67 Rogue Drum to disc conversion

The set up I purchased was the complete brake set up off a 79 Spirit that was cut off at the control arm and tie rod. So basically I have everything including the riser to the later coil suspension. Spindles, dust shields, rotors, calipers, pads hardware. Everything's was rusty from sitting for years so several bolts or nuts were seized up. I replaced all the nuts and bolts with grade eight fasteners of the correct length. Took all the pieces apart and sand blasted everything to remove rust, then spray primed and painted with black satin finish. Rotors were not worn just needed to be turned to clean and true them up. I have looked and you can purchase the master cylinder for a disc front drum rear car that I was considering doing. Or looking for a power brake master cylinder. Is there a porportioning valve to change also?

The Scarebird hub is a disc brake rotor with the rotor turned off, that's why it's so thick.

As far as a proportioning valve, you may not need one. I ran a 63 American without one (manual disc brakes, late 70s AMC similar to yours) and didn't have a problem with rear wheels locking up. Early disc brake systems all used some kind of proportioning valve. Cars with lite weight rear ends like the Spirit will use one, and need them. By the late 70s/early 80s Concords didn't have one, and many other cars deleted them also.

I would assemble it without a proportioning valve. Then take it out to a damp (wet, but no standing water) parking lot or a gravel/dirt parking lot/road. Run up to about 45-50 then slam on brakes, like panic stop. See if the rear brakes lock before the front. If they do the rear end will want to come around. Make sure you are driving straight, as a slight turn of the wheels will have the same effect. If the car brakes straight, even if all four wheels lock at about the same time, you don't need a proportioning valve.

I'd try again without hitting the brakes as hard as you can, but still stopping "hard normal", and what you'd consider normal braking. No rear wheel lock? No valve required. If the rears DO lock before the front under hard and/or panic stops conditions, you DO need a valve. I'd get an adjustable then adjust it until braking is good, but you could go for a 68-69 Camaro type. They are the same as used on 68-70 AMCs. Not adjustable, they start restricting rear brake pressure after 200 psi. That's a good place to start if you get an adjustable valve marked in pressure values.

i found it easier on one car to simply juggle rear brake wheel cylinders to get front/rear balance. only a slight pain to install, and  good excuse to shotgun the rears if you haven't. 

farna wrote: There were few cars made with non-power front disc brakes. IIRC AMC sold some with the K-H brakes, and they had a slightly larger MC bore. As Tom notes, a larger bore reduces pressure to the brakes, increases leg pressure needed. I'd stick with a 1" or 7/8" bore MC, or somewhere in between (I've seen a 15/16" bore, though it's not common). I think the late model Concords used something slightly under 1", might be 15/16" (books give a 0.889" or something like that, might be metric...). They would be disc/drum for the power brakes, but it really doesn't matter if power or manual brakes. The difference in construction is that manual brake MCS usually have something to retain the pushrod and the pushrod socket is deeper than PB MCs. Either will function manually though.

My 73 Javelin with power disc fronts were changed to manual disc, some time after 50k by the original owner, as the booster failed shortly before selling to me. Did not go into details, as the brakes felt just right. Never felt like heavy braking needed, and were very positive feeling. Looked like they kept the power disc master cylinder, just removed the booster and bracket, re-adjusted the rod to make it work. One of the best feeling brakes for a 70s and 80s car, without strain.

While all that is true, it has been proven that in practical application neither a metering or proportioning valve is actually necessary if the brakes are balanced properly. There is little difference in practical application. Balancing has much more noticeable affect on the handling of a vehicle.