Upgrading to 4.10's

Pittdawg

Original poster
Member
Dec 5, 2011
538
I found the following on gmpartsdirect.com:

"Differential, s-series, w/limited slip, bravada/envoy/trailblazer, 113" wheelbase, 4.10 ratio - 8.50 and 8.625 ring gear - 8.50 and 8.625 RING GEAR
06-09 $475.23"-$281.72

I currently have a G80 GU6 rear gear in my '08 Envoy. Am I correct to assume that if I purchase the above, it's just a simple swap of differentials? For instance, do the gears come from GM "set up" already? Isn't $281 an amazing price to put in 4.10's? Seems too good to be true. What am I missing here?
 

ScarabEpic22

Member
Nov 20, 2011
728
NO!
That is for the 8.6" rear, you have a 8". All SWB I6 trucks came with 8" rears. All SWB 5.3, LWB I6, LWB 5.3 came with 8.6" rears. The SS and Aero came with 9.5" rears.

Gears for the 8" diffs are sometimes more expensive as they're not nearly as common. The 8.6" diff shares parts with fullsize trucks so there are tons more options which brings the price down. Regardless of what you do, you'll have to set the gears up unless you buy a whole axle and swap that in. If you want more options for lockers and more strength, finding an 8.6" axle might not be a bad idea. Or a wrecked SS rear axle, already setup with a LSD and 4.10s.

Why do you want to go to 4.10s? I think 3.73s are the best, decent off the line and not horrible on gas. You've got 3.42s which for a highway rig are the best, do you need to tow more or just want more performance?
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
ScarabEpic22 said:
NO!
That is for the 8.6" rear, you have a 8". All SWB I6 trucks came with 8" rears. All SWB 5.3, LWB I6, LWB 5.3 came with 8.6" rears. The SS and Aero came with 9.5" rears.

Gears for the 8" diffs are sometimes more expensive as they're not nearly as common. The 8.6" diff shares parts with fullsize trucks so there are tons more options which brings the price down. Regardless of what you do, you'll have to set the gears up unless you buy a whole axle and swap that in. If you want more options for lockers and more strength, finding an 8.6" axle might not be a bad idea. Or a wrecked SS rear axle, already setup with a LSD and 4.10s.

Why do you want to go to 4.10s? I think 3.73s are the best, decent off the line and not horrible on gas. You've got 3.42s which for a highway rig are the best, do you need to tow more or just want more performance?

That's what I was worried about. Basically, I just want more performance. Also, I plan on going to a slightly larger tire when the tread on my stockers wears out pretty soon. So is it pretty straightforward to just swap in an entire axle with 4.10s? Do I only need the axle or are there other connecting pieces I need?
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
Pittdawg said:
That's what I was worried about. Basically, I just want more performance. Also, I plan on going to a slightly larger tire when the tread on my stockers wears out pretty soon. So is it pretty straightforward to just swap in an entire axle with 4.10s? Do I only need the axle or are there other connecting pieces I need?

So I did find an SS axle. Will my current brakes fit? Any other mods necessary?
 

ScarabEpic22

Member
Nov 20, 2011
728
Since you have an 08 (new style ABS, not an 02-05 [maybe 06, cant remember when it changed]), the axle should bolt right in. Brakes should swap easily too. I am not exactly certain what this swap entails, dont know if you need to use a different driveshaft yoke (think the SSs have a different driveshaft) or any other things.

I know there are a few people who have done the swap on TBSSOwners, usually from an SS to a 5.3L SWB truck.

Anyone know whats needed to do the swap?
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
Rear brakes are the same.
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
Thanks for all the input guys, everything you said was spot on. Since switching to 4.10's is so costly and labor intensive I'm shelving this idea for now. Going a different route to add power which I'll let y'all know about once I get my go fast goodies installed :wootwoot:
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
Pittdawg said:
Thanks for all the input guys, everything you said was spot on. Since switching to 4.10's is so costly and labor intensive I'm shelving this idea for now. Going a different route to add power which I'll let y'all know about once I get my go fast goodies installed :wootwoot:

I can't shake the mod bug :crazy: The cai, ported mani, ported tb and pcmforlesstune all made gains, in reverse order from most sotp to least. Going to bigger tires soon and I got the need for speed (torque actually). Too poor to do this but just purchased some 4.10s. Got a quote for installation for $400.00. Gonna put everything on the credit card :eek:.
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
Dropped off the Voy this morning for the install. Here's to hoping the gears get set up correctly!
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
Follow the breakin procedure so it all gets set in correctly!
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
HARDTRAILZ said:
Follow the breakin procedure so it all gets set in correctly!

