Axle ratio to tire size input needed

[vcode]

I'm looking at a 3.08 to 3.42 or (more likely) 3.73 conversion myself. But I'm keeping stock size tires. For the front, I'd probably just get a junkyard carrier and swap it completely. 3.73 units are available from the 07 and 08 4L60 trucks. But for the rear I will probably change ring and pinion, as I want to swap to a 9.5 semi-float 14 bolt at the same time, and those weren't available in 3.73.

My question to the group: How feasible is it for the DIY'er to change out ring and pinion? I've always heard it's a no-no due to the shimming challenges to get just the right pattern. But I've watched some vids and it seems possibly more doable than I thought. You can get a slightly oversized bearing for the pinion that makes a trial and error approach (by using paint and looking at the mesh pattern) easier. But worst case, I have a coworker that used to run a family transmission shop, and maybe her husband (one of the mechanics) would be able to help me get it set right.

It's not a bolt in for sure. My buddy has set-up ring and pinions and it just takes patience to get it right. Having an old-school guy help would be a good thing.....

 

[swathdiver]

I have the Premium Smooth Ride suspension with the Nivomat rear shocks/conventional front struts.

I thought you had a 2013? Did someone add the Nivomats? They were only used on the 2007s with the GMT900 body style.

I'm looking at a 3.08 to 3.42 or (more likely) 3.73 conversion myself. But I'm keeping stock size tires. For the front, I'd probably just get a junkyard carrier and swap it completely. 3.73 units are available from the 07 and 08 4L60 trucks. But for the rear I will probably change ring and pinion, as I want to swap to a 9.5 semi-float 14 bolt at the same time, and those weren't available in 3.73.

My question to the group: How feasible is it for the DIY'er to change out ring and pinion? I've always heard it's a no-no due to the shimming challenges to get just the right pattern. But I've watched some vids and it seems possibly more doable than I thought. You can get a slightly oversized bearing for the pinion that makes a trial and error approach (by using paint and looking at the mesh pattern) easier. But worst case, I have a coworker that used to run a family transmission shop, and maybe her husband (one of the mechanics) would be able to help me get it set right.

You can do it with the right tools. Measuring and setting the pinion depth correctly is crucial, as is getting the rotating torque of the pinion right. I'm doing this right now with my 9.5" 14-bolt with 3.73s and I torqued the pinion nut an 1/8" too far and put the rotational torque at 38 inch pounds when it shouldn't be more than 20. So I had to order some more nuts because I can't find the other two in the garage and some extra seals to be on the safe side.

Over the course of two years, I put together most of the GM tools required to overhaul an 8.6 or 9.5 axle. We'll eventually get the adapters and removers/installers for the 11.5 axles as my kids have a couple of Duramax's and old Dodge Rams now too. All AAM axles.

 

[mikez71]

Trans tune helps a bit for driveability/response. Not 1st gear, but anything after..

 

[Marky Dissod]

Trans tune helps a bit for drivability / response.
Not 1st gear, but anything after.

tcm tune makes it easier, more likely, and quicker to downshift to 1st (as well as all the other gears) than GM allows.

 

[intheburbs]

3.08 is what I call the "soccer mom" gear ratio. Combine that ratio with GM's excessive torque management, and you're left with what we colloquially call "a dog." The 3.08 exists for one reason only: CAFE.

If you're going to go through the effort and expense of regearing, it's only worth it (IMHO) if you do a double-jump. Either 3.08 to 3.73 or 3.42 to 4.10.

The second piece of the puzzle is getting a tune. One of the first things I did when I purchased my Suburban was a Blackbear tune. They dialed out 50%+ of TM. That was 10 years ago, and I think that's contributed to extending the life of the 6L90 to 250k and beyond. Also greatly improved throttle response.

So with 3.73 gears, stock size tires, and a tune, the Suburban pulls like a freight train to 100 mph and beyond. I always think of Robin Williams' genie in Aladdin every time I mash the throttle, "LIMITLESS POWER!"

I can certainly feel the difference between the 3.73 in my Suburban and the 3.42 in my Denali. The Denali is quick, and 1000 lbs lighter, but it can't walk away from the Suburban in a race. It jumps about 2 car lengths, but then cannot extend that margin. If I ever regeared anything, I'd go to 4.10s on the Denali. That would be SICK.

