just an update. some time back had a chance to work on this again. both my toner rings were not installed true, i.e. they "wobbled" significantly when rotated. in addition, one was touching the lug bolts on one side and the other side was virtually the same, but not as bad. lastly, both sensors are still around 80 thousandths from the toner ring.

i finally got a hardware/software combo that allow me to track the 4 wheel speed sensors (scanxl pro). i had taken it in to the gm dealer to have them put their tech2 on it but they were far from helpful (after $120). anyhow, at around 70 mph, without fail, the abs system throws an error, typically because 1 or both of the rear sensors are reading at least 2-3 mph more than the front 2 sensors. and around 75-80 mph i'll see 1 or both of the sensors sporadically actually drop to 0 mph! so, don't know what to do next. i've replace both sensors, switched them side to side, etc. guess i'll keep fooling with the toner rings. i wish i could figure out a way to get the sensors closer to the toner ring and decrease the gap to 40 thousandths or so.

and yes, the sensors are parallel to the ring.

i would like to see a few good pictures of a stock 4 ch setup with some measurements of sensor to toner ring, sensor to lug bolts, toner ring to lug bolts. might help me figure out what to do.

wouldn't ya know it. after i posted above i drove home from work about 50 miles and NO malfunction lights came on. and again this morning i drove back to work 50 miles and NO lights. first time in 1 year (3000) miles it's worked. weird. hope it continues!

since both rear sensors went to 0 mph sporadically at about the same time it seems like it must be a wiring issue or maybe a problem with the ebcm. it is strange that it waits till 70+ mph before acting up tho. would air in the brake lines cause any weird issues like this. although the brakes feel fine maybe i didn't get them bled completely after the rear end change.

just random thoughts. anybody have some input?

Air in brake lines (if present) will not cause ABS to just activate while not on the pedal. From my experiences when I worked for GM most of the issues like people are describing here are caused by faulty connections, corrosion within the harnesses, or problems with the EBCM.

If the reluctor rings are not in contact with wheel studs, running true, the sensor gap is correct and covering the reluctor ring properly, there is no reason for the system to have any issues with producing the correct voltage. Air gap between the sensor and reluctor ring is crucial.

Keep in mind the wheel speed sensor is just an electro-magnet... they can become weak over time.

ok - i am going to look at the entire wiring harness again just to see if there may be a faulty/loose connection. both are new sensors. the fact they both go to zero reading at approx the same time really points to wiring, although i don't understand why it seems to be triggered at 70 or higher. moving the sensor closer to the ring seems like it would be hard to do, at least for me. have to grind on the axle and sensor hole to get it to slide closer?!

Subscribing. About 475 miles into my 500 mile break in I got the ABS INOP light. Had code pulled and it was showing Left Rear Wheel Speed Sensor. Seems to go in and out. Only been on the expressway a handful of times, but I seem to get the LOW TRAC light also. Usually seems to happen when I downshift and hit a WOT run.

is it tied to a specific mph range?

What are the clearance specs for the sensor to wheel?

based on what i have read it should be around 40 thousandths (sensor to toner ring). however, i have not seen a specific gm spec regarding it. would like to have someone measure their stock 10 inch with a working 4 ch.

btw. put on another 75 miles today in lots of speed ranges. still no lights. amazing (and thankful!!)

Was your only change fixing the alignment of the reluctor rings? I'm pretty sure that's what my problem is. Rings are seated on too far, almost touching the axle stud bolt heads on both axles.

yes, 2 things:

1) too far on the flange, ie. 1 was touching the lug bolt heads and the other was almost touching, and
2) they were "twisted", ie. when spinning the wheel the ring would move in and out. i just placed a gauge on the toner ring and used a chisel to pry the ring on the flange to true it up.

i'm still concerned about the sensor gap but don't know how to fix it at this point. no real adjustments for that on the backing plate.

they could have been my problem, or it could have been wiring, or .....

Were you able to adjust the rings on car or did you have to pull the axles and remove/reinstall the rings?

on the car, easy to do. remove wheel, unhook ebrake from bracket and swing down over hub out of the way, and pry (gently) in whichever direction you need to go. obviously you'll need some type of stationary gauge to measure the "trueness" of the ring while you spin the wheel. then tweek it to make sure the wobble is removed as good as you can.

