rear differential spider gears

rssz28

Newbie
My rear wheel bearing failed on my 2007 Trailblazer. when inspecting the spider gears, they were damaged. I've tried getting new gears but to no avail. My local transmission and rear end expert ordered the kit. when we compared, they were different. He said they had 3 different ones listed and he had them all but they were not the same as mine. I went to chevy dealer and they said the kit has been discontinued. He gave me the old number but it doesn't show up anywhere. They were no help. The local parts store are asking for an axle code. I cannot find any codes on the axle where they say they are. the only numbers are stamped on the pumpkin and are as follows: 40035769 Powerlite CCL CAV39

I need to get this back on the road. Anybody have any information to help me out. Its an open carrier with 3.73 ring and pinion. 8.6 inch
 

Reprise

Lifetime VIP Supporter
Are you *sure* it's the 8.6? That part # 40035769 suggests it's an AAM 8.0, doing a quick google search. The AAM model # is AAM-800, per a Colorado owners' group (they got the same axle, up until about 2012)

Can you post the SPI label from the glovebox (also known as the RPO codes)?

GM did put 8.0 in. assemblies in these, as well as the 8.6 in.

Another potential source could be Yukon Gear; I'm on my phone, or I'd hop over there and take a look.
 

gmcman

Guru
Also, does the G80 diff use different spiders? I know mine started chipping teeth around 180K miles.
 

Mooseman

Master Blaster
Moderator
Looking at your profile, you have the 4.2 so it must be an 8.0. Check your glove box RPO code sticker for these codes:

G80: Locker (in its absence, it's an open diff)
GU6: 3.42
GT4: 3.73
GT5: 4.10

If new parts aren't available, I would suggest that you replace the entire diff or find parts from a similar donor. If your axle bearing got damaged, it's very likely the axle itself also got chewed up so an entire assembly would probably be more cost effective.
 

rssz28

Newbie
Thread Starter
its not a G80. Its a GT4 which is 3:73 gears, which I knew that. When I called various parts stores and the rear end shop, they asked me if it was a 7.6 or 8.6. with a very quick measurement I knew it was over 7.6 so I told them 8.6. I will measure more carefully and see if it could be a 8.0.
 

rssz28

Newbie
Thread Starter
Hey guys. Thank you very much. It is an 8.0 inch rear. after I had that, the parts came right up. I am ordering the gear kit today. I appreciate it. If I would have measured more accurately or counted the splines, I would have known the parts were wrong. These are 28 spline and all the other places were quoting me 30 spline.
 

gmcman

Guru
. Thank you very much. It is an 8.0 inch rear

I don't know if your earlier statement that it was a GT4 and not a G80 meant that it's also not a G80. Sorry to sound persistent, but just making sure.

If your diff looks like this, then it has the G80 option and I believe uses different spiders.

I believe more times than not, chipped spiders are more associated with the G80.

Screenshot_20201003-214358_Chrome.jpg
 

MRRSM

Lifetime VIP Supporter
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TBENVOYFULLREARDIFFNAXLES00.jpgTBENVOYFULLREARDIFFNAXLES0.jpgTBENVOYFULLREARDIFFNAXLES8.jpgTBENVOYFULLREARDIFFNAXLES1.jpgTBENVOYFULLREARDIFFNAXLES2.jpgTBENVOYFULLREARDIFFNAXLES3.jpgTBENVOYFULLREARDIFFNAXLES4.jpgTBENVOYFULLREARDIFFNAXLES5.jpgTBENVOYFULLREARDIFFNAXLES6.jpgTBENVOYFULLREARDIFFNAXLES7.jpg
 

zaid3ssaf

Registered Member
How do you guys measure the size? bolt hole to bolt hole across horizontally from the middle bolts? my codes are GT4, G80, and NP4 on 02 Bravada.
1621371977192.png

I'm getting the infamous thump when accelerating lightly from a stop but it only happens if I do interstate driving (>60 mph). I greased the yoke spline but no help. I will check the TC fluid level this weekend. I saw a thread where the guy had his diff chipping teeth :/.
 
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Reprise

Lifetime VIP Supporter
How do you guys measure the size? bolt hole to bolt hole across horizontally from the middle bolts?
It's actually the diameter of the ring gear inside, not the cover diameter. That's why you see diff identification diagrams showing the different types.
You have a 3.73 (GT4), with the Eaton locker (G80). But neither indicates the axle type - it's the shape of the cover, absent any other info (like part #s on the tubes, which will be corroded beyond recognition on yours, at this point) or a tag.

From what I can tell, you have the same carrier I do - which I have to look up, as I'm typing this on my phone. And from what I can see online, it appears to be the (on edit: 8.6") (there are a few different versions; what I remember about it is that it's a fairly well-regarded unit, and there's a ton of aftermarket support for it.)

The other carrier you see on most of the 360s has more of a diamond shape. I think (?) it's a (on edit: 8"), but not at all positive, just relying on my memory (and I don't have it.) That one's not so widely used, not quite as robust, not a ton of support, etc.)

Anyway, hope that helps a bit.
 
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Mooseman

Master Blaster
Moderator

Reprise

Lifetime VIP Supporter
Thx, Moose. :tiphat::hail:

OP - I took a look at your thread link, and that's basically the Eaton disintegrating & taking the spiders with it. Not the first time, to be sure, and why they get a bad rap from a lot of people (in general, not here at GMTN, specifically).

Anyway... don't take that as me suggesting yours has gone south, as well. We don't have enough info to hazard a guess, tbh.

When you go to change the fluid, one more thing you can do is check the free play (back / forth movement) on the pinion yoke. You may need to put the trans in neutral (and safely secure the truck so it stays put). You should not have a ton of free play - less than 1/4", optimally (although you should have *some* - just not a lot). If you have excess play, you *may* be looking at a pinion bearing replacement (a fairly big & hairy job).
 

zaid3ssaf

Registered Member
Thanks Moosman and Reprise, I opened the diff and haven't found anything missing or chipped teeth. Thank goodness. No back and forth play in the pinion gear at all, even when I was in neutral. However, the axle wasnt off the ground so maybe that why. I was lucky to have a drain bolt so it wasnt messy. I have no magnet so maybe I should invest in one.

I also couldn't find 75W-90 at 2 different auto stores so I ended up with Valvoline 75W-90 with LS additives from walmart. My understanding of other threads is that the LS additives won't harm G80 (locker) but no LS additives would harm the LS differentials?
 

zaid3ssaf

Registered Member
I have done a "drain and flush" and installed a new filter last september. I was not sure about the trans service history so I basically took the trans line off the cooler and let it drain, changed the filter, then ran the new fluid for 500 miles and drained again. No slippage or anything weird happened. I ran the truck intermittently through the cold iowa winter. It feels like it has a light misfire when I first start her but once RPMs fall down and it warms up it goes away.

240K miles yesterday :biggrin:
 

Reprise

Lifetime VIP Supporter
No back and forth play in the pinion gear at all, even when I was in neutral. However, the axle wasnt off the ground so maybe that why.

Yeah, it would be good to get both back wheels lifted. Sorry I didn't mention that. But you're probably fine, especially if you're not hearing any noise from back there.

If you have the drain plug (mine's in the very bottom of the carrier, near the pinion), I think it's magnetic. If you noticed some filings on the inside end of the plug (a bit sludgy), it's magnetic. I remember mine is, so yours likely is, too.
 

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