Thread: brake problem

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i have a 49 pont. street rod, disc on front drums on back, my m c is under floorboard residual valves on both ends. i have a poor pedal unless i pump pedal up. do i have air trapped in system or is my problem some other place? thanks hayless

There should be a porportioning valve for the disk brakes. if your having to pump I would re bleed the system, with a floor mount nc it is easy to trap air, you might want to go with a pressure bleader. What are the residual valves for?????
Yes you need residual pressure on drums but the proprtioning valve works that over I am told.

Be safe.

denny is right on, if its air it will be spongy and most of the time the padal will go all the way to the floor after it sits.

Take the residual pressure valve out of the front brake system, it will cause your discs to drag all the time.

RESIDUAL There are two different residual valves. A ten pound residual valve will maintain a line pressure to the rear to keep the drum brake shoes out close to the drums giving a higher firmer pedal. Without a ten pound residual pressure to the rear you will experience a spongy pedal. A two pound residual valve is required whenever the master cylinder is lower than the calipers to prevent backflow of fluid from the calipers to the master.

kyautomator, denny is right if the mastercylinder is lower than the calipers.



http://www.mpbrakes.com/valving.htm

thanks guys for allthe help, i gave up on my under the floor m c setup, i am now hanging my pedal on the firewall that way m c will be above calipers and i can do away with residual valves. thanks hayless

You still need a valve on the drum brake circuit. It's not just to keep the brake clearance low, with no pressure the seals relax and may let air in over time.

do you have a PROPORTIONING valve on your brakes? no matter what, like R Pope said you still need to have a PROPORTIONING valve and a rear residual valve anyway. if you have your brakes set up right it dont make no dif. where the mastercylinder is you, should be able to get brakes on it . thats a lot of work changing that over and i think you might have the same problem. JMO

you dont need the PROPORTIONING valve to bleed you brakes out, but if you dont have one you'll be doing it all over again.
are you sure the residual valves are on your car(i think they want work but one way, or they can be put on backwards) if you dont have one on the rear you want never have a good pedal.

my proportioning valve is built in with my combination valve, two reasons for moving m c 1- i think my m c may be bad and it is so hard to get to when adding fluid 2- i bought my booster from master power brakes it is a 7 in. now i find out it may be undersized so im using a 9 in. g m booster on firewall. should be finished with mods. sat. morning will let you know hayless

moving m c to firewall fixed my problem could have been bad m c or bad booster not sure all i know it worked . can i leave residual valves in system or do i need to take them out? thanks hayless

look at this diagram and see which setup you have now. http://www.mpbrakes.com/valving.htm

none of the above, what i have is firewall mount m c and booster i left both residual valves 2lb in fr. and 10 lb in back, i think my brakes are o k now so i might leave residual valves in hayless

Originally posted by DennyW
Well, I think you will be sorry if you leave the 2 pounder in the front since you moved the master cylinder up high. Your front dics will heat up more than they should going down the road. But, it is yours to try it. jmo.

you should have a PROPORTIONING valve and if you do then you should take it out of the front. denney is right. you should have at least as what is in the pic. second down on right. if you dont have at least one of the above then you gonna have a brake problem once you start driving it. need to check on that .

i think you all are right, i only tested my car around the block before i take her out for a long drive i will remove 2lb valve on front but keep 10 lber on back. thanks hayless