Trying to diagnose brake failure

[ticklechicken]

Car is a 96 GTS with 21k miles. I've had the car for 4 months and haven't done anything to the brakes. I inspected them after purchase and everything looked fine.

A few days ago, I drove the car for 20 minutes, and then it sat for 2 hours. After driving again for about 5 minutes, I got into the throttle pretty hard. A stop light ahead turned red, and I had to hit the brakes pretty firmly. The pedal went right to the floor. I think I heard a wheel lockup for a second as the pedal was pushed, but I'm not sure. I was too busy downshifting, pumping the pedal, and looking for escape routes. Not fun.

I pulled over and popped the hood. There was plenty of fluid in the reservoir. I walked around and didn't see any fluid leaking. I splashed a little water on each rotor, and they were very hot. They sizzled more than I expected, but I don't really have a reference for that. My guess at the time was that I somehow boiled the fluid in only 5 minutes. At this point, I'm thinking it's a dragging caliper.

I limped the car home. It was about 15 minutes at 45mph with no braking. At the very bottom of the pedal stroke, there was a small amount of braking. I checked the rotor temps when I got home, and they were all around 130

[Fatboy 18]

Hello, OK let's start with some basic stuff.

What is the colour of the brake fluid? Is it very dark in colour or a light golden brown colour?

When was the fluid last changed?

I would recommend a full system flush and refill with Motul 600 RBF DOT4 fluid.

How are the Pads?

[AviP]

Scary! I would start by taking out all the wheels one-by-one and examining for a leak at the calipers. Also examine the rotors on both sides. Check the lines for leaks. And if everything looks good, I would still do a brake fluid change. Also pads that have worn out to the backing could potentially feel weird.

[Fatboy 18]

Your brake fade used to happen to me a lot when tracking the car, I went a more radical route.

40mm Rear caliper piston upgrade (Toms 40mm Brakes) this changes the balance of braking on the car from 70-30 to 60-40,
you can still lock the fronts but the car is much better balanced.
Two piece rotors also help to get rid of heat.

Another thing I did was to build a Brake fluid recycle system for the front calipers.
https://www.flickr.com/photos/90582394@N02/albums/72157632214538274

Since I have done this, I have never had a problem with the brakes.

There are lots of brake options, but it depends on your wheel size which I presume is 17"

[99RT10]

If the pedal went right to the floor with no previous hard braking, I would suspect the Master. It is over 20 years old and these parts are not going to last forever.. The Master is an easy replacement, get a good named brand. If it is brake fade, the pads would have to be razor thin, but you said you checked the pad depth, correct?.

[ticklechicken]

Hello, OK let's start with some basic stuff.

What is the colour of the brake fluid? Is it very dark in colour or a light golden brown colour?

When was the fluid last changed?

I would recommend a full system flush and refill with Motul 600 RBF DOT4 fluid.

How are the Pads?

Fluid is light golden brown. No idea how old it is. Pads and rotors are in good shape. I'm prepping the car for some track says, so RBF 600 is already on my list.


Your brake fade used to happen to me a lot when tracking the car, I went a more radical route.

40mm Rear caliper piston upgrade (Toms 40mm Brakes) this changes the balance of braking on the car from 70-30 to 60-40,
you can still lock the fronts but the car is much better balanced.
Two piece rotors also help to get rid of heat.

Another thing I did was to build a Brake fluid recycle system for the front calipers.
https://www.flickr.com/photos/90582394@N02/albums/72157632214538274

Since I have done this, I have never had a problem with the brakes.

There are lots of brake options, but it depends on your wheel size which I presume is 17"

Because I had only driven 5 minutes in light traffic, I don't think this is an issue of brake fade. The only way I see that happening is with a stuck piston in the caliper, and that doesn't seem to be the culprit.

I do like all your other suggestions for track use. I will definitely look into that if tracking becomes a habit. When Larry Macedo was tuning my car last week, I was asking him about track prep. He mentioned that the Porsche brake air deflectors worked very well and that I should start with those.


If the pedal went right to the floor with no previous hard braking, I would suspect the Master. It is over 20 years old and these parts are not going to last forever.. The Master is an easy replacement, get a good named brand. If it is brake fade, the pads would have to be razor thin, but you said you checked the pad depth, correct?.

Pad depth is good. Plenty of life left.

Question about what I've put in bold. I've never heard that before. Can you explain this further?

[Fatboy 18]

Basically, the thinner the pad the more heat transfer from the rotor :)

[AviP]

Since you don't have leaks, rotors and pads are good, and fluid is not dark in color, I would think a brake bleed should solve it. You seem to have air in the line.

[GTS Dean]

Master cylinder could very well be the culprit. Check at the brake booster interface and see if there is any sign of fluid leaking. You could also loosen the nuts on the mounting studs a few turns at the front of the booster and jiggle the MC to look for fluid that hasn't leaked out yet.

The most inexpensive option is fresh fluid and a full system bleed. Remember that both front calipers have 2 bleeder plugs in them (inboard and outboard). Your pads and rotors might be glazed an not biting, but if your pedal goes to the floor, they aren't the source of the problem.

[WDW MKR]

My experience with stuck caliper pistons is soft pedal... not a sudden loss of braking. You’ll also know it as soon as you get out of the vehicle (if it’s bad enough to impact braking), as you’ll smell it and can quickly find the source by walking around the vehicle and feeling for the hotter corner.

[LATAMUD]

What about old brake hoses? If when the rubber heats up they are ballooning. Steel braided hoses can be had for around $200 - $250 for a complete set.

[Blue96GTS]

Since you don't have leaks, rotors and pads are good, and fluid is not dark in color, I would think a brake bleed should solve it. You seem to have air in the line.

+1 Air in the line(s).

[Old School]

Sounds like the master cylinder. Since the master cylinder is shared with the Ford Aerostar, they are common and cheap.

[MH60M]

Sounds like Master Cyl. to me.

On a similar note....Is there any benefit to running a Gen3 master in a Gen2? Also, where does the brake proportioning take place between the 2001+ Gen2 and Gen3 cars?

[99RT10]

Basically, the thinner the pad the more heat transfer from the rotor :)

Plus real road experience for me. on one mountain run, I checked my pads, thought they were good. I was mistaken. Pad was almost gone as was my brake pedal going down hill, not a good day.

[ticklechicken]

Sounds like the master cylinder. Since the master cylinder is shared with the Ford Aerostar, they are common and cheap.

Thanks for that tip. Just saved me a bunch of money.