Master cylinder help (93 Cobra with 98+ plus brakes)

I know you said you read the website but I read it about 100 times before I understood everything. I have a 4 wheels disc brake kit with the 15/16" bore MC. Brake pressure is great in mine. However, you have the 1" bore MC which is ideal for the sn95 swaps. Sounds to me like you may still have air in the lines. These brakes are VERY VERY hard to bleed. Did you bench bleed the MC prior to install? Also, my brakes didn't work properly until I went through almost 12 cans of brake fluid and bought a Motive pressure bleeder. That was the ONLY way I could get the air out.

From the SN95 site:

The stock master cylinders on the 87-93 Mustangs are marginal with just the install of larger front 73 calipers. The 3 port design is really to blame with the small 21mm bore. If you swap to rear disc, then a new MC is needed! There are 4 common MC upgrades out there for the Mustangs: the Lincoln/SVO unit, the '94-98 GT unit, the '93 Cobra unit and the '94-95 Cobra units. Each is a 2 port MC, so a conversion will be needed but they are all different bore sizes. Which one is the correct unit for you? Read on:

Here is a more specific information on the master cylinders mentioned:


'93 Cobra - (metric threads) 1.00" bore

'94-95 Cobra - (metric threads) 15/16" bore, stock plug in for low fluid sensor. Ports are reversed thread sizes from 87-95 LX/V6/GT


Low fluid sensor notes: The stock '87-93 master cylinder has a plastic reservoir with a low fluid indicator. The '93 Cobra and the '94-98 units all have this, but the SVO unit does not have this feature. You will lose the low fluid sensor if you use the SVO unit. This will not cause the dash light to stay on, just permanently off. For the E-Brake light on the dash to come on with the E-Brake, you need to make a jumper in the connection you just removed. Connect pins 2-3 (the 2 purple wires, not the black ground). Be sure to label the connection to know what it is for in the future. For the '93 Cobra and '94-98 units, it is a direct plug in.

Which Master Cylinder?:

87-93s: The 87+ mustangs all use metric threads on the master cylinders. They are 3 port units, thus you must convert to a 2 port setup to use any upgraded master cylinder.

3-2 Port Conversion Products

The SVO unit was a very popular swap until the '94-98 units came readily available. It is very inexpensive at $15 rebuilt, has a large bore, but requires adapting to SAE threads and you lose your low fluid sensor. This works BEST with the larger caddy or Lincoln rear calipers and the front SVO 73mm calipers, and is the only setup I recommend with the SVO unit! Other setups will be too stiff for most with the stock brake booster and it will not have enough pressure. The best all around unit is the '93 Cobra with the 1" bore, but it is more rare and it cost more. Its bore size is about ideal for most any brake setup out there presently.This is the unit I would recommend from most all brake swaps! The '94-98 V6/GT MCs would be good compromise for most everything with the addition of a 94+ V6 brake booster or use of the larger 99+ GT/V6 PBR front calipers. Pedal will be like stock if you use the SN95 brakes, or SVO/Lincoln front brakes with rear drums. You can find these for about $25 used at yards with the reservoir included. If you are planning on running the Cobra or Brembo brakes, then I would suggest the '93 Cobra or '94-95 Cobra 15/16" MC with the stock booster. This will give you a pedal that is not to hard. The last consideration is the cam in the engine. I make my recommendations off a stock 87-95 cam. If you are running a larger cam with less vacuum at idle, either drop a size in the master cylinder bore or set up to the larger 94-95 brake boosters to compensate. If the pedal is to firm after the master cylinder swap, then swap in the larger 94+ V6 brake boosters. Any of the 94-95s and 94+ V6 units will work. They are all larger than the stock 87-93 V8 unit, thus will give you more assist. I would not suggest trying to find the largest Sn95 booster out there as any are larger than the stock unit you are replacing.



Which Master Cylinder to use on fox3 ('87-93) cars with SN95 brake parts:
Well since you are using the Sn95 parts, you should use a SN95 master cylinder as they are designed together from the factory. The '94-98 V6 master cylinder will bolt directly into the PV to MC fittings that you have! You just need to convert the stock 3 port setup to a 2 port one . You can do this with fittings under the proportioning valve to keep things clean! The low fluid sensor is even a direct plug in!

If you use the '94-95 Cobra master cylinder for a softer pedal feel, you will need to get 2 fittings to swap the lines on the master cylinder. The cobra has fittings that are the opposite of the v6/GTs so they did not get mixed up on the assembly line.

Now you need to convert the stock 3 port MC to the newer 2 port MC design. You can either purchase a 93 Cobra combination valve from Ford for about $60, or use a 3-2 port conversion kit. The 3-2 kits is a T fitting that screws into the bottom of the PV and has an adapter for the 3rd port! It will work with the the '94-98 V6/GT MC, the '99 V6 units, the '94-98 Cobra, and '93 Cobra MCs! This is very neat looking at I am selling them at $25.00+ shiping! No Cut, No Flare! 3-2 Port Conversion Products

The other option is to use the parts from a '94-present NON-ABS mustang or '79-86 Mustang. They have a large fitting and special nut that will screw into the back of the stock combination valve. You will have to cut your stock 3rd port line and double flare the brake line there. Be sure to not remove any of the shuttle valve parts in the rear of the combination valve if you go this route.

Master Cylinder Notes:
1. If you install a new MC or upgrade the calipers, you will need to adjust out the brake rod booster to take out the slack in the pedal; this is of course after being sure there is no air in the system. There will be about 1-2" of travel in the pedal that does not push on the MC bore. This is when you need to adjust out the booster. Adjust the brake booster rod out 1-1.5 turns. Click here for a diagram
2. If you plan to go to rear disc brakes, then the 2 port MC will be required along with the FMS M-2450-A plug and an adjustable proportioning valve.
3. For the 93 Cobra Mustang, you can keep the stock master cylinder and proportioning valve; just adjust out the brake booster rod 1.5 turns with the larger 73mm calipers. It will work great with the SN95 parts, adjust the booster as needed.
4. The '96 and newer V8 Mustangs use a Hydroboosted master cylinder. The mounting flanges are vertical vs. the horizontal flanges required on the vacuum boosted units. Thus they are not compatible with vacuum boosters in the ealier mustangs!