I've got a Jeep Grand Cherokee and this issue of anti-lock brakes functionality came up with regards to the use of Part-Time 4x4 in snowy weather.
We know how Part-Time mode operates on the four wheels. Given that, how does this affect a vehicle with anti-lock brakes, since ABS monitors the rotation of each wheel? If all four wheels are moving at the same rate, don't you lose the ability of the ABS to independently monitor each wheel speed and brake optimally/properly on a slippery surface that may NOT affect all four wheels?
Dunno about a GC ... but my Subaru had 4 channel ABS and AWD. The ABS simply prevents any wheel from locking when braking thus retaining full steering ability ... geez that was well put ... if only I could talk that good in the real world.
Darned few Grand Cherokees have a part-time 4x4 system, are you sure your Grand Cherokee has a Selectrac system that includes the part-time
4x4 mode? And a part-time 4x4 system does not lock the wheels together so they are in "lock-step" with each other, the part-time 4x4 system only locks the front and rear axles together...so tires are still free to lock up on one side.
In my opinion you should pull the relays when you are in 4x4 or there should be a switch. ABS is only good for dry pavement. See Bill's link... I also have seen a bunch of ABS vehicles calmly just keep on going totally out of control until that tree finally stops them. On the street in snow, that would be another vehicle or power pole.
The collision fixing folks must just love ABS come winter. LOL!
If you have the owners manual for your Jeep, it should warn you to stay off the brakes in the snow. Both my manuals state to use the gears to almost stop, then hit the brakes. The gears can hold you at the 'threshold' braking point really well with a little practice.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
That is fine except when you are doing 6+ mph and hit the brakes. The ABS kicks in and stays on until you let off the pedal or roll to a stop. (or tag the tree)
If the ABS magically turned off as you slowed past 5 mph, then you could lock the brakes and stop. It sure doesn't appear to do that because the wheels 'don't' lock.
But they DO lock and grind to a stop. My TJ has ABS and I've never had one single problem off road. Honestly has anyone complaining about Jeep's ABS ever actually driven a Jeep with ABS?
Now I have driven ABS systems that behave like some are saying Jeep system do, and strangely enough they were all in GM cars and trucks. My GMC pickup truck's ABS cycled quite nicely as I rolled into a slippery intersection. But that was before I learned how to drive an ABS equipped car. When you are posed with a situation where the ABS is cycling inappropriately (keep in mind my TJ has never done this) you, . . . . . pump the brakes. duh, just like they taught you in drivers ed. By definition the ABS works in slippery conditions and in off roading you find your self in slippery conditions all the time. Heck that is part of the fun. So if you don't know how to drive, don't blame the equipment.
Been there done that, well only in snowy, slippery parking lots . The brake peddle bucks and kicks under my foot and you can hear the system making a grr grr grr sound. Other tests I've done are 4 low, 20+ mph, jam on the brakes. The system cycles until I get down to some low speed and then the tires lock and I grind to a halt. I don't know what the exact speed is when the brakes lock, but I'd guess that its between 10 and 5 mph. Braking distance is about the same as when I pump the brakes.
IMHO ABS isn't really of much use on the dry, or for that mater for most drivers. I read somewhere that most drivers simply jam on the brakes and drive straight into the obstacle rather than braking and steering around the problem. And for those drivers ABS is truely a bad thing because it increases braking distances. Unfortunately there are those out there that don't know how to drive and all the ABS/non ABS in the world isn't going to make a bit of difference for them.
But, anybody can disable any ABS system simply by pumping the brakes. They had a big advertising campaign here a couple of years ago telling people to not pump the brakes on ABS equipped cars in slippery conditions. These guys that are rolling down hills with the ABS cycling (and I don't believe they are driving Jeeps that are in proper running order) simply need to lift their foot and put it down again, repeat. I know that is easier said than done, cause I had that rolling downhill experience with my GMC.
Personally I use ABS as an early warning system on the slippery. Sometimes it is hard to tell if the roads are just wet or if they are icy. If I brake and it cycles I am clearly going too fast and need to slow down. And if I ever need to brake and steer around a problem it is one less thing to pay attention to. Basically I've delegated the emergency braking to the computer. However, delegation does not mean abdication, yah still gotta drive.
It 'really' hurts my feelings when someone I am spotting for just calmly drives into the freaking tree!
100% for 'sure' his front wheels were turning right up to the end!
He then did the same run a second time with the relays pulled. Bingo, he could stop before hitting the tree and do the 3 point turn around the corner.
He did this two different days with the same results. Same deal for another TJ out with us.
There is one other spot where the TJ's go totally out of control and the spotter better be off to the side or they will get run over because there is no way that Jeep is stopping until it hits bottom.
I can't comment as to why your aftermarket ABS doesn't work the same as the GM's or the stock TJ's though as you imply below.....
No I don't own one, I just have spotted for them on the trail.
It 'really' hurts my feelings when someone I am spotting for just calmly drives into the freaking tree!
100% for 'sure' his front wheels were turning right up to the end!
He then did the same run a second time with the relays pulled. Bingo, he could stop before hitting the tree and do the 3 point turn around the corner.
I have never trusted ABS off road since and do not recommend it for 4x4 use. If I or anyone needs the extra control of 4x4 driving, they need braking control too.
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