NEED HELP Rear Differential identification and possible rebuild!!

[darknight76]

Hello everyone and thanks for any and all help in advance!

I'm new to the forums, was brought here by watching the videos of a member (may03LT) after buying my well used, but decent condition, 2002 Trailblazer LS 4.2 I6 2x4 with just over 250k on the odometer. I originally bought it as a vehicle to drive while I work on my '98 Grand Prix. Well since I've had it I've had to replace the Oil Pressure Switch (IMO Stupid) due to the Gauge (fake) constantly going to 0, found out that the fan clutch is almost gone (think its original and surprised it's lasted) and now plan on replacing it, and now I believe the rear differential needs to have all its bearing replaced. The problem I'm having is identifying the diff I have to be able to order the parts from RockAuto.

What I have been able to find out so far is that I have a 3.73 Gear ratio and RPO code GT4 (GT4 Rear Axle (5X1) 3.73). What all that tells me is that I think I have a 8.62 ring gear and if that is correct I know what I need to order, however any additional input I could get would be greatly appreciated. I really don't want to order parts and find out I've gotten the incorrect master rebuild kit. This is the first time I'm going to be doing work on a differential.

Again thank you for any, and all input.

 

[Mooseman]

Welcome to the Nation!

You likely have a 8.0 ring gear. The 4.2 short wheelbase got the 8.0 and the EXT got the 8.6. Later years, all 5.3 and EXT (4.2 and 5.3) got the 8.6 while shorties still got the 8.0.

Unless you're just replacing bearings, if I were you, I'd find a complete diff from an EXT or 5.3 and swap it out. Look for one with the G80 locker.

 

[darknight76]

Something I should have put in the original post is that, while accelerating through 15-25 mph it has a "rumble and shake" from the rear. If I just coast through 25-15 she is fine, but if I break there is a bit of a "clunk". If that makes any sense.

I think I will look around for a later model EXT with a G80 and see if I can afford it before I get a master rebuild kit.Thanks for the suggestion @Mooseman.

 

[Mektek]

If you install an 8.6" in place of an 8", do you have to replace the pinion gear as well?
Or can you just shove the 8.6 in place of the smaller one without any other changes?

 

[djthumper]

The 8.6 will just go right in.

 

[Tiggerr]

If you install an 8.6" in place of an 8", do you have to replace the pinion gear as well?
Or can you just shove the 8.6 in place of the smaller one without any other changes?

If your meaning the entire axle as a unit yes straight swap...
if your thinking swapping carriers...thinking that's not gonna gonna work....I'd think he 8.6 housing would be different
Just mentioning it since you asked about pinion gear being the same

 

[Mooseman]

Swap the entire differential. Straight swap and you keep your drive shaft. Probably cheaper than a rebuild and less labour intensive.

Sounds like your current diff is done. If you tear into it, you may find more stuff broken as you go.

 

[darknight76]

So straight axel swap it is. Now to find one. It's Detroit, gotta be a few around.

 

[darknight76]

@Mooseman or anyone, did the G80 ever come in a 3.73 gear ratio in the GMT360 platform? I don't want to have to figure out how to fix my speedo if I don't have to right now, got a lot on my plate as it is...lol.

 

[djthumper]

It is, the are rare. you can go here to see what is around you http://car-part.com/

 

[Mooseman]

For some reason, it has only non-interchange for the rear diff from TB's only. Look for Envoy XL as well.

 

[darknight76]

Well, I think I have found my new rear axel. I found two options I'm going to call on today, hope they are fully loaded for the listed price (G80 diff included). If so and if I can get there to get one I might be changing my axel in thunder storms and rain this weekend.

2004
Rear Axle Assembly
GMC Truck Envoy XUV 4.2L,AT,POZZY 127,000 A 17C038 $100 Highway Truck Parts USA-MI(Ferndale) Request_Quote 248-543-9900 Request_Insurance_Quote

2004
Rear Axle Assembly
GMC Truck Envoy XUV 5.3,AT,POZZY 161,000 A 17F061 $100 Highway Truck Parts USA-MI(Ferndale) Request_Quote 248-543-9900 Request_Insurance_Quote

 

[Tiggerr]

If those don't work out look for Rainier rears... I believe they all came g80/3.73... it was standard not an option....

 

[Mooseman]

And Saab 9-7x. The 5.3 all seemed to have the 3.73 although they had the G86 limited slip instead of the G80 locker.

Too bad you're so far from me. I have one sitting in my parts Saab and there are two 5.3 Envoys in the local u-pull.

 

[Mektek]

If your meaning the entire axle as a unit yes straight swap...
if your thinking swapping carriers...thinking that's not gonna gonna work....I'd think he 8.6 housing would be different
Just mentioning it since you asked about pinion gear being the same

I've heard before that the housing is the same for both. I find it hard to believe that you can just swap the carrier with a larger ring gear and keep the old pinion gear.

 

[darknight76]

Well after doing some research here on GMTNation I've decided that no matter what I'm not changing my gear ratio. Since I have an '02, apparently its virtually impossible to reprogram for the new ratio/tires. So I'll stick with the 3.73, even though I had thought of going to the 4.10.

 

[darknight76]

Well been awhile since I did the original post and thought I would update the post. I found out that the differential was not bad, also that the U-Joint wasn't a problem either. The problem that was causing all the noise and vibration was the fact that both upper control arms on the rear axle were rusted and busted. The temporary solution has been to weld stock steel into the broken sections after cleaning and trimming away the rot.

The fix has been holding and the control arms will be replaced soon, and the differential is working fine.