8.5 diff tear down and rebuild

[Matthew Jeschke]

Okay, funny story, my rear differential is acting up. Truck won't move unless I put it in 4wd. I want to field questions here as I tear it down. I've watched the customary Youtube Tutorials, etc. I may just buy another unit from junkyard but need to know what I've got first

Is there a way to know what gears and differential configuration I have by looking in glove box?

 

[swathdiver]

Okay, funny story, my rear differential is acting up. Truck won't move unless I put it in 4wd. I want to field questions here as I tear it down. I've watched the customary Youtube Tutorials, etc. I may just buy another unit from junkyard but need to know what I've got first

Is there a way to know what gears and differential configuration I have by looking in glove box?

Yes! Your axle ratios and type will be in your "G" codes. You can add a G80 if you don't already have it and if you find a 2WD, Suburban LTZ, Denali or Escalade, they will have the larger AXN 9.5" axle which will bolt right up to your truck. G80 is the locking differential, which is a combination locker/positraction unit.

Most trucks will have GU4 (3.08) or GU6 (3.42) gears. The 2007-2008 trucks will have those and GT4 and GT5 (3.73 and 4.10).

 

[Matthew Jeschke]

Sweet I see the G80 code as well as GT4 for 3.73. My truck is a 2001, I am assuming the 3.73 is because is Z71 package? Yo7 had mentioned it being less comon for those years.

Also curious is posi standard on there or are they open diffs?

Next I woundered about the bigger tougher gears, 9.5. However will that effect my ground clearance? I am asuming by at least 1/2 inch?

Sent from my SM-G925V using Tapatalk

 

[swathdiver]

Sweet I see the G80 code as well as GT4 for 3.73. My truck is a 2001, I am assuming the 3.73 is because is Z71 package? Yo7 had mentioned it being less comon for those years.

Also curious is posi standard on there or are they open diffs?

Next I woundered about the bigger tougher gears, 9.5. However will that effect my ground clearance? I am asuming by at least 1/2 inch?

Sent from my SM-G925V using Tapatalk

Yes, the G80 combines the functions of both a positraction unit and a locker.

@randeez recently put an AXN under his truck, he can tell you about that better than I. All I would say now that I realize you have the older body style, is to stick with the older body style when sourcing axles. Things will swap much easier. And don't forget drum and disc rear brakes, more work to swap over from one to the other.

 

[Matthew Jeschke]

Great news, it's a positraction and locker. Thanks for sharing... Bad news, wow it's really chewed up. I got the service cover off and about gagged the oil smelt so bad. It's been serviced maybe once in 230,000 miles.... I say that only because somebody goobered RTV everywhere.

I think I need to pull the whole rear end out and tear it down now. There's what looks like needle bearings fishing around in the bottom of the case. The passenger side carrier / axle shaft bearing was out of the race. The ring and pinion gears are chewed up (likely from when it stopped moving). And that's all I can see for now. Metal shavings everywhere, small metal particles all over in the oil. Looked more like silver than oil. Pretty bad.

Silly me I assumed all the noise was from my front diff, and some was, but the rear diff was also bad. Literally next task on my plate was to remove the service cover and inspect, then it blew up :/

 

[randeez]

not sure what would have came those years with a "linked" 9.5 sf. not even sure if the denali/escalades came 2wd for those years. seems they put them behind large engine/2wd models for 1/2 tons. maybe look into avalanches/escalade ext. would make for the easiest swap.
not sure if the later year 07-14 2wd axles would work

 

[Erickk120]

I would be willing to bet you it was only serviced once because the previous owner felt something wasn't right, so he decided to change his oil, that shall take care of all the growling and weird noises, right?

Are you taking us into the ride when you rebuild this one? its a lot to ask but it would be cool to see how it goes, or at least post the money shot pattern when you are done
The bearing pitting shall buff right out with a polisher

Forgot to add, at least the gears inside the unit look to be in good shape, unlike mine I had pitting on them when I took it apart.

 

[Matthew Jeschke]

Sure I'd love to share what I learn. I'm curious can you elaborate on bearing pitting?

This is a completely ridiculous thing to ask but that ring gear and pinion are shot right? There's no way those could be reused? Cause *ahem* their the most expensive part of it all lol

 

[Erickk120]

Sure I'd love to share what I learn. I'm curious can you elaborate on bearing pitting?

This is a completely ridiculous thing to ask but that ring gear and pinion are shot right? There's no way those could be reused? Cause *ahem* their the most expensive part of it all lol

Even if you could get away reusing it I would rather not, they have seen better days and are pretty much shot. Oh no I was joking about how the roller bearings. They are just beat to death, and deformed. I wonder how they came out of the cage and races though. Since you said you found them gutted already am surprised you didn't hear much from the rear end in those conditions.

Yeah the ring and pinion are the most expensive items. I don't have much experience re-gearing but I've done a few, I used USA standard gears for my 04 z71 since I didn't want to throw the whole 200+ for a set of yukons, or Motive blues gears. They are pretty much Yukon gears that didn't pass the top quality control so instead of throwing them away they just rebrand them to USA standard and sell them cheaper, same strength and all as yukons, just didn't pass QC, Mine are pretty quiet, those can be had for around $150 and there is a coupon in amazon for $20 off atm, so thats around 120 for gears.
Might not be as easy to read the pattern as yukons though, or atleast mine gave me a little headache trying setting up or could have been that I didn't hollow my set up bearing properly and it ended up being eggshaped instead of a circle. I realized that way after I was done though, but helped me learn new skills.

 

[Matthew Jeschke]

Maybe I order those gears now. It's a long story for which I have another thread going. It started having drive resistance, and had LOUD gear noise like my vette w/ manual tranny at 140mph. I hooked up microphones to front diff to diagnose as I thought that was problem. It was... So I fixed it. Not realising it was ONE of two problems. I literally drove the truck for a block to test repair to font diff. Still had noise. Pulled in driveway, my driveway has an incline, rear diff started slipping trying to climb driveway. I put it in 4wd and pulled into garage. Literally, THE next thing on my list was to remove service cover and inspect rear diff. I think the slipping is what tore up those gears