Greg D wrote:Why are drums OK on the rear?
When you apply the brakes the momentum shifts the weight forward. This decreases the weight on the rear wheels.
Under hard braking if the friction is the same on the front & rear brakes the rears will lock up because there not enough weight/traction to override the brakes. A proportioning valve helps too - it's necessary on some vehicles.
Modern cars that have rear discs also have anti lock brakes - you probably wouldn't want to adapt one of those to your truck.
My truck doesn't presently have a prop valve. This same brake system was fine on the Uni, untested on the 64. I drove the Uni on water, snow, ice, and of course dry pavement - I had NO problems with the rears locking too easily. I also have a pretty serious difference in the front & rear tire sizes. The big rears have more traction and need a bigger brake than the smaller fronts - sort of has the same effect as the prop valve. This was "estimated" on my part and it seems to be fine. That doesn't mean it'll work on the 64 or another truck - the long wheel base helps too.
This is exactly right.
Rear discs without ABS on a pickup aren't really going to be an improvement. Car systems frequently have a totally different proportioning valve arrangement as well. These trucks use a pressure sensitive valve, where the cars I've worked on with 4 wheel discs use a valve that is tied into body deflection, i.e. when the nose dives and the rear jacks the valve mechanically can detect this. They are mounted at the rear axle.
On a truck, unless you're hauling something the front brakes really are the only ones that matter. Rear drums on trucks were factory fine for decades and no one complained about bad brakes, provided the fronts were disc. It's difficult to make a ABS system work with drums, which is really the only reason you see 4 wheel disc brakes on trucks now.
