1956 Buick Brake Proportioning Valve rebuild

[Beemon]

I feel like this is a very overlooked part that plays a large role in the performance of the brake system. I always have good brakes, but it's always at the firewall, or close to it. I've never had issues stopping, but the shop manual says that the pedal should go halfway to the firewall under properly adjusted brakes, not all the way. When I pump up the brakes, it builds resistance, but if I let it set, the pressure drops.

 

For those that don't know, this is a 2 way valve that restricts flow in one direction (back to the master cylinder). In the aftermarket world, these are known as residual valves. It's essentially a weighted diaphragm that allows free flow towards the wheel cylinders, but then builds pressure back to the master cylinder so the fluid can't all drain back, and keeps the lines primed for the next stop.These residual valves are essential for master cylinders mounted below the wheel cylinders, because due to pressure differentials caused by height differences (specifically gravity), all the fluid will naturally drain back to the master cylinder vs stay in the lines, whether properly bled or not. These systems are not required for master cylinders that are at the top of the firewall because gravity keeps pressure on the lines. So in essence, you're working against gravity.

 

Enough of the theory, how's how I did it:

 

I put the large piece in a vice and hit it with the impact gun to break the copper compression washer. Once it came apart, it's broken into 3 pieces: the pressure spring, the one way check valve, and a rubber gasket seal. When you push your foot into the pedal, fluid flows through the 1-way check valve (top hat) and into the wheel cylinders. When fluid flows back, it's opposed by the check valve and must overcome the spring force to return to the master cylinder. You can't see very well from the photo, but the top of the bottom piece where the valve sits was rusted across the top. I couldn't find anything wrong with the check valve, except it was allowing flow in both directions, but the rust was the same on the bottom of the top hat. I took 220 grit sand paper and scuffed the rust off. Also, hard to see, but the rubber washer was also badly corroded.

 

These are the replacement parts. I've had them sitting around since I rebuilt the master cylinder. I kept asking myself "what the hell are these for? Spare parts?"

 

Old rubber pulled off, it's just a rubber washer. Note the discoloration and wear.

 

And finally how it all goes back together. Pretty simple design, really. Looking forward to giving it a test drive after my NOS front wheel bearings arrive tomorrow.

 

And for those who care...

 

I finally got my hands on some 1955 Roadmaster drums and backing plates! Painted the drums red for "high performance" braking action... my car is kind of a bastard. Also please excuse the finger... I guess I take after my grandfather after all.

[NTX5467]

Is this an effort to make the brake drums invisible behind Buick Red Wheels?  Let us know which area starts to indicate "heat" first.

 

NTX5467