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Discussion Starter #1 (Edited)
I have upgraded power front drums to wilwood disc brakes (front only; drums in the rear) and have searched this site to learn about what other changes I need to make to the braking system on my '67 cougar.

I now believe I must change the old drum/drum master cylinder, but the wilwood one sold is too big (8.15 in) to fit between the power booster and shock tower.

Would using a new disc/drum master cyl from mustangs unlimited or some such work? Or could you foresee any problems or incompatibilities with using this m.cyl? For anyone else who has done this, what m.cyl did you use?

Rob
 

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You said the car had power drums before, right? Have you driven the car with the disc brake upgrade? I would think that the power drum/power disc master cylinder and booster would be the same. If you have a parts store near by, you could ask.
 

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Discussion Starter #3
Yes the car had power drums before the change. I have driven the car several times-at first just in the neighborhood twice to test brakes, then further but still staying local-and then the master failed where the m.cyl meets the booster. Puddle of fluid with trail down front of booster to the ground below. The m.cyl was on the car when I purchased it in 2006 and of questionable origin.

My question is whether such an aftermarket disc brake system would harm an OEM m.cyl, and I have not seen discussion of this point. The folks at wilwood were steering me towards their nice m.cyl, but it's length will not allow it fit
 

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You should be able to use a stock disc/drum power master without issue. A somewhat different setup but for example I use a stock disc/drum master with Cobra front and rear discs on my car.

There could, however, be a ECI/Non-ECI compatibility issue... :buck:
 

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Discussion Starter #6
Vert,
Your reply helps, thanks. I am also trying to figure out whether I need to install a proportioning valve; on front+rear disc setups (like yours) I am told this is a must.

But with front disc/rear drum setup like mine, my sense from reading here and talking to the folks at wilwood is that the prop valve is not needed, but I get conflicting information.

Wilwood told me to install a residual pressure valve in the rear brake line to maintain minimum pressure for the rear drums, and no prop valve was needed.

But others have said that since the front discs require more pressure to operate, under hard braking the rear drums would lock first since they require less pressure and that could cause a dangerous spin or other bad situation. Any thoughts anyone?

Rob
 

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You said the car had power drums before, right? Have you driven the car with the disc brake upgrade? I would think that the power drum/power disc master cylinder and booster would be the same. If you have a parts store near by, you could ask.

The power drum/drum master is different than the power disc/drum master, as the power drum/drum master have two equal size reservoirs for the fluids, and the power disc/drum have bigger reservoir for the front brakes
 

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I have a stock power disc/ drum set up on my 1968. I want to install A WIlwood front and rear disc kit. Is the kit all I need?
 

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Just use the disc/drum replacement master cylinder. The drum/drum m/c's have a 10 psi check valve in them (usually), might cause the front discs to drag slightly. I'd use the proportioning valve to fine tune the rear lockup point...
 
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