powermaster and rear disks-residual valve??

[summit]

Is there a residual valve on the powermaster that needs to be removed for using rear disk brakes? If so where and how? I'm not quite ready to switch to manual brakes yet, but am afraid my rear pads may be dragging unless I modify the powermaster. Any ideas?
greg

 

[Roger]

Good question. I've also been considering rear discs & have the same question.
I would contact Baer concerning this, whenever the penny jar gets full enough.
I've heard about using a 4-wheel disc master cyl from a TA or ?, but I had too many problems with the vacuum setup, I went back to the PM.

 

[TurboPhil]

Originally posted by summit
Is there a residual valve on the powermaster that needs to be removed for using rear disk brakes? If so where and how? I'm not quite ready to switch to manual brakes yet, but am afraid my rear pads may be dragging unless I modify the powermaster. Any ideas?
greg

The residual pressure valve is on the frame below the master cylinder (just follow the brake lines to it). Its actually called a combination valve, I modified mine by taking it off and removing the residual valve from the rear circuit and the pressure regulator from the front circuit and leaving only the piston under the hydraulic warning switch but its really simple to do once its off the car but you will have to tap and put pipe plugs were you pulled the two valves out as I remember. Another thing you need to do with running the stock 10-bolt rear with C-clip axels is put a Wilwood 2psi residual back in the rear circuit to control inconsistent pedal due to caliper kickback from the axels moving in and out, I put the 2psi valve in the line leaving the master to the rear brakes.HTH…Phil.

 

[GNVAIR]

Gut the valve on the frame rail and use a 79-81 Trans Am master or a 79-85 Eldorado, Riv or Toronado master cylinder with a stock dual diaphragm booster for a G body. You will find the Power Master will not supply enough assist with the rear discs once you add the master cylinder with the larger bore to the equation.
If you have problems with a vacuum conversion, then you have other problems such as a bad check valve or tapping for vacuum in the wrong spot. Its very rare that a dual diaphragm booster goes bad on these cars. You never hear the TTA guys complaining that they have problems and they have 4 wheel discs with vacuum assist from the factory AND there is nothing really different about their engine set up. IMHO, if anyone has problems there is either a mechanical fault OR it is in their mind.

 

[summit]

Thanks guys. I bypassed the combination valve and am using a wilwood adjustable one so that takes car of that concern. I'm still using the powermaster and it seems to be working fine as far as volume. If I do change it will be to a manual brake setup purely for weight reasons.
Greg Kring
Arlington, Texas