Brake Questions
 

The car is in the paint shop, drive shaft is being built and the only thing left is to finish the brake system. Classic has promised my pedal assembly would be here monday so all I have left is to build the master cylinder setup and connect lines and bleed the brakes. My question relates to thoughts and recommendations about what size and type of master cylinder to use with a manual brake set (no booster). My car has stock Mustang brakes on the rear and Wilwoods up from. I have a Wilwood adjustablt bias proportioning valve that I will install once I have the pedal box mounted. The only lines I have left to bend or run are one from the rear to the master cylinder and one from the master cylinder to the proportioning valve then to the front T. I have read lots of postings but thought I would ask again before I buy my master cylinder. Thanks to all of you who have aided in building my car. The beer is in the frig when you stop by. Chuck

http://www.wilwood.com/products/peda.../pedaltech.asp

CS.. this is being covered in another post. Unless someone can tell us a matching Cylinder to your setup, check out the above thread.

We've used the late 80's Corvette MC with good results, BUT, it could be better. Any other thoughts here?

DV

Am using power brake booster, and 4 wheel disks, so this may or may not apply. Manual disk/drum may need different MC.

Master cylinder is Ford part# D9AZ-2140-A. It came with the M-2300-C rear disk brake conversion kit from FMS. It brings the brake lines out on the engine side for easier connection and service than the Vette MC. Since the kit is an adaptation from the '87 - '89 T-bird turbo coupe, the MC is likely the OEM for that car.

But if you are looking for an option to the Vette MC for 4 wheel power disks, a bolt on for the MII booster, is aluminum, not iron, and installs easier; look into it.

Just upgraded my rear pads to semi-metallic courtesy of Stainless Steel Brakes (Earl Ruleman), and car does stop well.

Master Cylinder.....Confusion.
 

I recieved the Master Cylinder I ordered from NAPA today. I attempted to get the one that Jack21 uses on his car. I liked the idea of getting one I didn't have to modify and had the connections on the Pass side and not the Driver side. The one Jack21 got with his kit was D9AZ-2140-A. I cross referenced that on the NAPA site and got 39467. This is what I got.

Jack21 mentioned his was "Aluminum" mine is Iron. Also, this unit has a small front bowl and a large aft bowl. Is this correct for Front and Rear Disc brakes? I know some are recommending Masters with equal size bowls? What's the difference and how does a Drum/Drum master differ from a Disc/Drum master and a Disc/Disc Master. I need an education on Master Cylinders!

My brakes are Baer designed for Mustang II front and the Baer Disc brake upgrade for the Ford 8.8. The front is dual caliper and the rears are single caliper. It would make sense to me that the front bowl would be smaller for the rear single piston calipers and that the front would require the larger bowl for dual piston calipers. Does the size of the bowls indicate the amount of fluid transfer to the brakes front to rear? I was planning on installing an adjustable Prop valve on the rear but I'm wondering with the small bowl if I will get enought braking in the rear to use it. Anyway I'll stop talking now...someone please edumacate me!

cs69r, If the rear brakes are drum then you can use the stock Mustang II manual brake master. It will work with the Wilwoods. If you have the stock Mustang rear disc then as DV said I use a corvette master, but I don't think they make a Corvette master for manual brakes.

Jimp, the size of the reservoir really doesn't have much to do with the ability of the master to handle rear disc. It's the internals of the master that make the difference. You really aren't moving much fluid with a brake system adjusted properly. Discs tend to take less fluid since they are riding so close to the rotor. The master sets up the proper volume and pressure to the entire system.
Don

It's all in the cylinder "bore" not cylinder "resevoir! :)

DV

Master Cylinder
 

Don/DV,

The master I have appears to be exactly 1" bore. This seems appropriate for my setup. Baer recommended 15/16 bore. The question I have is, does the piston when depressed move the same amount of fluid to the front and rear brakes? I thought maybe the size of the reservoir might have some indication of how much fluid might be transfered comparitivly between front and rear. Also, after doing some additional research it appears that you can use just about any dual master cylinder provded the bore is correct for the application for a Disc/Disc setup as long as it doesn't have a "Residual Valve" built into the Master Cylinder for the rear brake connection. The residual valve will prevent the disk brake from releasing because it's designed for a Drum brake. Does anyone know how I can tell if the master has a residual valve by looking at it?

JimP, If Baer said 15/16 bore that's what I would use. The problem with a bigger bore is pressure. You can get the volume but not enough pressure. I can't answer about the amount of fluid with a certain type master or which would have a built in residule valve.
Don

Master Cylinder...
 

Don,

That's the problem. I can't seem to find any specs on most of the Master Cylinders out there. They are all designed for specific automobiles. Is there a site that shows specs on Masters? Most of the Aftermarket ones (that I'm sure won't bolt to the Must II booster without modification) are all well over 1" bore. The reason Baer is recommending 15/16 is because that is what apparently the Mustang II Master was but I can't use that one with rear disc brakes. Does 1/16 larger bore really make that much difference? I'm sure the Cobra is much lighter than the Mustang II and I've got alot more leverage with 13" rotors so a little more foot preasure I would think shouldn't be a problem. What bore size is the Vette one you use?

The one I use is a 1" bore. You're probably right 1/16 isn't going to make a big difference. It is really hard to find one that size without an application. Give it a try.
Don

Master Cylinder
 

OK, I think I got this figured out now. Bore determines pressure in the brake lines. Larger bore/less pressure, smaller bore/More pressure. Master Cylinder Piston volume determines volume available to transfer to the Caliper piston.

I took the Master I recieved apart to look at the pistons. The front piston (for the rear brakes) was about half the volume of the rear piston (for the front brakes). That indicates I only have half the volume available to transfer to the rear brakes comparied to the front. This is OK because I'm using single piston calipers in the rear and dual piston calipers in the front, so I will only be using approximetly half the volume when braking is applied to the rear brakes compared to the front but the pressure will always remain the same. Had I been using dual piston calipers front and rear I probably would have a problem with this Master Cylinder because I would need equal volume available front and rear. There also is no residual valve in the Master Cylinder. Apparently that was something that was on OEM Masters and replacement masters don't usually have them and you must install a residual valve in the lines between the Master and the Caliper if you are using rear drum brakes.

Problems arise with rear disk conversions when a Disc/Drum Master is used that doesn't supply enought volume to the rear brakes. Disks use more volume than drum brakes so the Master Cylinder piston may not provide enough volume from proper rear wheel braking. Drum brakes typically have a very small piston in the brakes and the residual valve keeps pressure in the lines at all times so they only require small amount of volume from the Master Cylinder comparied to the larger rear disk brake caliper pistons.

This link hand great information: http://www.mpbrakes.com/MASTERS.htm

Don,

Can you tell me if the Vette Master has equal size pistons in it or if it has one smaller and one larger pistons?

Jim, I've never had one apart but I assume that since it's from a Corvette with 4 wheel disc they should be the same. Good research!
Don

JimP,
Excellent class in Master Cylinders 101. I'm going to save your comments for future use! Well done!
DV

What year Vette? I have an '88 I can check for piston size the next time I visit my daughter who gave up her garage so I could store Vette there.

The one I use is from a 1976.
Don