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View Full Version : Do I really need to use a porportion valve?


newschool
03-06-2007, 01:15 PM
I have a 67 Camaro and I bought an after market chrome 7" brake booster, master cyclinder, and porportion valve and the master cyclinder had four outlet lines. Do I really need the porportional valve or can I just pipe the lines up to the mastercylinder? I am running a disc/drum set up and a 245/45/17 tire on the back. Is anyone running without the porportion valve?

Any help is appreciated,
Thanks

Payton King
03-06-2007, 01:56 PM
drum brakes run about a 55 front 45 rear bias...disc are about 70 f and 30 rear. If you do not run one, the rears will lock up and it will be a bad scene.

You did not state if it was adjustable ...which I would reccommend

newschool
03-06-2007, 02:44 PM
The porportion valve is adjustable. Do I just keep adjusting until the rear brakes stop locking up?

Payton King
03-08-2007, 02:40 PM
adjust it until they do not lock up. Make sure you do a really hard panic stop where it unloads the rear wheel.

ItDoRun
03-08-2007, 06:19 PM
I don't know if the booster makes a difference or not, but I'm running manual LS1 front brakes and rear drums with no proportioning valve. I did, however, run a residual valve between the front and back brakes. I think it depends on what master cylinder you are using. I have the Strange tandem master cylinder.

Eric Bryant
03-09-2007, 07:30 AM
Lots of factors add up to the required front/rear pressure bias - master cylinder bore areas (if different between front and rear), brake caliper/cylinder bore areas, pad area and coefficient of friction, vehicle weight bias, front and rear tire sizes, and driving style. I suspect, however, that with drum brakes out back, a prop valve of some sort would be a very wise idea - drums typically operate at lower pressures than discs.