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66 Disc/drum master cylinder

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I have a 66 with front discs, rear drums and the "original" 66 single pot disc/drum master cylinder. The upgrade was done by a previous owner (which is why I'm not sure how it's supposed to be plumbed).  The brakes work OK but it seems like the pedal comes up just a bit if I pump the pedal once when stopping.

The master cylinder has two outlets on the front (one straight out the front and one beneath the master cylinder body).  The front discs are currently plumbed to the lower outlet through a distribution block and the rear drums (through a proportioning valve) to the straight-out-the-front outlet.

Is this the correct plumbing for this master cylinder (have not found this info in the 66 shop manual, the Mustang Haynes manual or in the MPC)?

Second question: I can't remember ever seeing a residual pressure valve in the system and the master cylinder has none that I can see. Strictly speaking, do I need one? Was there one originally somewhere in the system and if so, where should it be placed?


First welcome. By your description you do not have the correct master cylinder, distribution block and are missing the porportioning valve. The master cylinder is from a T-bird and as you can see in the picture, has a large diameter from the gold cover. The distribution block is special as it has one line in and two lines out for the front discs brakes only, while the rear brakes get their fluid from a seperate line on the master cylinder and it is routed thru a special valve to retard the pressure to the drum rears, second pic.  Your best bet is to get a 67 dual bowl master cylinder (and rod), an adjustable proportioning valve and plug up the unused port on the distribution block with a special kit. All this is available from National Parts Depot Don't bother trying to find original new or used 66 disc brake parts. The p-valves start at about $250 and the distribution blocks are about $100.

Thank you for the reply Jim!  The master cylinder I have is correct for a 66 with disc/drum (bought it from John's Mustang when I was in Houston) - same as item 1B on page 55 of the NPD catalog.

On your car (VERY nice!!!) does the front-most outlet from the master cylinder go to the rear brakes or the front brakes?

Thank you again!  John

The front (upper) port goes to the proportioning valve then to the rear brakes. You may consider getting a front disc brake line set to use with a proportioning valve as the kit includes the prebent to length lines with the correct fittings. I don't recomend stainless lines as they don't seal as well.
And thanks for the comments on the car, only it's not mine. I didn't have a photo of either of mine that gave a good view of the master cylinder.

Here is a pic of the conversion I did from a jelly jar to a dual bowl on my '65.    You can get a rebuilt 1967 Mustang dual bowl  MC from Autozone or just about any parts place.  The kit you get from NDP with the pre-bent lines don't fit, so you have to do some re-manufacturing.  I know the lines next to the MC should  be coiled, but I have had absolutely no problems with my set-up.  I have shoes all the way around, so can't answer anything about the proportioning valve, but it sounds like you already have one.  The only thing I have is a distribution block, so don't need one.  A strong suggestion to you is to replace the jelly jar with a dual bowl MC for safety reasons.  I went ahead and replaced the brake lines to the front while I was at it.  God knows how old those lines were, and the rubber next to the wheel looked like it was rotted.  Don't forget to bench bleed the new dual MC before putting it on the car.  A correction to Jim's suggestion about a new rod.  You need to use the old 66 MC rod. 


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