Odd Problem with brakes - 986 Forum - The Community for Porsche Boxster & Cayman Owners

JayG · 08-30-2019, 03:21 PM

I am having a wierd problem with the brakes on my 04 996 Targa. From what I know, it is the exact same braking system as a 986S. If I am wrong, feel free to correct. It ABS only, no PSM or PASM

In any case what is happening is most of the time the pedal is rock hard and the brakes work perfectlty. Sometimes with even pressure on the pedal,iot ios rock hard and then it drops a small amount and feels slightly soft, but still the brakes work fine.

Every now and then, you can feel ABS engage. The odd thing is it sometimnes happens art freeway speeds with just slight pressure on the pedal. There is no way I am on the brakes hard enough to lock the wheels. It also happens occasionally at slow speeds coming to a full stop. That I could think was actual wheel lock.

The other thing that happened a few times is brakling from around 30 mph and the car pulled hard to the left. That has only happened 2 or 3 times.

I have repleced the master cylinder thinking that might have been the problem and nothing changed. I did a full flush and bleed when I replaced it.

I am thinkiing it might be the ABS controller or a sticking piston in one of the calipers. Can I swap the ABS controler from my 04 986S with the 04 996? Do they require any programming?

Any thoughts to what the probklem is?

911monty · 08-30-2019, 04:03 PM

Doesn't sound fun or confidence inspiring. The first thing I'd check is the speed sensors at the wheels. I imagine an 04 has the 4 channel system meaning the ABScan control each wheel front and back,The sensors can get dirty from brake dust and cause issues. Then check the connectors.Also hook up the durametric and check for ABS codes. Whatever you do have fun!

Fiddlebog · 08-31-2019, 01:00 AM

Quote:

Originally Posted by 911monty

Doesn't sound fun or confidence inspiring. The first thing I'd check is the speed sensors at the wheels. I imagine an 04 has the 4 channel system meaning the ABScan control each wheel front and back,The sensors can get dirty from brake dust and cause issues. Then check the connectors.Also hook up the durametric and check for ABS codes. Whatever you do have fun!

yes, brake dust can seriously mess up those sensors. Don't ask me how I know.
Be careful with cleaning them, though. Brakleen is bad for them, or anything else with plastic bits.

maytag · 08-31-2019, 04:47 AM

Are you running anything out-of- factory specification? Specifically wheels and tires?

I agree that bad (or dirty) wheel sensors can wreak havoc.

Sent from my SM-G970U using Tapatalk

JayG · 08-31-2019, 11:28 AM

Good idea on the sensors, thanks. I could always pull the ones from my Boxster and swap them outy.

I'm running 19" wheels. It was never an issue in the last 4 years

JayG · 09-03-2019, 06:19 AM

In thinking about this some more, I don't see how speed sensors would effect the pedal moving a little after it was rock hard. It makes soense for ABS engaginge at speed, but not the pedal

Can I sswp the ABS control unit between my Boxster S and My Targa?

Racer Boy · 09-03-2019, 10:44 AM

How are the wheel bearings? You could be getting pad knock-off, which happens when the rotor can move around laterally, which pushes the pads back into the piston. It doesn’t take much to cause this, and even a little knock-off can cause a soft, or sometimes long pedal. And it’ll be inconsistent.

I had a race car with those symptoms, and it took me a while to figure it out.