Which brake master cylinder for this setup?

[DadsFFR]

I'm currently building a roadster for my dad. The front brakes are from a '95 Gt and the rears are the FFR rear disc set-up for a solid axle. I have the master cylinder from the parts car ('92 GT) which had the '95 front brakes on it but it had rear drums. Will this work with the new rear disc set-up or do I need to get a different master cylinder?

[skullandbones]

I had a 92 GT MC. It looked a little wimpy since I had upgraded to some larger discs in the front and Cobra 95 discs in the rear. So I purchased a F-150 MC that has the same configuration as the 92 but a much larger cylinder (about twice as large). My theory is that this will produce more power to the caliper pistons without creating too much more pedal pressure, if any. See what you think. The only downside is a little different plumbing but you have to do a certain amount anyway so it's pretty much a wash. I think you should definitely include a proportioning valve, IMHO. There again, you are doing the plumbing in that area so it's just a couple of extra steps. Good luck, WEK.

I put them side by side so you could see the difference.


4167

[DadsFFR]

What year F150 MC did you use? Did you also use the '92 Gt pedal assembly? Thanks for the response!

[skullandbones]

Sorry about that. It turned out to be a 95 F-250 (Auto Zone # NM3021). I actually tried more than one before getting the one I liked. I did use the donor pedal assembly but still may change it out for something else. I have clutch pedal issues. Still in the middle of evaluating that one. Of course, I created the problem by getting a HD Ram clutch assembly. But what I have will suffice thru the go kart phase. Isn't this fun?!! See you later. WEK.

Note: Going the donor route is problematic in that when you see a really nice setup that is something other than your donor version, it creates accessory envy. If you are not swayed by that tendency, then you are OK.

[DadsFFR]

Thanks for the info. Ya I have to say that if I could do it over again I would not have bought a donor car. I ended up replacing half the parts because I wasn't happy with the condition of them. Then the ones I am going to use require tons of cleaning and paint.

My 2 cents on the clutch..I have a centerforce dual friction in my mustang that has nice easy pedal pressure. I will probably end up using the same one in the roadster.

[skullandbones]

You're welcome. It's too bad that we had to both experience donor regret. I said almost the same thing you just did in another thread. I will be lucky if I have one donor part left when all is said and done. However, maybe that's good. I remember on my other roadster project (Devin), I went through 4 major revisions before I "finished". At least on this project it's happening during the 1st build. I am not changing clutches though until I have to. Thanks for your input.

[Jeff Kleiner]

...I purchased a F-150 MC that has the same configuration as the 92 but a much larger cylinder (about twice as large). My theory is that this will produce more power to the caliper pistons without creating too much more pedal pressure, if any.

I'm afraid your theory is incorrect. A common misconception is that a larger master cylinder will create more pressure. While a larger master cylinder produces a larger displacement for a given stroke, it will take more force to create the same system pressure. The end result after changing to the larger master cylinder will be a harder pedal that requires much more pedal pressure to create the same amount of braking force. For instance, changing from a 3/4" master cylinder to a 1" requires ~77% more force on the push rod.

Lots of guys have had great success using a 1994 Mustang Cobra master cylinder with a 15/16" diameter bore when running 4 wheel discs.

Cheers,
Jeff

[Brian Z]

For 4 wheel disc brakes we recommend using the 94-95 Cobra Mustang master cylider without the mustang distribution block.

Jeff is correct on this one.

Best regards,

[skullandbones]

I stand corrected. Sorry to DadsFFR for that error. Thanks to Jeff for straightening me out. After some rethinking it does make sense now. I should have followed good logic and gotten the master cylinder that matched my 95 Cobra rear end. Thanks for the heads up. WEK.