Gt convertible brake problems.

MacMAgoo

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Oct 2, 2022
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My son replaced the front pads and in the process damaged the right caliper. He replaced with a used unit and then did not drive the car more than a few miles and parked it. He did use it on occasion. Fast forward 6 months and he finds himself with three cars so Daddy buys the Mustang.
I immediately felt here was a brake problem because there was practically now pedal before the car began to stop. I am talking about maybe 1/4 inch. It seemed to stop ok but with a bit if extra effort.
I took it in the road a few days ago and at a stop light noticed smoke coming from the right front. I checked and it was so hot the lug nuts boiled water.. It is now home and I am about to take the brakes apart. I am going to list what I will check and ask if anyone has additional suggestions. By the way this has the Hydro Boost system, something I have never delt with. Is there anything regarding that system I should be aware of?

First thing I am going to check is the slide pins. I would bet $100 he did not lube them. At the same time I will check for stuck pistons and cocked pads. It has been a long time since I had to do brakes and I do not think I could recognize heat damaged rotors unless they were burned blue. Any suggestions what I should look for?

Regardless what I find in the hardware I will bleed the front brakes. Hell I might as well bleed them all assuming I can get help. Is there anything special about bleeding the HydroBoost system? It looks pretty straight forward.

I know the HydroBoost uses power steering pressure to charge the booster. The steering appears to be fine except on the highway if I want to move right or left it answers fine but will NOT come back to center unless I command it.

Am I on the right track with my plans? Any suggestions? Has anyone ever had this experiences?
 
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weendoggy

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Jan 14, 2019
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Aptos, CA
If they were that hot, I'd change calipers, rotors and hoses. I'm not saying they are all bad, but you're not going to help yourself in the long run. However, if the rotors are good, make sure they are true, no cracks and keep them. The one thing I'd definitely do is change both front brake hoses. Many people think sticky brakes are due to pads/calipers, but in reality, the hose is usually the culprit. Depending on the age/miles on the car (not mentioned), brake hoses may LOOK good on the outside, but it's the inside that deteriorates and causes the hang up. I'd also recommend replacing them with good SS lines that are made for the car.

Bleed the entire system good. Maybe use at least a pint or more of fluid. I have bleeders, but use a partner to pump/push the pedal to bleed them. You may have ABS which will help with a person braking. Start at the RR, LR, RF then LF in that order. Always the farthest one from the master cylinder first.

As you mention, lube the sliders, caliper assy. as needed. Don't worry about the Hydroboost, it's not causing the problem. If you replace the rears, be sure to screw-in the caliper piston before putting new pads on. You DO NOT push that one in to compress like the fronts.
 

MacMAgoo

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Oct 2, 2022
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I was pleasantly surprised when I took the brakes apart that they had been done correctly, even greased the pins. The rotors had very little wear and a dial indicator showed no warp, so I am going to keep them. The pads had even wear. I am sure the problem is in the right caliper, so I am going to replace it along with the brake hoses. This is a 2001 with 166,000 miles so it is due.
I appreciate your mentioning the hoses because I did not think of them.
 

MacMAgoo

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Oct 2, 2022
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I was pleasantly surprised when I took the brakes apart that they had been done correctly, even greased the pins. The rotors had very little wear and a dial indicator showed no warp, so I am going to keep them. The pads had even wear. I am sure the problem is in the right caliper, so I am going to replace it along with the brake hoses. This is a 2001 with 166,000 miles so it is due.
I appreciate your mentioning the hoses because I did not think of them.
One other thing, he did not recall if he screwed the rear pistons in. What could be the problems if he did not?
 

Mustang5L5

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99-04 GT/V6 calipers are notorious for the pistons seizing in the bores. When these cars sit, especially with old brake fluid, moisture in the fluid essentially freezes the pistons in the bores.

Being a used caliper was swapped on, i can see this happening. In fact, it's pretty common to get a reman caliper and have those seize in the bore. I would check the caliper itself and see if the pistons can move freely. If you take a caliper off, you can stick a block of wood in the middle and slowly press the brake pedal. Both pistons should come out easiler and equally, and then you should be able to somewhat push them back in easily.

The hydroboost shouldn't really change much in terms of how the system operates over vacuum brakes. The PS pump supplies high pressure fluid to the booster first, and then to the power steering rack, with a low pressure return from both units. It should self bleed, assuming the fluid level is correct. With the engine running, pressing HARD on the pedal should cause some strain against the pump. That's normal.

Rear calipers are the screw type. But they wouldn't cause the issue you are seeing in the front. I bet $1 that caliper is junk. Seen it 100 times before
 

weendoggy

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Jan 14, 2019
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Aptos, CA
One other thing, he did not recall if he screwed the rear pistons in. What could be the problems if he did not?
You can do damage to the threaded screw/piston/caliper itself. Kind of hard to do, but I've seen it done. Plus, if you try to put pads in, you won't get it past the rotor if you try due to the piston being "out". It will automatically adjust as you apply the brakes and/or e-brake. A simple tool is all you need to screw the piston back in when changing pads. Just keep that in mind.
 

