Fox Brake pedal too stiff

keel · Monday at 11:27 AM

I was doing some spirited driving over the weekend and realized that in order to get full braking power I need to put way too much effort into the pedal. To be clear, I don't think there is anything mechanically compromised with the braking system, just something wrong with the way I set it up.

I'm running SN95 Cobra brakes on all four corners, gutted OEM proportioning valve and a Wilwood adjustable to manage brake bias, and a 1993 Cobra master cylinder with a Fox V8 booster. I've done some research and it seems like a '93 Cobra booster is what I need to get the pedal feel I'm after, but I also wonder if I need to go to a different master cylinder too. Looking for some opinions for this combo and how to proceed so I can get it right without messing around too much.

AeroCoupe · Monday at 9:40 PM

Cobra MC is the preferred MC with the 94-04 cobra brakes on our cars.

Several folks have run the Fox booster with success so I would not just say they don’t work. Most run the 1993 Cobra booster as the studs on it fit the existing g firewall holes and it does provide more boost than the Fox unit can.

Based on my experience I would run the 1993 MC and booster. Stick with known brands of boosters.

Mustang5L5 · 2026-09-22T11:52:17-0500

Which generation Cobra brakes do you have up front?

If you have the 94-98 versions, you'd really want the 94-95 Cobra 15/16" MC. (they can be used with the 1" 93 cobra MC but first stop on cold pads might be a little lacking)

If you have the 99-04 versions, the 93 Cobra 1" MC is the right one.

1993 Cobra booster should be run with both.

Easy way to tell is to cut the wheel and look behind at the piston bores. 94-98 are ribbed, 99-04 are smooth

keel · 2026-09-22T12:41:19-0500

I'll have to take a look. What's the difference between them internally?

86HO5.0 · 2026-09-23T05:08:12-0500

94-98 are 38mm. 99-04 are 40.5mm IIRC.

The 94-95 Cobra M/C (15/16") works great with the 38mm calipers and stock Fox booster. The Cobra M/C is marginally larger than the Fox M/C, roughly 1/16".

Mustang5L5 · 2026-09-23T08:45:38-0500

Off-topic, but information that deserves to be recorded.

Years ago I was conversing with a Ford engineer on corral who did the brake system for the 1994 Cobra. This is the story he told me regarding the development of the 1994 Cobra brakes. Originally the setup came with a 1" bore MC. Well apparently on cold pads and such, the system was unable to lock up the brakes or at least approach lockup until some heat was generated in the pads. They were demonstrating the car to execs and were underwhelmed by the initial braking performance on the first few stops on the largest braking system Ford had ever put on a mass production car. SO the MC was changed to the 15/16" bore.

keel · 2026-09-23T10:52:45-0500

Would a 94-95 Cobra MC work with both types of brake calipers? Or would it be over assisted for the later calipers with the larger piston?

I figure I'm going to have to remove the MC anyway to install the booster and if I had to choose then I would rather the braking power be on the stronger side. Especially after reading what @Mustang5L5 said about the development of the '94 Cobra.

86HO5.0 · 2026-09-23T16:31:36-0500

The 94-95 MC would be a better match for the 94-98 Spec Cobra brakes.

I'm running the 94-95 MC, stock 86 booster with 94-98 spec Cobra brakes FR and Rear. Braking power is VERY strong. I've also deleted the stock prop valve and installed a FRPP adjustable proportioning valve where the stock prop valve was located. Excellent setup, highly recommended.

AeroCoupe · 2026-09-23T18:27:59-0500

@86HO5.0 - just a vocabulary thing but if you deleted the brass block below the MC you deleted the combination valve. That brass block houses the proportioning valve and shuttle valve hence the name combination valve. Again, just wanted to pass on something I learned a few years back.

Fox Brake pedal too stiff

keel

Active Member

AeroCoupe

lube between the nut and the face. I know my lubes

Mustang5L5

That is…until I whipped out my Bissell

keel

Active Member

86HO5.0

Active Member

Mustang5L5

That is…until I whipped out my Bissell

keel

Active Member

86HO5.0

Active Member

AeroCoupe

lube between the nut and the face. I know my lubes

Similar threads

Fox Brake pedal too stiff

Active Member

lube between the nut and the face. I know my lubes

That is…until I whipped out my Bissell

Active Member

Active Member

That is…until I whipped out my Bissell

Active Member

Active Member

lube between the nut and the face. I know my lubes

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