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Is this normal?

T

TomYates

New member
I was driving my 987 Boxster the other evening down a good B-road after it had been raining, so the tarmac was fairly damp, but drying. A rabbit decided to run into the road and stop, so not wanting to pull pieces of rabbit out from my radiator all weekend I had to hit my brakes pretty hard and when the ABS kicked in the car very quickly darted left and then right within a split second. It was pretty scary, because if I'd been passing someone coming the other way, or I was close to the grass verge I could have had an accident.

Is this normal for the car to do this, was it caused by the wet road, or do I have a problem with my ABS? When I brake normally, or not very hard the steering wheel doesn't move a millimetre, so I'd guess the discs are fine. They do squeek from time to time also. Is that normal too?
 
We run a driving school and I am a Qualified Instructor. Not having been beyond the limits of ABS I don't speak from experience, however, we will always teach pupils that you can still loose control with ABS. There is a point when even the automated systems will go beyond their limits.

I have PASM in my Boxster and while on holiday in France earlier this year the back of the car hopped out of line on a wet road so the system met it's limit.
 
Yes, I have PSM. What worries me is that the car was going in a perfectly straight line at the time. Perhaps it's my inexperience as a driver too.
 
The message I was trying to put across is that you might have all off these systems like PASM, EBD and ABS that take control when you have lost it but they also have their limits and you could have passed them causing the problems you had.

You might still want to get the car checked.
 
Ah I see. I think I'll take it to a garage have them checked over. I've only had the car a month, but it's just had a porsche service and mot 3 months ago.

By the way, was you cornering or braking when the back kicked-out in France?
 
Just going round a corner off of a roundabout not braking. Weather was terrible though, the sort of day when you need faster wipers than the top speed. You can feel over safe with the electronic systems but they do save many lives.
 
I've been on a CATS training course at Millbrook where we did ABS and on-the-limit (before ABS kicks in) braking. In theory, in consistant conditions, and providing you don't move the wheel while you brake, it should stop in a straight line. However, variations in the surface conditions (how much water there was under each tyre) will probably leave you with a certain amount of weaving as it stops. The idea of ABS is to give you control over the car as you brake - not necessarily to allow you to brake in a shorter distance. In fact, if you know what you're doing, you can stop quicker using the on-the-limit method.

PSM and ABS are different systems, although PSM does make use of the ABS sensors to monitor the rotational speed of each wheel. PSM is designed to control the power the car puts down and does its best to eliminate wheel spin. All Boxsters have ABS; I believe that ABS remains active even if you switch off PSM.

Regards squeaking, I did notice mine was doing it a little yesterday.
 
My example of PASM was to show these systems can loose control. ABS and EBD (varies brake pressure to each wheel to keep the car stable) remain on all the time regardless.
 
It sounds perfectly normal to me - the ABS brakes each wheel independently - as Spyderman says different amounts of water, variations in road surface etc all affect the braking effort given each wheel.

Why not take the car to a quiet piece of road and deliberately trigger the ABS at low speed? - in the dry on a consistent surface it should go in a straight line, if not then take it to get looked at.

And as Colin says:

Ye Cannae change the laws o'physics...


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I had this experience on track not too long ago. The cause was toe angle being different on my wheels.
As I broke hard the cars weight moved forward hard causing the front wheels to toe out assymetrically and the car 'squirmed' left and right. You would only notice this effect under hard braking. After correcting the toe angle I tried braking hard on track the last 2 weekends and the car was perfect braking from 150-40mph.

Check your geometry it may be out

 
Incidentally, the ABS is 3 channel, and operates independently on each front wheel, but if one back wheel is sensed to lock, then it operates on both the backs at the same time. Just for info....


Edit: the above is true only for non-traction controll or PSM cars (like mine!). Those with TC or PSM have full 4 circuit ABS.
 
Thanks a lot for your replies there! I'll try it out again in the dry to see if does it again. If so, I'll have the geometry checked out.

Is it normal for the brakes to squeak at relatively low speeds though? It only does it occasionaly, like when I'm slowing down to turn into my driveway.
 
Having done numerous high speed stops on Porsche demo days, i can say that on good tarmac the car should stop in a straight line. Even swerving under maximum braking didn't upset the car one iota (this was in 987 series cars with PSM, ABS and no doubt a few other tricks over the 986 cars).

Road camber and rough tarmac do make a big difference though.
 
Just for interest, as I am sure it isn't relevant to your issue, my brother noticed a problem with the ABS on his Cayenne Turbo just after he bought it. If you really stood on the brakes, one wheel would lock, and stay locked until the car almost reached a standstill. No faults were shown on the system, and the techs at Porsche Reading were scratching their heads for quite a while. Eventually, they found that two of the brake lines were connected to the wrong ports on the ABS pump!
 
What you describe is not normal and isnt part of the spec

The car should not pull to one side, the car should stop straight and level - indeed you can steer at the same time and the system compensates for this as weight moves about and load is either applied or lessened to each wheel, If you have psm then the yaw sensor should have detected the non inputed movement and corrected that before you got so far out of line - something is not right here
 
When the snow fell I felt the ABS kicking in all the time on my 996 C4 cab. Even in a straight line at very, very low speeds the rear squirmed a bit although it was easy to control.

When I went round a corner at less than 5 mph the rear swung right round and the ABS kicked in on braking - it was a bit of a scary moment - even though about 6 inches of snow had fallen.

Quite whether this answers the question is another matter, but it seems that ABS is not the absolute answer to braking in adverse road conditions - although it does help.
 
What was the road surface like ?
Where I live there are deep gauge marks left by lorries in the the road and some funny cambers- If I break very hard in certain places my Boxster can squirm left or right
 
Ordinary Central London roads - a bit rutted. Came off the Marylebone slipway and the ABS kicked in at once even though I was travelling at less than 5 mph. Rear wobbled around a bit but controllable.

On turning righ [in very heavy snow], I lost the rear even though I was travelling at less than 10 mph. Luckily, nothing was coming towards me and I was able to sort things out.

I suppose that the rear lesson is that 4 wheel drive and ABS are not the be all and end all of car driving and safety.

I hasten to add that my car had been serviced not long before teh snow and I assume that all was working correctly.
 
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