ABS problem.

[Phoenix0783]

I've searched but I couldn't find anything, so...
I have an early '95 with a 351. Everything was working great until I replaced the front rotors. Now it stops fine until I'm down to about 15mph and then the abs system goes crazy and it barely slows anymore. I'm thinking I put the exciter ring for the abs back on the hubs too far and the sensor isn't picking it up very well. The haynes manual said to just put them on. So for now I unplugged the abs actuator thing just to get the brakes working. Ideas?

[SigEpBlue]

I did the same thing when I replaced one of my hubs, and experienced the same thing (fun, isn't it? ). Many companies, for some reason, are making the ring shoulder too deep, so the signal from the front wheel ABS sensor becomes very weak, and the ABS assumes that the wheel has locked, hence the truck starts doing the Charleston upon stopping.

Check the ring-to-sensor clearance. It's got to be the same as the other side, as that's how the ABS module senses speed differential between the wheels, and less than 0.070-inch.

This is from the Ford service CD:

L4 CHECK LEFT FRONT BRAKE ANTI-LOCK/LEFT FRONT BRAKE ANTI-LOCK SENSOR INDICATOR SENSOR AIR GAP


l Remove the left front brake anti-lock sensor from the wheel end.

l Inspect mounting boss and sensor mounting plate for any metal flash or debris. Clean as necessary.

l Remount left front brake anti-lock sensor securely.

l Measure the air gap between the sensor and tone ring teeth. Repeat in at least two more wheel positions to ensure that gap does not vary as the wheel is turned.

NOTE:
Feeler gauges can be mounted to a welding rod and inserted between the vanes of the rotor to measure air gap precisely.

l Is the gap consistent and less than 0.070 inch?

Yes
REPLACE left front brake anti-lock sensor. GO to «L5».

No, gap is greater than 0.070 inch
Air gap is too large. REPLACE left front brake anti-lock sensor indicator. Here, you'd just move the exciter ring inward, closer to the sensor, instead of replacing the sensor indicator. GO to «L5».

No, gap is not consistent
Left front brake anti-lock sensor indicator is not pressed on straight or axle end play is too great. GO to «L6».

[Phoenix0783]

That sounds like fun...

Thanks for the info!

[TheNorm]

I've had the same issue for over a year. Finally disconnected the ABS fuse. It's time for new rotors and I want to fix all of it if possible.

Took a look at the sensor to ring clearance... at least 3/16" (!!)

Oh, couldn't find a feeler gauge (4th or 5th set loaned out...) but it turns out a hack saw blade is about 0.075". Grind off the teeth, then a little more and it fits in the rotor vanes.

Going to fix it tomorrow and will post how it turns out. Thanks for the data on that!

[TheNorm]

Great Success.

I pulled the Warns, then the rotor/hub assembly. Punched out the lug bolts, pulled the toner ring (which was pushed all the way to the machined shoulder stop on the hub, and INCORRECT for proper ABS sensor spacing) and replaced the rotors.

I put the toner ring back on, and left the top face even with the top edge of the hub. That was TOO LITTLE clearance to the ABS sensor. I just kept fitting it and tapping the toner ring in carefully until I had about the right clearance.

I'm pretty sure on both sides I was a little on the high side of the needed 0.07" clearance. I'd say around .085" or so. There's going to be variance anyhow since I used a hammer to tap the ring in instead of a square press.

Just as I finished it started raining... perfect test platform. With the ABS fuse still out, I was able to skid easily on the wet road. I let the pads set a little and then put the ABS fuse back in. Test drove it and the ABS works perfectly... nice even stops, ABS kicks in as needed.

Finally, I pulled the dash and re-installed the ABS warning light. It comes on and goes out as it should.

Lastly, I guess I'll pull codes, though I can't recall if this is part of the OBD or not...