ABS pump sensation?

I need some help diagnosing a new problem. I recently a rear axle seal replaced and have a new concerning issue after getting my truck back. I’m feeling what feels like a motor kicking on when I apply the brakes. It doesn’t happen every time and seems to appear towards the end of a longer slow down. Kinda like when approaching a red light when you’re not in a big hurry to stop. It happens right before you come to a stop. The sensation only lasts a couple of seconds, as soon as you try to figure it out, it’s gone. It seems to make a sound that sounds like a small motor/pump activating. I can definitely feel it though the brake pedal. Any help diagnosing this would be greatly appreciated.

 

IAC may be kicking on as your engine comes to rest. That can kick your RPMs up briefly

 

ABS?

 

If you find a slick spot or condition on the road, step hard on the brakes, even at moderate speed to see if you can get the ABS to engage. If it does, you'll be able to compare it with the sensation you are describing and be able to tell if they are the same.

 

No abs light on
It’s supposed to rain here on Sunday, so I’ll have an opportunity for some slick spot testing then.
Some more research has me looking at cleaning the speed sensor for the wheel that had the axle seal replaced.

 

This is usually caused by a bad, dirty or not properly installed wheel speed sensor.
We usually see this at work and when we look at the sensors, one is pushed out a little by rust.

 

Cleaned off the sensor, reinstalled, same issue with the pump. Gonna try some stops in the rain tomorrow to see if the abs kicks in.

 

Update- after cleaning and reinstalling the speed sensor, the problem is still there. Now it’s even more consistent. I unplugged the sensor and drove home from work, no abs pump activation! Abs light on. So I’m thinking this, with the sensor unplugged, light on(at least I know that’s working!) the system is not getting any information from that position, hence the light. Sensor plugged in, pump activating 7-4 mph because it’s getting the wrong information. My plan is to replace the sensor. One from oriellys is around $170. Factory Toyota is $250ish. Is the real deal worth the extra cash?

 

Before you buy a new sensor, look down into the hole that the sensor fits into, and make sure the toothed tone wheel is centered in the hole. If the tone wheel is pressed too far onto the axle shaft, or not far enough during bearing replacement, you’ll get this problem. And with the recent history, your most likely cause.

 

Roger that. I’ll check it out.

 

If you find you need a new sensor and you are going to buy aftermarket, try Rockauto. The prices for the various brands of wheel sensors they offer range from about $20 to $121. At those prices, and because the install is not difficult, it might be a worth foregoing the Toyota part.

 

Check the wire to the sensor for any nic's or damage along the length of the axle tube, and especially near the u bolts. Both sensors should run up to a connector on the drivers side frame rail just in front of the lspv. Open that connector up, and thoroughly clean it with electric contact cleaner, allow ample time for it to dry, and reconnect it.

 

Upon further investigation, the toothed wheel seems to be centered the same on both sides of the axle. That being said, it is positioned slightly towards the the inside, away from the wheel.

 

This is the drivers side.

 

That Tone Ring is close enough to center I’ve seen them further off than that and still work fine. plus replacing the seal would not cause the tone ring to move on the axle.
To move the tone ring would require putting the axle shaft in a press
The tone Ring does look a bit dirty I’m surprised they didn’t clean it off to get the gear oil off that being said a dirty Tone ring shouldn’t cause this issue.

 

This weekend I’m gonna clean the sensor better, instead of just wiping it off. I’ll double check all the wires then. It sure is nice having a bad ass support group like tacomaworld to help me figure this shit out, thanks guys!

 

Gotta update on the situation. I replaced the sensor with a Delphi unit from rock auto( thanks 1schoir)and went for a short test drive. Problem seems to be solved. A little more time will tell. My concern is this, when I removed the old sensor, it looked wet with water and some milky oil. Could water be getting to the area where the gear ring is? Any help would be greatly appreciated.

 

When was the last time you changed the rear diff gear oil?

The diff has a vent on it, which water can get into if it's failed. They usually clog though and lead to the axle seals blowing out and letting the gear oil get to the tone ring. Sounds like you're due to for some new axle seals at a minimum. The axle seals are actually a pretty DIY friendly job.

 

Well, it was actually the leaking passenger side getting replaced that started this whole journey. I guess next thing on the list is checking the vent tube. I’ve been meaning to get around to changing the diff/transfer case fluid for a little while.

 

Pull the drum off on the side that looked wet see if any gear oil has made its way past the seals and through the bearing.
Might need a seal on that side also.
Check the axle vent make sure the top part spins freely if it’s stuck or plugged it could cause the axle to over pressure and leak past the seals.