pump ($60-$100) hooked on to the farthest open bleeder. The fliud is drawn through the whole system. Keep a close eye on fluid level so air doesn't enter, or it time to star over. I keep going til fresh looking fluid comes out. Some times it pulls a high vacuum but no movement, then pump the brakes a few times then it gets going on its own.

I have seen an old system used by a garage that pressurizes the master cylinder with a coffee can sized resevior of brake fluid. The presure was regulated around 30-40 psi of compressed air. That was the slickest thing I had ever seen. you could fill the resevior with two quarts, way more than you'ld ever need. it had a metal plate with a rubber seal that went on top of the master cylinder with a chain clamp that wrapped around the cylinder. All you had to do was to go to each bleeder and crack them open til they looked good.

Another way is to remove the lines from the master cylinder and bleed it by itself. Obvioiusly there is no bleeder valve there, so I just leave it open and pump the brakes a few times to get the fluid passing through. There may be air bubbles in there still, but at least fluid is getting through. then hook lines up and try pump bleeding them again. you could also crack open a line down on the rear axle by the rubber hose. just one more smaller step to get purged.

Or it could be a bad master cylinder.

 

More than likely the Brake Proportioning Valve.

Brake fluid absorbs water and the BPPV is subject to internal rust and can cause pressure to circuit problems.

 

I agree with Mil1ion. It sounds like the proportioning valve is
seized. Several of our sponsors should have what you need.

Glenn

 

The coffe can bleeder is called a pressure bleeder and you can get adapters for most master cylinders incuding the plastic resivoir ones. You can find a kit to bleed master cylinders at most autoparts stores. The kit contains a couple small barbed fittings to screw into the master cylinder, a clip to hold the hoses and some small hose to loop the outlet back onto the resivoir section. Cheap, easy and works well.