Which way is easier/cheaper?

matermark

Registered Member
My only vehicle the trans blew a cooler line on the thruway (highway, 65MPH+) and lost 3rd/4th... this is only related to the trans because I am no longer in the auto parts/repair business and I need to find a wrencher near me, but I digress.

This vehicle is an Envoy XUV w/SLT trim that was loaded to the gills, about the only thing I can think of it is missing is Rain Sensing wipers. It has the UM8 Navigation system w/Bose and XM Radio, Electric Adjustable Pedals, etc. It now has only 77,2xx miles and I intend to keep it

These came stock with 3.73 gears, HOWEVER, the original buyer or dealer ordered 3.42 gears for some reason--I assume for highway driving. It has the LM4 aluminum 5.3L V8 and backing into my driveway is a little scary--if you feel like you need to move another 12-18 inches, you need to feather the pedal because the gear ratio makes you cover the distance more quickly than a 3.73 or 4.10.

So that brings me to the topic of the post. Which is easier? Which is cheaper?

a) having new gears, preferably 4.10's, installed properly in both the front & rear differentials? will 4.10's work with the 3.42 G80 unit or does it need a different carrier? I know very little about this rearend, I assume it's the 8.6. (sorry, I'm a 12-bolt '60's-'70's musclecar guy.)

b) finding good used or reman'ed differentials, front & rear, and installing the complete units

................................................

It's been a while since I did any wrenching on cars & trucks and my buddy who worked for beer died recently. I don't have a garage and live in the Northeast (Western NY) and am subject to bad weather. I'm getting old and have a bad back/leg and can't do much.

I know 3.73's will be a much easier conversion but I don't do any long trips and need to haul some compost or lumber every now & then and performance is more important than gas mileage right now. I'd like to concentrate on this cost/job, but I also will need a transmission job too, I'll save the trans & lines for another thread, but please comment on this one first. If anybody's available for work in WNY please let me know. Thanks for any help.
 

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Mooseman

Master Blaster
Moderator
Swapping gears in the front diff is no easy task since it's an enclosed diff with the setup and proper gear tooth pattern. Getting the diff out and back in is also no easy feat in itself. There are a couple of methods in the FAQ, however, they were originally for the I6 and don't know if those methods would work on the V8.

Your XUV should be equipped with the 8.6" rear as with all other V8's so gears are plentiful. Installing and setting them up is the challenge.

If it was me, I would swap the complete diffs. Faster, easier and probably cheaper.

Another problem is that your speedo will be off and ABS will be out of whack because it is expecting to see 3.42 speed on the tail shaft. Reprogramming of the PCM as well as the ABS module and possibly the BCM will be required. As far as I can tell, on 02-05 trucks, it is done using the VIN from a truck with the desired gears. The challenge is finding that VIN. And being a rarer XUV may be even more of a challenge.
 

TollKeeper

Gold Supporter
@limequat - If I am remembering correctly, its a lot simpler than that for the re-gear. Its just a matter of sending out the PCM, since its a standard PCM like the GMT800's have, and getting it tuned for the correct gear set. Am I correct?

My XUV also was fully loaded like yours, with the GU6 3.42. Yours is the 2005, first year for the power pedals, and I have the 2004. How is the DOD/AFM holding up? Thats usually where the trouble starts. I believe you have the LH6 for the 2005 model thou.

I personally prefer the 4.10s GT5 with the G80. But as I am getting older, I think I am going to go with the 3.73 GT4/G80 instead. Better fuel mileage, while still providing good power. I already have a 4.10 GT5 front diff.. But it can be a challenge finding the rear (without having a million miles), as a lot of GT5's are also a 9.0 inch, with G86 LSD (from the TB SS) instead of the G80 locker. This diff will work, but will require you to modify the driveshaft as the nose of the diff is longer.

I would also just swap out the entire rear/front end for a good used unit. These things are usually pretty near bullet proof. Mine has 200k on it, and still on the original seals and bearings.
 

matermark

Registered Member
Thread Starter
@limequat - If I am remembering correctly, its a lot simpler than that for the re-gear. Its just a matter of sending out the PCM, since its a standard PCM like the GMT800's have, and getting it tuned for the correct gear set. Am I correct?

