Ok Here is the deal. I race a 70 Buick with 4 wheel drum and is has issues. Cast drums on all 4. I have replaced all wheel cylinders and brake shoes. I loosened up all the front control arms to make the front end lift quickly to transfer weight to the rear. I did start getting a pull in the front when I brought up the rpms and hit the brakes and it did help to tighten up the lower control arms a bit but the proportionit valve on 4 wheel drum is a block on the resale sites but the valve on this GS is a valve with a switch. so how can people who sale those valves say they are for front disc? The information I am getting is that you have 4 wheel drum than you have a block and if you have a front disc you have a valve. So I guess in 70 you still have a block but with a pressure valve in it. What I think is that the 70 should have both so lets just put the disc brake valve there to take care of both systems. Can some one tell me why the 4 wheel drum car has a praportianate valve on it?
The proportioning valve is for front/rear brake bias. It limits hydraulic pressure to the rear brakes so the rears do not lock up before the front, regardless if the car has front discs. The valves are different between drum and disc brakes, but the purpose of the valve is the same.
i dont think it's a proportioning valve, my 67 has the same thing and i think it's designed to cut brake fluid off to either the front or rear brakes in the event of a pressure loss. i think it's called a pressure differential switch. the little electrical connection on it is to light up your brake light if it trips in the event of a brake failure
But aren't brake systems set up to be on separate diagonal circuits, so that if you spring a leak in a brake line, you will still have one front and one rear brake that work? Is there also a switch that can cut off the supply of fluid to a leaking line? If so, that sounds like a great idea. I am just not very knowledgeable about brake systems so I am unaware of such a thing.
Never heard the diagonal thing before. Every brake system I have ever seen is separated front to rear. The line to the back is usually a 1/4" line splitting to two 3/16 lines at the differential and the front is 3/16 lines to each side.
Ron is it? I'm pretty sure the distribution block on the frame rail is the same for both drum/drum and disc/drum cars in 1970. The difference here is both cars have the distribution block, but disc cars also had a separate proportioning valve/hold off valve mounted by the master cylinder. I could be wrong o No: Here's a photo of the hold-off valve by the master cylinder.
