possible bad rear diff? need advice

[89Suburban]

I predict its not gonna make it 6 mths

Do you recognize that center section? That "I" piece between the spiders? What is that? Is there supposed to be clutches in there? I don't think that is a G80 "Gov Bomb" setup.

@Doubeleive did you see this?

 

[swathdiver]

Do you recognize that center section? That "I" piece between the spiders? What is that? Is there supposed to be clutches in there? I don't think that is a G80 "Gov Bomb" setup.

@Doubeleive did you see this?

It is a stock G80. The "I" piece is the thrust block.

 

[Doubeleive]

well, a busted carrier is no reason to replace the vehicle. a decent replacement is only about $650 (maybe a smidge more due to inflation)
you might make it a while like that, it might make noises, no telling how long.
I agree with others though, something made it crack.
just baby it for now I would only go the speed limit, drive like granny

 

[89Suburban]

It is a stock G80. The "I" piece is the thrust block.

Ok there must be some pieces missing? Unless that is the backside of it?

 

[swathdiver]

Ok there must be some pieces missing? Unless that is the backside of it?

 

[swathdiver]

The OP needs a new carrier and the internals. It's is easier and less expensive to just replace the differential with a used one from LKQ.

If he had 3.42 gears, he could have my old one, it's been sitting on my driveway for a year and nobody wants it. Nothing wrong with it.

 

[B-train]

Hey fellas. Day off today, so I ventured up to my in laws. He's got a lift, and I was able to use some power tools to remove the cover and take a peek. 1st, the fluid was black, the magnet inside the cover was coated in nastiness. Worse news, appears the spider gear housing has a nice crack in it. I cleaned the inside of the cover and wiped out the diff as good as possible. once I saw the crack my heart sank. But, my father in law asked me if I wanted him to weld it. I figured it couldn't get any worse, so I let him. he tacked it in a few spots, and then on the longer flat section he put a bead. I'm not a welder, but it looks like it should hold. I only need another 6 months with this truck and then I'll be in a better position to get another vehicle. (I have 5 payments left). not sure if the weld will hold, but I drove it back home and it still seems like the left rear is locking up (kinda reminds me of a posi that kinda hops when turning left. let me know what you guys think. I had the rubber gasket on there, so I just cleaned it and put a light bead of RTV, and encircled the bolt holes. no leaks. View attachment 474061

 

[j91z28d1]

I feel like we need to see the other side of the diff?

 

[j91z28d1]

oh my fault, I missed the cracked case. ouch

 

[salisburyv]

The OP needs a new carrier and the internals. It's is easier and less expensive to just replace the differential with a used one from LKQ.

If he had 3.42 gears, he could have my old one, it's been sitting on my driveway for a year and nobody wants it. Nothing wrong with it.

I have 3.08. will the 3.42 work? or will my mileage be worse than it already is? I have found a few complete units, none near me of course. I'm waiting to hear back on 2 of them. Both state 10 bolt, G80, GU4. 3.08. that's me!! one is $249, the other is $400. both graded A. hopefully I can snag one. I really am not ready to give up yet. I can install it. I put 4 rears in my old Pontiac Gran Prix. and that one had drum brakes, I hate drum brakes.

 

[Tinman265]

Think I'd be looking for a used rear differential. I don't think that will make it long.
You have a 3.08 gear (GU4 RPO code).

Because you have an AWD you would have to do both differentials to the same gear. 3.42 is by far more desirable in my opinion but not worth it unless you do a lot of towing.

 

[Marky Dissod]

I have 3.08. will 3.42 work? or will my mileage be worse than it already is?

If you do not have a lead foot, your MpGs will likely improve.

 

[salisburyv]

Think I'd be looking for a used rear differential. I don't think that will make it long.
You have a 3.08 gear (GU4 RPO code).

Because you have an AWD you would have to do both differentials to the same gear. 3.42 is by far more desirable in my opinion but not worth it unless you do a lot of towing.

I usually don't tow.

