Master Cylinder/Booster/Prop Valve Combo for 4 Wheel Discs?

Hey All, I'm getting ready to do my 351W and 4 wheel power disc brake swap on my 70 Grabber. I have a couple questions. First off, I am going to be using a stock Maverick booster assembly, and I want to get a 4 wheel disc brake master cylinder for it. I figured that I could use a 4 wheel power disc master cylinder from a Granada/Versailles/Monarch, but checking them out, they mount differently on the on G/V/M booster, and will not bolt to the Mav booster. Any suggestions? Maybe I could use a new plastic reservior from a 4 wheel disc brake Explorer, Mustang, etc.. Also, I can never get a definite answer from anyone about what prop valve/distribution block to use for the 4 wheel disc system. Some say the drum/drum block works great, and others say get a disc/disc one. I'll probably get one for a 4 wheel disc brake G/V/M to be safe about it. What do you think? Thanks!

-Corbin

 

I would get one of those inline adjustable proportion valves from Ford Motorsports or Summit and put it on the rear line. I still say all those blocks do is turn on the brake light when one system fails. They probably do a little proportioning just by the size of the orifice on the rear lines. Either way, its probably not enough when converting to rear disc. This is the way I'm going when I do the Comet.

 

I left the factory one on mine, works great.
Dan

 

Hey Dan, Have you taken the car out in a deserted parking lot on a rainey day and tried locking up the wheels? Bettry to find out there than when you really need them.

 

Nope, still havent done that. Car is up in the air now, seems it always is. They are never ever done.
Dan

 

I don't think you need a proportioning valve with 4-wheel discs. The proporitioning valve proportions the PSI between the rear drums and front discs. I would think you only need a distribution block like on an all drum car ...

 

I kept the factory disc/drum prop valve on mine and used a master cylinder from a 1976 Corvette. I had to fabricate different lines that connect from the prop valve to the M/C because the ends are different(I read that you can use some sort of adapter as well..), and I had to elongate the mounting holes a little bit. Other than that it bolted right on

The only problem that I have is that the vacuum booster is not as effective with the increased line pressure necessary with 4 wheel discs, and it kinda feels like I don't have power brakes at all...but I am working on a solution for that...

 

Why not just have front disk brakes and rear drum brakes?

 

When I did my 1980 Fox body Cougar a few years ago I used a master cylinder out of a 94 6 cyl Mustang because it had the biggest bore that I could find within my budget (cheap). I can't recommend a booster because I had Fox parts on both. Most of the master cylinder bolt patterns are similar, so slotting a little like MavMark is very possible. The plunger rod is where the custom work comes in sometimes unless you just get lucky.

As far as the prop valve - I gutted my valve so it was effectively a distribution block and added one of the adjustable ones from Summit to the rear line like Dennis was talking about. With even pressure going all around (even with one line going to both rears) my rears locked up before the fronts (not good). I just started cutting the rear back until they all locked about the same time. My advice is to use the adjustable prop valve. Even if you take the master cylinder and all 4 discs off the same car - you may still need to fine tune the bias because what ever car you get the parts from will have different weight transfer characteristics than the Maverick.

Cleaver

 

Where is the fun in that?

 

Thanks for the insight guys. As far as the front disc/rear drum, this is what I have on my 73, and they work well, but for the extra power, (and future plans ) of the 351W I want really good brakes. Drums are not even close to disc as far as effectiveness, safety and stopping power. Plus they look awesome compared to drums. Front discs made a huge difference on my 73, and I have no doubt that 4 wheel discs will be even better than those. When I stomp on the brakes, I want to STOP. If this rear disc swap goes well, I'll be putting discs on the back of the 73 as well. I am using the Explorer discs.
-Corbin

 

Cleaver is right on what to do.
It must be understood that a radical change in engineering the brakes completly makes any stock system componants useless for the correct front to rear bias brake pressures.
An original system is engineered based on the weight of the car, the brake swept area of the pads, pad friction, disc performance, weight tranfer to the front, tire diameter and tire grip.
To make up for all that you don't know, go with an adjustable valve in the line to the rear and set the operation based on trial testing.
Not doing this risks locking up the rears wheels, losing control of the car in a panic stop.
Not doing this results in early pad wear at the end doing the most work stopping the car considering the front does the greater share. If the rear is not doing it's share you still have less than the best possible performance.
Just saying 'mine work fine' is not the answer unless the testing has been done.
Some other items to consider are the larger master bore will cause a higher pedal application pressure to stop the car.
The master should be from a disc brake car because the disc caliper displaces much more fluid using a larger piston as compared to a small drum brake cylinder. This may make the master operation run out of fluid per stroke and not fully apply pressure to the caliper.
There is much more to this than meets the eye so do it with some knowledge because it's your life and that of others thats on the line.
In an accident sutuation that is blamed on brake failure and found to be the results of a modified car make a lawyer and his client rich and you very poor.