When Switching from rear drums to rear discs...


Do I need to use a Different Master cylinder?

Do I need to add a stand alone proportioning valve?

Can I use the Stock Proportioning valve or bypass it completely?


I currently have Wilwood dics up front and the stock Warning light / Distribution block / Proportioning valve combo. Stock 10" Rear Drums in the Back from a Volare/Big Bolt pattern A Body.


I also have a 79-89 Mopar Aluminum Master Cylinder with the Plastic fluid Tank. Id woud be for a stock 79-89 volare/aspen diplomat/ any F/J/M Body.



Thanks for your Help!

Greg

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http://www.youtube.com/hyperpack

Greg,

I would keep the existing master cylinder, but remove the residual pressure valve if there is one. The residual pressure valve used with older drum brakes keeps the wheel cylinder cups in contact with the cylinder bore and prevents air from entering the system. On newer master cylinders and wheel cylinders there is no check valve and the wheel cylinder cups have expanders inside them. I would bet a dollar you don't have a residual pressure check valve, but you could give the brakes a pump and then crack a rear bleeder or attach a gauge to see if the system is holding pressure.

If this is a race car you don't necessarily need a proportioning valve if you get the caliper piston and pad material area exactly right. Ha! Road race cars often use dual master cylinders with an adjustable balance bar to adjust the brake bias, but that adjustment is used to maximize threshold (maximum) braking. Proportioning valves have a benefit on a street car in that the put the rear brakes to better use in low speed stops and then "knee over" to limit the rear brake pressure and prevent lockup during aggressive deceleration.

So, which car is getting rear discs?

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Joshua

the rear discs are going on the ruster project.

much less rotating and static mass then the old 10" drums.. Also will be upgrading to a set up super light rear wheels.

Greg

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http://www.youtube.com/hyperpack

Josh has got it. Keep same master and prop valve (or replace factory block with a tee if you like). Install adj valve in rear line for fine tuning. I have unmodified late model alum masters and factory prop/dist blocks in all of my cars with an adj valve in the rear line.

Lou

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Home of Slant6-powered fun machines since 1988

The Valaint got an Explorer rear with disc. I used a 75 Master and stock 75 block. .....lines and hoses

I modified none of it.

It worked really well....and if anything I would have wished for more rear bias.

I would use a stock Volare setup if I had to do it again.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

cool...

thanks guys. the parts I ordered then should be sufficient

I got an extra prp valve and I can install it later if needed.


Greg

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http://www.youtube.com/hyperpack