 

[swathdiver]

I have 3.08. will the 3.42 work? or will my mileage be worse than it already is? I have found a few complete units, none near me of course. I'm waiting to hear back on 2 of them. Both state 10 bolt, G80, GU4. 3.08. that's me!! one is $249, the other is $400. both graded A. hopefully I can snag one. I really am not ready to give up yet. I can install it. I put 4 rears in my old Pontiac Gran Prix. and that one had drum brakes, I hate drum brakes.

Physically, it will bolt right up. But you have a 4x4 and would need to swap out the front differential as well, about $400 and then adjust the programming for the speedometer in the least.

3.08 trucks are gutless compared with 3.42 geared trucks all else being equal. City mileage ought to be better with the 3.42s and highway mileage a little less. GM and the EPA didn't rate them any different fuel economy wise back when they were in production.

 

[Marky Dissod]

3.08 trucks are gutless compared with 3.42 trucks all else being equal. City mileage ought to be better with 3.42, and highway mileage a little less.

ANY highway economy penalty, would mostly be the driver's responsibility.
The benefits come in smiles per gallon when fuel economy is NOT the goal, city & towing MpG, and that the 6L80 may last a bit longer.

GM and the EPA's CAFE tests didn't rate them any different fuel economy wise back when they were in production.

CAFE MpG tests did rate 3.42 lower, but only to the right of the decimal point, as in small fractions of / less than 1MpG difference -
which never show up on a Monroney sticker anyway.

Point is, every GMT900 suv that came with 3.08 (and every other GMT800 vehicle that came with 3.08 or less) should have come with 3.42.
The driver would likely never have noticed the MpG penalty.

 

[salisburyv]

thanks for all the info guys, I really appreciate it. I found a unit locally for $250 out the door (plus my core). same year, RPO code , 8.5" ring and pinion and ratio (3.08) I'm gonna go pay for it tomorrow, then they'll pull it for me and I can get it. I tried to use the truck this morning, but it started banging pretty hard and I didn't want to get stuck on the road, and miss work, so I limped her home and took the wife's car. I'm so relived that it's local and I won't have to pay for freight. Donor only has 100k on it, so it should be nice and quiet again. I'll change the fluid and pop the cover off before I install it. Anything I should be telling the salvage guy to leave on there? I'm assuming they're just gonna cut it outta there. I need to see what the interior color is, might ask for some interior bits I want as well. I'll post up when it's road worthy again. thanks again!!

 

[strutaeng]

Oh, that's AWESOME news!

Hopefully everything goes well and you keep on trukin'...

 

[West 1]

Should be a very straight forward swap. Keep clean fluid in the diffs and they will out live the truck. #250 is a great deal on one with only 100K on the clock. I swapped a 4.10 rear to a 3.42 rear just to see if my MPG was a big increase. Even from 4.10 to 3.42 I did not find much difference. I did like the quiet cruise on the freeway while taching 1,800 RPM rather than 2500 rpm. Other than that the 4.10 was the superior gear in the Tahoe I had with a 5.3 and 4 speed automatic trans. 3.08, no thanks unless you are always on flat ground.

 

[salisburyv]

Should be a very straight forward swap. Keep clean fluid in the diffs and they will out live the truck. #250 is a great deal on one with only 100K on the clock. I swapped a 4.10 rear to a 3.42 rear just to see if my MPG was a big increase. Even from 4.10 to 3.42 I did not find much difference. I did like the quiet cruise on the freeway while taching 1,800 RPM rather than 2500 rpm. Other than that the 4.10 was the superior gear in the Tahoe I had with a 5.3 and 4 speed automatic trans. 3.08, no thanks unless you are always on flat ground.

99% of the time its a highway cruiser. I go up to Maine regularly, my daughter goes to college up there. The ride is very smooth, and with larger wheels/tires than stock it always feels well planted. I have a nice sound system in it, and the miles just melt away,lol. I'm hoping to get a look at the new rear end when I get to the salvage yard. I might grab the coil springs and possibly the calipers if they're reasonable.

 

[salisburyv]

ok. I paid for the unit. They are gonna try to get it to me before Christmas, but he said def by the 26th. Do you guys have any tips/tricks I need to know? what else should I replace while I'm doing this? U joints? Bushings? any info would be helpful. Thanks in advance