95 SR5 4x4 ABS Question

I recently replaced the left front wheel bearing on my 95 Tacoma. It drives smoothly now and is quiet.

However whenever I brake now, I can hear (and feel in the brake pedal) the ABS system activating as I slow to about 5 mph. Otherwise everything seems fine. The ABS light is not on.

When I picked up the knuckle from the machine shop, I did not look to confirm that the tone ring was positioned correctly (to be opposite the sensor). So I guess my question is... if the tone ring was put on the wrong end of the bearing and the sensor therefore is not reading anything, would that create the symptom that I have?

If not, how do I approach this problem?

Note: I did not remove the sensor from the knuckle as I feared breaking it. I unplugged it under the hood and kept the wire attached.

 

I can think of two things off the top of my head, please dont take any offense, it seems that there is tension on the boards these days... anyway, does the ABS light illuminate during the bulb check portion of the start cycle?
I would take the 60 amp ABS fuse out and drive her around to see if it is actually the ABS system you are feeling. Not doubting you, just trying to verify the complaint.

If the ABS sensor is too far away from the tone ring, or has crap on it or is damaged a false positive could be induced. Both sine waves from the front ABS sensors should be pretty equal in amplitude and frequency. Any difference and the ABS ECU reads this change in the spinning rate (frequency) between the left and right wheel and bleeds pressure off that brake line.

 

This.

Your description would make me look at the caliper/pad/rotor condition / operation first. And it certainly costs nothing to do that while you are in there checking things out.

 

Hi - and thanks for the reply.

Yes the ABS lamp lights during bulb check.

Ok I will pull the fuse and drive it - altho I am 99% confident of what is happening. But it's good to verify.

Unfortunately I was not there when the machine shop did the work. But they are an experienced shop with a good reputation and I spent time with the manager going over the process before leaving it with them. It's possible that there is crud obscuring the sensor, but I have no way to check that.

Does it make sense that this only happens as I am slowing and almost to a stop?

 

It's not a caliper / rotor / pad issue as far as I can tell.

It's that distinctive pulsing of the brake pedal and the sound that comes from the ABS unit on the right (opposite) side of the truck. I'm pretty familiar with it.

 

Ah. Significant.

But, the tack @Glamisman suggests will certainly help verify. Let us know what you find. For the good of the order and all that.

 

Ok I pulled the ABS fuse.

The ABS dash light is now on all the time. Braking is smooth and normal now.

 

Ok so it is an ABS issue. The system is too simple in operation for a difficult diagnosis. eek... I just looked up the price of a wheel sensor, $200. That rules out the cheap test of trying a new one. I guess we are back to a possible misinstalled reluctor ring. It looks like the reluctor ring should be pressed on with the "cup" facing inwards. Not sure if it can be installed backwards.

 

I don't think the ring can be installed backwards unless the spacer is also put on wrong. These guys at the shop were very particular about everything, but mistakes can happen of course.

Yeah I had tried pricing a new sensor before I decided to leave the old one in - but I couldn't find one anywhere at any price. Where did you find one for $200?

I suppose I could pull the knuckle out and do what I should have done the first time - eyeball the ring to make sure it is lined up correctly with the sensor. I could also try to remove the sensor to see if there is dirt or debris inside? But I don't know if I can get it out without destroying it.

I had unplugged the sensor at the connector under the hood. Everything looked ok but I could separate that connector and make sure everything is clean.

What bugs me about this symptom is... why only at 5mph??

 

I went back and re-checked... yep you are right, the speed sensor my search returned was for 2WD not 4WD.
I think you can get that wheel off the ground and look between where the axle meets the bearing and spin it to see if it looks ok or wobbles or? The 5mph thing is confusing.

 

I have run into a kinda similar scenario on a different Toyota. Was after guy that had work done at a iffy reputation shop and he just heard I was Yota enthusiast is all, he's a friend of a family member. Anyways, I unbolted and pulled the ABS sensor at the hub and found the sensor had a little bit of grease or crap on it. Didn't think it would change anything and maybe it didn't. But after cleaning it off and looking through sensor hole with flashlight and spinning the tire while watching the hole and verifying its all clear I reinstalled sensor and that slight ABS style of pulsing went away they said. Never heard anything more on that one. The sensor does have to be able to pick up the tones clearly from the tone ring. Hope you're not needing a new sensor. I have had to replace one of those only once on a customer's Corolla.