Master Cylinder Change?

[FomocoReformed]

So while I'm laid up from working on the car with my hand injury I've been going over my plans in detail for putting everything back together and I have a question about the master cylinder.

My car was originally a manual brake car with 9in drums on all 4 corners. I now have a 73+ front disc setup with proportioning valve and the rear is an 8.8 from an explorer with the ford discs on it. I'd like to retain manual brakes since I love how they work when properly set up. Also for space saving in the engine bay. I know I need to buy a new master cylinder for the front discs but would a stock manual/disc master cylinder also be able to correctly actuate the ford rear discs or am I going to have a problem with incorrect hydraulic pressure in the lines? I think I remember reading something in the past about the rear drum setup MCs not completely releasing pressure from the lines to the drums, or I could be thinking of something completely different my memory isn't so great.

Any help on what MC I should use would be appreciated, or if I can modify a stock MC to work with the ford read discs. :burnout:

 

[BillGrissom]

If you get an older MC, insure it doesn't have "residual valves" in the outlets. I understand most are removable (haven't seen). That is the problem with "locking up pressure" you read about if using disk brakes. Indeed, they aren't even needed for drum brakes since they changed to the "spring w/ caps" design.

I suggest a modern aluminum MC to save weight. I put one on my Dart and Valiant. Cloud car MC's (Breeze, Stratus) until ~1999 have standard 1/16" double flare outlets on driver's side, which is best (bubble flares are trickier). I used an MC/booster on my Dart w/ 73 standoff brackets and a manual MC on my Valiant (not installed). The later usually means a 4-2 hole adapter ($45), but I just drilled 2 holes thru the firewall/brake bracket w/ a big washer covering the gap. With disk in the rear, you don't need much reduction in pressure (if any), so don't use a fixed factory valve but rather an adjustable one, and adjust it by locking up the brakes on a wet parking lot (fronts should skid first).

 

[FomocoReformed]

I like the idea of modernizing it with a stratus MC, is there anything that needs to be modified to install it other than the firewall mounting?

 

[BillGrissom]

I just read a discussion on another thread about the brake pushrod length (search for it). Some say that the aluminum cylinders have shorter travel, or maybe a different starting position and that the $45 adapter accounts for that. They say if you don't use the adapter, you need a shorter pushrod. Seems suspect since the aluminum MC looks like it may have more piston travel.

I'll investigate further on my Valiant w/ manual brakes. I did quickly check the installed pushrod depth against my original MC and seemed "close enough", but that was just a tape measure effort (~1/4"). The final answer is when all installed. The MC piston should go in just slightly to keep the brake light switch off, but not enough that you lose pedal travel. You can adjust the switch a little, but you don't want the pedal coming too far out either. It should sit near the accelator level so you can move your right foot between them easy, though I often drive an automatic with 2 feet in touchy situations, despite what was taught in driver's ed. I just re-program my brain back to go kart driving days.

If installing power brakes, like I did on my Dart, if you use both the booster and MC from a cloud car (on factory Dart brackets), those boosters have an adjustable pushrod between the booster and MC, so easy to get it perfect.