I took out my 1999 996 recently on the freeway and about 20 miles into the trip all 4 brakes engaged forcing me to limp off the freeway . No warning lights were visible on the dash (abs/psm etc). Took it to a well respected indie mechanic and he resurfaced the rotors and did a complete brake job with new fluid however the following day the brakes locked again after a short 15 mile trip.

Anyone have an idea on what could be causing this behavior?

Note that I had the brake booster replaced about 18 months ago because the brake pedal was not returning to it's original position. Indie didn't find anything suspect with the new brake booster.

I have the following aftermarket parts installed:

Dectane led rear brake lights
Wheel spacers
Fister exhaust

Any help would be greatly appreciated as it's been at the mechanics for over a month now and he is still trying to diagnose the problem.

 

My advice is take it to a PORSCHE garage not an indy. I do all my own DIY but things I cannot fathom or a job more complicated than I can do I take mine into a PORSCHE garage. Something is seriously wrong so let them fathom it out for you. Money well spent in your case.

 

I had a similar problem with a Fiat Spider. Once the brakes would heat up the brakes would engage. My problem was remedied through an adjustment of the brake booster.

 

Just wanted to say thank you to everyone that responded and provide an update.

Looks like the brake booster was installed incorrectly by a previous mechanic and the pin was not correctly aligned. I didn't notice this for quite some time because the car is not a daily driver and has not been taken on any extended trips until recently. The 30+ mile extended trip was sufficient to cause the brakes to engage.

The mechanic replaced a few o-rings,adjusted the brake booster, and took several 30+ mile trips to see if he could reproduce the issue. Just got home and looks like we are good for now.

Again, thank you to everyone that responded.