Well I have 4.88 gears ordered for the rear of my 2WD to compensate for the 37" tires. I have been doing a lot of research the past couple weeks to find a solution to the ABS light problem, and think I have found it. I too called Hypertech, and their programer does not cure the problem, as I doubt anyone's would after understanding the problem.
I'm not a professional mechanic, but here's how I understand this system: You have baically 3 speed sensors - the 2 ABS wheel speed sensors in front (1 at each front wheel) and the rear vehicle speed sensor (VSS) at the rear of the transmission. All three are monitore constantly and compared to each other.
If all you do is change your tire diameter, you will not get an ABS error, because although the sensors are turning at a different speed now with the bigger tires, THEY ARE ALL READING AT THE SAME SPEED. The speed will be wrong however, and this is why the speedo is off.
The big problem occurs when you re-gear the rear end, because what happens is now the driveshaft is turning faster at a given speed than it used to (which is what we want it to do - raise our rpms back up) and so THE REAR VSS READS OUT A SPEED DIFFERENT FROM WHAT THE FRONT WHEEL SPEED (ABS) SENSORS ARE READING - THIS MISMATCH IN SPEED IS WHAT IS CAUSING THE ERROR. The Hypertech or probably any other programmer will not be able to correct this as it can only modify the signal going to the speedometer to change the speed shown - it cannot do anything for the mismatch!
So what the hell can be done about this mismatch
Thankfully, there appears to be an answer. A company called Abott Enterprises makes a product called the "Abott Electronic Ratio Adapter". I bought one through Mike at THE TOY SHOP in Pomona, CA (909-620-5849). They specialize in gearing and tranny work for Chevys. The adapter splices in to the purple wire going into the VSS fitting on the rear of the tranny. There is 1 green and 1 purple wire - Mike says the purple is the one to use. You also need to run 1 wire to ground and one to a ACC power lead. Inside the adapter is a group of 12 dip switches. By altering the setting of the dip switches, you change the electrical current going to the rear VSS, and this changes the mph reading to match what the front wheel speed sensors read, and Bingo - no more ABS light!
The adapter comes with a booklet of the various dip swithes and the corresponding ratios they represent. The adapter wasn't originally made for these gear changes, so they don't tell you how to figure out the right settings - but I figured it out simply enough given some numbers Mike gave me for typical gear ratios. Basically all you do is take your stock ratio (3.73 in my case) and divide by the new ratio (4.88 in my case again) - this gives you the ratio for the adapter - in my case again this would be .765 (the adapter ratios vary in increments of .005). For 4.56 gears the ratio would be .820, which is what Mike used for a recent truck he did.
Now it would be great if it worked right off the bat like this, but with variables like they are, sometimes the ratio on paper doesn't equal out the speed to the sensors and you have to go up or down to get them matched up perfect so the ABS light goes off. The IDEAL way to do this is to hook up a TECH-II scanner to your truck, which will give real-time readouts of both the front wheel speed sensores and the rear VSS. If you are still 2 mph off, you just change the ratio with the dip switches and go for another drive - repeat untill the rear speed matches the front and you're good to go. Don't bother with the scanners you see on Ebay - they only read the rear VSS and nothing else. You need the TECH-II scanner or equivalent to read the front ABS sensors. The dealer has these scanners, and maybe some other shops do to - they are expensive - around $2500 I'm told.
The second option is what I'm gonna do, 'cause my dealership sevice personnel are A$$holes. They wanted $92 just to hook up to my truck and turn off the seatbelt warning chimes, AND refuse to honor my truck's warranty untill I send my SS instrument cluster to California to get the odometer miles transferred from the stock cluster. Said my warranty is void right now because my odometer is off, even though I coudn't possibly put 36,000 miles on my truck in 7 weeks since I bought it - but I digress. Since I will never give them business again, and know they won't help me with the TECH-II scanner, I'm going to use the trial and error method. I'll set the adapter to the proposed setting, and drive for 3-4 miles (it takes 3-4 miles of driving around to trip the ABS error light, because if it was instant, every time you went around a corner or spun the rear tires it would go on). If no ABS light great!!!! If so, shut the truck off to clear the light, change the dip switch settings to the next ratio, and repeat. Mike just had a truck that required a ratio of .870 for a 4.56 setup to eliminate the light - that's 10 settings away from the proposed setting of .820 . So it might take me a while, but I'll get it and I won't need the $2500 scanner or the A$$HOLE dealer.
Now - one more thing - all is not hunkie-dorie yet!
This modification will trigger the check engine light for some reason due to the speedo still being not calibrated. This is where the Hypertech or other programmer comes in - YOU WILL STILL NEED A PROGRAMMER TO CORRECTLY CALIBRATE THE SPEEDO AND GET THE CHECK ENGINE LIGHT TO GO OFF!!
Whew - sorry for the long post, but hopefully this will help a lot of us with this problem, and for those of you who have not re-geared due to hearig about this, you now know there is a solution and can go ahead with the re-gearing, which should dramatically restore lost power and transmission life that is lost with taller tires!
