'41 ford with power brakes, 17" vac.,GM calipers in front, 10" drums in the rear.Can't get the brakes to lock up. Pedal doesn't pump up so no air. Pedal goes down about 2.5" and solid while on the brakes. Have bled all, adjusted the rears. If I sort of spike the brakes they're not too bad, not good and sometimes if I apply normally I wonder if the car will stop. I'm wondering about a bad metering valve in the front circuit stopping pressure to the front. no prop. valve. any ideas appreciated.
connect one of those master cylinder bleeders where you open the valves and push all the air out. works well with speed bleeders, http://www.tooldiscounter.com/ItemD...kw=MITMV6838&gclid=COD6meSfy9QCFQaXfgodsXQILQ maybe a buddy has one you can borrow?
I'm wondering if what you're calling a "metering" valve is actually supposed to function as a "proportioning" valve, although it would be non-adjustable. In many instances they were referred to as a "brake combination valve". Does the car go nose down with a hard application of the brakes? Will the brakes lock up on gravel or wet pavement?
removed prop. valve as I couldn't see any difference adj. all the way in either direction. I have a metering valve ( disc hold off valve) in the front circuit. Not much nose down and will not lock up on any surface
Is the master cylinder firewall mounted or under the floor? If on the firewall you probably don't need a valve in the front circuit. You might want a residual valve in the rear circuit for the drums though. With the return springs on the drum brake shoes there's a tendency when the brakes are released for the shoes to retract too far and it displaces excess fluid back into the m/cylinder. Then it takes more pedal stroke to pump up the brakes the next time you need to stop. The residual valve holds a few pounds of pressure in the circuit to prevent this from happening. Disc brakes have no return springs and when released they move just enough to create an air gap between the pads and rotor without displacing much fluid.
A brake specialist told me to check the pressure at each wheel, once with just pedal pressure and then with engine running to see if there is ample pressure to each brake. I don't have my notes with me to tell you what to look for. Good luck with your issue.
Is the Booster New? Did you Check Vac @ booster Feed. This sounds like the Booster to me. Make sure Check Valve is pointing right Direction.
Is the booster working?? I had the same symptoms when my booster split the diaphragm.. To check if it's working, pump the brake pedal without the engine running to get rid of the residual vacuum in the booster, press the brake pedal down with your foot and hold it while starting the engine.. If it's working, the pedal should sink down a bit more..
The way you describe the brake pedal feel, your booster is not working. With the engine running the pedal should be "soft" but not sink. ^^^shut off the engine and pump the pedal, it should be rock hard after about three pumps. Make sure you have manifold vacuum to the booster. Rick
Sounds like you need to start with a brake adjustment. Get the shoes as close to the drums as you can, then proceed from there. ........ Jack
Ran into the same issue on a 35 Ford all new parts but would not lock the wheels. Ended up putting a larger booster and a vacuum storage can on the car. It had residual valves and an adjustable proportioning valve . Under floor master cylinder. Tried everything, adjustable brake rod from the pedal, new calipers ,new master cylinder, new 7 inch booster, pressure bled the brakes. Finally went with an 8 inch booster with vacuum storage can and it slid the wheels.
What is the current master cylinder bore? What's the diameter of the booster, and is it a single or dual diaphragm?
and the pedal ratio? My guess is that the m/c diameter is 1.125" and so you're not getting enough line pressure and also as a consequence the linings have glazed. Higher line pressure (1"m/c) and some progressively heavy stops will bust the glaze and bed the pads in properly. Got that shirt. Chris
Did you have the lined shoes arced so that the curvature of the shoes mate exactly with the inside diameter of the drum on each wheel ? If not, you're only getting a fraction of the possible stopping power since you're only using a fraction of the available brake lining surface area. Linings on shoes are made to be close to new diameter drums. If the drums have been turned, the linings won't match to the new surface.
Some of those GM calipers are the low drag type with seals that pull the pads away from the rotors. They had a special step bore master that takes up the slack before the smaller bore builds braking pressure. Going to a smaller bore master will take even more travel to get them to engage if you have these. They make aftermarket replacement calipers without the low drag seals and a larger bore for more clamping pressure.
All Corvette dual masters were disc/disc, but can be used for drum/drum or disc/drum applications, so they and their design are more universal than the other very common dual, the drum/drum disc/drum Mustang.
All good info above: BUT, you do realize that your "new" brake setup on your car is FAR LESS than the car was originally equipped? You have front discs of unknown diameter & 10" drums in the rear, whereas the original setup was large 12" drums all around? 41 brakes are great brakes when properly setup. Put the 41 stuff back & be really happy Good luck on this. IMO, you have made a big down grade to your car.
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