Use a proportioning valve or not?

SCOTT SST2871 · 03-17-2009, 10:15 AM

I have a 71 pontiac ventura with the chrysler style alum. Master cylinder..until this week it had 4 wheel drum brakes and the stock dist block..i just installed the stock style front disc brakes on it and plan on putting rear discs on it this summer.would you run the dist.block that came on it or no prop.valve at all.i do drive the finish line aggresively!!
Scott fifield

superstreet268 · 03-17-2009, 11:08 AM

If you plan on installing rear discs i would install a proportioning valve on the rear so you can decrease pressure to the rear. and take the oem valve off. i have experience with this i almost turned my car around once at the finish line was not a good experience.

Ron Finney · 03-30-2009, 08:42 AM

Scott,

Since your car did not have discs on the front originally it probably does not have a metering valve in the system. A metering valve holds off the front disc brakes until the rear spring pressure is overcome so that brakes can be applied proportionately. Chances are that your system being 4 wheel drums, will just have a proportioning valve which balances front to rear braking, since approx. 70% of braking is done by the front on most cars. What this means is you may have to install an aftermarket proportining valve to limit the front brake pressure to keep from burning them up until you get the rear discs installed. Right now the OEM valve assumes you have 4 wheel drums and will apply bias to allow more front braking which is required due to enertia and weight transfer. Now that you have the discs up front you have a bunch more braking up front and maybe too much. You would probably be wise to take the old valve out of the system and just use the new proportioning valve to equalize the brake pressure. Once you have the rear discs, you may find you need to move the prop. valve to the rear side since you will have much more braking capacity as was suggested in the other post.

03-17-2009, 10:15 AM	#1
SCOTT SST2871 Member Join Date: Oct 2008 Location: PORT ST JOHN FLORIDA Posts: 226 Likes: 0 Liked 0 Times in 0 Posts	Use a proportioning valve or not? I have a 71 pontiac ventura with the chrysler style alum. Master cylinder..until this week it had 4 wheel drum brakes and the stock dist block..i just installed the stock style front disc brakes on it and plan on putting rear discs on it this summer.would you run the dist.block that came on it or no prop.valve at all.i do drive the finish line aggresively!! Scott fifield

03-17-2009, 11:08 AM	#2
superstreet268 Junior Member Join Date: Feb 2009 Location: palmetto fl Posts: 8 Likes: 0 Liked 0 Times in 0 Posts	Re: Use a proportioning valve or not? If you plan on installing rear discs i would install a proportioning valve on the rear so you can decrease pressure to the rear. and take the oem valve off. i have experience with this i almost turned my car around once at the finish line was not a good experience.

03-30-2009, 08:42 AM	#3
Ron Finney Member Join Date: Jul 2008 Location: Greenwood, IN Posts: 168 Likes: 0 Liked 0 Times in 0 Posts	Re: Use a proportioning valve or not? Scott, Since your car did not have discs on the front originally it probably does not have a metering valve in the system. A metering valve holds off the front disc brakes until the rear spring pressure is overcome so that brakes can be applied proportionately. Chances are that your system being 4 wheel drums, will just have a proportioning valve which balances front to rear braking, since approx. 70% of braking is done by the front on most cars. What this means is you may have to install an aftermarket proportining valve to limit the front brake pressure to keep from burning them up until you get the rear discs installed. Right now the OEM valve assumes you have 4 wheel drums and will apply bias to allow more front braking which is required due to enertia and weight transfer. Now that you have the discs up front you have a bunch more braking up front and maybe too much. You would probably be wise to take the old valve out of the system and just use the new proportioning valve to equalize the brake pressure. Once you have the rear discs, you may find you need to move the prop. valve to the rear side since you will have much more braking capacity as was suggested in the other post. __________________ Ron Finney 396V S/C Last edited by Ron Finney; 03-30-2009 at 08:47 AM.