Front Brakes Lock Up

[Blowbyu]

My 99' has decided to lock up the front brake calipers. I had to hit the brakes hard at about 45 MPH, brakes worked perfect as I stopped short of the other 9 cars in the pile up.

I drove about a mile to a stop light where the brake pedal felt "hard". When I took off from the stop light (or tried to) it was as if I had installed a line lock. I was forced to do smokey burn outs to get the car off the road. Had to have the car put on tow truck to get it home. Front brakes were locked up solid. I cracked the brake lines loose on the Kelsey Hayes unit and the front brakes released. Wow that was easy...wrong, problem still exists. I step on the brakes easy just one time and the front brakes stay locked untill I release the pressure.

Anyone have a clue as to what might be going on? Which Kelsey Hayes unit do I have on this 99'?

Thanks for any help!

[mike_sekinger]

I remember a very long time ago, that I had a problem with my Sport350. The symtoms were very similar to yours, and it turned out to be the brakes light switch which is installed beneath the brake pedal. There had been a problem with the part and had been replaced by the garage.... only it was wrongly installed and was locking the pedal when depressed.

It hardly soundly likely, but a very quick check will confirm if this is the case.

[Artie]

My 99' has decided to lock up the front brake calipers. I had to hit the brakes hard at about 45 MPH, brakes worked perfect as I stopped short of the other 9 cars in the pile up.

I drove about a mile to a stop light where the brake pedal felt "hard". When I took off from the stop light (or tried to) it was as if I had installed a line lock. I was forced to do smokey burn outs to get the car off the road. Had to have the car put on tow truck to get it home. Front brakes were locked up solid. I cracked the brake lines loose on the Kelsey Hayes unit and the front brakes released. Wow that was easy...wrong, problem still exists. I step on the brakes easy just one time and the front brakes stay locked untill I release the pressure.

Anyone have a clue as to what might be going on? Which Kelsey Hayes unit do I have on this 99'?

Thanks for any help!

Perhaps your brake pads are worn too far and when you pressed the brakes hard, you wore the pads down to almost backing. Now when the pedal is depressed the pistons travel beyond their allowable limit and get wedged in their respective bore...It happened to me on my RX7.

Artie

[glynherron]

Perhaps your brake pads are worn too far and when you pressed the brakes hard, you wore the pads down to almost backing. Now when the pedal is depressed the pistons travel beyond their allowable limit and get wedged in their respective bore...It happened to me on my RX7.

Artie

Nice idea Artie, but the pressure in the system would die when the brake pedal was released......

No idea why the pressure wont release though, unless the small amount of free play (about 1mm??) at the pushrod on the master cylinder has gone. Without this free play, the pressure will stay in the system

Good luck

Glyn

[Rob]

I had same problem as Mike S - switch interfering with the top of the pedal. Not easy to spot, but a simple fix (thankfully).

[actwon]

My 99' has decided to lock up the front brake calipers. I had to hit the brakes hard at about 45 MPH, brakes worked perfect as I stopped short of the other 9 cars in the pile up.

I drove about a mile to a stop light where the brake pedal felt "hard". When I took off from the stop light (or tried to) it was as if I had installed a line lock. I was forced to do smokey burn outs to get the car off the road. Had to have the car put on tow truck to get it home. Front brakes were locked up solid. I cracked the brake lines loose on the Kelsey Hayes unit and the front brakes released. Wow that was easy...wrong, problem still exists. I step on the brakes easy just one time and the front brakes stay locked untill I release the pressure.

Anyone have a clue as to what might be going on? Which Kelsey Hayes unit do I have on this 99'?

Thanks for any help!

First question:

1. Are both calipers locked up?

If so, I would stay away from the ABS system. You could be causing more harm than fixing the issue.

2. Have you checked the vacuum hose? (It is a large diameter hose in the front of the motor, usually attached to the red wastegate vacuum hose).

Squeeze the hose to see if there is pressure in the hose. If so, there is something in the vacuum system that is keeping the pressure from being released.

