I know my Anti Lock Device has gone bad and did get one at a junk yard today. I'm wondering has anyone installed one of these. I know I have to bleed it once installed. It has a line coming in from the Master Brake Cylinder and one going to the rear wheels. Should I bleed the Anti Lock first then move to the 2 rear wheels. Assuming that's the right sequence...

1987 F-350, 460 cu.in. No fuel injected.. Rear anti lock only.

 

The shop manual says to bleed right rear, left rear, RABS module. However some years ago I replaced the RABS module on my `87 F250 and was able to get great brakes just by bleeding the module.

 

Thanks for the reply. I just hope this is the fix to my problem. A pedal that slowly goes to the floor while sitting a traffic light. Talked to a mech. friend of mine and that's what he says it is. Think also I need to adjust my back brakes before bleeding this device.

 

A brake pedal slowly going to the floor sounds like a bad master cylinder in my experience.I had a 1980 Bronco,without RABSof course,that had the same symptoms you're describing.Replaced the master and all was well.The RABS light is always on in my '88 F250.Other than having to readjust my rear shoes(even with new hardware)every few thousand miles,they work OK.

 

Your friend doesn't have any idea what he's talking about. You need a new master cylinder.

 

A bad master cyl coul;d well be the problem but so could a bad RABS module. There is an easy mod you can do to the RABS module to eliminate it as a possibility before you replace it. Let me know if you want the info.

 

My friend is a Master Mech. and has been one for over 40 years. He had me do a test and don't remember the exact steps now because it was over 6 months ago. It because of the test it was determined it was the Anti Lock device. Think I'll go with the guy with the knowledge.

 

Yes I would like any info you have available.

 

The correct name for it is the RABS Hydraulic Control Module (HCM).
There are two solenoid operated fluid valves inside it along with a fluid dump chamber with a spring loaded piston.
When the speed sensor on the rear diff detects that both rear wheels have locked under braking, the computer closes one of the solenoid valves so that no more fluid can go to the rear brakes and opens the other valve so that fluid can flow from the rear brakes into the dump chamber and so unlock the rear brakes. The sequence is then reversed and repeated if the brakes lock again. When the braking is finished and the pedal released any fluid in the dump chamber is allowed to return to the resevoir under pressure from the spring loaded piston.
If the valve controlling fluid flow to the dump chamber is bad then fluid can flow into the chamber when the brake pedal is pressed, so giving a sinking pedal.
If you look at the end of the HCM you will see a large hex bung. Unscrew this bung (under spring pressure all the way) and remove the spring from the chamber (no fluid will come out). Replace the hex bung. Pump the pedal a few times to fill the chamber with fluid and then see if you still have a sinking pedal. If the pedal is good then the HCM is bad. If pedal still sinks then HCM was not the problem and you can replace the spring and look towards the master cyl as a problem.

 

check price on new master cilinder and do both of them and youl be way ahead.

 

not really Andy. the rabs module like used on the early trucks will give you that sinking feeling on the brakes also.
the only way i have found to get a solid pedal that does not slowly fall to the floor while sitting at a light is to eliminate the RABS module.

 

That's perfect info. Thanks, I will be dealing with this tomorrow. Let you know what I find out.

 

Learn something new everyday.Curious to see what the problem is.Thanks for the info LAZY K.

 

Rained all day today but will let you guys know what happens. Its important that people come back and tell their story on whether it worked or not.

 

Will be tackling this problem tomorrow. Will let you know what I find.