Manual Disc conversion without Prop valve

[Don Frelier]

I have a disc master cylinder from a 70 and SSBC discs on the front, no adjustable valve installed (even though I have it).
Under panic braking the rear will lock up, which happened just last week. But normally it stops nicely with moderate brake pedal pressure.

 

[wagonman]

Wagonman, how is the stopping power compared to the drums? Pretty grabby even though they are manual and not power assisted? I have never had a manual disc car, only power disc.

Not grabby at all. The E booger master is a 1 1/8 bore IIRC and has a hard pedal and you need a strong leg, plenty of reserve. I have used a stock drum-drum cyl with a 15/16th bore and it was softer but worked with not as much reserve. The bigger cyl can be used with a booster and I will probably upgrade this winter and add PS as well. So My Wifey can drive it. Maybe not! HA. Also looking at the 11 3/4 rotors if I can score a deal on the pin type caliper adaptors. I know Dr Diff has them but I am a Cheap old bastard and prefer OEM Ma Mopar.

 

[andyf]

Hey all, so I have a 68 Runner with manual drums all the way around. I am starting to feel my drums get warped and am thinking it is time to upgrade to front discs. I can get the spindles, bearings, hardware, calipers, and rotors for $500.00. Seems like it's the time to do the swap. I am seeing a few of my buddies run a disc front and drum rear without a proportioning valve. I really don't wanna tear into the brake lines to modify for a prop valve so whats the opinion on here about running the manual discs without the prop valve? I have a manual drum master, but I will pop the residual valve out of the rear reservoir so it doesn't hold pressure against it like the drum system does. Whats your guys take of this that have done it?

A prop valve is required any time you mix disc and drum brakes. Disc brakes are linear, drum brakes regenerate. So if you don't have a prop valve to blow off the pressure the rear drums will lock up under hard braking. You don't want the rears to lock when you are try to stop hard since that will put you into a slide. The problem is that people who don't drive the cars hard will tell you that it works fine. It does work okay until you need to stop hard and then it won't. So at the worst possible time, the brakes won't work properly for you.

 

[91r/t]

Yea, now that I know I do not have to modify my lines to use the stock type prop valve (72-76), I am going to install it in place of the distribution block I have now for the drums. Just didn't wanna have it look non stock or cut the lines up.