ABS and clutching
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  1. #1
    2000+ Brad's Avatar
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    ABS and clutching

    This is something which I have never really thought about much, but with the type of driving I do on occasions, it seems very important.

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    In a non-ABS car you have to dis-engage the clutch when you emergency brake, and it is also wise to do the same if you intend to come into a corner hot where there is a large risk of locking the front wheels up and stalling the engine...

    so, in an ABS car is this also the case? Regardless of ABS or not I would always dis-engage the clutch in an emergency, but say you were having a fang in the wet and you brake to a point where the ABS was coming on quite hard. If you still had the clutch engaged, would this cause either the engine to stall given the wheels will be stop-starting, or damage to the driveline/clutch from the stress undergone?
    B to the R to the A from the D
    1994 MX5 Clubman...are you sure it's not French?

  2. #2
    1000+ Posts dino's Avatar
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    hi...interesting question....
    i suppose the trick is that if you are ever braking that hard one should have their clutch foot ready for deppression (although its not always as easy to do as it is to say ..ive done it a few times...the car stalled but at least i didnt hit (or run the poor bastard of the dog over))otherwise an abs car should should perform the same way ,in ref to stalling, as a non abs car, although if u have sufficient movement and if u r in the right gear car should restart (ie jumpstart) reasonably easy...i know my 205 gti with a pretty heavy duty starter motor can be jump started with me in the car and one leg (partially out )pushing it....
    YOUR point ceartinly throws new light on those that believe THE foot rest should be used during heavy breaking ie for support etc...bla bla bla...
    why ONE needs a foot rest in a manual car is BEYOND me....but i wonder of the topic by a 205 gti inspired tangent...
    in ref to mechanical damage I....would not have the faintest....but its usually the last thing on my mind when im braking to avoid an accident (usually caused by a LONG pair of legs....strange though ..if the missus is in the car...and i avoid the accident ,caused by the above mentioned reason...i still get hit, usually across the top of my head...the ABS hasnt helped me much in that department)....

    its 2.38 am now...and the above crap is a definite sign that its time to get some LONG (there s that word again) REST...

    cheers

  3. #3
    Moderator Alan S's Avatar
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    I've got ABS on my 16 Valve but the dramas that come about I don't think happen in real life if you always drice an ABS car; I think it's when you do as I do & have two non ABS cars as well as an ABS one.
    The first time I drove the BX with the ABS working I nearly $#!+ myself. I had backed down the driveway (remembering that my driveway is about 100m long) given it a bootful and as I got closer, I hit the pedal as I normally do. Now if anyone has ever driven a car that the brakes have failed on they would know that as soon as the brake fails, a little green man inside your head makes you believe that the car is now going at twice the speed you thought it was. tongue tongue
    Looking directly at me is the tail end of Adrians TZi saying "Hit me!! Hit me!!" and the harder I stand on the pedal, the faster the little green man has me believing I'm going. By this stage, my knee feels as though it's going to shatter when all of a sudden it stops dead...no skid & no pedal kick back. This is good I think so I go for a drive. The "kicky" pedal will happen on grass, not very evident on gravel/bitumen mix and harly noticeable at all on wet road, so I can't see it causing any real problems to driveshafts.
    Where the problem did arise was when later that day I took the TZi out for some reason, drove to the top of the street and ........... put evrybodys noses on the windscreen eek! eek!
    As far as disengaging the clutch goes, I really don't see the point in needing to drive an ABS car any different to a non ABS as far as that goes due to the fact that the pulsating will only occur under very stressful braking and only for a short period of time and in any case, providing the wheels are turning (which they would be) the driveshafts & final drive would be getting driven by the car & not the engine so these stresses would still be on the majority of components in teh final drive train.
    The biggest problem I find is getting used to non ABS without clobbering your passengers or getting Liberaced by the following vehicle. moon dance
    I also must point out that I keep my wheel sensors regularly cleaned which I feel helps prevent a lot of strange happenings with ABS.

    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

  4. #4
    Real cars have hydraulics DoubleChevron's Avatar
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    Very strange question,

    yeah the car may stall if you lock BOTH front wheels at the same time, but, but, it'll start immediatly again as soon as you let your foot of the brakes.

