Brakes Brakes drag when warm. How to diagnose?

FastDriver · Nov 20, 2023

Guys, since the Cobra Brake swap on Black Jack, the brakes drag only after driving for a decent amount of time... maybe 20 minutes of driving.

I've jacked the car up after getting home from such a drive, spun the tires on all 4 corners, and it seems to be coming from the fronts on both sides. The rears are a little less clear, as I have to turn the axles with the wheels and can't tell for sure if it's brakes. They also don't drag when cold. I can tell when driving because when coming to a red light, I'll slow to ~3-5mph and let it coast to a stop. When I've just started driving for the day, I can't feel a sudden stop when coasting to a stop; it just gradually stops with any sudden end. Later, though, presumably after they're warm, it comes to a more sudden stop at the very end... kinda hard to describe.

I've adjusted the plunger between the booster and the master cylinder to the point that the pedal depresses a bit before engaging. I've also, suspecting the e-brake cable, jacked the car up when cold and spun the rear without any drag, seemingly.

Anyways, does anyone have any ideas of what I might check to diagnose things?

AeroCoupe · Nov 20, 2023

In there any possibly the brake fluid is heating up and expanding? Would be from the exhaust being too owe to one of the lines.

FastDriver · Nov 21, 2023

Good thought. I'll take a look.

qikgts · Nov 23, 2023

Dovetailing to AeroCoupe... Brake hoses often swell on the inside and can restrict flow, that potentially could cause the calipers to stay engaged. If the hoses are old may be cheap insurance and a solution all in one.

90sickfox · Nov 23, 2023

To check if it is a hose, prop valve, or master just drive the car until brakes are hot and dragging. Jack it up amd make sure the wheel is hard to spin and then crack the bleeder on the caliper. If brakes free upits a restriction in the path or residual pressure.

I have no faith in aftermarket brake pads lately. I've had several sets that have needed filing in order to move freely. Pads should easily slide back and forth in the brakets. If they are too tight the metal will expand and cause your type of issue. If they are too loose it can cause a click when using the brakes.

FastDriver · Nov 23, 2023

All the hoses are new with my swap to the Cobra brakes. At first, I didn't think cracking a bleeder would tell me much, but that would be to differentiate between it being bad pads/sliders or pressure.

Never heard of that one. Thanks, @90sickfox

A friend threw another idea at me to check, too. I have that MM kit to completely get rid of the plugged stock prop valve. Not sure exactly how it could be holding pressure in, but can't hurt to get rid of it.

Mustang5L5 · Nov 27, 2023

The passages in the combo valve corrode and get blocked and can act like a check valve. I've seen it happen

FastDriver · Nov 27, 2023

combo valve = stock prop valve?

I've got the MM adapter to remove it.

Mustang5L5 · Nov 27, 2023

Yeah. It's technically a combination valve. The proportioning valve is in the front, and a shuttle valve is in the rear.

Ybfav84 · Mar 21, 2025

FastDriver said:
combo valve = stock prop valve?

I've got the MM adapter to remove it.

Did you figure it out? I’m having the same problem

FastDriver · Mar 22, 2025

Still dealing with something, there. There were two things happening, at least. The emergency brake cable was causing drag. When it snapped, that cleared up that problem. I need someone who can weld to fix the ebrake handle and tack in the correct threaded manual adjustment adapter.

The other problem is still unclear to me, and it does intermittently drag, as well as I can hear it pop when it shifts as I transition forwards to backwards and vice versa. I'm planning to pull the calipers off and take a look and possibly replace with some old Baer PBR calipers that I have on the shelf. Maybe new pads, rotors, and calipers will clear it up or give me the critical clue.

Ybfav84 · Mar 28, 2025

FastDriver said:
Still dealing with something, there. There were two things happening, at least. The emergency brake cable was causing drag. When it snapped, that cleared up that problem. I need someone who can weld to fix the ebrake handle and tack in the correct threaded manual adjustment adapter.

The other problem is still unclear to me, and it does intermittently drag, as well as I can hear it pop when it shifts as I transition forwards to backwards and vice versa. I'm planning to pull the calipers off and take a look and possibly replace with some old Baer PBR calipers that I have on the shelf. Maybe new pads, rotors, and calipers will clear it up or give me the critical clue.

Before you do that
Have you tried loosening the master cylinder a bit to see if it the booster rod?

FastDriver · Mar 29, 2025

Ybfav84 said:
Before you do that
Have you tried loosening the master cylinder a bit to see if it the booster rod?

Backed off that rod about 1.5 turns. Seemingly helped, but did not solve. Do I just keep going? Or, is it the brake fluid, lines, or some other hydraulic issue.

The intermittent part of it is what confuses me. After driving 5-10 minutes, it seems to drag. But if I get put on the highway, it frees up. When I start it up, it's no issue. When it drags, the pedal is at the top, but when it's not dragging, I've got an inch or so of pedal before the brakes engage. I was thinking I'd completely flush the brake fluid, and see of that helps.

General karthief · Mar 29, 2025

Drive it around till the brakes start dragging, start at the front, jack up the front and see if either side drags, then go to the rear.
my money is on a caliper sticking or a rubber brake line plugged.

FastDriver · Mar 29, 2025

I think it's at all 4 corners. Definitely the front 2. Had to beat the calipers off when I swapped pads and rotors last weekend.

General karthief · Mar 29, 2025

You couldn't open the bleeder and release the pressure ?

FastDriver · Mar 29, 2025

I'm sure I could have. I generally don't do that unless I've got a buddy helping to ensure I keep air out of the line.

Noobz347 · Mar 29, 2025

I'm confuzeled again.

Is this the one you swapped the pads on where the key on the pad didn't fit the caliper?

You still have issues after that?

FastDriver · Mar 29, 2025

limp · Mar 29, 2025

If you have no help, my neighbor " with the 6 million dollar jeep" swears by the " one way" bleeder screws ........ \

Brakes Brakes drag when warm. How to diagnose?

I was uncomfortably high & wearing a helmet

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

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wonder how much it would cost to ship you a pair

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wonder how much it would cost to ship you a pair

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wrap a little cheese around it and its a done

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