Brakes Pulse Violently on Snow
CF Veteran
Joined: Aug 2009
Posts: 1,047
Likes: 3
From: Hanover,Ont, Canada
Year: 1991
Model: Cherokee
Engine: 4.o
I think it will only show a light if the computer senses an open circuit. If there is continuity it's looking for an electrical pulse generated by the tone ring.
A short will still show continuity as the circuit is still "Live" just not picking up the pulse, in effect telling the computer that the wheel is stopped or not moving.
If the computer sees 3 wheels moving and one already stopped it will release the pressure to that wheel. Remember the reason for ABS. A locked wheel is a wheel out of control. you lose control of a vehicle when all the wheels are locked up.
A short will still show continuity as the circuit is still "Live" just not picking up the pulse, in effect telling the computer that the wheel is stopped or not moving.
If the computer sees 3 wheels moving and one already stopped it will release the pressure to that wheel. Remember the reason for ABS. A locked wheel is a wheel out of control. you lose control of a vehicle when all the wheels are locked up.
Thread Starter
Newbie
Joined: Jan 2010
Posts: 7
Likes: 0
Model: Cherokee
This is what we've tried (without success)
The brake pedal on my 1999 Jeep Cherokee pulses violently when braking on snow covered roads and the brakes may be locking up. They work fine on dry roads no matter how hard I brake, but performance on snow or ice is scary once the ABS kicks in. I have had this vehicle for 10 years, so I know that the behavior is abnormal. The ABS light does not report a failure. Any help would be appreciated.
With my wife at the helm, I observed a drive-by. When braking on light hard-packed snow, I noticed that both front wheels locked up before the rear wheels stopped rolling.
My mechanic pulled the wheels and cleaned the tone rings, not that he thought they needed it. He also inspected the sensors and wiring. Using a scanning tool, he determined that the sensors look OK during deceleration.
His current thought is that the ABS unit is defective. For the time being, he has pulled the two ABS fuses and the vehice is running without ABS. As expected, with the fuses removed, the ABS light now comes on. So, that has me wondering why the ABS light wouldn't come on if the ABS unit is defective.... It still appears that the front brakes lock up under ABS control... on snow or ice. However, the brakes work fine on dry pavement where the ABS doesn't kick in.
Any other ideas as to the source of the problem?
CF Veteran
Joined: Aug 2009
Posts: 1,047
Likes: 3
From: Hanover,Ont, Canada
Year: 1991
Model: Cherokee
Engine: 4.o
The front wheel speed sensor air gap
is NOT adjustable. The correct front wheel speed
sensor air gap is from 0.40mm to 1.3mm (0.016” to
0.051”). Preferred rear sensor air gap for drum
brake systems is 1.1mm (0.043”). Acceptable air gap
range is 0.92mm to 1.275mm (0.036” to 0.050”). For
rear disc brake systems, the preferred rear sensor
air gap is 1.2mm (0.047”). Acceptable air gap range
is 0.95mm to 1.45mm (0.037” to 0.057”). All wheel
speed sensors have a resistance between 900 and
1300 ohms.
Correct antilock system operation is dependent
on tone wheel speed signals from the wheel speed
signals from the wheel speed sensors.
Here is a little blurb from the FSM , I would check the wss resistance values, as well you can hook up a multimeter set to ac voltage and spin the wheel at each sensor, compare the readings.... the sensor itself maybe ok, but perhaps the gap is incorrect or the tone ring is damaged..? Not really sure what else to suggest..I believe they are equipped with a G switch as well, this is used as an imput to the antilock module, it tells the module how fast you are slowing down. This should be under the rear seat..........Good luck!
is NOT adjustable. The correct front wheel speed
sensor air gap is from 0.40mm to 1.3mm (0.016” to
0.051”). Preferred rear sensor air gap for drum
brake systems is 1.1mm (0.043”). Acceptable air gap
range is 0.92mm to 1.275mm (0.036” to 0.050”). For
rear disc brake systems, the preferred rear sensor
air gap is 1.2mm (0.047”). Acceptable air gap range
is 0.95mm to 1.45mm (0.037” to 0.057”). All wheel
speed sensors have a resistance between 900 and
1300 ohms.