Man, so I drove ~ 340 miles round trip to Dayton for Trans Am Nationals last weekend. Low Trac light going off and on the whole time. It would stay off for anywhere from 2-5 minutes, then come on for about 7-8 seconds, just enough to shut off my cruise control then go away. I would just hit resume on the cruise and it would go, but 2-5 minutes later it did it again.

I had MWC assemble my rear and just swapped over wheel sensors. Are they really just that sensitive that it needs to be measured within 40 thousandths between sensors/ring?

i've had my drag radials on for the last few weeks so haven't had a chance to see if my problem has gone away for sure using the stock wheel setup. since the drag radials are oversize it will always turn on the lights.

don't know how sensitive the sensor/ring distance is. unfortunately, if you are out of spec (whatever that is!) there is no easy way to adjust it. the only real easy adjustment is the ring trueness itself and the distance from the wheel studs.

So has anyone thought about just installing a rear that doesn't have TCS provisions? I'm looking to order my 9 inch in the next few weeks and I'm really considering just doing away with the tcs all together as a lot of you guys seem to be having quite a few headaches with it after you swap rears.
I know I lose ABS if i were to do this, but would there be any other consequences?

You can buy an abs delete kit. I've considered that myself but am going to try adjusting the rings first, if I ever get time

I looked at adjusting the rings and it didn't help. They were true so no reason to mess with them. :-(

btw - my abs lights came back on again before i parked the car for winter. i'll be getting it out again in a couple weeks and look again at the problem. maybe order a new sensor or two again. frustrating &*?!!**!!

I have been following this for a while now and thought i would chime in. I am not bashing any company. Let make that very clear. I am simply sharing an experiance and stating the facts. I had a problem and Midwest made it right. I had a 9 inch from Midwest and had the same problem. i called and complained and he told me it was the reluctor rings. so i orderd new rings and bearings and had them installed. 290 dollars later it didnt fix the problem. i then called him back again and told him that it was in his housing and that the tube must have been welded incorrectly. he told me it wasnt possible but bring the car to him and he would look at it. so i trailered the car 2 and 1/2 hours each way and he tried to fix everything but the rear because he was sure that it was perfect. we changed harnesses,abs modules,speed senors, measure od of wheels. i did my research and found that the left rear reluctor ring had 20 thousands more air gap than the rr and was causing my low trac light to come on at 60-80 mph and my abs to start coming on like i was on ice at 85mph. This is simple math as well. if you have twenty thousandth more air gap on one side than the other then the voltage created will not be the same. Thus throwing false codes. so long story short i wasted days off of work and several hundred dollars to fix an air gap problem you cant fix. Now you also need to double check that the bolts holding the backing plate on are all ground down enough not to lodge the backing plate one way or the other. (we found this was the case on mine) it help the issue but didnt fix it. the only way he could was to grind down the backing plate and move the sensor closer to the reluctor ring. which isnt the right way to do it. so he bought me a strange 12 bolt for a stait up exchange. 3300 for the 9inch with all the options and 2700 for the 12 bolt. you do the math. I have had no issue with the 12bolt and have used all of the original factory parts. Midwest is a good company to work with and stood behind thier product and made it right. just do your homework, put the facts together, and call him. If you dont think i am correct put your ten bolt back in and check for yourself.

wow, just wow. i was told the same thing - that there is no way the rearend can be wrong. hmm.

do you recall what your air gaps were? the last thing i had tried was machining part of the actual plastic sensor housing to see if i could get it to slide closer to the reluctor ring. it seemed like it might have worked for a bit but as you can see in my latest posts the problem came back. my next thought was to try to actually machine the rearend backing plate and housing to allow the sensor to sit closer. i'll probably try that this spring and buy a couple new sensors again to rule out any chance i may have damaged them trying to get it to work.

i am NOT going to reinstall my 10 bolt. its a problem i can live with if i have to. i love the looks of the mwc rearend and it has worked flawlessly in all other respects.

btw - i assume you kept your 4ch abs with the strange 12 bolt?