I'll keep you posted as I go - gears SHOULD be here within the next week.
Doc
I'm not a professional mechanic, but here's how I understand this system: You have baically 3 speed sensors - the 2 ABS wheel speed sensors in front (1 at each front wheel) and the rear vehicle speed sensor (VSS) at the rear of the transmission. All three are monitore constantly and compared to each other.
If all you do is change your tire diameter, you will not get an ABS error, because although the sensors are turning at a different speed now with the bigger tires, THEY ARE ALL READING AT THE SAME SPEED. The speed will be wrong however, and this is why the speedo is off.
The big problem occurs when you re-gear the rear end, because what happens is now the driveshaft is turning faster at a given speed than it used to (which is what we want it to do - raise our rpms back up) and so THE REAR VSS READS OUT A SPEED DIFFERENT FROM WHAT THE FRONT WHEEL SPEED (ABS) SENSORS ARE READING - THIS MISMATCH IN SPEED IS WHAT IS CAUSING THE ERROR. The Hypertech or probably any other programmer will not be able to correct this as it can only modify the signal going to the speedometer to change the speed shown - it cannot do anything for the mismatch!
So what the hell can be done about this mismatch
Thankfully, there appears to be an answer. A company called Abott Enterprises makes a product called the "Abott Electronic Ratio Adapter". I bought one through Mike at THE TOY SHOP in Pomona, CA (909-620-5849). They specialize in gearing and tranny work for Chevys. The adapter splices in to the purple wire going into the VSS fitting on the rear of the tranny. There is 1 green and 1 purple wire - Mike says the purple is the one to use. You also need to run 1 wire to ground and one to a ACC power lead. Inside the adapter is a group of 12 dip switches. By altering the setting of the dip switches, you change the electrical current going to the rear VSS, and this changes the mph reading to match what the front wheel speed sensors read, and Bingo - no more ABS light!
The adapter comes with a booklet of the various dip swithes and the corresponding ratios they represent. The adapter wasn't originally made for these gear changes, so they don't tell you how to figure out the right settings - but I figured it out simply enough given some numbers Mike gave me for typical gear ratios. Basically all you do is take your stock ratio (3.73 in my case) and divide by the new ratio (4.88 in my case again) - this gives you the ratio for the adapter - in my case again this would be .765 (the adapter ratios vary in increments of .005). For 4.56 gears the ratio would be .820, which is what Mike used for a recent truck he did.
Now it would be great if it worked right off the bat like this, but with variables like they are, sometimes the ratio on paper doesn't equal out the speed to the sensors and you have to go up or down to get them matched up perfect so the ABS light goes off. The IDEAL way to do this is to hook up a TECH-II scanner to your truck, which will give real-time readouts of both the front wheel speed sensores and the rear VSS. If you are still 2 mph off, you just change the ratio with the dip switches and go for another drive - repeat untill the rear speed matches the front and you're good to go. Don't bother with the scanners you see on Ebay - they only read the rear VSS and nothing else. You need the TECH-II scanner or equivalent to read the front ABS sensors. The dealer has these scanners, and maybe some other shops do to - they are expensive - around $2500 I'm told.
The second option is what I'm gonna do, 'cause my dealership sevice personnel are A$$holes. They wanted $92 just to hook up to my truck and turn off the seatbelt warning chimes, AND refuse to honor my truck's warranty untill I send my SS instrument cluster to California to get the odometer miles transferred from the stock cluster. Said my warranty is void right now because my odometer is off, even though I coudn't possibly put 36,000 miles on my truck in 7 weeks since I bought it - but I digress. Since I will never give them business again, and know they won't help me with the TECH-II scanner, I'm going to use the trial and error method. I'll set the adapter to the proposed setting, and drive for 3-4 miles (it takes 3-4 miles of driving around to trip the ABS error light, because if it was instant, every time you went around a corner or spun the rear tires it would go on). If no ABS light great!!!! If so, shut the truck off to clear the light, change the dip switch settings to the next ratio, and repeat. Mike just had a truck that required a ratio of .870 for a 4.56 setup to eliminate the light - that's 10 settings away from the proposed setting of .820 . So it might take me a while, but I'll get it and I won't need the $2500 scanner or the A$$HOLE dealer.
Now - one more thing - all is not hunkie-dorie yet!
This modification will trigger the check engine light for some reason due to the speedo still being not calibrated. This is where the Hypertech or other programmer comes in - YOU WILL STILL NEED A PROGRAMMER TO CORRECTLY CALIBRATE THE SPEEDO AND GET THE CHECK ENGINE LIGHT TO GO OFF!!
Whew - sorry for the long post, but hopefully this will help a lot of us with this problem, and for those of you who have not re-geared due to hearig about this, you now know there is a solution and can go ahead with the re-gearing, which should dramatically restore lost power and transmission life that is lost with taller tires!
I'll keep you posted as I go - gears SHOULD be here within the next week.
Doc
gears, so that should be fine for most of us.
Here it is: 