3. If neither of these are the issue, have you bled the system? <-- Shot in the dark.....

4.

[Blowbyu]

I remember a very long time ago, that I had a problem with my Sport350. The symtoms were very similar to yours, and it turned out to be the brakes light switch which is installed beneath the brake pedal. There had been a problem with the part and had been replaced by the garage.... only it was wrongly installed and was locking the pedal when depressed.

It hardly soundly likely, but a very quick check will confirm if this is the case.

Thanks Mike but the pedal only locks with pressure in the brake system, crack a brake line, release the pressure and the pedal moves freely.

Perhaps your brake pads are worn too far and when you pressed the brakes hard, you wore the pads down to almost backing. Now when the pedal is depressed the pistons travel beyond their allowable limit and get wedged in their respective bore...It happened to me on my RX7.

Artie

Damn it Artie I wish my maintenance was that bad, could then be an easy fix. 4500 miles on new slotted and drilled rotors and Porterfield pads when this happened. Only 14K miles on the car.

I do have new caliper seals on order, but the pistons release once I crack a brake line.

Thanks Artie!

[Blowbyu]

First question:

1. Are both calipers locked up?

If so, I would stay away from the ABS system. You could be causing more harm than fixing the issue.

2. Have you checked the vacuum hose? (It is a large diameter hose in the front of the motor, usually attached to the red wastegate vacuum hose).

Squeeze the hose to see if there is pressure in the hose. If so, there is something in the vacuum system that is keeping the pressure from being released.

3. If neither of these are the issue, have you bled the system? <-- Shot in the dark.....

4.

Yes both calipers lock up. I removed the fuse for the ABS system, for fear of damage, prior to starting to trouble shoot.

I have not but sure will check the vacuum hose tonight.

Bleeding the system was one of the first things I tried, and please give me any other "shots in the dark".

Thanks

[fjmuurling]

Internal collapsed brake hoses ????

Freek

[actwon]

Yes both calipers lock up. I removed the fuse for the ABS system, for fear of damage, prior to starting to trouble shoot.

I have not but sure will check the vacuum hose tonight.

Bleeding the system was one of the first things I tried, and please give me any other "shots in the dark".

Thanks

Ok....

Hmm, not sure what else to tell you. You have a '99; so that means you have the Brembo fronts. The only other thing I can think of is that you may need to rebuild both fronts. However, that doesn't make sense to me. The odds of both calipers locking up at the same time is high. <-- Huge shot in the dark!

What type of Brake Fluid are you using? That could be your culprit. If you use to incorrect type of fluid, it can damage your brake/abs system. It can, possibly, cause your caliper locking up. Now that I think of it, it may be your fluid. Use mineral DOT 4 only. Do not use DOT 5 specified fluid.

I hope this helps you.

[glynherron]

Have you checked at the brake pedal that the free play exists?

You should be able to press the pedal with your hand a little before the pushrod starts to move towards the master cylinder/brake unit

My locknut has come loose on my clutch pedal, your locknut may have come loose on the pushrod.

Fingers crossed its this !!!

Glyn

[actwon]

Ok, let's try this one.

Important question:

When your calipers lock up, does your brake pedal rise back to standard position or does it sit closer to the floor?

[FLiPSyDe71]

Was a solution to this problem ever resolved?... I have a very similar problem.  The other day I was driving home at night and had to go hard on the brakes as well to avoid an accident.... the pedal became hard to push after some time and the car vibrated and was sluggish.... I was able to get it home but knew that one or both of my rear brakes were not releasing properly and had progressively gotten worst as I got off the highway and into city stop and go driving.  Luckily, I don't live far from the off-ramp but by the time I got to my driveway, I could hardly press the brake and the car had a hard time rolling.  The next morning, I jacked up the car and both wheels rotated without and issue... it seemed that the "line lock" released but not sure as to how or why that happened.  I'm afraid to drive it now, but not sure where to look first.  

Any insight to this issue would be greatly appreciated.  Thanks!  -Jay