blacksquid

Driving yesterday when the wheels started to lock up on me. I hurried to a side street but could not pull over to the curb as the locked completely. I think it was just the rears. The brake pedal was all the way up and I could not push it down at all. No codes were thrown.

I called AAA to get a tow. As I was waiting for the tow truck to arrive, the brakes started to ease off and I was able to get the car out of the middle of the street. The car is at the shop now but and will get looked at in a day or so.

Any ideas about what could be wrong?


John

NuttyProfessor

Hey John, I've had this problem before... it ended up being a malfunctioning master cylinder. However, if it's just the rear wheels, it could be the parking brake system locking up on you. The parking brake system has drum style brakes on the rear wheels only. Anyway, I would get it to a brake shop immediately.

blacksquid

Thanks Professor! The car is waiting patiently at the shop now. I'll report back with the cause.

DBJoe996

Sounds to me like the master cylinder as well. Guess we will wait to hear what the repair shop says.

rockhouse66

+1 Do we win anything?

808Bill

Any chance the parking brake wasn't released all the way? Shoes get hot and swell.

blacksquid

Cassette storage unit from a '99 996?

blacksquid

I just found the following PelicanParts. Describes my problem exactly.

Brakes Locked
Comments and Suggestions:BadUrbanKarmaComments: I had the same problem when I first bought my car used, 14 yrs old. I had to get towed the first time it happened. After that, I just carried a wrench to relieve the pressure at the caliper bleed valve. The problem was eventually solved by having the ABS electronics repaired. I think one of the circuits was causing one of the ABS block valves to activate, restricting normal flow. The Bosch 5.7 ABS electronics are notoriously fragile.January 31, 2018
Followup from the Pelican Staff: Thanks for sharing your experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
EringofastComments: Sorry but i dont understands why brake line pressure would be held up after the booster that would cause this? The vacuum in the booster is holding the rod pressure so when I pull the vacuum line at the booster the car frees up.
I'm not trying to be difficult but just trying to understand how the line pressure would cause this.
Could the brake line pressure regulator cause this which is clipped to the side of the ABS control pump?October 11, 2017
Followup from the Pelican Staff: A line restriction. - Nick at Pelican Parts
pacervilleComments: This seems to be a common problem, I know of my car and one other where the entire system booster, master cylinder, ABS controller, brake push rod, new front brakes and rotors, bled the brakes, you name it. All 4 brakes lock up. The only way to relieve the pressure is by pulling the brake pedal up by hand. Once the brake fluid is cooled, the brakes are ok, until it warms up again. Any answers?September 12, 2017
Followup from the Pelican Staff: I have not seen that issue. Sounds like a faulty master. - Nick at Pelican Parts
EringofastComments: Help!
1999 996 the brakes start to come on by them self after about 15min of driving. I've pulled the and fuse same. After this happens the front brake lockup car will not move. I've pulled the vac line to the booster and car will roll again. I've changed booster, master. Any theories?August 20, 2017
Followup from the Pelican Staff: You will have to test pressure at the brakes to see what is happening. MOnitor line pressure when issue is present. Then work your way toward the master to see where pressure is being held up.
An alternate method would be to crack lines open to find the source of the hold up. - Nick at Pelican Parts

Imo000

The rear brakes were dragging and when the calipers got hot, the fluid expanded and locked up the rotors.

blacksquid

You have a choice:
1. Cassette Storage Unit
2. Genuine Porsche CD Changer (no magazine)
3. Rear Bumper Crash Absorption (I installed a 1.25 receiver hitch)
4. Rear License Plate Holder

Porschetech3

Seems like I remember a TSB on the 99's about water getting into the brake booster causing it not to return to rest position. If I remember the cure was to replace the booster and install a new drain valve under the booster next to the battery..

DBJoe996

Your memory serves you well. I remember the first time I washed my car and just happened to look down into the areas next to the battery. Both compartments were filled with water, the drivers side enough to slosh around under the brake booster. Cleaned out drains and now check them often. It only takes one leaf to block them. The drain valves were redesigned with a split in them to allow water to drain better and all the way down in those compartments, but it is best practice to check them often. It is amazing how much trash and leaves somehow get in there.

Imo000

My brother's '00 Carrara 4 has this problem. You need to pull the pedal back with your foot or else it will drag. Got a replacement booster that I will install in the next few weeks.

Paul Waterloo

Here are two recent threads:


https://rennlist.com/forums/996-foru...s-problem.html


https://rennlist.com/forums/996-foru...-sticking.html

blacksquid

The front cowl drains were blocked when I got the C4 last year. Cleared them and now I check them often now since the car lives outside.