    My CX has ABS, it's actualy kinda a pain in the arse, I find it REALLY hard to keep my foot rammed hard on that pedal when I so used to lifting off a bit when I feel grip becoming comprimised. I've tried it on gravel, and my foot got a nice massage & the car took forever to stop (ABS and gravel roads don't mix ...)

    My ABS light has been on for a couple of weeks now, the backing plate for one of the back disks had come loose, and was hanging by the ABS wiring, betcha the [email protected][email protected] thing has fractured the wiring loom

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  5. #5
    who? when? huh? GTI124's Avatar
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    I've had one of my ABS equipped cars stall after an emergency stop. I'd recommend disengaging the clutch, but only if you have time. If I'm running out of time, I wouldn't worry about stalling the engine until the very last moment.

    My 2 cents

    <small>[ 02 December 2002, 11:09 AM: Message edited by: GTI124 ]</small>
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  6. #6
    1000+ Posts tekkie's Avatar
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    take the following anyway you want...

    When doing the 4wd training lately (work related) we have been told not to touch the clutch when braking in emergency. Why?because the engine compression promotes wheels turning and limits the chance of lockup. So in effect you get more control in emergency situation. Stalling an engine will not harm it. Ramming a car into an obtacle cause you have locked up your brakes on the other hand....
    The braking distances on brake pedal to the metal during emergency braking (with gear engaged and foot off the clutch) cut about 1/4 off the braking distance on gravel. Its very hard to do that as the left foot wants to clutch it at the end.

    ABS cuts off around 30 kms/hr (I think or thereabouts). So in effect ABS is OFF when you are about to stop and the engine will stall like any other manual car.

    Cheers all.
    .
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  7. #7
    2000+ Brad's Avatar
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    In the defensive driving course I went on they said that the main reason for disengaging the clutch during emergency breaking is so that the engine is still running to allow you to get out of danger should there be any after you stop.
    B to the R to the A from the D
    1994 MX5 Clubman...are you sure it's not French?

  8. #8
    1000+ Posts Rod Hagen's Avatar
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    Interesting.

    When I was learning to drive I was taught not to touch the clutch until the very last second in an emergency stop, to get the best out of both engine braking and subsequent moveability!

    Some cars back then (and probably still now) would stall anyway because of carby & fuel tank slosh and starvation issues though. In fact , leaving the clutch engaged until the last second was meant to reduce the likelihood of this because, in theory at least, it meant that the engine kept on turning over while the drive train was engaged.

    Cheers

    Rod

    <small>[ 09 December 2002, 08:33 AM: Message edited by: Rod Hagen ]</small>
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  9. #9
    1000+ Posts tekkie's Avatar
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    I guess there is a lot less chance of meeting another car after emergency braking when 4wd'ing.
    Another reason being that the diesel compression will stop you from sliding.... err that would take a while to explain but generally in steep areas, the time when the car would just start to move after you clutched it might be enough to build up the momentum which cannot be stopped by locked wheels (loose surface conditions). I guess it applies more during 4wd'ing than road driving.

    cheers
    .
    1300cc's of jap buzzbox delivered the times below.

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  10. #10
    2000+ Brad's Avatar
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    Tekkie- missed the fact that you were taking about 4wd'ing, which understand is a totally different ball game. I agree you should always leave the clutch engaged when braking in a 4wd situation, until the very ast moment wen the engine would stall.
    B to the R to the A from the D
    1994 MX5 Clubman...are you sure it's not French?

  11. #11
    1000+ Posts CHRI'S16's Avatar
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    Interesting question phasis,
    one factor to also consider is engine speed, whats to happen if it revin at lets say 5000 rpm? will the clutch slip?? in some abs systems the abs wont come in till its necesary but uses the engine to control wheel traction (ie Porsche and Nissan) and in the SGM M3 (ie real triptronic ) when i cane these from 45k's to almost stop the abs kicks (smoot concrete) i alot but never has the car stalled? is the ecu of the car opening the clutch?? perhaps we should too?? im not 100% percent on all this, but one thing is for sure,- when ever that middle peddal is pressed something has to take the wear be it pads, discs even transmision.
    wonder how big race teams ie F1 and wrc cars how do they over come this, wheel lock ups are common o f1's but its very rarely the driving wheels, wrc's are constantly rippig the brackes, i know that they dont even use the clutch to change gear but what about when sk/flicking or handbraking?? we want answers damm it!

    my two cents too.
    xqisid
    ... ptui!

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