1993 mustang to98 brake conversion

[Arty]

I have a 93 mustang gt with Front disc rear drum brakes. It was converted to a 98 Mustang GT 4 wheel disc brakes. The problem we're having is the braking is weak like the booster isn't helping enough. I need to stand on the pedal to stop & it wont lock up the wheels. I put a new booster on no difference. I was told that I need to to put a proportioning valve from a 98 to make this work. I bought one but it has one more port than the old one and I don't see how this will help with the braking problem. Has anyone ever done this conversion.

[Skeezix]

GOOGLE

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[OctoMeans9]

The proportioning valve will help deliver better pressure more evenly across the system but the master cylinder also needs to be changed. Did you use the master cylinder from the 98 or keep your current one? A 4 wheel disc brake master will give better overall pressure and fluid volume to the system than using your stock disc/drum master cylinder.

[jsgarage]

Changing the master cylinder to match the rotors is important. Most disc/drum master cylinders used a 'keep-alive' valve built into the master cylinder (or somewhere else) that holds 2 psi in the front calipers. But drum brakes use an 8-12 psi valve. In converting to 4 wheel discs, this can result in dragging the rear pucks constantly, with possible overheating and resulting loss of performance both going & stopping. Second, especially with power brakes, 4-wheel discs normally use a much larger bore master; with power assist you won't notice the extra size except that the pedal doesn't move much. But it delivers far more fluid and pressure.
Plus, some mfgrs use a built-in proportioning valve somewhere in the chassis, that's calibrated for stock tires and brakes. Obviously, this isn't gonna work well for your conversion. You need a Ford or maybe a Haynes Shop manual to locate & identify this stuff for safety. And if all else fails, temporarily add a pair of 0-2000 psi gauges to the front and rear bleeder screw holes in your calipers for tuning. Expect to see about 1200 psi front & around 1000 psi rear (with vac assist) when things are working correctly. If your pressures are lower, likely the booster is bad. I'd also replace any 10-yr-old rubber hoses with steel-braided.