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Discussion Starter #1
I just bought a 70 Mustang PDB setup for my 70 coupe with manual drums. My manual master cylinder is brand new and I would like to use it in place of the old MC that came with the booster. I know this has been asked before and my search of the forum says it can't be done but I would like to know why. My shop manual says both the power and manual MC's in 1970 had 1 inch bores. So what is actually different between the boosters?
 

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The boosters are the same. I think what you'll run into is overly sensitive brakes. I have 2 F150's, one manual and one power brakes. There's not a whole lot of difference in brake effort between them. However, if I took the master cylinder off the manual and put it on the power brake truck I'm pretty sure that when I tried to stop I'd be locking up the brakes every time.
I've driven Cadillacs and stuff that seemed to have terribly sensitive brakes. All it was is that they are designed that way and it took getting used to. If you feel like fooling with it, try it.
You might end up with "Cadillac brakes", or it might not be driveable. Be sure to do thorough testing on how it works before you go into any kind of traffic. If everything bolts up fine but the car ends up being uncontrollable, it's the same as saying "that won't work".
Your brakes are vitally important.
 

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Boosters are probably the same. The master cylinders are not the same. The drum/drum unit has equal size chambers while the disc/drum master has a larger chamber for the disc brakes. Drum/drum masters also have residual valves. You'll also need a proportioning valve in the line to the rear brakes.
 

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Discussion Starter #4
I miss typed. I mean't to ask what is different with the MC's. Your right about the chambers. I just looked at them side by side and the front chamber is significantly bigger on the disk/drum unit. The proportioning valve came with the setup so I'm ok there. I just need to get new lines, hoses and the correct brake pedal.

thanks
 
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