71 demon brake questions.

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71DodgeDemon340

71DodgeDemon340

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Ok guys. i have a 1971 dodge demon. Originally drum brakes all the way around. did the disc brake swap with the 73 and later chrysler A body upper control arms and spindles, im using remaned calipers for a 79 plymouth volare and new 73 plymouth duster brake hoses. new raybestos manual master cylinder, all new brake lines, using an oem combination valve. heres the problem, when i go to bleed the brakes i start to get pedal but after the bleeder valve has been opened and the pedal goes to the floor to bleed the air out and after i close the valve and then pump the brakes theres no pedal unless i pump it up. also after you start to get pedal and let it sit then try to pump it again it goes to the floor, is there still air in the system? im going to try and use a vacuum bleeder tommorow and see if that helps, any other ideas would be appreciated.
 
are the bleeders on the top side of the caliper?
if they are on the bottom you can't get the air out
 
There is a large brass plug on the side of the combination valve. You will need to remove the plug and recenter the piston that is under it before you can get any fluid to the front brakes. The factory valve has this provision to keep from pumping the master cylinder dry in case of a brake line failure. When you get the valve recentered, put the front of the car on jackstands, fill the master cylinder, crack the bleeder that is farthest from the master cylinder, and let the car sit until fluid comes out the cracked bleeder. I usually use a piece of clear hose that will slip over the bleeder and put the other end in a bottle with enough fluid to cover the end of the hose and go to bed. When I get up the next morning, I bleed the brakes. When you are bleeding the brakes make sure you don't push the brake pedal more than halfway to the floor or you will need to reset the combination valve again. Hope this helps.
 
Somewhere I read about the early wheel cylinders on the rear didn't have a spring between the piston cups. The drum only master cylinders had compensator valves in them to maintain some pressure on the wheel cylinders to prevent fluid flow back to the master cylinder in order to maintain pedal height. The newer disc brake master cylinders did not have the compensator valve due to them putting a spring in the rear wheel cylinder to hold the seal/pistons apart. This in essence acts like a built in compensator. You may have to add that spring to or replace your wheel cylinders with newer year models.
 
>> In the mid-1970s, Chrysler eliminated the rear brake residual pressure valve from the master cylinder. Its function was to prevent any air from sneaking into the system via the rear wheel cylinder cups. In its place, Chrysler substituted "expanders" in the rear wheel cylinders. (Expanders are dish-shaped steel inserts that exert outward pressure on the cups.) If you should decide to use a master cylinder from a 1975-up car, be sure you have the expanders in your rear wheel cylinders. For at least 20 years they have been universal in all replacement wheel cylinders and rebuild kits.

From here http://www.moparaction.com/Tech/archive/disc-main.html.
 
yes i have bench bled the master cylinder, its for a 1973 plymouth duster with front disc and rear drums, rear brakes are adjusted, and im getting fluid to the front calipers, just not keeping pedal, although i have been pushing the pedal all the way to the floor when bleeding, but if this messes with the combination valve will it automatically recenter itself or will i have to take the brass plug out and do it manually, i dont think its stuck because im getting fluid to all wheels. also i think the rear wheel cylinders are for a 71 duster with 10'' drum brakes. but to see if the combination valve is stuck im i turn the key to the on position and hit the brake pedal to the floor the brake dummy light should come on right?

thanks for the info guys.
 
If the light is good, it should come on. Never let the pedal go to the floor.
Try this; go to the back, just barely crack the bleeder- no air? do the same to the other side.

Now go to the front, barely crack a bleeder and push; you might feel a click in the pedal, and or the light goes off. Don't push further until the bleeder is closed, If that worked, the valve is now re-centered.

Re-bleed, only push the pedal half way down.
 
thanks everyone. found the problem today. had the bleeders towards the bottom of the caliper, so i took them off and set them on a block of wood so the bleeder was at the highest point, then i ran a clear tube from the bleeder into a container with brake fluid in it and then i cracked the bleeder and a ton of air came out. so did that with both the front calipers. then while i had the calipers off and the bleeders at the top i used a vacuum bleeder on both the front calipers and both the rear lines, bolted the calipers on and topped of the fluid and hit the pedal. boom! had a good hard pedal. :burnout:
 
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