Fox Brakes sticking after booster rep.

Maciasmarci · Nov 17, 2022

Hi, I have a 1990 5.0 with 99-04 mustang spindles/ caliper conversion. I am recently experiencing brake sticking at the front when I drive for about 15-20 mins. I’ve recently replaced the stock brake booster for a 1993 cobra booster and thought it was the adjusting rod but I backed it all the way off to eliminate that being the issue. After that I replaced my brake calipers ,rotors, pads and both cables… bled air and took for a test drive. After 15-20 mins I had the same brake smell and car was still braking on its own as I experienced prior to replacing parts. Master cylinder is new . After the drive I jacked the front end and I needed a bit of effort to turn the wheels by hand. Any help much appreciated.!

Mustang5L5 · Nov 18, 2022

The 99-04 GT/V6 calipers are notorious for pistons sticking, especially brand new remans. It's usually an issue with cars that sit with old brake fluid laiden with moisture.

I don't know the source of your calipers, but if they are used this is most likely the issue. Remove the calipers and try to push the pistons in and not how difficult they might be. Shouldn't take much effort and all four should be equal in force.

AeroCoupe · Nov 18, 2022

When you say you replaced "brake calipers ,rotors, pads and both cables" what do you mean by cables? Are you referring to the rubber line between the caliper and the hard line on the body? Reason I ask is it sounds like collapsed soft lines to me without knowing if all of the components you replaced were new, reman, or just some parts you had lying around as Mustang5L5 is indicating above.

Maciasmarci · Nov 18, 2022

Mustang5L5 said:
The 99-04 GT/V6 calipers are notorious for pistons sticking, especially brand new remans. It's usually an issue with cars that sit with old brake fluid laiden with moisture.

I don't know the source of your calipers, but if they are used this is most likely the issue. Remove the calipers and try to push the pistons in and not how difficult they might be. Shouldn't take much effort and all four should be equal in force.

That may be true . The only reason why I don’t think it’s the calipers is because they can be pushed in with a clamp fairly easy and also the brakes only started doing that after I replaced my brake booster from autozone.

Maciasmarci · Nov 18, 2022

AeroCoupe said:
When you say you replaced "brake calipers ,rotors, pads and both cables" what do you mean by cables? Are you referring to the rubber line between the caliper and the hard line on the body? Reason I ask is it sounds like collapsed soft lines to me without knowing if all of the components you replaced were new, reman, or just some parts you had lying around as Mustang5L5 is indicating above.

Sorry yes I meant to say I replaced the rubber lines

Mustang5L5 · Nov 18, 2022

Take it for a drive and get it to the point the wheels are locking up. Loosen up the two nuts holding the MC to the booster and slide the MC forward slightly. Do the wheels then free up?

I know you said you backed the rod way off, but this will double check that the booster rod itself isn't somehow sticking and pushing on the MC. Since the issue happened when you changed booster, i would focus on the booster and how it interfaces with the MC. Pedal bind? Booster rod hanging up? That sort of stuff

AeroCoupe · Nov 18, 2022

Which booster do you have on it, a Fox or SN95?

Maciasmarci · Nov 18, 2022

Mustang5L5 said:
Take it for a drive and get it to the point the wheels are locking up. Loosen up the two nuts holding the MC to the booster and slide the MC forward slightly. Do the wheels then free up?

I know you said you backed the rod way off, but this will double check that the booster rod itself isn't somehow sticking and pushing on the MC. Since the issue happened when you changed booster, i would focus on the booster and how it interfaces with the MC. Pedal bind? Booster rod hanging up? That sort of stuff

I haven’t tried that but I will today. Thanks

Maciasmarci · Nov 18, 2022

AeroCoupe said:
Which booster do you have on it, a Fox or SN95?

It’s the fox body one from a 93’ cobra

AeroCoupe · Nov 18, 2022

Excellent choice! I did one of mine with the SN95 and the other with the 93 Cobra and so much easier. What master cylinder did you install?

AeroCoupe · Nov 18, 2022

So its a slow day and this problem caught my curiosity. I am going to throw this out there but I have never seen this so I cannot vouch for it. The combination valve may be failing in such a way that it it holding pressure on the front brakes. Found a couple of instances on a couple sites were the stock one was replaced and it solved the problem. So you understand what I am talking about when I say combination valve it is the brass block that has the proportioning valve and shuttle valve in it and also has a switch in it that illuminates the brake light in the dash if you have a failure.

