'Working to make your car go faster can sometimes involve addressing what is slowing your car down. That's the situation we're facing with our hot street/strip car. The brakes are dragging mercilessly because of mismatched components causing excessive brake-pad wear, overheated rotors and slowing us down at the dragstrip. This situation has been eating through brake pads, ruining rotors, and slowing down the car at the dragstrip. This story is going to help you find out if your car has a brake-system problem and show how to correct this issue.
Brake-System Problem-Solving
Is your car incredibly difficult to push around? Are the brake pads completely worn to the backing plates in less than 1,500 miles? Do your rotors look black and scabby after a few thousand miles? Is your car slower at the dragstrip than it should be? While these symptoms are extreme, any even close indicate a disc-brake system that is holding the pads against the rotors even though the driver is not attempting to slow the vehicle.
To many, the thought of someone having these issues on their car and not knowing it seems surprising. But we know of cars out there that have these problems, and, until now, those owners didn't know why.
Dragging Brakes
In general, dragging brakes usually arise from mismatched components. Like most vehicles with this problem, the vehicle being improved in this story gained rear disc brakes in place of the production drums when an aftermarket rearend was added. This should have helped the vehicle performance, but it actually hurt it. That's because the production front-disc/rear-drum proportioning valve was left on the vehicle. This stock proportioning valve has a residual pressure valve in it that helps to slow the rate at which the brake shoes relax from the drums. Unfortunately, this feature makes the rear-disc brake pads drag on the rotor-causing excessive heat buildup and pad wear, slowing the vehicle.
Figuring out how to go faster sometimes means minimizing the things that slow you down-like a brake system that is dragging! |
This is the stock GM proportioning valve that came on many late '60s and early '70s A-body vehicles (Chevelle, Skylark, LeMans, and Cutlass) for a front-disc/rear-drum system. If you install discs at all four corners, this needs to be removed and replaced with a proportioning valve for a disc-brake system (or a manual prop valve-as is being done in this story). |
A Wilwood proportioning valve (PN 260-8419) and some 31/416- and 11/44-inch steel brake lines were acquired to make this improvement. The brake line is available at most local auto-parts stores, and the proportioning valve is available from all the large mail-order houses. |