Brakes Foxbody Brakes still soft

86posmustang · Nov 5, 2025

My mustangs brakes are still very soft even after a new master cylinder and a whole system bleed and bench bleed.

General karthief · Nov 5, 2025

What's the setup?

AeroCoupe · Nov 6, 2025

Assuming the car is a 1986 by your user name. Does it have stock spec brakes, original soft lines, and the original booster? What rotors and pads are on it? Still drum brakes in the rear? Did you convert it to a full SN95 setup? If you set the e-brakes will they stall the car if it’s a stick or hold the car with it in gear for an auto?

Lots of details you can provide that will help to figure this out.

86posmustang · Nov 7, 2025

More information: The Mustang is an automatic with the 5.0. The car features new drum brakes in the rear, while the new master cylinder is of the same design as the original model. The front brakes are stock (not including brake pads). original brake booster and brake lines. The E brake does seem weak. The pedal is very stiff when turned off. but almost to the floor when on.

General karthief · Nov 7, 2025

Bleed them again

Mustang5L5 · Nov 7, 2025

Does it pump up when the engine is running? In other words do a quick double pump on the pedal and see if that firms it up.

Engine off. After a few pumps to bleed off vacuum, is the pedal rock hard with little to no travel when you stand on it?

The combo valve unit is notioius for rusting up and causing bleeding issues. When you bleed the brakes, do you get strong flow from all the bleeders, or does one or more brakes dribble out?

86posmustang · Nov 7, 2025

It doesn't pump up when running

Mustang5L5 said:
Does it pump up when the engine is running? In other words do a quick double pump on the pedal and see if that firms it up.

Engine off. After a few pumps to bleed off vacuum, is the pedal rock hard with little to no travel when you stand on it?

The combo valve unit is notioius for rusting up and causing bleeding issues. When you bleed the brakes, do you get strong flow from all the bleeders, or does one or more brakes dribble out?

No it doesn’t pump up when running. And when it’s off the pedal moves an inch and half but it doesn't pump up either. And I don’t recall having any flow problems when bleeding the brakes.

AeroCoupe · Nov 7, 2025

Its either a bad master cylinder (yes you can get one new out of the box) or it was improperly bench bled (sounds like you know how to to do this) and/or you need to inspect the soft lines on the front calipers and the one above the pinion of the rear end for swelling when the pedal is pushed.

Shakerhood · Dec 1, 2025

Possibly the push-rod is not adjusted to the correct length and maybe not pushing all the way into the MC.

General karthief · Dec 2, 2025

The symptoms you describe tell me that the master cylinder needs a bench bleed or is defective, air somewhere in the system.
40+ year old car needs a good brake system inspection and rubber line replacement..

nicholase · Dec 3, 2025

How did you bench bleed the master? Air in your lines is the most likely. Sometimes bench bleeding the master gets people. Running down how you bled the brakes would rule that out.

Rear drum brakes not adjusted properly can cause a spongy pedal as well as a weak e-brake. Are the shoes adjusted close to the drum? Slight resistance while turning drum.

Brakes Foxbody Brakes still soft

86posmustang

New Member

General karthief

wonder how much it would cost to ship you a pair

AeroCoupe

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

86posmustang

New Member

General karthief

wonder how much it would cost to ship you a pair

Mustang5L5

That is…until I whipped out my Bissell

86posmustang

New Member

AeroCoupe

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

Shakerhood

General karthief

wonder how much it would cost to ship you a pair

nicholase

I lubed and pushed, until it was all the way in

Similar threads

Brakes Foxbody Brakes still soft

New Member

wonder how much it would cost to ship you a pair

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

New Member

wonder how much it would cost to ship you a pair

That is…until I whipped out my Bissell

New Member

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

wonder how much it would cost to ship you a pair

I lubed and pushed, until it was all the way in

Similar threads

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