Rear anti lock brakes don't work. No light on dash

[mickreed]

I have a 92 bronco and I noticed this week while driving in the snow that my rear anti locks don't work.

The idiot light on the dash is NOT on. But in the snow going down hill and touch the brakes, the back end tried to pass the front. Not good.

Fuses look good. I'm going to check them once more after work tonight.

 

[Seabronc]

This won't make you feel any better, but that is a common Bronco trait.  The front brakes are more effective than the rear.  The best way to get around the problem is to use 4X4 when on slipery snowy roads.  You can have the back brakes adjusted, but they don't seem to last long.   The problem is that in 2 wheel drive the front brakes start to grab but on slippery surfaces the engine keeps driving the rear wheels.  If it is in 4x4 the front brakes counteract this tendency because they now control the drive train.

Not much help, but that is the way it is.

You could install rear discs.

Good luck,

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[Seabronc]

Also, if you don't want to leave it in 4x4, leave the hubs engaged and pop it into 4x4 when a similar situation comes up.  However, I recommend 4x4 on all slipery snow covered roads.

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[nelbur]

Does a '92 have anti-lock brakes?

 

[mickreed]

Yes it has rear only anti locks. They use to work.  They did a nice job for years. and you could feel them working. Now they skid real easy on slippery surfaces   Seems strange I wouldn't get an idiot light if they were malfunctioning.  The abs light in the dash comes on for a few seconds when I start the engine just like it should. Fuses are good.

In normal driving conditions it's not a huge deal, but in the snow going down hill it's bad news.

 

[miesk5]

yo, For posterity;

RABS Overview; "...The Rear ABS is what is called an "open" hydraulic system. When an ABS stop is initiated and wheel lock is detected, the isolation or inlet valve closes, preventing any more fluid from going to the rear wheels. Then, if necessary to prevent lockup, an outlet or dump valve opens to bleed fluid out of the rear brake lines. That fluid goes to an accumulator and is held there for the remainder of the stop.In RABS "open" system, if there is a low fluid condition and the red warning light comes on, the ABS electronic control unit will detect this condition, turn the amber ABS warning light on and disable the system. The vehicle operator will still have basic brake system performance, but the benefit of RABS is lost.The reason for disabling the RABS is that the low fluid condition could be caused by a leak in the brake system, decreasing its performance..."
Source: by Ford

RABS Self Test & Diagnosis Codes; "...The possible flashout codes are listed and explained in the Flash Codes Chart. Note that Codes 1 and 16 are not used. Flashout Codes Whenever the yellow REAR ABS light comes on during normal operation, a flashout code may be obtained to aid in problem diagnosis. If the vehicle is shut off before the code is read from a RABS-I module, the code will be lost. In some cases, the code may reappear when the vehicle is restarted. In other cases, the vehicle may have to be driven to reproduce the problem and, if the problem was associated with an intermittent condition, it may be difficult to reproduce. Therefore, whenever possible, it is recommended that the code be read before the vehicle is shut off. RABS II modules have been designed with Keep Alive Memory to preserve stored codes during key-off, and are to be used to service all prior year RABS I systems, except for 1987 and 1988 Bronco II vehicles. WARNING: PLACE BLOCKS BEHIND THE REAR WHEELS AND IN FRONT OF THE FRONT WHEELS TO PREVENT THE VEHICLE FROM MOVING WHILE THE FLASHOUT CODE IS BEING TAKEN. NOTE: If the red BRAKE light is also on, due to a grounding of the fluid level circuit (perhaps low brake fluid), no flashout code will be flashed and the REAR ABS light will remain on steadily. NOTE: If there is more than one system fault only the first recognized flashout code may be obtained. Obtaining the Flashout Code A flashout code may be obtained only when the yellow REAR ABS light is on. No code will be flashed if the system is OK. There are certain faults (those associated with the fluid level switch or loss of power to the module) that will cause the system to be deactivated and the REAR ABS light to be illuminated, but will not provide a diagnostic flashout code. Before obtaining the flashout code, drive the vehicle to a level area, and place the shift lever in PARK for automatic transmissions and NEUTRAL for manual transmissions. Notice whether the red BRAKE light is on or not (for future reference) and then apply the parking brake. If a RABS(-1) module is installed, keep the ignition key in the ON position so that the code will not be lost. RABS II modules have been designed with Keep Alive Memory to preserve stored codes during key-off, and are to be used to service all prior year RABS I systems, except for 1987 and 1988 Bronco II vehicles. WARNING: PLACE BLOCKS BEHIND THE REAR WHEELS AND IN FRONT OF THE FRONT WHEELS TO PREVENT THE VEHICLE FROM MOVING WHILE THE FLASHOUT CODE IS BEING TAKEN. To obtain the flashout code, locate the RABS diagnostic connector (with the Bk/Or wire), and attach a jumper wire to it. Momentarily ground it to the chassis. When the ground is made and then broken, the REAR ABS light should begin to flash. NOTE: If the red BRAKE light was on (as noticed before the parking brake was applied), the problem may be with the low fluid level circuit and, in this case, no flashout code will be flashed and the light will remain on steadily. The code consists of a number of short flashes and ends with a long flash. Count the short flashes and include the following long flash in the count to obtain the code number. For example, three short flashes followed by one long flash indicates Flashout Code Four. The code will continue to repeat itself until the key is turned off. It is recommended that the code be verified by reading it several times. In addition, the first code flashed may be too short because it may have been started in the middle. It should be ignored..."
Source: by Steve

http://www.supermotors.net/vehicles/registry/media/280857

 

[mickreed]

Thanks miesk5, that helps some. The thing that seems weird and the reason I can't pull codes is that the ABS light is not on so there are no codes to pull.  Like I said the ABS light comes on momentarily when I start the rig, I assume it does some sort of self check.

I'll keep digging.

 

[Seabronc]

Anti lock brakes let loose when they detect the wheel is not turning as in skidding which will allow the engine to turn the drive shaft and if your front brakes are locked it will have a tendency to put your rear wheels up front.  I'll bet you that if you slammed the brakes on while driving on a dry surface you would feel the characteristic chatter of the antilocks.  If your rear brakes drums are out of adjustment they will not stop the wheel from turning and your antilock system will not think it has anything to do.  Slippery snow covered surfaces is just where these problems show up.  You will most likely never detect the problem on dry surfaces.  Stock bronco brakes are famous for this, they are not the best brakes in the world, especially for a vehicle as heavy as the Bronco.  The rear brakes are also famous for not staying in adjustment,  it may be that the rear drum hardware needs a complete cleaning and even new parts.  Get them serviced and adjusted and the problem may go away for a while.  I still recommend 4x4 as a means of preventing the problem on slippery snow covered roads.

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