Correct antilock system operation is dependent
on tone wheel speed signals from the wheel speed
signals from the wheel speed sensors.
Here is a little blurb from the FSM , I would check the wss resistance values, as well you can hook up a multimeter set to ac voltage and spin the wheel at each sensor, compare the readings.... the sensor itself maybe ok, but perhaps the gap is incorrect or the tone ring is damaged..? Not really sure what else to suggest..I believe they are equipped with a G switch as well, this is used as an imput to the antilock module, it tells the module how fast you are slowing down. This should be under the rear seat..........Good luck!
Senior Member
Joined: Feb 2009
Posts: 811
Likes: 0
Model: Cherokee
based on the what has been said so far, i dont think you have a problem. i have an 04 F250, 08 F550 and a 97 mazda. they all do the same as described, feels erratic but that is how ABS works. if the computer detects a "lock-up" it will reduce pressure to free it up then reapply pressure. this on/off pedal pulsing feels wierd. on dry roads you have much greater traction so the ABS is seldom used even in a panic brake situation.
CF Veteran
Joined: Jul 2009
Posts: 1,254
Likes: 11
From: London Ontario Canada
Year: 2000
Model: Cherokee
Engine: 4.0
based on the what has been said so far, i dont think you have a problem. i have an 04 F250, 08 F550 and a 97 mazda. they all do the same as described, feels erratic but that is how ABS works. if the computer detects a "lock-up" it will reduce pressure to free it up then reapply pressure. this on/off pedal pulsing feels wierd. on dry roads you have much greater traction so the ABS is seldom used even in a panic brake situation.
Agreed. That would be my diagnosis.
It takes some getting used to ABS on real slippery surfaces BUT it will slow you down faster than if you don't have them.
Thats why its called Anti-lock Brake System.
Hook it back up. It's doing what it's supposed to do.
Member
Joined: May 2009
Posts: 215
Likes: 0
Year: 1996
Model: Cherokee
Engine: I6 4.0 HO
Since the fronts are disc too they're gonna stop a lot quicker than the rears therefore, locking up. At least how I view it.
I personally, am glad my jeep doesn't have ABS. Just not a fan of it.
I personally, am glad my jeep doesn't have ABS. Just not a fan of it.
Thread Starter
Newbie
Joined: Jan 2010
Posts: 7
Likes: 0
Model: Cherokee
I still suspect an ABS problem
I have been trying to convince myself that the ABS is working properly. I understand the theory, so I expect the noise and pulsing brake pedal when I try to stop on ice. However, it just seems so much more "violent", so much more frequent, and seems to handle much worse during deceleration.
I have been driving this Jeep for 10 years, so I think I know how it should feel and handle on one inch of snow. Maybe it's just a case of hypocondria, but my mechanic also thinks it is handling badly.
I will take it on the road shortly, without ABS, and see how it feels from a control (i.e., tracking) standpoint during deceleration. Maybe part of the problem is front-end alignment.
Keep the ideas coming. How can I exclude the ABS control module?
Barry
I have been driving this Jeep for 10 years, so I think I know how it should feel and handle on one inch of snow. Maybe it's just a case of hypocondria, but my mechanic also thinks it is handling badly.
I will take it on the road shortly, without ABS, and see how it feels from a control (i.e., tracking) standpoint during deceleration. Maybe part of the problem is front-end alignment.
Keep the ideas coming. How can I exclude the ABS control module?
Barry
CF Veteran
Joined: Sep 2009
Posts: 5,376
Likes: 1
From: NC
Model: Cherokee
Interesting seeing this question now. I was visiting my dad over the past week and I was driving his exploder in ice and snow. I noticed the same thing. I would push down on the pedal and the brakes would work but once I pressed down harder on the brakes to completely stop the brakes would grind and pulse and act like they did not want to work at all. I figured it had something to do with the ABS but couldn't figure out what it might be. Ill have to e-mail dad and let him know a possible solution.
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