My XUV also was fully loaded like yours, with the GU6 3.42. Yours is the 2005, first year for the power pedals, and I have the 2004. How is the DOD/AFM holding up? Thats usually where the trouble starts. I believe you have the LH6 for the 2005 model thou.

I personally prefer the 4.10s GT5 with the G80. But as I am getting older, I think I am going to go with the 3.73 GT4/G80 instead. Better fuel mileage, while still providing good power. I already have a 4.10 GT5 front diff.. But it can be a challenge finding the rear (without having a million miles), as a lot of GT5's are also a 9.0 inch, with G86 LSD (from the TB SS) instead of the G80 locker. This diff will work, but will require you to modify the driveshaft as the nose of the diff is longer.

I would also just swap out the entire rear/front end for a good used unit. These things are usually pretty near bullet proof. Mine has 200k on it, and still on the original seals and bearings.
My XUV is an '04 too. While searching for a vehicle to replace my ZR2 (with a bad tranny), I couldn't find any ZR2's that weren't ridiculously priced for something nice and stumbled onto an XUV and fell in love with the idea, so searched since FEB2020 thru SEP2020 before I found mine.

During the search, I passed on a Magnetic Red Metallic I6 with 4.10's in Great Falls Montana. It had a GM Accessories front bra and G67 Air Level Control.

I also passed on another Mag Red Met in Twin Falls Idaho that had the 5.3L, G80, G67, UC6 6-disc, but lots of little paint chips... and a billet grille.

The GT5 4.10's were only available on I6's, not V8 (on the XUV.) Mine is a LM4 aluminum 5.3L, no DoD--that was the '05 LH6 motor. Mine has G80 and G67 and everything on the G67 works! I even bought a spare set of new air springs so I have no intention of converting to coil springs either. I would love to figure out how to install a lift kit on it too...
 

limequat

Hobbyist
@limequat - If I am remembering correctly, its a lot simpler than that for the re-gear. Its just a matter of sending out the PCM, since its a standard PCM like the GMT800's have, and getting it tuned for the correct gear set. Am I correct?
For the PCM, yes. But it's true that - if there is a wide discrepency between OEM ratios and the new ratios- the ABS will fault out.
 

Mooseman

Master Blaster
Moderator
So if you wanted to find a 4.10 in a 8.6 diff, you'd have to find one from a TB EXT or Envoy XL with the 4.2 since you say that the 4.10 never came with the 5.3. The SWB trucks would have the 8.0 diff with the 4.2 and that wouldn't survive long behind the 5.3. TB SS diffs are usually pricier and, as mentioned, would require shortening the driveshaft.

I might have been wrong regarding tuning the PCM as I was thinking of the 4.2. I'm not sure which PCM it uses but the 5.3 of that era might be programmable for gear changes. @limequat may be able to confirm this.
 

matermark

Registered Member
Thread Starter
If I have to locate a TB w/4.10's and it won't be a 8.6 and uses a different driveshaft, wouldn't it be easier & cheaper just getting gears installed in mine? I wouldn't have to worry about driveshaft lengths nor spring pockets for the G67 being different if I want to keep my air ride... I guess I may not rule out 3.73's completely yet, but if I beef up the trans to a 5-gear planetary set, the 5-gear is 2.84 1st, not 3.06--that would make 3.42's only pull like 3.08's or 3.23's (3.17's), 3.73's would feel like 3.42's (3.46) in 1st, and 4.10's would accel like 3.73's or 3.90's (actually 3.81)... I tried using gears that you's may recognize but true calculations are in parenthesis's. Wow, I didn't even know GM had a 9"... is that truck only? Biggest back in my days in cars was the 12-bolt at 8-7/8" used in most of the Chevy Big Blocks & Pontiacs, also the 1st & early 2nd Gen Z/28...
 
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matermark

Registered Member
Thread Starter
So if you wanted to find a 4.10 in a 8.6 diff, you'd have to find one from a TB EXT or Envoy XL with the 4.2 since you say that the 4.10 never came with the 5.3. The SWB trucks would have the 8.0 diff with the 4.2 and that wouldn't survive long behind the 5.3. TB SS diffs are usually pricier and, as mentioned, would require shortening the driveshaft.