I would definitely NOT switch to larger tires and keep the 3.08 ratio. If you do regear, go 3.73, but wait on the tires until you've had some time to live with the new ratio. You might like it so much you don't want to do anything to reduce power.

 

[mikez71]

3.08 is what I call the "soccer mom" gear ratio. Combine that ratio with GM's excessive torque management, and you're left with what we colloquially call "a dog." The 3.08 exists for one reason only: CAFE.

Though I -PLAN?- to go 3.42's someday (stock tires, not towing), after the AFM disable and trans tune, I find the 3.08's adequate for car duties..
I haven't even thought about the 3.42's lately, which was the FIRST thing I wanted to change when I bought the truck. Kind of don't want to change now because of the hassle/cost when it's running good, but I'm sure I'll change my mind once I'm fully loaded down..

tcm tune makes it easier, more likely, and quicker to downshift to 1st (as well as all the other gears) than GM allows.

^ Better, more detailed description. Also upshift later in mid-throttle area definately helps some occasions..
I'm satisified with the '15+ shift schedules for soccer mom duties, which is all I've been doing.

I drove manuals all my life (from day 1 driving test) and couldn't stand auto's, but these new automatics, I'm pleased..
I feel it's the #1 improvement that newer cars have over older cars (well, and more power across the board). Kind of like disc brakes vs drum..

 

[Marky Dissod]

3.08 is ... the "soccer mom" gear ratio. Combine 3.08 with GM's excessive torque management, and you're left with what we colloquially call "a dog." 3.08 exists for one reason only: CAFE.

Stipulated. Wholeheartedly agree.

If you're going to go through the effort and expense of regearing, it's only worth it (IMHO) if you do a double-jump.
Either 3.08 to 3.73, or 3.42 to 4.10.

For a minority, it may be worth a single jump.
My '02 Z71 already has OE 3.73. 4.10 may not impress me arse as much as 4.30, but
city MpG will improve,
highway MpG will barely change (under 65MpH - after that aero drag screws all our bricks),
and the transmission will last longer before its next rebuild.
It's not where ya start, it's where ya FINISH.

The second piece of the puzzle is getting a tune.
One of the first things I did when I purchased my Suburban was a Blackbear tune.
They dialed out 50%+ of Torque Management.
That was 10 years ago, and I think that's contributed to extending the life of the 6L90 to 250k and beyond.
Also greatly improved throttle response.

This also gets misunderstood and underappreciated.
Most people who don't get tuned
think tunes are only for the leadfooted
don't understand how much customization is available
fear getting caught by Kalephonyuh's creeping fascism
think GM OE cannot - or should not? - be improved upon

I would definitely NOT switch to larger tires and keep 3.08.
If you do regear, go 3.73 - but wait on the tires until you've had some time to live with the new ratio.
You might like it so much you don't want to do anything to reduce power.

Stipulated. Wholeheartedly agree.

 

[mikez71]

This also gets misunderstood and underappreciated.
Most people who don't get tuned
think tunes are only for the leadfooted
don't understand how much customization is available
fear getting caught by Kalephonyuh's creeping fascism
think GM OE cannot - or should not? - be improved uponStipulated. Wholeheartedly agree.

^All true!^

Love it! Haven't seen it spelled that way before..

 

[SilverSurfer5300]

I thought you had a 2013? Did someone add the Nivomats? They were only used on the 2007s with the GMT900 body style.

It is a 2013.
This is my RPO code sticker from the glove box:


Bottom line, second from left. ZW7. I don't know if I have some kind of uncommon special edition or not, but I didn't think so??

 

[swathdiver]

It is a 2013.
This is my RPO code sticker from the glove box:
View attachment 427320

Bottom line, second from left. ZW7. I don't know if I have some kind of uncommon special edition or not, but I didn't think so??

Ok, so you have regular ACDelco shocks out back unless someone installed Nivomats. 2007 was the last year that ZW7 was paired with G65 which was the Nivomats back then.

When such trucks were new, there was a noticeable rake to them as they were designed to run comfortably with a load on and tow. At 11 years old and if you have ACDelco shocks out back, there should still be some rake to the truck unless the springs are really wore out. Mine were and the suspension was overhauled at 162K miles three years ago.