abs problem with new hubs

[60ratrod]

ok so i replaced both of my front hubs on my 01 tahoe since they were making humming noises. but now my abs does one of two things, its over active when braking and slowing down at 20mph and slower with the light off, or its inactive and i have normal brakes at all speeds with the abs light on. this all started when i replaced the driver's hub. since it started there i replaced the new speed sensor with the old sensor off the old hub since i knew it was good. no change. i did inspect the reluctor ring on the inside of the new hub for any damaged teeth and there are none. but i did notice a couple things. the first is the old hub is packed full of grease where as the new one doesn't have much on the inside. is this or will this be an issue down the road? also, there was what looked like shims on the new hub under where the sensor bolts to the hub. could this also be an issue? i reinstalled the shims when i swapped in the old sensor since they came with the new hub, even though there weren't any shims on the old hub. i think my first course of action with this will be to remove the shims and take a piece of wire and measure the distance from the top of the teeth on the reluctor to the mating surface of the sensor and compare the old against the new. or is there something else that i should be doing?

[usmcchevy]

Removing the shims should do it. Just make sure the sensor dosent rub on the teeth. One time I managed to break one of the wires at the connector when I swapped hubs, so it might be worth it to inspect those.

[60ratrod]

Yeah i kinda figured the shims might be a problem after tooling around on gm's SI. I was trying to see if there was any diagnostic processes covering low speed abs actuation when i came across a bulletin about low speed abs actuation that's caused by corrosion forming under the wss mounting surface. I talked to my dad about it and agrees that the shims might be the problem and that i should measure the tooth to mounting surface distance
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[clinebarger]

What brand hub are you using....I have had this problem with cheap "house brand" hubs. I like ACdelco, BCA, & Timken.

[60ratrod]

Unmarked, white boxed ebay brand. Yeah nothing beats delco, but i was a bit on the broke side
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[clinebarger]

Originally Posted by 60ratrod

Unmarked, white boxed ebay brand. Yeah nothing beats delco, but i was a bit on the broke side
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Cheap bearings!

[60ratrod]

well i'll get the delco units when these die. but for the time being i'm going to fight this abs issue i gave myself with the aftermarket hubs til i either get it fixed or i resort to pulling the abs fuse. at least with the hubs i'm only $106 in the hole.

[60ratrod]

I fixed the problem. It was a gap problem just like i thought. The issue was the new sensors are longer than the old sensors. The new sensors measure at 18.99mm, and the old sensors measure at 18.32. So what i did was i removed both shims from the driver's hub since i reused the old sensor and used one .20mm shim under the passenger sensor. The new sensors are too long for the hubs and will rub with out any shims. Otherwise the new hubs measured the same as the original hubs. So it was an issue with the sensors, not the hubs
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[C10-Driver]

I'm having the same problem... I haven't had time to deal with it lately but I it sounds like you have it figured out for me.

[60ratrod]

yeah, if they are the original hubs then check for corrosion under the speed sensor as per the tech bulletin. if its a new aftermarket non delco unit then measure the speed sensor and see if there are shims under it. the original sensor measures at 18.32mm. the new ones on the random ebay white box hubs measured at 18.99mm, which is too long without shims, and will rub on the reluctor ring. what i also did was measure the thicknesses of all the shims and installed the one that measured out at .20mm, which was just enough space for the sensor not to rub and the sensor to work properly. here's the gm bulletin that gave me the idea, straight from their service information site:


Condition
Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set.

Cause
The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface.

Correction
Measure AC voltage and clean the wheel speed sensor mounting surfaces.

Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in the General Information sub-section of the Service Manual.
Disconnect both the front wheel speed sensor connectors at the frame and harness.
Place a Digital Volt Meter (DVM) across the terminals of each wheel speed sensor connector.
Rotate the wheel clockwise approximately one revolution per second. The minimum reading should be at least 350 ACmV's. If the reading is less than 350 ACmV's, remove the wheel speed sensor. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual.
Plug the wheel speed sensor bore in order to prevent debris from falling into the hub during service.
Clean the wheel speed sensor mounting surface using a wire brush, sand paper, emery cloth, scotch brite, or other suitable material. Be sure to thoroughly clean the wheel speed sensor surface. There should be no rust or corrosion.
Check the sensor head to determine if it has been warped/distorted due to the corrosion build up or other causes. Check the mounting surface on the sensor head for flatness by placing it on the edge of a metal machinists scale or other suitable straight edge to measure the flatness. Check the sensor for flatness in multiple (minimum 3) positions/directions. If the sensor head is distorted, replace the sensor.
Apply (spray) two thin coats of the specified rust penetrating lubricant (corrosion inhibitor) to the complete sensor mounting surface on the bearing hub. Allow to dry for 3-5 minutes between coats. Use ONLY Rust Penetrating Lubricant, P/N 89022217 (in Canada, P/N 89022218).
When the corrosion inhibitor is dry to the touch (about 10 minutes), apply a thin layer of bearing grease to the hub surface and sensor O-ring prior to sensor installation. Use ONLY Wheel Bearing Lubricant, P/N 01051344 (in Canada, P/N 993037).
Install either the original sensor or a new one in the hub. Ensure that the sensor is seated flush against the hub. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual.
Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel. The voltage should now read at least 350 ACmV's.