I might have been wrong regarding tuning the PCM as I was thinking of the 4.2. I'm not sure which PCM it uses but the 5.3 of that era might be programmable for gear changes. @limequat may be able to confirm this.
What wheelbase is the TBSS? The XUV is 129.0". I don't know if 4.10 gears were offered in other Envoy V8 models in same or other years, I just know they weren't offered in V8 XUVs. Were 4.10's ever offered with V8 TB or Buick or Isuzu? If you think about it, an aluminum LS motor in a vehicle w/4.10's has to be a little scary... at least to GM... or Goodyear or General or Michelin...
 

Mooseman

Master Blaster
Moderator
I wouldn't have to worry about driveshaft lengths nor spring pockets for the G67 being different if I want to keep my air ride...
Only time driveshaft length is an issue is with a diff from a TBSS because it is a 9". The spring pockets are all the same. In fact, don't get attached too much to that air ride as you will likely convert it to springs when it fails as it is an expensive system to fix.

if I beef up the trans to a 5-gear planetary set, the 5-gear is 2.84 1st, not 3.06-
I wasn't aware that there are different gear sets for the 4L60E. I did find this article that talks about it.
http://www.superchevy.com/how-to/tr...g-the-ultimate-4l60e-with-better-gear-ratios/
I think it would be counter productive to your efforts to go to a taller (numerically lower) first gear.

Wow, I didn't even know GM had a 9"... is that truck only? Biggest back in my days in cars was the 12-bolt at 8-7/8" used in most of the Chevy Big Blocks & Pontiacs, also the 1st & early 2nd Gen Z/28...
Yep. They put it in the TBSS to survive behind the LS2 6.0L. I also have one in my 08 Avalanche with the L76 6.0L. It's not quite as powerful as the LS2 but enough that it could grenade an 8.6" diff.

What wheelbase is the TBSS?
Same as the other SWB 360's. 113.0"

I don't know if 4.10 gears were offered in other Envoy V8 models in same or other years, I just know they weren't offered in V8 XUVs. Were 4.10's ever offered with V8 TB or Buick or Isuzu? If you think about it, an aluminum LS motor in a vehicle w/4.10's has to be a little scary.
Probably not because the gas mileage would have been horrendous, even with overdrive. I know it is with my Avy. I haven't heard of any V8 360, except the TBSS, to have 4.10 gears.

Because of the rarity of the 4.10 gears, you'd probably be ahead to get the gears installed in your existing diff. Your front diff will still be easier and cheaper to just swap the whole thing with one from 4.10 junker. Those are all the same, I6, V8 or TBSS, all years however some '02 did have an issue with leaks from a design flaw that was corrected in later years with an extra mounting bolt.
 

TollKeeper

Gold Supporter
The XUV did come with a GT5 4.10, I found one in a local salvage yard last year, 05 SLE XUV. I would have bought it, but when I opened the pan, the sprockets were completely grenaded, and it didnt have the G80.

All XUV and LWB are 8.6 inch regardless of gearing
All SWB with 4.2L are 8.0 inch regardless of gearing
All SWB with 5.3L are 8.6 inch regardless of gearing
All SWB with 6.0L (SS and Aero) are 9.0 inch regardless of gearing, and are also G86 LSD

Do you mind taking a look at your door jamb sticker.. Would love to know the build date of your XUV. I am betting it must be one of the last 04 models. As far as I know, none of the 04, in any model, had the adjustable pedals. Would love to adapt them to mine, if I keep it.. My XUV may be on the chopping block with another kid on the way... Went and looked at an Escalade last night.

For the PCM, yes. But it's true that - if there is a wide discrepency between OEM ratios and the new ratios- the ABS will fault out.
Can you tune the ABS module? I would imagine going from a 3.42 to a 4.10 would cause such a fault. And does it make a difference on whether or not its a 3 pole system (04 and earlier), and the 4 pole system (05 and later)?
 

Mooseman

Master Blaster
Moderator
And does it make a difference on whether or not its a 3 pole system (04 and earlier), and the 4 pole system (05 and later)?
It does. What I'm thinking is that the 3 pole systems, the ABS module uses the two front sensors and gets the single rear signal from the PCM, which is where that signal goes to so maybe only the PCM needs to be programmed. On the 4 pole, the ABS uses all four for itself and the PCM still uses the tailshaft speed for the speedo and transmission shifts. IIRC, the 06+ PCM are programmable for speedo output.
 

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