When braking hard on low traction surface and the ABS activate while the car is in gear, should you depress the clutch pedal because the tires momentary lock up. Even though the engine won’t stall, could the pulsation from the wheels locking up and disengaging rapidly cause drive train or engine damage if you do it often.

 

When ABS engages, I don’t believe that it LOCKS all the wheels at once. Rather is applies brakes pressure to each tire on an individual basis to avoid tire lock up. This should not in any way effect the health of your eninge.

 

depress

 

funny, i discussed this this weekend with my nasa instructor at the hpde event at summit point. he said he does not do it (clutch in duing braking) but that he had a discussion with his race buds about it, and suggested i try it. i tried a couple times, but my brakes by sunday were so shot, rotors again, it made me nervous i can see some logic as you would not be working against the drivetrain during braking. perhaps cronohunter or robi will post their opinion/experience. i'd be interrested too. i raced bikes for a number of years and i always had the clutch in banging down gears while breaking HARD... but motorcycles are a completely different animal, and the brakes, front and rear, are independant.

 

He is talking about a low traction surface... like ice...not a road course.

 

clutch in, then "heel/toe"

 

i was really talking anytime when you would brake hard enough to lock up the brakes, which would occur more often in low traction situation like rain or snow. but lets say in autox, do you clucth in when you come to a corner where you know you're going to brake hard enough for the abs to come on.

 

heel/toe not needed in autox, just leave it in 2nd the whole time.

 

not that this is really a problem in our cars but clutch in braking could be quite dangerous... if enough vaccum load was applied it could stall the car.... which in turn means losing some braking force from the brake booster and loss of power steering....

 

Many different scenarios:

Coming off a high speed straight into a slow turn, you will do some serious braking. As others have mentioned, you will be braking and then heel and toe it to the point where you have reached the speed you want to enter the turn....

As for the ice scenario it really depends, but I would most likely push the clutch in prior to impact ...

Generally, the only time I put the clutch in (and keep it in) and apply the brakes is when I have spun and am going the wrong direction .....

 

i dont know about the clutch in idea....I find that either way, in or out the abs works effectively.

ABS works on a simple principle, pumping brakes ususally will allow momentary gains in traction, so the ABS system pulses, very quickly, the brakes and you eventually regain traction.

Just the same, ABS needs to have constant pedal pressure. Most drivers get scared because of the vibration ABS generates in the pedal, and the worst thing you can do is pump the brakes, as the ABS system as to essentially regroup, which in the long run adds time to the equation and time, when sliding, is no good.

 

you would never wanna clutch in on an abs activation unless you were in the wrong gear for the corner exit in which case you'd heel toe and it's just another day.

there won't be any drive train damage, why would there be? diffs? your front is open or open under braking (non accel), center? it'll only move if there is a gross difference between front and rear tire speed. rear? it'll help stop the tire on the other side until it locks but the actions are so fast that likely there is no affect between the rear two wheels.

so... in that autocross situation where you're in second the whole time... no need to clutch chances are you releasing the clutch and being unable to rev match exactly at such an odd situation such as leaving the car in the same gear will cause more damage when you either clutch out pull or clutch out push out of the braking zone.

 

the front wheels are always connected to the engine while the clutch is engaged and in gear with viscous coupling or ACD. my concern is that when abs activates and the clutch is still engage and the car is in gear, the pulsation would reach the engine through the drive train. if your wheels stop, your engine stop even though only for a fraction of a second. if the wheel only lock up one side at a time, then the engine doesn't stop because engine rotation is transferred to the non locking wheel. i'm not certain of what's really going in this situation, that's why i prompted the question.

 

you wheels would have to lock all at once in order to stop the engine. if only one wheels locks the compression stroke is still powered by the other three wheels and so on.

if you spin out or something you should always have "both feet in" cuz in that case you will lock up wheels all around and what not.

but for something like a racing situation where your grip is good but abs wants to keep it better... you shouldn't have to do anything like that.

 

^ sounds good, i just have to keep an eye on the tach to see what the engine is doing next time i brake hard enough to activate abs and the clutch still engaged.