ABS, slippery roads and locking up ...

[zcacogp]

Chaps,

The In-Laws live in Shropshire. And last weekend we made the pilgimrage up there to see them.

Last weekend was pretty wet. And Shropshire is a county of narrow roads, mud and hills. And although I 'only' drive an S2, it still has enough power to get into trouble ...

... on one occasion, I rounded a blind corner at the top of a hill, only to come across a van heading up the hill towards me. The road was muddy, I braked firmly, and was greeted by a rapid "whirring" noise from the front of the car and a VERY spongy brake pedal. It felt like the brakes weren't working, but the car stopped elegantly enough and in full control. Van passed by, I set off again, gingerly on account of the brakes, but they have worked fine ever since.

I presume this was the ABS cutting in? The reason I am unsure is that I have never activated the ABS before, and was expecting it to give rather more of a vibration feeling through the whole car, not just a distant whirr. And I wasn't expecting the pedal to feel dead at all. And there was no flashing warning light on the dashboard telling me that the ABS had been triggered. Were my expectations wrong?

Anyway, this line of thinking led on to musing about going slowly down steep and slippery hills ... my habit is to leave the car in gear, and thus control the descent using engine braking. However, if you do this in a 944 (or any RWD car), you are braking the rear wheels and not the fronts. I am therefore assuming it is possible to lock the rear wheels and thus spin the car, without even touching the brakes. Is this a real concern, or does it never happen?

Sorry for such remedial questions.


Oli.

 

[appletonn]

Oli, sounds like the ABS to me. After I fitted the new disks and Porterfield pads (which incidentally squeal like a bar steward when cold [8|]), I had to follow Peter's guidance on bedding them in, which involves braking hard from increasingly higher speeds... Unfortunately the roads were damp and I triggered the ABS on more than one occasion leading to a dead feeling pedal with more travel than normal - and slightly white knuckles..[]

I have only known of locking up the rear wheels as you describe if coasting down the hill in a low gear and then dumping the clutch (trying to bump start a diesel rwd car [8|]) - I would think that as long as the rear wheels were turning, it would be extremely unlikely that they would lock just through the engine braking, it hasn't got that high a compression ratio.

Don't quote me on that though...[8|]

 

[Diver944]

When the ABS activates it does make the pedal feel very spongy in an on and off kind of way. This is the hydraulics releasing the brakes and modulating the pressure and is perfectly normal. It will feel worse the slippier the conditions are as it may take a long time to get proper grip again. It is less alarming when activated on a bone dry road because grip is achieved so much quicker as you slow down.

There are no warning lights when it is activated, only the red one on the dash when it's broken or faulty.

I would encourage everyone to find a safe place to do so, maybe a wet empty car park and slam the brakes on from 30-40mph and see what it feels like. It's also a good check to make sure it's working before you really need it []

 

[Wigeon Incognito]

I had a play with mine to get a better feel for the brakes and when the ABS cut in it felt exactly as you described. It was decidedly different to the way it has felt on more modern cars I've experimented with but similar to the feel of my MX-5.

Am I correct in thinking 944s only have a two channel system, i.e. it works only on the front wheels )but independantly wheel to wheel) which could account for a feel different to that of more modern systems?

It isn't the most primitive type of ABS (that'd be single channel, one release circuit acting on all four wheels) but a step behind 3 (2 channel front plus a channel at the rear) or 4 channel (independant on all four wheels).

 

[Hilux]

presume this was the ABS cutting in? The reason I am unsure is that I have never activated the ABS before, and was expecting it to give rather more of a vibration feeling through the whole car, not just a distant whirr. And I wasn't expecting the pedal to feel dead at all. And there was no flashing warning light on the dashboard telling me that the ABS had been triggered. Were my expectations wrong?

The ABS (at least in mine) I have only tested on track. It is a bit old fashioned in that it is relatively slow in its on/off action (and therefore lets you trail brake a bit when you`ve overcooked it into a tight corner [8|]) however I personally did not feel the pedal went soft. Pauls comment re the seemingly soft/never going to stop feeling is accetuated on a wet surface.

BTW have you the original rubber hoses and decent (new) brake fluid? Braided hoses and new fluid do perk up the brakes, feel wise certainly.

 

[sawood12]

The ABS system is quite slow compared to the machnice-gun rat-tat-tat-tat vibration you get from modern cars. I had a moment a few weeks ago approaching a bend on a country lane with mud on the road. I hit the brakes and the ABS cut in immediately but unfortunately because the ABS was on I wasn't braking at all due to the slippery surface. I had no option but to turn the corner and hope for the best and braced myself for the drop into the ditch. Sure enough as I turned in the rear slid out but to my delight I was able to hold the car in a perfectly executed power slide around the corner. I was very pleased with myself once I pinched myself a few times to make sure I wasn't dreaming. I remember looking in the rear view mirror at the brand new BMW 3 series behind me and he was all over the road. So much for the 'ultimate driving machine' bristling with all the latest in traction control systems. My slide was far more controlled[]