1991 Cherokee ABS problems: HELP NEEDED!

[Headache]

I have problems with the ABS on my (late) 1991 Cherokee. It has had the 702 recall and has, as far as I know, the notorious Bendix ABS-9 or -10 system.

The problems started after my wife had been in a traffic jam, causing her to keep the foot on the brake pedal for several minutes with the transmission in 'D'.

Directly after that, she parked the car and shut off the engine to do some shopping. After she returned and started the car again, the brake power assist was gone. When I made a test drive myself, I found out that the ABS pump did not work any more, only to find out that during a 2nd test drive, the ABS pump was working again, but now almost continuously. Frequently, the 'check antilock' control light flicks on and now and then, when there is no power assist, the red brake control light also lights up.

After 4(!) days of work, the mechanics of my dealer still have not been able to find the cause of the problem. The control unit indicates three errors:
- an error at one of the wheel sensors, but I can't imagine that this would affect the power assist
- 'accumulator low' when the brake control light is on
- an 'unknown' error.

The present situation is that about 50% of the time I have power assist. The dealer said that the ABS pump is o.k. as he has checked it separately. However, it will not always switch on when needed. According to the dealer, the cause can be about anything, including the wiring and he can give no indication of the costs of getting the d''ned thing repaired.

I unhooked the ABS control unit, but the problems remained.

On www.jeepforum.com, it was suggested that I should replace the whole ABS/brake system with a conventional one and this is what I intend to do. However, as I live in the Netherlands which is not particularly known for its outstanding and experienced jeep mechanics, I want to get as much input as possible. I read the article on http://www.naxja.org/html/techarticles/uninstall_OEM_ABS.htm.

My main question is: what could be the cause of the abovementioned troubles. Could it e.g. be a faulty pressure sensor?

In addition, all ideas or suggestions are welcome!

Thanks in advance,
Headache André

 

[Wiley Coyote]

Headache, I also have a ’91 with the dreaded Bendix ABS. Mine has been non operational since I bought it 2 years ago. The quick fix was to remove the brake relay in the fuse box under the hood. This completely disables the ABS and makes the system act just like a standard non-ABS. I have run mine this way for the last 2 years and it works just fine. Yes, the front bakes will lock up if you push on them hard enough. There are at least 5 sensors in the system that I know of: one in each wheel and one in the brake line after the Bendix pump. A fault in any of the sensors will cause the whole system to do strange things. Have your shop read the codes and compare them to this list:

801: Solenoid under voltage
802: Parking brake not seen
803: Anti-lock/brake warning lamp inoperable
805: Differential pressure fault
806: Boost pressure fault
807: Low accumulator
808: Modulator fault
809: Self test failure
811: Relay fault
812: Pump/motor fault
813: Brake switch fault
814: Low fluid
815: Right rear speed sensor
816: Left rear speed sensor
817: Right front speed sensor
818: Left front speed sensor

If its one of the speed sensor codes (815-818) the Factory Service Manual has instructions on how to check it with a voltmeter and/or adjust it. Old fluid will collect moisture and cause the system to have faults. If you don’t know the last time the brake fluid was changed, drain the system and refill it with DOT 4. It may not fix the problem, but at least it’s a cheap and easy place to start. Good luck.

Wiley Coyote

 

[Christopher]

You're better off just ripping the ABS out and replacing it with a standard booster & M/C. Those ABS can be a PIA and very dangerous.

 

[Headache]

Thanks for your reply. Guess what: the problems have disappeared after I released pressure from the system by pumping the pedal for some 40 times. I did this to check all pressure switches at high and low pressure. Having released the pressure 5 times, problems where gone.

Maybe there was some dirt or an (air) void in the system...

Anyway, as soon as problems come back, I will rip out the whole system!

Thanks!
André

 

[sidriptide]

i would start collecting the needed parts now.. so when/if it happens again you have what you need.. and you don't lose use of the vehicle at an inconvenient time.... plan for the swap and do it before it causes problems that make an unsafe situation.... good luck
mike

 

[DaveD in Canada]

My '90 has the dreaded Bendix ABS, and hasn't been without its problems. Had to replace the accumulator when the pump ran almost continuously. At one time the ABS warning light came on, and the dealer said it was a bad wheel sensor....WRONG! I finally traced it down to a bad protection diode in the ABS computer, a $2 fix.
As much bad press as these systems get, I wouldn't disable or remove mine for anything. I try to maintain it, and it rewards me with superb ABS performance on our snowy and icy winter roads, a real safety feature for me. I know it can fail, but it will almost always give you a heads-up first, and will not leave you with no brakes at all.
And of course, the system has some components covered under the lifetime warranty.

 

[Christopher]

Mine left me with no brakes....Twice :smsoap: ......With my family in the car and no warning at all. It has to be the worst system ever IMHO. The lifetime warranty is a joke. They should be forced to replace the system with one that works and won't get soeone killed.