Drag car brake/proportioning question

[demon322]

The residual pressure valves are there because the master cylinder is frame mounted. This was a common problem with street rods where the master cylinder was low mounted. IIRC a 2 lb valve was used for the rear brakes & 1/2 lb was used on the front along with a proportioning valve. It's been a while since I've worked on that type of system. I had a street rod with Mustang II manual front disc brakes & drum rear brakes with just a proportioning valve that "seemed" to work great under normal braking. The master cylinder did not have the residual valves in it. The first time I had to get on the brakes hard, the pedal went to the floor. Two quick pumps & they were back up. I did some research & talked to some other street rod owners/builders. I put the residual valves on my car & all was good with the world.

This sounds a lot like my setup and may explain why they went that route. Thank you for sharing.

 

[yellow rose]

I wondered that myself as this is the only car I’ve had with this type of setup. I assume it was put there because the firewall was cut out and moved back and the brake pedal is floor mounted instead of hanging under the dash. So the rod comes out of the front of the MC and attaches to the brake pedal. I plan on leaving that all as is. So I can keep the residual valve and plumb in a proportioning valve when I replace the lines in case it is needed. The front has wilwood hubs and discs and a mustang II front end. I will check the rears when I get back to the shop but I think they are aftermarket pieces as well.

Many race cars have the MC mounted like that. Mine did. Especially in early A body stuff there isn’t room for the MC I the OE location.

 

[Duane]

Thanks for all the thoughtful replies guys!

So if I go with a proportioning valve can I eliminate that residual valve or should I run both? Is this type ok? That way it could mount under the car with the MC and the adjustment could be in the cab.

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That flap looks like it is just to seal the **** pit. Depending on who you talk to, a race car should have an adjustable pro portioning valve to decrease front braking or increase rear braking depending on how you look at it to offset the skinny and fat slicks that are common on race cars.
Stock pro portioning valves are for stock cars with four identical wheels. The last thing you want in a race car is to lock up those skinny front tires at 120+ mph imho.

 

[demon322]

That flap looks like it is just to seal the **** pit. Depending on who you talk to, a race car should have an adjustable pro portioning valve to decrease front braking or increase rear braking depending on how you look at it to offset the skinny and fat slicks that are common on race cars.
Stock pro portioning valves are for stock cars with four identical wheels. The last thing you want in a race car is to lock up those skinny front tires at 120+ mph imho.

I agree about the flap and I plan on replacing that also during this job as this one has split over the years.

Thanks for all the replies guys. The consensus seems to be to add an adjustable proportioning valve while I replace the brake lines. And then do some testing and experimenting to see what works best with my combination. As a few have mentioned I do have big slicks our back but skinny tires in the front. Better to have it plumbed in to adjust if need be than to have to go back and add one later.

Thanks all.