i'm considering replacing my rear drum brakes with disc. my current drums appear to be 10 inch. i've read comments that rear drums ie. 11 inch drums would be fine. problem is that if i'm going to tear it apart would the disc rears be better? many new cars have 4 wheel disc brakes, must be somthing to it.

Thanks for your advice. John

...if I'm going to tear it apart would the disc rears be better? Many new cars have 4 wheel disc brakes, must be something to it.


I'm putting 4-wheel disc brakes on my '68.

It's true that most of a car's stopping power is supplied by the front brakes, and a front disc, rear drum combination would be sufficient in most of these cars.
However, bottom line, disc brakes are better and more efficient than drum brakes. Disc brakes are also less prone to fading and pads are a lot easier to replace than brake shoes.
Not to mention the fact that 4 discs just looks better through the wheels than two drums in the rear.

If you're going to be tearing it down anyway, I'd replace those rear drums with disc brakes. It's not really a difficult job either.

Regards,
-Greg

Great minds and all that. thanks john

True a disc brake does dissipate heat better than a drum by virtue of it's greater exposed surface area. However under normal street use heat is unlikely to be an issue.

It might be arguable that disc brake pads are easier to change out than drum brake shoes. I am not sure that either one is significantly harder/easier to make a real difference though.

One big advantage to the drums is you already have a compatible system for them. Changing to disc brakes changes things significantly... requiring corresponding changes to master cylinder, proportioning valve, and brake line plumbing. Not to mention emergency brake linkage.

One advantage to disc brakes not mentioned is they have a faster on/off cycle time although a driver may not be able to tell.

An advantage to drums is they have a degree of self-energizing to boost braking power that disc brakes do not have. This is part of why trucks were late adopters of disc brakes compared to cars (weight hauling and stopping favor the self-energizing).

That's interesting. i anticipated plumbing change but the new hoses are included in the kit. What about the master cylinder and porp. valve has to be changed? I already have front disc's and two cylinder master (front and rear system)
Has anyone made this upgrade to rear disc's? What problems did you run in to?

Thanks John

Technically you need the braking force in the front and rear to equal the traction available after adjustments for weight transfer. So as you apply brake pedal force to maximum braking your tires all enter the skid mode at the same time (actually the fronts should enter the skid just a hair before the rear for optimum control).

There are obviously a LOT of parameters that feed into this.

The OEMs spend a fair bit of time trying and tweaking different combinations. Swapping from one OEM drum to another OEM disc system from similar cars would probably get you pretty close. But the parts are designed to all work together which is why I mentioned the master cylinder and proportioning valve. Due to the self-energizing aspect of drum brakes they often operate at a different line pressure than disc brakes. Some of this is tuned by way of the different piston sizes in the two systems. But that also means a difference in fluid flows between the two as well. In general drum brakes run a smaller piston and thus displace less fluid than disc brakes. The two also have different initial response characteristics with drums needing a little more time to engage than discs.

I suspect that a prior owner did a front brake conversion on my '68 El Camino some time in it's history. They used the later single piston calipers rather than the potentially troublesome calipers used by the factory in '68. They may have changed the master cylinder... I don't know for sure. They incorporated the hold-off valve as per factory practice but did not change the distribution T in the brake lines down on the frame. So for all intents there is no proportioning valve. The result is a system where the back end locks up way before the front end. In fact I do not think I have ever been able to lock the front end. I have an adjustable proportioning valve to put in it someday when I get to it...

I have 4-wheel disc in my 59
Not all that impressed with them at all.
Unimpressed to the point rear discs are not even being considered for the 66