Need more info.

Which rear disk swap did you do? The 4-lug turbo coupe setup? If so, with the front 60mm calipers, you want to run a 1993 Cobra 1" MC.

WHat SN95 MC did you use? There are two. The 94-95 GT/V6 1 1/16" bore MC, and a 94-95 Cobra 15/16" bore MC.

Also, you'll probably want to use the larger 1993 cobra/94-95 SN95 booster.

 

The 93 cobra BRAKE BOOSTER is what you need. The master cylinder can come from a 93 cobra too. But the softness is controlled by the booster. You will have to clear the driver side shock tower on an 88. A couple dings from a hammer will do the trick.

 

Thanks a lot.

I have the Turbo Coupe brakes front and rear. I used new calipers, new drilled and slotted rotors as well. The Booster is a brand new Fox Mustang piece (not Cobra), the master cylinder is from a 94/95 SN-95 non-cobra, brand new as well.

I had heard that the Fox Booster (non Cobra) would work, so I got one. The brake pedal being a bit soft is fine with me, but not being able to lock the brakes, and they just don't seem to have the grab that they should.

That's why I was thinking the 93 Cobra MC would help, but I wasn't sure.

I appreciate any and all opinions.

 

So the oem configuration with 60mm fronts and TC rears is the 1993 cobra setup, which means the smaller 1" bore MC and the larger 205mm tandem booster which offers almost 2x the assist of the fox booster.

With the non-Cobra SN95 MC and fox booster, your pedal should actually be harder. The larger bore takes more effort to lock the brakes up, and the fox booster won't give you the level of assist you need to do so either. But a soft pedal may suggest you haven't fully bench bled all the air out.

I'd recommend the 93 Cobra MC and booster setup. When I did my m2300k setup, I tried to get away with not swapping the booster. I was unable to lock the brakes up (not an ideal way to judge brake performance anyway). I swapped in the booster and it made a huge difference in braking performance.

 

I appreciate the info. I'll start gathering parts.......again.

 

You might also want to check that the master cylinder pushrod is adjusted correctly.

If needed, steps to do this can be found here. http://www.maximummotorsports.com/assets/install/pdf/brakes/MMBAK-17.pdf

 

Adjustment of the booster pushrod will only affect the height of the brake pedal. It can not have any affect on braking performance.

If the brake pedal is soft, you have air in the system. Currently the m/c diameter is too large for the rest of the parts. If anything the brake pedal should be too stiff. If the brake pedal is soft, the pedal will travel too far and you will lose mechanical leverage due to poor geometry.

Changing the brake booster is almost definitely a waste of money and time. Only do this if you want a way over sensitive brake pedal. Ford used the Mustang Cobra booster in applications with pads that had a low cf and low bite. This is to meet brake force requirements in 0 degree climates.

What brand and compound brake pads are in the calipers? If they are ceramic, then throw them out and get some real brake pads. If they have a high carbon content (look black or dark gray), then the rotors must be bedded in for them to work properly. Until this is done, you won't know anything about the brakes.

 

It's likely I'm missing something here. Please help me to understand.

Adjustment of the booster pushrod will only affect the height of the brake pedal. It can not have any affect on braking performance.

Are you suggesting it's not possible for the pushrod to be too short, where it's a length that it can't move the master far enough and that condition wouldn't negatively affect performance?

 

I have to agree with Jack on this.

I would drop in MC bore size and use a power bleeder. Also, you've got air in the system. No matter what, a spongy pedal is related to air.

 

Let me clarify.

If the pushrod is too short, when the brake pedal is depressed, the pedal will move the pushrod some distance, before it touches the back of the piston in the m/c. No braking will occur in this free play zone. The brake pedal will move extremely easily as you are only deflecting the brake booster diaphragm.

There are two possible small issues with this.

If there is a lot of free play, the brake pedal geometry will be poor once the m/c piston does start moving. This can result in a lower pedal ratio, which will cause higher brake pedal efforts. There would have to be a lot of play for this to occur to a noticeable degree.

The more free play there is, when the pushrod does hit the m/c piston, there is going to be more brake assist than expected. This is because the brake booster is a position sensitive device. The more displacement, the more assist. With a lot of free play, the brake assist will be more nonlinear. No braking, no braking, then more braking than expected suddenly.

Of course if the pushrod is too long, the brakes can end up staying locked, but this person doesn't have this problem.

I wouldn't bother with a power bleeder. It may help things. I suspect that the m/c needs to be bench bleed on the car. It probably has air in it.

 

I really appreciate the comments. I ordered a new 93 Cobra MC. I'll start with that and reply with the results.