Upgrade to G80

[Knightslugger]

I'm looking to see what's involved with a DIY upgrade to the G80 Mechanical Locker, and i'm a little confused as to what all i need to get it done.

Do i need the whole enchelada (meaning a whole new rear axle) or just some internal swapping? There's a gear kit that's $310.96 from GMPartsDirect:

Gear kit, bravada/envoy/trailblazer, 113" wheelbase, w/positraction - 8.50 and 8.625 ring gear - 8.50 and 8.625 RING GEAR

Is this all i need to buy and replace or is there more to it?

[AlekG]

Since you have the short wheel base I6, your rear housing and internals are for the 8" ring and pinion set, not the 8.6"

To upgrade to the mechanical locker (G80), you need the unit (which replaces your open spider gears) and a Full Install Kit. You can get a rough idea of pricing from this page (http://www.drivetrainspecialists.com/categories/gm/gm-80/).

Or from Randy's Ring & Pinion.

One final warning, installing gears is a very tricky job. Unless you have done it before on other vehicles I would not recommend a DIY, leave it to the professionals. Just my opinion.

AG

[Knightslugger]

OK, thanks for the warning!

Now, by "The Unit", you mean the Differential Case? if that's the case, i'm not seeing anything on GMPartsDirect that's for 8", Open or otherwise. they all say 8.5 or 8.625

What am i not understanding here?

[wardak33]

i've never heard of anyone putting in a locking differential...i have to see pics of this install!!!!!:D

[Knightslugger]

by your wording, i presume you know this to be an impossibility?

The reason i'd rather install components (if that's even possible) is because i've been looking for complete rear axles with the G80, and even from junkyards their calling for $1250! I don't know how some of you guys are getting it for under $300... which makes me wonder if you guys are replacing internals instead.

[AlekG]

i've never heard of anyone putting in a locking differential...i have to see pics of this install!!!!!:D

Sorry if I am stating the obvious ... our vehicles have the option of a locking differential from the factory. Its RPO code is G80 so that is what has been used as a name around here. Its actually an Eaton mechanically locking differential called the Gov-Loc.

As for replacing the differential, the rear is the "easy" one for professionals. What has a lot of 4x4 drivers held up is the front, which is totally ridiculous to replace ... as I learned from my 4.56 gear project.

You can read about it here:
http://forums.trailvoy.com/showthread.php?t=42226

AG

[AlekG]

by your wording, i presume you know this to be an impossibility?

The reason i'd rather install components (if that's even possible) is because i've been looking for complete rear axles with the G80, and even from junkyards their calling for $1250! I don't know how some of you guys are getting it for under $300... which makes me wonder if you guys are replacing internals instead.

I checked into GMPartsDirect as you did and it looks like the database was updated and now there is no mention of the 8" housing and ring&pinion. This is very bad as it is a fact that ALL short wheel base I6 trailvoys ship with the 8" rear axle. Only the extended vehicles and V8s got the 8.6" rear.

You can see the actual GM part here:
http://www.drivetrainspecialists.com/categories/gm/gm-80/products/product-1823.html
http://www.ringpinion.com/ProductDetails.aspx?ProdID=1357

You used to be able to punch in that GM part number (40016076) to the database and get the part. Now, nothing comes up so I don't know what is going on. Maybe they changed the part number which has happened before on other parts.

As for entire axle housings, have you tried using http://www.car-part.com ?

Using this resource I found a local 2004 rear EXT axle (8.6") for $170, but that was an uncommon find.

I did a quick search based around ZIP code 53201 (Milwaukee) for the 3.42 axle and found all sorts from $350 and up. It just takes some emailing/calling (and perhaps going there) to narrow things down. Remember, you would need:
- 2002 to 2005 year (in 2006 the rear ABS system switched)
- match your gear ratio
- make sure its from an I6 short wheel base (8")

Hopefully this helps.

AG

[WOOLUF1952]

I'm curious. If you buy the entire rear axle assembly Would there be a problem using the 8.6" as long as the gear ratio is the same?:undecided

[AlekG]

I'm curious. If you buy the entire rear axle assembly Would there be a problem using the 8.6" as long as the gear ratio is the same?:undecided

No, that's what I did here:
http://forums.trailvoy.com/showthread.php?t=42226

AG

[Knightslugger]

so basically it's far easier to swap a GU6 Non-posi 8" complete assembly with a GU6, G80 8" complete assembly... and you suggest not to even screw with internals if you don't know what you're doing inside them (i can handle the whole axle itself, just not the insides).

drop the old one out, put the other in. right? just that simple?... one giant bolt on.

[AlekG]

so basically it's far easier to swap a GU6 Non-posi 8" complete assembly with a GU6, G80 8" complete assembly... and you suggest not to even screw with internals if you don't know what you're doing inside them (i can handle the whole axle itself, just not the insides).

drop the old one out, put the other in. right? just that simple?... one giant bolt on.

If you replace the entire axle, the rear seems to be pretty easy, yeah. You just need to know your way around the u-joint. And you need an extra jack as that sucker is heavy.

One thing though to watch out for with a used one is that you don't actually know the condition of the differential and r&p until you open it up. But you can take the cover off and take a look without actually touching anything. You would probably want to change the oil in there anyways ...

Oh, and the ABS year thing ...

AG

[Knightslugger]

Right.

Awesome.

That's what i'm going to shoot for then.

Thanks for your help! When i'm done, i'll give you a shout out!

[gcurrlin]

Did you ever complete this project? I am considering the same thing on my 2004 TB EXT and would love to hear how yours went.

[Knightslugger]

it was far more expensive than i had originally planned for, and was set aside.