Brake slips down hill!

[geoff]

Here's one that has my dealer perplexed so far...

The brakes on my wife's 997 tip will sometimes slip and then grab at the bottom of our driveway at speeds under about 5 MPH. It's steep, but not extremely steep. Speed doesn't seem to matter. Happens in either first or second gear. The service manager is speculating it might be ABS related, and may come over some time to try to reproduce the problem. It happens on a dry asphalt surface. No skidding or anything, just unnerving to my wife.

Has anyone else seen anything like this? Are there any known issues with ABS programming on the 997? The car is totally stock, and it's happened to me as well as to my wife.

[djantlive]

Brake slip meaning brakes releases? Is this going up the incline? Are you rolling onto the drive way in one continuous motion without coming to a stop?

[geoff]

Brake slip meaning brakes releases? Is this going up the incline? Are you rolling onto the drive way in one continuous motion without coming to a stop?

<{POST_SNAPBACK}>

Heading downhill in my driveway, maybe 5 MPH, and have to stop at the bottom of the driveway for my gate to open. Press on the brakes (not real hard, since going slow), the pedal presses, it feels like the brakes are slipping, then the brakes grab again. It's never been felt in any other car, and my '01 Boxster (manual) does not do it.

At first I thought it might be the transmission, but I've had it happen in tip manual mode in both 1 and 2, and in the automatic mode. I haven't noticed any dash lights coming on when it happens to help pinpoint what's going on.

It's not always repeatable, maybe one out of 5 or 10 times. Driveway surface is dry asphalt, so water / wet is not the issue.

[Loren]

Does the ABS light come on when this happens?

[geoff]

Does the ABS light come on when this happens?

<{POST_SNAPBACK}>

Not as far as I can tell. It it has, it's been an extremely short blink only

[ar38070]

How new is the car? With brand new brake pads and rotors brake performance may be weak until the pads have bedded in (at least 100-200 miles).

[geoff]

How new is the car?  With brand new brake pads and rotors brake performance may be weak until the pads have bedded in (at least 100-200 miles).

<{POST_SNAPBACK}>

about 5,000 miles - my wife's daily driver. New in March '05, been doing it since new

[ar38070]

Any possibility that the rotors are somehow getting wet where the car is parked?

[DD694]

Any oil, grease or any other slippery substance been sprayed on the wheels & rotors?

[geoff]

Any oil, grease or any other slippery substance been sprayed on the wheels & rotors?

<{POST_SNAPBACK}>

Car parked inside our garage - dry. Only happens slowly downhill in our driveway, haven't experienced it anywhere else. So don't think it's oil, etc on wheels, pads, rotors.

[DD694]

How about one or more warped rotors? This condition would likely be felt every time down the hill or even on the flat.

What happens if you are in neutral coming down the hill?

[geoff]

How about one or more warped rotors? This condition would likely be felt every time down the hill or even on the flat.

What happens if you are in neutral coming down the hill?

<{POST_SNAPBACK}>

Wouldn't warped rotors be apparent other times as well?

I haven't tried it in neutral. Good idea. :thumbup: I'll give that a try

[djantlive]

I am guessing the slope of the driveway causes the tire to loose traction and ABS may have kicked in. 997 front end is notorious to lose traction on uneven pavement or slope due to little weight in front. Try stopping the car earlier on the slope or at 2-3 MPH to see if this still causes an issue still. If so, the culprit could be in the ABS, PSM (if equipped), tires. You may also try entering the driveway at an angle to make the car less skid prone.

[0586slb]

I have a 986 Boxster S and an Audi A4. On the A4, the ABS is software version 5.0 and V5.3 on the Boxster.

Now with version 5.0 and 5.3, ABS carries out a self test every time you start. (from ignition on.) So as you move away from rest after starting the engine, the ABS runs the pump for about 0.25 seconds and checks the solenoid valves, when the wheel speed sensors reach about 6kph.

99.9% of the time you'll be on the gas to move off, so won't feel anything. However, in the A4, once I started downhill with my foot on the brake (a rolling start) and felt the self test through my foot. Occasionally I'll perceive the headlamps dim slightly.

I've experienced this in my Boxster too, though where I park I always have to use the gas to move off - being on the level.

I wonder if your experiencing the self test, having a downhill driveway, the cold engine will idle faster so the forward creep will be stronger in your Tiptronic so, as a rule, you'll be moving off with the foot brake applied?

[geoff]

Have been on a business trip all week, so haven't had a chance to try to reproduce the problem when not in gear.

Normal routine is as follows: back car out of driveway (relatively flat area), stop, put in drive, and head down the driveway. About 100 feet from garage to bottom of driveway. Stop, push clicker, and proceed after gate opens. Stop on other side of gate at street to make sure no cars coming, then proceed. Bottom of driveway at street has enough slope that nose will scrape ever so slightly unless going very slow.

The slip occurs when stopping right before the gate, or when stopping right after the gate before hitting the street. It doesn't feel like any kind of traction problem, and like I said, nothing similar happens on my Boxster, or any other car I've driven down the driveway.

I think PSM is standard on the 997, so the car has that. Not sure if that would affect braking. Tires are original Michelin Pilot Sport

[DD694]

I suggest that you call PCNA customer service and speak to a technical person. Also get your dealer to involve the regional Porsche technical person. If the problem is reproducible, they should be able to determine the cause and correct it.

