Mustang Front Brake Mystery

[Michael Gates]

Hello everyone. I’ve tried going through the braking information here, comments and videos to find an answer to this problem, but haven’t been able to figure it out. Nor has my Chilton’s manual, the internet or my mechanic been able to shine any light on the subject.

I have a 2004 Ford Mustang GT. It has 4 wheel factory disc brakes. The front setup is dual piston, the rears are single spiral calipers.

Recently I did a brake job. I took the calipers off and painted them when I did the brake job. I masked all the rubber and valves off when I painted them, and then reinstalled them with new wearable parts. Those parts included:

1) Russell stainless steel lines (all 4 wheels)
2) Power Stop Street Warrior Z26 pads (front and rear)
3) Power Stop slotted and cross drilled rotors

While I was doing the job, I completely cleaned all four rotors (because I was painting them) and also took the slide pins out, cleaned and re-lubed them with a brake specific silicone based lubricant. After I reinstalled all the hardware, I bled the system twice. No air and only clean fluid is currently bleeding out if I open then system.

The problem I’m having now is that the front calipers are both dragging. I was able to push the pistons in with a C-clamp and had no problem getting them over the rotor when I installed them. The problem arose after I bled the system. The car is still drivable, but there’s a noticeable performance difference and the front wheels are warm to the touch when I shut down the vehicle after driving it. I’m getting a lot of brake dust wearing off the new pads too. I’ve had the car in the air and the back two calipers seem fine. Both rear wheels rotate normally, and both seem to hold firm with the brake pedal depressed. The fronts however, will only turn with a great deal of force applied to the outside of the tire (I couldn’t generate enough leverage to turn them with the wheel taken off.)

Here’s what I know:

Pads and rotors are new.
It’s not the slides, because I can see them operating normally when I bleed the system.
Both front calipers are dragging at the same rate.
Both rear calipers are operating normally.
Fluid comes out of the valve under pressure during the bleeding process, indicating that the new lines are unobstructed and operating normally.
My mechanic can’t figure it out either, so I figure it’s not a rookie move on my part that caused the problem.

The mechanic is pointing the finger at the calipers, but that seems unlikely to me as they both contain dual pistons and are both dragging at the same rate – indicating that I somehow managed to damage 4 pistons in exactly the same way. One of the other guys in his shop said that maybe it’s the proportioning valve. Could I have damaged that during the bleeding process? Does anyone else have any ideas?

Topic

[Andrew]

Seems a bit strange that you can see the caliper slides working when you bleed the system. There shouldn’t really be any discernible movement. I assume this is happening straight after you’ve pushed in the pistons and the mechanism is seating. It’s best to seat the pads before you bleed.

You seem to have covered most reasons for binding brakes, other than the pads themselves not releasing. Try taking a caliper off, pushing in the pistons, reinstalling then checking by hand that both pads move in and out freely. I just want to know that the pads are not fouling any part of the caliper assembly.

Lastly, I know it’s early days but it would be nice to know if the inner or outer pads are showing more wear.

[Michael Gates]

I mentioned that because I knew that he first thing anyone was going to tell me to look at was the slides. While I was bleeding the brakes, I was watching the top of the calipers where they sit on the slide, and you could see the caliper tense up and move a very small amount along the slide when pedal pressure was applied. Then I could see it release afterwards and slide back, the entire travel being maybe a few millimeters, but enough to indicate that the slides weren’t binding. And the pads were seated. I agree that it wouldn’t make a lot of sense to bleed the calipers either disconnected or without the pads in it.

It’s also too early to look for pad wear. I tried taking a look at that last night, but I couldn’t see any difference.

[Andrew]

[quote=”MOGatesGT” post=94584]And the pads were seated. I agree that it wouldn’t make a lot of sense to bleed the calipers either disconnected or without the pads in it.
[/quote]

I meant pump the brake pedal to push out the pistons before bleeding, but it sounds like you did.

How about the pads – do they move freely in the caliper?

[Michael Gates]

They seemed to be ok when I put them in, but I can’t tell because I have a caliper/pad/rotor/pad/caliper sandwich in there now that they’re not releasing all the way. I checked the outers through the wheels to make sure they weren’t angled or anything weird like that and they seem to be seated properly. This afternoon I’m going to try to get the calipers off again and compress the pistons like you’d suggested to see if they generate the same problem again. It was an idea I’d had but it seemed to me that it was unlikely that was going to change anything. At this point though, I’m not sure what else would be causing it.

I do know that the damper on the master cylinder is adjustable, but my mechanic told me he wasn’t going to touch it because it shouldn’t be that and backing that off was “looking for trouble.” The master cylinder was replaced about 5 years ago with the pads at less than 50% and hasn’t been in there with a new set of pads since. Also, I was concerned that if I did that the rear brakes wouldn’t grab at all.

[John Hugon]

When you removed the old parts, any abnormal wear?

I assume the aftermarket front brake pads and rotors are at factory specs? If they are, raise the front of the vehicle up(both front tires not hitting floor) pump brake pedal and release, make sure the front brakes are dragging, back off brake master cylinder retaining nuts two turns and pull master cylinder against nuts.Check and see if wheels spin free. If so,check brake light switch,if ok,reset brake pedal to master cylinder push rod to factory specs. If front wheels are still dragging, remove master cylinder reservoir cover and put back on and check to see if wheels spin free. If so master cylinder reservoir cover vent is obstructed. If front brakes are still dragging release front caliper brake fluid lines; one at a time at the master cylinder and check if wheels spin free. If they spin free the master cylinder is the issue. If front wheels are still dragging, remove front brake calipers one at a time and see if the caliper pistons retract. If the pistons are seated at factory specs, you have brake pad to rotor clearance issues.

Lets me know what you come up with.

[Michael Gates]

Alright guys I think the problem is resolved. My methodology is probably going to traumatize all of you, so consider yourself warned.

I took into consideration all of your feedback. Thank you both for your input. I also considered my own observations and those of the mechanic. The two of us concluded that the problem was not severe enough to cause a rotor overheat, that there was no smoking, etc. Also, the car’s ability to stop had never been an issue, so it was safe to drive. The car would still move under it’s own power. So the two of us took it on a test drive. We found that it would roll under the weight of the car if stopped on a substantial hill. After we got back I took it out again, then again, then again – each time for a longer run after stopping to confirm that the rotors weren’t overheating, that nothing was smoking and so on. After several consecutive short runs, I did a freeway loop (there’s a loop around the local freeways here in the bay area that makes about a 25 mile circuit with straights, curves, and hills) and confirmed again no rotor overheat issues. The next day I drove it 50 miles, and the following day 100. After that it had worn off some of the pad and it seems to be almost normal. The pads are $70/set of 4 and they last for 100k miles, so I’m ok with losing a little bit of them at this point. It’s still rubbing slightly, but not enough that it causes noticeable side effects or heat anymore. I have two theories on the cause of the problem:

1) The master cylinder damper was incorrectly set when it was replaced about 30k miles ago. Pads would have been at about 40% at the time, so if it was set too tight they still could have cleared the rotors, which were also probably not factory thickness anymore.

2) The Powerstop equipment I bought may have been slightly out of spec. My brother had installed Powerstop rotors and pads on his F-250 a few years ago, and despite me having told him about my problem didn’t mention that his had rubbed until I was a week into trying to figure out what was wrong with my car.

At this point I’m considering this project done, but thanks again for the support.

[Author]

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