MacMAgoo

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Oct 2, 2022
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99-04 GT/V6 calipers are notorious for the pistons seizing in the bores. When these cars sit, especially with old brake fluid, moisture in the fluid essentially freezes the pistons in the bores.

Being a used caliper was swapped on, i can see this happening. In fact, it's pretty common to get a reman caliper and have those seize in the bore. I would check the caliper itself and see if the pistons can move freely. If you take a caliper off, you can stick a block of wood in the middle and slowly press the brake pedal. Both pistons should come out easiler and equally, and then you should be able to somewhat push them back in easily.

The hydroboost shouldn't really change much in terms of how the system operates over vacuum brakes. The PS pump supplies high pressure fluid to the booster first, and then to the power steering rack, with a low pressure return from both units. It should self bleed, assuming the fluid level is correct. With the engine running, pressing HARD on the pedal should cause some strain against the pump. That's normal.

Rear calipers are the screw type. But they wouldn't cause the issue you are seeing in the front. I bet $1 that caliper is junk. Seen it 100 times before
Finally got two new calipers and hoses in. My son and I installed yesterday with no problems. Everything fit fine and I thought we were home free BUT, after over an hour of bleeding we have NO pedal at all. Decided to try again today.
Hooked up a single person bleed kit and ran bout a pint through each caliper. Got a lot of air at first but now flows pure fluid. Still no pedal and calipers will not move at all. In addition with no pedal I bet the rear brakes are not working either.
I have never run into brakes that would not bleed. Open to suggestions.
Would the ABS be a problem?
 

weendoggy

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Jan 14, 2019
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Something's definitely not right. When bleeding them ( I use another person at the pedal ) will the wheel stop once you close the bleeder (hope it's on top). After all the air's out, that wheel should lock when you spin and apply the brakes. If fluid is reaching the caliper, it's going through the ABS.

Also, are you talking about the front or rear? I doesn't matter to me, but I thought your issue was in the rear. When bleeding from a bare system, I only use about two pints total and all is good. RR, LR, RF, LF in that order. If rear, are the pads in correctly? The nubs/tabs should be at 6/12 o'clock and that's the position the piston should be in with the slots in those same places.
 

MacMAgoo

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Oct 2, 2022
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Something's definitely not right. When bleeding them ( I use another person at the pedal ) will the wheel stop once you close the bleeder (hope it's on top). After all the air's out, that wheel should lock when you spin and apply the brakes. If fluid is reaching the caliper, it's going through the ABS.

Also, are you talking about the front or rear? I doesn't matter to me, but I thought your issue was in the rear. When bleeding from a bare system, I only use about two pints total and all is good. RR, LR, RF, LF in that order. If rear, are the pads in correctly? The nubs/tabs should be at 6/12 o'clock and that's the position the piston should be in with the slots in those same places.
I am dealing with the front brakes only. I assume since I have no pedal at all the rears are not working but the rear is not off the ground to check. I have been bleeding the front only. With all the bleeding and air I got out, the pistons have not moved at all. If the pistons grabbed the rotor I would be ecstatic. I'm at a loss but today I will run more fluid through the system and see if it will work. Storms coming tomorrow and it is in the driveway so it has to move today even if I have to use my boat anchor to stop.
 

Mustang5L5

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Finally got two new calipers and hoses in. My son and I installed yesterday with no problems. Everything fit fine and I thought we were home free BUT, after over an hour of bleeding we have NO pedal at all. Decided to try again today.
Hooked up a single person bleed kit and ran bout a pint through each caliper. Got a lot of air at first but now flows pure fluid. Still no pedal and calipers will not move at all. In addition with no pedal I bet the rear brakes are not working either.
I have never run into brakes that would not bleed. Open to suggestions.
Would the ABS be a problem?


There are two bleeder screws on the master cylinder. Bleed those as well.

After bleeding those, you may need to bleed the front brakes again.
 

weendoggy

Active Member
Jan 14, 2019
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Aptos, CA
I am dealing with the front brakes only. I assume since I have no pedal at all the rears are not working but the rear is not off the ground to check. I have been bleeding the front only. With all the bleeding and air I got out, the pistons have not moved at all. If the pistons grabbed the rotor I would be ecstatic. I'm at a loss but today I will run more fluid through the system and see if it will work. Storms coming tomorrow and it is in the driveway so it has to move today even if I have to use my boat anchor to stop.
You have air in the system. Need to start in the rear, but follow suggestions 5L5 mentioned as well as myself to get a clean start. Bleed the MC first then move on to wheels in order. Best option is a power bleeder or use your trusty helper to do the pedal work.
 

CAMTWO1070

Active Member
Dec 17, 2021
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NY
One thing about hydroboost is its a pretty good system but when things get sticky things get crazy and what most dont know is the hydroboost setup has whats called an accumulator and when the brake components are good also done right and bled using a 1 man power bleeder, before you start the vehicle you must refill the accumulator by pressing the brake pedal about 25-30 times or the accululator can get damaged and cause brake issues you described and to your question about rotor condition....

If the rotors are shiney like mirrors they need to be deglazed and dulled down using rotor scuffers or a power sander...If they show shine and ripples that can be felt with the fingertips they need replacing or cutting...

If the rotors are semi shiney or dullish shiney and flat on both sides theyre good..........

Good Luck
 
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