Changing the ring and pinion going to create drama?

[72timemachine]

My friend has a 2006 Chevrolet 1500, 2wd with the 4.3 engine mated to a stock manual transmission. He wants to install a higher gear ratio with limited slip.

He had the original ring and pinion fail a while back and kept the old parts. Not sure if we figured it out correctly but I believe his original numbers from off the ring gear calculated to 3:23. He tells me the truck loaded with his tools is a real dog off the line but is great on the freeway.

The question is, if he replaces his ring and pinion to let's say a 3:73, will the ecm recognize this change and start storing trouble codes? Will the odometer need to be re-calibrated?

Thank you for any help.

[hatzie]

The VSS signal is folded spindled and mutilated by the PCM and the PCM feeds the results to the instrument cluster over the serial databuss.

He will have to change the PCM and ABS computer calibration to match the tires and axle ratio.

I know you can change the tire size in the ABS computer with a Tech 2 I'm not sure if you can change the axle ratio with the Tech 2 or if you have to get a new calibration from GM.

HP Tuners or something similar is needed to mod the tire size and axle ratio in the PCM.

[72timemachine]

Thank you for the information, I feel smarter now, keyword "feel". I will tell my friend to start saving his money if he decides to press on with this endeavor, personally I would get a different truck with a bit more grunt but that's just my personal taste.

Thank you.

[hatzie]

I've done some more reading about the ABS computer and gear swaps.
It will definitely upset the ABS computer and the Tech 2 can't fix it.

You need a pinion reluctor ring that matches the new gear ratio so that the two front and single rear ABS speed signals match.

Not enough thought went into the rear axle ABS sensor system design. The front pickups are in the wheel bearings. They're the same regardless of the gear ratio in the front axle and they are the same on both sides. One part multiplied over millions of trucks.
With the pickups on the pinion they have to be specific to a gear ratio set. If the engineering guys had thought about reducing differing parts they would've put the pickup ring between the ring gear and the carrier. This would be on the output side of the gears so the signal would match the wheel speed no matter what gears are in the axle.

A tuner (your software & hardware or a shop) should be able to set the axle ratio and tire sizes in the PCM and a Tech 2 or MDI with GDS or Tech2WIN can set the tire size in the ABS computer.

[72timemachine]

Thank you for the update on what can now be called, "mission impossible". Well that's unfortunate, seems GM sorta shot themselves in the foot on giving customers the option to easily change their gearing preference.

Thank you for all of your help, I am now off to tell my friend it's v-8 time...no offense to the v-6 crowd out there, Formula 1 engines are pushing a 1000 hp.