Help!!!!!!!!!

[TMat]

I have a brake problem and am at my wit's end. Here's the situation:
1. 69 camaro
2. New LS1 calipers, rotors, braided flex lines.
3. New 15/16 manual master cylinder.
4. New metering block
5. I have no leaks

The problem is after I bleed the brakes, I will roll the car 50 feet and the pedal will go almost to the floor. If I then pump the pedal, the pedal gets firm. I have no leaks, everything is new. Why am I having this problem?

Is the master cylinder size wrong? Should it be 1"?

I need serious help, I don't know what else to do.

Thank you in advance for all help.

[rocketrod]

Did you bleed the master cylinder?

[TMat]

Yes, Master Cylinder is bled.

The car originally had rear drum brakes, do I need a different residual pressure valve in the rear line?

[TMat]

Anybody? I have tried everything I can think of, I have bled the system numerous times. After bleeding the pedal feels firm, but if I move the car 50 feet the pedal goes to the floor. I can then pump the pedal and it becomes firm.

I have found and fixed all leaks and re-bled the system.:hmm:

[6'9"Witha69]

Residual pressure valve is needed. There are different requirements for disc and drum applications. 10 psi is for Drums and 2 psi is for Discs.

http://store.summitracing.com/egnsearch.asp?Ntt=Residual+pressure&searchinresults=false&Ntk=KeywordSearch&DDS=1&N=+115

Do you have a prop valve in the rear lines?

[TMat]

I have a metering block which came with the disc/disc master cylinder, installed. Do you think it could just be the residual pressure valve?

thanks for the help!

[6'9"Witha69]

I had a problem going from a power Disc/Drum setup to a manual disc/disc. Same problem as you stated above. In fact, if the car sat for more than a few minutes it lost pedal. I installed the valve, bled it again, let it sit for a couple days and the brakes were still right up!!

FYI, disc disc blocks are not metering blocks as they are on Disc/drum applications, they are simply a distribution block. Disc/drum setups use a metering setup in the block accompanied by a hold off valve in line to the rear brakes. Disc setups simply need to distribute and not meter. This is why prop vales are used with dist blocks.

\short answer.

[TMat]

this residual pressure valve is located in the rear line just below the drivers door correct? It's not part of the master cylinder.



Or can I replace the res. press valve with a proportioning valve?



Thanks a lot for your help. This problem has been bugging me for months.

[quadfather]

i would check to see if you have a rotor runout issue, or if the caliper mounts are flexing when you apply the brakes . it sounds like the pistons may be getting pushed back in when you roll it.

[Karch]

Try a different m/c. It sounds like the m/c is allowing fluid past the first seal. Is it wet behind the m/c if you pull it off?

[TMat]

I discovered what the name of the valve is located on the underside of the floorpan on the drivers side frame rail. It is called a disc brake correction valve or hold-off valve (www.inlinetube.com) in the proportioning valve section. Does anyone know if I need to keep this with a 4 wheel disc master cylinder or can I eliminate it all together and run a 1 piece brake line from the master to the rear axle?

This valve is the only thing I can think of that might be causing my problem. Everything elese checks out OK.

[scottyz]

I am also having a similar problem with a 89 LX mustang. Changed to larger piston front calipers and rear disc brake conversion. Pump up the pedal nice and hard. Let off for 5 seconds and the pedal will drop. If you pump it up and hold it the pressure does not seem to leak past but once you let off for 5 seconds the pedal will drop again. Will this residual pressure valve stop this pedal drop?