I own a 1997 F-150, V-6. I have a problem with the rear wheels locking up when I apply the brakes. At the moment I have to slowly apply the brakes so that it won't lock up. I had someone check it out and he said it could be two things: proportional valve or the worse case the ABS module. The module I understand is pretty expensive. In your opinion what should I do?

Thanks in advance for the help,

Regards,

Tommy Pietersz

 

Does it mainly happen first thing in the morning or any time?
Can you ever get the front brakes to lock up?
Can you ever get ABS activation on all 4 wheels at the same time?
Does vehicle speed have any factor?

I doubt that it's an ABS module, though there's a possibility for the HCU, small as that may be. Prop valve or lack of front brake activation is the most likely.

 

i have a 98 f-150 xl 4.2 with the same problem. i think it is because abs is only on the front and not on the back brakes.

 

Ford only makes 2 types of ABS, 4 wheel and rear only, thus I assure you that rear lockup is not due to no ABS on the rear wheels. Also, the hydraulics for base brakes and ABS originate from the same hydraulic control unit (HCU).

Since brake pads and shoes are hydroscopic (absorb moisture), rear lockup may be normal after letting the truck sit overnight when cold or damp outside. But after a few applications and the pads/shoes are warm, that problem should go away. So if the problem persists, it may be something else.

 

The problem persists during the day. I also noticed its not related to rain or cold. Even at slow speed it locks up. So if you're not carefull with the brakes, it will slam you forward into the steering wheel.
I can't get the ABS to work on all four wheels. The rear will always lock up.

Thanks for the help.

 

My friend has a 98' F-150. He has just started experiencing that rear brake lockup problem. It only happens when it is damp or rainy outside. I know a lot of the older models have had this problem for years. One fix was that there is a special tapered brake shoe that can be used on the rear brakes. (I am not sure if these are Ford shoes). I know this does not help everyone, especially those with low miles on there brakes but I kinda feel that it may be the nature of the beast. If it were a RABS problem, you may notice the pedal settle a little bit. The pedal may also seem a bit spongy. Just my experience.

Jakegypsum // Ford fleet, soup to nuts.

 

There is a TSB for rear brake lockup in high humidity or in rain, I believe its 99-10-07 (I recommended it earlier today to someone, but it may be 98 instaed of 99). It applies to more years than just those listed in the TSB, which I believe is 1997-99 , so it should already fall in.

It may be a proportioning valve for rear lockup at any speed and no front ABS activation, or just ineffective front braking (many factors can cause lack of fronts).

 

Thanks again for responding to my problem. I did some more analyzing. I just noticed I had a typo on the year, its a 1998 F-150 with RABS. Where I live its very dry and the temp. is around 80F. I don't think its the rear brake pads absorbing moisture.

My ABS light stays constantly on. My brake pedal feels mushy. When I brake, I have to gently start depressing the brake. And just a little. If I don't the rear locks up immediatly. It is extremely sensitive.
When I come to a complete stop, I have the brake just a little depressed. At that point I can depress it more and I hear a wooshing sound (and mushy feeling).
Under the master cylinder, if I'm not mistaken its called the proportioning valve (the rear brake line goes through this aluminum box and exits to continue to the rear). There is a wire plugged into this box. I disconnected it to see if I feel any change but it stayed the same. I think may because the ABS isn't working and so the rear locks up. I think it is either that valve or the module is defective. Sending the wrong pressure to rear.

Also if I by pass that prop.valve and hook up the line directly to the master cylinder (for the meanwhile until I get the problem resolved), will it work as a normal brake without ABS. Or will I still have the slam-in-the-steeringwheel rear lock up?

I appreciate any suggestion you can give with this problem.