Most know all of this below is when swapping over to SN95 brakes on a Fox and most know this but just in case.

Typically when installing the SN95 brakes on a Fox the factory proportioning valve side of the combination valve is gutted and a solid plug is installed.

This is one place to get the plug:

Brake Proportioning Valve Plug, 1979-2004

After gutting the proportioning valve side of the combo valve a manual proportioning valve for the rear brakes is installed at the union that is on the firewall or at least that is a super convenient place to put it.

Factory Union

Aftermarket Manual Proportioning Valve Installed

You can get the manual proportioning valve from several different places but again MM has them. You will need the SAE one as the factory union has 3/8-24 threads. The other thing you will need is a 3-2 conversion kit so you can tie the three lines from your old Fox 3 port master cylinder to the 1993 Cobra or SN95 2 port master cylinder.

You can eliminate the combination valve all together. This will require the 3-2 kit, a manual proportioning valve, and a combination valve elimiantor kit. You install the 3-2 kit with a 1993 Cobra MC or SN95 MC, install the eliminator kit, install the manual proportioning valve for the rear brake line, and then properly bled the system.

All of the Fox to SN95 parts can be found here:

1" 1993 Cobra master cyl.

Or you can do what this guy did:

Has anyone used the MM proportional valve eliminator kit and adj proportional valve?

The reason I ask is I've stripped my stock prop valve when changing the master cylinder and the OEM piece is proving to be difficult to find. Also, my brakes are still stock. Has installed these with the stock brakes? If anything, I think it will look better under the hood. Edit: I realize...

vb.foureyedpride.com

CAMTWO1070 · Nov 18, 2022

Maciasmarci said:
Hi, I have a 1990 5.0 with 99-04 mustang spindles/ caliper conversion. I am recently experiencing brake sticking at the front when I drive for about 15-20 mins. I’ve recently replaced the stock brake booster for a 1993 cobra booster and thought it was the adjusting rod but I backed it all the way off to eliminate that being the issue. After that I replaced my brake calipers ,rotors, pads and both cables… bled air and took for a test drive. After 15-20 mins I had the same brake smell and car was still braking on its own as I experienced prior to replacing parts. Master cylinder is new . After the drive I jacked the front end and I needed a bit of effort to turn the wheels by hand. Any help much appreciated.!

Sounds like you need to replace the rubber hoses going to the front calipers and the rearend....

When they collapse internally they trap the fluid pressure in the calipers and slowly let it bleed off plus as the brakes get hotter they activate more when the brake fluid starts to expand from boiling....

Everytime I replace my brakes in all my vehicles I replace both front rotors plus the rubber hoses and all springs ,clips pins and sliders too....

I also replace or repack the wheel bearings plus the wheel bearing races and change the wheel bearing seals plus set wheel bearing lash and replace the brake fluid too.............

Every 100k I go the extra mile and replace both calipers, the brake booster and both rear wheel cylinders along with rear brake shoe backer plates if heavily worn or warped and I also replace the rearend seals and rear axle bearings plus change pinion seal,reset pinion lash and replace the rearend fluid and rear brake drums..

I can honestly say if any of my vehicles is involved in an accident one of the things that cant be questioned is the mechanical ability of my vehicles due to age also normal wear and tear as i replace anything that looks questionable....

Good Luck

Maciasmarci · Nov 27, 2022

I’ve found the issue . As soon as the car gets warm and I drive around the brakes start to stick, so just to make sure it wasn’t a brake pedal issue, I pushed up against it and it seemed to release the brakes and the car would roll back like normal. Thanks a lot for the help.!

Fox Brakes sticking after booster rep.

Maciasmarci

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Mustang5L5

That is…until I whipped out my Bissell

AeroCoupe

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

Maciasmarci

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Maciasmarci

Member

Mustang5L5

That is…until I whipped out my Bissell

AeroCoupe

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

Maciasmarci

Member

Maciasmarci

Member

AeroCoupe

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

AeroCoupe

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

Has anyone used the MM proportional valve eliminator kit and adj proportional valve?

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Fox Brakes sticking after booster rep.

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That is…until I whipped out my Bissell

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

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Member

That is…until I whipped out my Bissell

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

Member

Member

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

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

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