Will do! Just got call from the shop, she's ready to be picked up and "the install went smoothly" :biggrin:

It's gonna be hard to wait to drive it like I stole it!!! :crazy:
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
Picked her up. Unless I am imagining things it feels a bit more torquey. Not quite the jump I was anticipating but I'm "babying" her during the break in period. Confusingly, when I got up to 71 mph my rpms were at 2000, just like with the 3.42s. However, when I drove past one of those speed sensing signs, it read I was going 35mph and my speedo was showing 44mph :eek:. Since my pcm was programmed for 3.73's, does 9mph to high on the speed sound about right for the change in gears?

Here are pics of the old gears btw
View attachment 21146
 

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Sparky

Member
Dec 4, 2011
12,927
The math shows your computer is thinking it has 3.42 gears, not 3.73 or 4.10. Your speedometer (and odometer) is fast by about 17%. When you were going 71 MPH according to your speedo you were only doing 59 or maybe a little less (sounds like your speedo is slightly off already to begin with as the math doesn't fully add up).
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
Sparky said:
The math shows your computer is thinking it has 3.42 gears, not 3.73 or 4.10. Your speedometer (and odometer) is fast by about 17%. When you were going 71 MPH according to your speedo you were only doing 59 or maybe a little less (sounds like your speedo is slightly off already to begin with as the math doesn't fully add up).

Ya I'm quite confused myself. My glove box rpo says my truck came with 3.42's. When I had my pcm tuned by PCMFORLESS, Kelly said my vin number showed 3.73's in her "GM program". I thought she said she programmed 3.73's even though I told her my glove box said 3.42's but maybe there was some miscommunication and she did end up leaving the programming at 3.42, I dunno. Clearly, my speedo is very far off :confused:
 

Sparky

Member
Dec 4, 2011
12,927
They probably got the computer, which was set for 3.42 from the factory, and left it alone.

I expect the RPO code list to be accurate more often than a tuner's VIN database lookup tool.
 

TXBlazer

Member
Nov 21, 2011
533
Cypress, TEXAS USA
If PCM4Less programmed your Truck, you need to send it back and have them update the gearing in your tune. And don't let them tell you it has a different gear. They screwed up my tune by entering the wrong gearing, which will put your speedo off and your mileage as well as your oil life indicator, it throws off so many things, it's unreal.
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
TXBlazer said:
If PCM4Less programmed your Truck, you need to send it back and have them update the gearing in your tune. And don't let them tell you it has a different gear. They screwed up my tune by entering the wrong gearing, which will put your speedo off and your mileage as well as your oil life indicator, it throws off so many things, it's unreal.

He changed his gearing so he has to do the same as I do and pay $50 to update the tune.
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
Decisions, decisions. I also plan on changing to larger tires down the road. Do I update the pcm now, do I wait, do I update the pcm now and account for the larger tires before I have them on? :crazy:
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
I have waited. I got everything pretty well where it will be for awhile and honestly am going to have them change a few other things than just tire size and gearing. Glad i waited for a little bit.
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
So I rode her a bit harder on my drive into work this morning...:wootwoot:

Definately better torque and smoother power delivery to the wheels...still have not floored it yet and can't wait to do so.

Also, it feels as if the tranny has closer gear ratios now. I'm not sure if this is related to my speedo being off and the shift points being wrong or simply the engine revving quicker/more freely, but I like it :thumbsup:

I honestly don't understand why the 4.2 does not ONLY come with 4.10's. These gears are perfectly suited to this higher revving engine. I'm now debating whether or not I will actually go with larger tires as this ratio honestly feels perfect.
 