[1999Porsche911]

Try disabling the ABS system and see if you still have the problem.

[geoff]

And the answer is :(

They all do it!

Took the car in for an oil change at just under 8K miles and the brake problem. My service advisor was finally able to reproduce the problem on a steep driveway, and on Friday had another 997 in for service, which he took to the same driveway, and it had the same problem ... err, "feature". It's definitely ABS related. He hasn't tried it with a 996, but my Boxster doesn't exhibit the same symptoms in our driveway.

They sent a "P tech" (sp?) in to Porsche, and I asked them to also check with the district service manager when he's around.

I told the salesman this afternoon when I saw him, and he wasn't happy about the problem.

[0586slb]

Geoff, did you ever get a difinitive answer for this? Was my 'ABS Self Test' theory correct?

[geoff]

Geoff, did you ever get a difinitive answer for this? Was my 'ABS Self Test' theory correct?

The car hasn't been back to the dealer since it was in for an oil change in September, and they were able to reproduce the symptoms on another 2005 997. It DOES still do the brake slip thing at the bottom of the driveway.

I'm nor sure about your ABS self test theory. After backing out of the garage, depending on how our other cars are parked, it takes one or two forward and backward turns to point down the driveway, and we have to slow down once or twice before our gate (all downhill and driving forward). After exiting the gate to the street and putting brakes on, that's the only time the brakes slip. It happens whether in gear or neutral, and in either Tip mode or manually in 1st or 2nd. It's still irritating, especially since my '01 Boxster has never done this. Based on the time involved, I think the ABS self test would have probably happened sooner.

The next time the car is in (probably soon since the radio now changes stations at random - I think there's a TSB on this), I'll have it checked again and report back.

[skinpath]

I am new to this forum . While surfing for DIY items, I read your problem of wheel slipping.

I have the same problem since my 2005 997 c2 was 17 miles. It happened only when going down to my basement garage in a steep driveway( 30degree). My guess is that it has something to do with the ABS because it feels like ABS is functioning. Because it never bother me so I ignore it. My car is 9700 miles now and give me no trouble. I will be looking forward to your follow up.

[geoff]

Since my original posting, several discussions with dealer service personnel. The "feature" is reproducible on other 997s, including the service manager's personal car (or so she says)

I also asked the question to the PCA experts - see https://www.pca.org/tech/tech_qa_question.a...5-4672B8EB5BBC} for the answer from Peter, who I think is Mr. Tool Pants' good buddy. It's also a feature with the 996, but more pronounced with the 997.

It sounds like it's a combination of rear engine, automatic transmission and general vehicle design. Just one of those things you live with. :o Just one more reason why you shouldn't put an automatic in these cars!

A friend just got a new 997 turbo with tiptronic. The next time he's over for dinner, we'll have to experiment with his car and see if the feature also occurs in his car. The turbo is all wheel drive, so it might behave differently.

[skinpath]

My 997 c2 is a stick model. Thanks.

[1999Porsche911]

Geoff, did you ever get a difinitive answer for this? Was my 'ABS Self Test' theory correct?

The car hasn't been back to the dealer since it was in for an oil change in September, and they were able to reproduce the symptoms on another 2005 997. It DOES still do the brake slip thing at the bottom of the driveway.

I'm nor sure about your ABS self test theory. After backing out of the garage, depending on how our other cars are parked, it takes one or two forward and backward turns to point down the driveway, and we have to slow down once or twice before our gate (all downhill and driving forward). After exiting the gate to the street and putting brakes on, that's the only time the brakes slip. It happens whether in gear or neutral, and in either Tip mode or manually in 1st or 2nd. It's still irritating, especially since my '01 Boxster has never done this. Based on the time involved, I think the ABS self test would have probably happened sooner.

The next time the car is in (probably soon since the radio now changes stations at random - I think there's a TSB on this), I'll have it checked again and report back.

Just drive to the dealer and right through the front windows. Tell them that the brakes slipped again. That should get someone looking into it. Or better yet, wait for the service manager to leave and rearend him in the parking lot.

Edited September 27, 2006 by 1999Porsche911

[geoff]

Geoff, did you ever get a difinitive answer for this? Was my 'ABS Self Test' theory correct?

The car hasn't been back to the dealer since it was in for an oil change in September, and they were able to reproduce the symptoms on another 2005 997. It DOES still do the brake slip thing at the bottom of the driveway.

I'm nor sure about your ABS self test theory. After backing out of the garage, depending on how our other cars are parked, it takes one or two forward and backward turns to point down the driveway, and we have to slow down once or twice before our gate (all downhill and driving forward). After exiting the gate to the street and putting brakes on, that's the only time the brakes slip. It happens whether in gear or neutral, and in either Tip mode or manually in 1st or 2nd. It's still irritating, especially since my '01 Boxster has never done this. Based on the time involved, I think the ABS self test would have probably happened sooner.

The next time the car is in (probably soon since the radio now changes stations at random - I think there's a TSB on this), I'll have it checked again and report back.

Just drive to the dealer and right through the front windows. Tell them that the brakes slipped again. That should get someone looking into it. Or better yet, wait for the service manager to leave and rearend him in the parking lot.

Service manager is a 'her', not a 'him' :) Rearending dealer's staff cars probably wouldn't earn me any favors in the future.

What I find most interesting is Peter Smith's (PCA) comment that this also affects the 996 model. I guess high speed stopping power is good, but really slow speed stopping isn't so good!