MK2 Brake Issue

[BaldEagle]

I have a new to me MK2. I have found the rear brakes are not working very efficiently. Below is a list of parts that I have in my brake system and looking to make sure I have the proper parts that should work together before I start looking into mechanical issues. My gut tells me that I have the wrong master cylinder is on the car as the brake pressure going to the rear is very light, but want to make sure before I replace. Also want to know what the proper replacement would be.

Master Cylinder - Wagner FF122014 - 2 stage
Front - 1 piston ford calipers Part # VFCC2386-8 - off 1994-2004 Ford Cobra. 10.75'' vented Rotors
Rear - 1 piston Ford calipers part #355-L - off 1987-1993 Mustang. 10.75'' Rotors

I would appreciate any advice.
Keith

[Gordon Levy]

Are you using the Mustang prop valve? If you are, removed it or gut it.

[Jim Schenck]

If the pedal effort is good and everything else is working then putting more aggressive rear pads, like Hawk or Carbotech, is a good way to increase rear braking. I don't know that exact master cylinder number but what you want is a 7/8 in. bore or at most a 15/16 in. to give the best mix of effort and capacity. You also can add an adjustable proportioning valve to the front lines if you still aren't getting enough out of the rear, but I would do the pads first as they will make the brakes better overall as well.

[BaldEagle]

Thanks for the replies. I know the car has a proportional valve installed in it but I think it is hooked up to the rear brakes. I have turned it completely both ways and continue to get low pressure our the rear calipers. The front calipers get good pressure all the times. That is what is leading me to believe that I have the wrong master cylinder in the car.

Does anyone have a recommendation on a good 7/8 bore master cylinder? Part # or year/make/ model to pull from. I would prefer one with a medal reservoir.

[Gordon Levy]

I have a great master cylinder. Please give me a call at 520-494-2745.

[mikeinatlanta]

Using a donor master has always been an issue with these brakes. There are many ways to work the issue and many colorful debates.

Just my opinion, but I agree with using pad compounds for fine tuning but disagree with the concept of reducing front line pressure to compensate for poor rear line pressure (prop valve in front).

You can't go wrong with giving Gordon a call. He is about the best resource out there for understanding the best solution within your budget. Myself, I wouldn't go anything less than dual masters, however, the forum vendors have long history of knowing how to make what you have work well.

[Jim Schenck]

1994 Mustang Cobra master cylinder would be 15/16, but with metric bubble flares so you need adapters to go to standard lines. Also the 1984 Jeep Cherokee master cylinder is 7/8 and is a good match with the factory Mustang rear brakes which have a pretty small piston in the caliper.

Putting the prop valve in the front wouldn't be the first answer in designing a system from scratch however if you are just looking to improve on what you have it will make the car stop better than it does now. Back when the challenge series didn't allow bias bars or wildwood pedal box setups that was how many of the cars were raced, including mine at the time, and it made a noticeable improvement over not having it there.

If you were wanting to make a bigger change to try and getting better braking overall then the best way to balance the system is with larger rear calipers (larger piston diameter) which would then shift bias toward the rear so you could keep the prop valve in the front. Kits that use the GM metric rear calipers or the wildwood single piston kit are examples of this.

[BaldEagle]

Thanks again for the info guys. If i go with the Jeep Cherokee Master do i need to add inline residual valves or are they built in to either the master cylinder or the brake calipers?

[Gordon Levy]

No..