Swap rear 3.08 gears for 3.42

[HeidiHoe]

Hello all, I just picked up my PPV. It has smaller tires than the civilian models and I have a set of 275/55R20 michellin defenders to replace them. To keep the computer happy and maintain an accurate speedo I would need to change the 3.08 gears to 3.42. Question is should I purchased a new gear set and all the related bearings and seals or swap out the entire rear with a rear end from a wrecker yard?

 

[gooffeyguy]

What size tires are on it now? As long as the overall tire diameter stays pretty close you'll be ok.

As a cheaper alternative to a rear gear change, Just about any handheld tuning device (Diablo, etc) will allow you to input tire size so it will adjust the speedo and trans accordingly

Sent from my SM-G930V using Tapatalk

 

[OR VietVet]

Welcome to the forum from Oregon. What @gooffeyguy said about tire diameter and the reprogramming. If you choose the other way, a low mileage entire rear diff is pretty easy to swap out and bleed the brakes on.

What surprises me is that a PPV would have such a high 3.08 gear in it.

 

[iamdub]

What surprises me is that a PPV would have such a high 3.08 gear in it.

It's cuz of the 6L80.

 

[HeidiHoe]

What size tires are on it now? As long as the overall tire diameter stays pretty close you'll be ok.

As a cheaper alternative to a rear gear change, Just about any handheld tuning device (Diablo, etc) will allow you to input tire size so it will adjust the speedo and trans accordingly

Sent from my SM-G930V using Tapatalk

What size tires are on it now? As long as the overall tire diameter stays pretty close you'll be ok.

As a cheaper alternative to a rear gear change, Just about any handheld tuning device (Diablo, etc) will allow you to input tire size so it will adjust the speedo and trans accordingly

Sent from my SM-G930V using Tapatalk

The tires used by law enforcement people are winter rated uhp tires sized 265/60R17. Also, according to a large GM service center, the PPV tahoe's computer is locked and they can't make any changes so going the civilian tire size would through off the speedomter at the least. Swapping the gears and tires would match the original set up

 

[HeidiHoe]

It's cuz of the 6L80.

The 6L80 first gear is 4.03, combined with the rear gears of 3.08 and a relatively small tire makes for decent acceleration.

 

[gat0r]

i doubt the ECM is locked. that sounds lazy on that "service center's" part. more likely they dont want to figure out what all the upfitter may have done.

will be interested to hear update on that.




eta:
the mechanic & a serv writer at my dealer tried to tell me my ECM was locked b/c of callaway. they would have to mail ECM back & forth if anything was to be done to it.

that was all B.S., i have worked w/ Blackbear to tune mine. no issues.

 

[iamdub]

The 6L80 first gear is 4.03, combined with the rear gears of 3.08 and a relatively small tire makes for decent acceleration.

Right. That's what I was telling Ron in that reply. It can have such a high rear gear and not be a slug off the line because of the 6L80's low first and second gears. 3.42s would make it noticeably stronger off the line.

 

[gooffeyguy]

I think a Tech2 can change the tire sizes.

Maybe post this over in the PPV/SSV section and see what those who own these say.

Sent from my SM-G930V using Tapatalk

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics, please.

IMO, a tune would be the best option for you, and you will get the additional advantage of getting your TCM tuned for better transmission shifting performance.

 

[HeidiHoe]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics, please.

IMO, a tune would be the best option for you, and you will get the additional advantage of getting your TCM tuned for better transmission shifting performance.

GM website regarding the PPV Tahoes says that the outfitter reprogramed the transmission to shift at higher rpms than stock. I havent put many miles on it yet and havent had an opportunity to stretch its legs yet

 

[HeidiHoe]

I think a Tech2 can change the tire sizes.

Maybe post this over in the PPV/SSV section and see what those who own these say.

Sent from my SM-G930V using Tapatalk

That is am excellent suggestion, thank you

 

[GoToGuyRon]

Hello all, I just picked up my PPV. It has smaller tires than the civilian models and I have a set of 275/55R20 michellin defenders to replace them. Hi, i did a research and math. Doing nothing with the 20's installed. Your indicated (speedo) at 55.5 mph, your actual speed of movement will be 60. Or conversely. The 17's at 65 mph, 2278 rpm. With the 20's , 2278 rpm will actually be 70 mph. So with larger diameter speedo will be 5 mph under. I did the math with your 3.43 regear. Not pretty unless your pulling stumps. Later

 

[Bill 1960]

Regarding your original question, the cost for the parts is similar whichever way you go, gears vs axle housing. Labor time isn’t much different either.

The advantage for a housing swap is most shade tree mechanics can do that in their driveway. Fewer people have the skills and tooling for a gear swap so they end up hiring it done.

The advantage for a gear swap is you end up with a known all new moving parts assembly, compared to the unknowns of a recycled assembly.

 

[GoToGuyRon]

The one problem, important maybe. High perf' vehicle, option codes, does it have limited slip (positraction, locker) ? Your known is that it came eqipt with higher performance parts. Retaining your known parts and swapping out ring and pinion would be my move. Bigger risk obtaining an unkown history unkess you plan on rebuilding a used unit. You will still have update the "brains ". The computer will have to be informed of applicable changes for optimal performance. I did some math and your cruise rpm would be substantially higher. Your mileage would take a hit.

 

[1BADI5]

On my '10 PPV I went from 3.08 and open diff to 3.73s and limited slip/locker

Great mod for the money. I went with Yukon Gear and Axle, ring/pinion, Duragrip and complete master install kit.

 

[HeidiHoe]

Thanks to all I talked with a young but gifted gearhead about what i wanted to do and he went on about unsprung weight in great detail. Apparently the steelies and tires originally equipped on the PPV offer an excellent combination of traction and handling characteristics that swapping to 20 inch rims and tires would compromise. My PPV is equipped with a limited slip locking rear end with very low miles on it so until I am ready for a revamp I think I will leave it as is. I drove this bad boy conservatively for 280 miles at 60 mph and achieved 23 mpg so for now I am happy.

 

[HeidiHoe]

The one problem, important maybe. High perf' vehicle, option codes, does it have limited slip (positraction, locker) ? Your known is that it came eqipt with higher performance parts. Retaining your known parts and swapping out ring and pinion would be my move. Bigger risk obtaining an unkown history unkess you plan on rebuilding a used unit. You will still have update the "brains ". The computer will have to be informed of applicable changes for optimal performance. I did some math and your cruise rpm would be substantially higher. Your mileage would take a hit.

The plan was to change to 3.42 but with a larger tire (275/55R20 vs 265/60R17) which would leave the overall combo within 2.5% of each other. Computer wouldnt even notice

 

[thompsoj22]

Thanks to all I talked with a young but gifted gearhead about what i wanted to do and he went on about unsprung weight in great detail. Apparently the steelies and tires originally equipped on the PPV offer an excellent combination of traction and handling characteristics that swapping to 20 inch rims and tires would compromise. My PPV is equipped with a limited slip locking rear end with very low miles on it so until I am ready for a revamp I think I will leave it as is. I drove this bad boy conservatively for 280 miles at 60 mph and achieved 23 mpg so for now I am happy.

Function and reliability are the benefit for making the choice to keep the original configuration of the vehicle. You got some good info from the "gearhead" that saved you time and money plus the unforseen time and money of making modifications to your drivetrain. Enjoy your new PPV which is way cool just as it was designed!

 

[HeidiHoe]

As suggested, I have wandered over to the PPV specific section. I greatly appreciate all the responses and suggestions. A scanner, tuning device, Tech2 are all in the works.