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I swapped out front drum for disc a few years ago. That has been working great. Now I am swapping rear drums for disc. What should I do for bias? Adjustable prop valve? What about something to do with keeping the brake fluid from backing the rear disc pads from loosing contact with the rotors?

 

[Rich-L79]

You will want a proportioning valve. If you pick a master cylinder well matched to the front and rear discs you have you shouldn't need a residual valve.

Here's a good choice for the proportioning valve: http://www.speedwaymotors.com/Speedway-Proportioning-Valve-Knob-Style,1977.html

 

[Scotch]

You should get a disc/disc master. A '79 Trans Am unit should be perfect- Cheap too! If you get an adjustable prop valve you wont' have to fight to bleed one. Just keep adding rear pressure until you like it (usually when the rears lock up just after the fronts in a panic stop).

No worries about rear pads pulling back on rear discs- Drums need residual pressure valves, discs don't.

 

[TMessick]

Before you go buying new parts, let's back up a bit and sort out what you have now...

What master cylinder are you currently running? Guessing a "stock-type" power disc/drum master cylinder? Did it come with the kit? Some kits come with a "universal" 1+1/8" bore master cyl which will work fine with rear discs OR drums. Just need to make sure the master cyl does NOT have residual pressure valves in the rear outlet.

When you installed the front discs, did you install a new proportioning valve or combination valve as part of the kit? Most kits seem to include a new "Combination Valve" which acts as a distribution block, hold-off valve, and proportioning valve. If so, you probably have a disc/drum combination valve and the easiest thing would be to replace this with a disc/disc combination valve, which should be a straight replacement.

Rear Discs will need MORE pressure (higher knee point) than rear drums, so you can't just install another adjustable prop valve in the rear line -- you need to either replace the combination valve with one with la higher knee point OR you could replace it with an adjustable setup...

You can check out Inline Tube for some pics of the Combination Valves. I'm guessing you have something like PR102 on there now (?)
http://www.inlinetube.com/Prop Valves/pro_valves.htm

 

[osdmike]

Also check size of brake lines.
I think You should go 3/16", both front and rear,when using disc/disc.


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