Sparky

Member
Dec 4, 2011
12,927
Pittdawg said:
I honestly don't understan I'm now debating whether or not I will actually go with larger tires as this ratio honestly feels perfect.

MPG. Highway mpg will be lower.
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
Sparky said:
MPG. Highway mpg will be lower.

Due to the lower gears or larger tires... There is a balance there. My lower gears have helped my mpg, but i was previously undergeared.
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
HARDTRAILZ said:
Due to the lower gears or larger tires... There is a balance there. My lower gears have helped my mpg, but i was previously undergeared.

That's my point....the 4.2 is undergeared with anything but 4.10's...I have the stock tires right now and that's my opinion. I clearly can't really determine any mpg loss or improvement right now but I can tell you the driveability is vastly improved.
 

Sparky

Member
Dec 4, 2011
12,927
HARDTRAILZ said:
Due to the lower gears or larger tires... There is a balance there. My lower gears have helped my mpg, but i was previously undergeared.

True. My old Camaro came with 3.08 gears from the factory. CRAP. I upgraded the axle to 3.42 and my mpg went up as well.

It does make me wonder sometimes if the 3.42 in my Trailblazer isn't enough, and if 3.73 would be better for both performance and mpg. And since I want to eventually lift it and go with bigger tires, well... If only the front differential wasn't such a pain.
 

gsf1200m

Member
Dec 15, 2011
55
How much did this end up costing you? It is something I have thought about before and it sounds really great with your review. I think its probably too much for me though.

EDIT-I just realized you have 2wd. Never mind then. If that was the case I would be all over it.
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
gsf1200m said:
How much did this end up costing you? It is something I have thought about before and it sounds really great with your review. I think its probably too much for me though.

EDIT-I just realized you have 2wd. Never mind then. If that was the case I would be all over it.

$377 for all parts (ring & pinion and master install kit) and $300 for labor. I could have saved about $160 by foregoing the rebuild kit.
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
:wootwoot::wootwoot::wootwoot::wootwoot::wootwoot::wootwoot::wootwoot:

All I can say is I am a very happy camper. If anyone is considering upgrading from 3.42s to 4.10s do it!!! Whether it is worth it from 3.73 I can't say but for 3.42 there is no doubt.

I am still waiting to put some more miles on the new set up before I really floor it, especially from a stop. Quick question for you gearheads out there, is the master install kit linked here (DRK320DMK GM 8 Master Timken Bearing Kit) good for beefing up any of the weaker factory components or pretty much the same as stock? I'd like to know just how "careful" I need to be with this smaller sized 8 inch rear end...hehehe:rotfl:
 

DenaliHD66

Member
Dec 4, 2011
597
Pittdawg said:
:wootwoot::wootwoot::wootwoot::wootwoot::wootwoot::wootwoot::wootwoot:

All I can say is I am a very happy camper. If anyone is considering upgrading from 3.42s to 4.10s do it!!! Whether it is worth it from 3.73 I can't say but for 3.42 there is no doubt.

I am still waiting to put some more miles on the new set up before I really floor it, especially from a stop. Quick question for you gearheads out there, is the master install kit linked here (DRK320DMK GM 8 Master Timken Bearing Kit) good for beefing up any of the weaker factory components or pretty much the same as stock? I'd like to know just how "careful" I need to be with this smaller sized 8 inch rear end...hehehe:rotfl:

You've got me all hopped up on doing the same to my 3.42s for the 4.10s. I have 4wd though, what all do I need and where can I find the parts?
 

Pittdawg

Original poster
Member
Dec 5, 2011
538
DenaliHD66 said:
You've got me all hopped up on doing the same to my 3.42s for the 4.10s. I have 4wd though, what all do I need and where can I find the parts?

You can start here:
Home Page

You need front and rear ring and pinion sets and install kits.
 

Sparky

Member
Dec 4, 2011
12,927
Or complete front and rear differentials from a junkyard (may be easier/cheaper than replacing the gear sets). I can replace the entire rear axle in an afternoon ever since I had pulled and installed mine a few times last fall lol that was so frustrating getting bad parts that were supposedly "tested."
 

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