Drum vs. Disc Master Cylinder Questions

[roachrider]

I just bought a set of axles for my truck. They're disc in front and drum in back. The master cylinder I have is from a drum/drum truck. I know the reservoir are different sizes for drums and discs. Which one needs a large reservoir?

Could I use my drum/drum MC with a disc/drum or disc/disc setup? If not, who would you guys recommend for buying a MC from?

Anyone know of good online guides for making a brake system?

[tazzman68]

Sounds like you will need a new MC, the fronts use the larger resevoir you will also need a power brake booster, and a proportioning valve. Can anyone think of anything else?

[roachrider]

So I'm thinking an adjustable proportioning valve since I do a lot of towing that puts different weights on the back tires. Does that make any sense?

[tazzman68]

I've never seen an adjustible prop. valve. Not to say that you can't get one, or make one. But to my knowledge, the inside of a proportioning valve, is nothing more than different sized passages to restrict the increased pressure to the rear wheels, bringing the pressure back into the range required to operate drum brakes.

[roachrider]

http://www.magnumforceracing.com/wilwoo ... sidual.asp

I'm thinking something like this.

[tazzman68]

I was going to say earlier, that I would wxpect to see something like that on an aftermarket braking system like Wilwood, or Baer. I would check with the manufacturer first regarding towing applications, but I see what your trying to do,....I think
If you do this, let me know how it works out, or PM me and I'll send you my phone number, and you can just call me. I live out Mt Hwy a bit, but still have a Tacoma addy.

[FORDification]

The disc-brake master cylinder is definitely different from the drum-brake version. The drum-brake MC will not work safely on a disc-brake setup.

Read the following thread for some more info:

http://fordification.com/forum/viewtopic.php?t=441

An adjustable proportioning valve really isn't necessary...the stock prop valve from your donor truck will work just fine. However, they're really not that expensive so it certainly wouldn't hurt anything to install it...and with a little tweaking you might even be able to optimize your front-to-rear bias a bit. However, should you ever decided to go to 4-wheel-discs, than I'd definitely suggest an adjustable unit.

[roachrider]

Are there any MC's that I could buy that would allow me to run disc/drum now and disc/disc later? At around $130, I'd like to only purchase it once, but I can't afford the rear discs right now.

Or....since the disc brake reservoir is larger, would buying a disc/disc MC work for a drum/disc setup?

[roachrider]

After reading the post you linked to, it's sounding like I would be best off to just find a donor truck that has disc/drum brakes and steal the master cylinder, booster and proportioning valve from it. What should I expect to pay in a junkyard?

[roachrider]

Whoa! Cool. For that price, everything just got a lot more doable. I'll get to work on it and keep you guys posted. Thanks for clearing all this up for me. Gotta figure out the suspension now

[tazzman68]

Hey roachrider, just letting you know, South Hill Auto and Truck Wrecking, has several of our trucks in right now, they are over on 128th, just on the other side of Canyon Rd.

[Mikey]

You will want to check out www.mpbrakes.com

A drum m/c will have a 10 pound residual valve built in to take up the slack of the return springs. If you use a disk/disk m/c on a disk/drum set up, buy an in-line 10 pound residual valve for the drums or it won't feel right.

A proportioning valve is actually a combo valve. For a dis/drum set up it will have a proportioning valve to reduce pressure to the drums and a metering valve to reduce pressure to the fron disks during a low pressure stop. The m/c will have a 10 pound residual valve for the drums. If any of these valves are not included in a dis/drum set up, you will experience an out-of-balance feel at some point of you braking....
Good luck,
Mikey