Won't move in 2wd

[HoeLuvr]

Hello, All. New here. I have scoured this forum as well as many others and can't seem to find the answers I need. So I thought I would ask yous guys.

I have a 2004 Tahoe Z71 4WD not AWD. Just aquired. The issue is, it will not drive in 2wd. It will drive in 4wd. The rear drive shaft IS engaging in both 2wd and 4wd. Fluid in rear diff was empty. Like bone dry! refilled with 75-90 full synthetic. Did not help. To late to save? What is in there that could burn up? How can I know for sure the rear end is bad before I go to the junkyard and place a $200 gamble on another one? Should I rebuild/upgrade this one?

I do have to rebuild the front diff as well.

Any help would be greatly appreciated!

 

[B-train]

You probably done have any spider gears left in the rear diff. I encountered that once as a tech 22 years ago on a S-10. Dude mud bogged the shit out of it and had the same result you speak of.

Also, since it was empty, you might was well find a bone yard axle to put in. Don't even mess with it further. Pull the rear cover off and have a look-see.

 

[strutaeng]

The rear end sounds like is burned up.

How did you drive it home? In 4x4 mode? Does it run both in 4HI and 4LO?

Jack up the rear end, put in Neutral and remove the driveshaft. Try to spin the rear differential by hand. It should have some resistance, but you spin freely.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

Can you get the truck up off the ground with a set of jacks and jack stands and see how the rear wheels turn (or not turn)?

 

[HoeLuvr]

You probably done have any spider gears left in the rear diff. I encountered that once as a tech 22 years ago on a S-10. Dude mud bogged the shit out of it and had the same result you speak of.

Also, since it was empty, you might was well find a bone yard axle to put in. Don't even mess with it further. Pull the rear cover off and have a look-see.

That was my thought as well. Probably pull apart just to see what it looks like in there.

The rear end sounds like is burned up.

How did you drive it home? In 4x4 mode? Does it run both in 4HI and 4LO?

Jack up the rear end, put in Neutral and remove the driveshaft. Try to spin the rear differential by hand. It should have some resistance, but you spin freely.

Yes. I drove it home in 4wd. Both 4HI & 4LO work. I was very worried that I wouldn't make it because the front diff is all but shot also.

So with the truck on the ground, 2WD, in drive or reverse, the rear driveshaft will actually start spinning in the correct direction (forward or reverse) and the truck will not move. I guess I'm not sure what jacking the truck up, removing the driveshaft, and spinning by hand will tell me. Will the wheels engage if it's still good? Will the wheels spin also just because of friction? Please elaborate. I will try this tomorrow just for my own education.

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

Can you get the truck up off the ground with a set of jacks and jack stands and see how the rear wheels turn (or not turn)?

I will get some pics over the weekend. I am sure i will be posting more as i have some plans for this tahoe. I will also try to get it off the ground and see what happens.

Thank you all for your advice.

 

[strutaeng]

That was my thought as well. Probably pull apart just to see what it looks like in there.

Yes. I drove it home in 4wd. Both 4HI & 4LO work. I was very worried that I wouldn't make it because the front diff is all but shot also.

So with the truck on the ground, 2WD, in drive or reverse, the rear driveshaft will actually start spinning in the correct direction (forward or reverse) and the truck will not move. I guess I'm not sure what jacking the truck up, removing the driveshaft, and spinning by hand will tell me. Will the wheels engage if it's still good? Will the wheels spin also just because of friction? Please elaborate. I will try this tomorrow just for my own education.

I will get some pics over the weekend. I am sure i will be posting more as i have some plans for this tahoe. I will also try to get it off the ground and see what happens.

Thank you all for your advice.

Ok, so if your driveshaft is spinning but your wheels are not, no need to do what mentioned about jacking it up: your differential gears are blown. In my mind I was thinking something was binding, but that's not the case.

I wouldn't even bother with axle if I was you. Pull your RPO code on gear ratio and if you want a G80 and head straight to the junkyard and get another complete axle.

And the front as well?

What's the story with the truck anyways? How did the PO manage to blow both axles? Where did the oil on the rear axle go? Leak maybe?

 

[HoeLuvr]

So story is, I've known this truck for the past 15 years or so. Colorado truck. Very little rust. Young guy bought it and put a 4 inch lift on it. Aftermarket wheels and bigger tires. Everything else remains stock. Father in law bought it 10 years ago, never did any routine maintenance on it. Hardly ever drove it. Brother in law bought it 4 years ago, again never drove and one oil change. One of my nieces drug a tractor blade down the passenger front door leaving a huge open gash(I'll get pics when I have the chance). My son bought it 2 years ago and started doing what he could when he could as far as repair and maintenance. Which wasn't much or enough. Front diff started howling so pulled front drive shaft and started looking for replacement on Marketplace. Suddenly rear-end went out. So I went out reinstalled front driveshaft and limped it home. He didn't want to put the money in it so I bought it from him.

This is still a rust free truck that runs great. So I'll fix it and then some.

 

[rockola1971]

When you replace the guts of your rear diff or just put another unit in, remember that the axle ratio has to match the old one because the old one matches the front diff axle ratio. When the front and rear diff ratios dont match VERY BAD LOUD things will happen.

 

[HoeLuvr]

Well, here she is, in all her glory! I willgo to the boneyard shortly and grab another door. But first I must address this.

Kinda hard to tell, but that is my rear pinion gear. Mirror smooth. Where did the teeth go?

There's some of them. I can't believe this thing even moved on its own. The rest of the teeth are in the bottom of the housing. I've been wrenchin most my life and I've never seen a pinion gear like that. Needless to say I am going to replace this whole assembly. It's the gt4/g80 so 3.73 locker. Yes I know it needs to match the front. But that's always good to point out for those who don't know. I'm going to try to find a Hoe that I can pull the front and rear from. Did any of these 04ish years come with 4.10's? With same wheel bolt pattern? I need to look up the RPO Code for that. Luckily, the yards only have about 20 of this model in inventory at any given time! What a shame. When I get this rear-end out I'll pull that ring and pinion and take better pics. Probably go on my customer states shelf lol!

 

[Doubeleive]

View attachment 433939View attachment 433940View attachment 433941
Well, here she is, in all her glory! I willgo to the boneyard shortly and grab another door. But first I must address this.
View attachment 433942
Kinda hard to tell, but that is my rear pinion gear. Mirror smooth. Where did the teeth go?
View attachment 433943
There's some of them. I can't believe this thing even moved on its own. The rest of the teeth are in the bottom of the housing. I've been wrenchin most my life and I've never seen a pinion gear like that. Needless to say I am going to replace this whole assembly. It's the gt4/g80 so 3.73 locker. Yes I know it needs to match the front. But that's always good to point out for those who don't know. I'm going to try to find a Hoe that I can pull the front and rear from. Did any of these 04ish years come with 4.10's? With same wheel bolt pattern? I need to look up the RPO Code for that. Luckily, the yards only have about 20 of this model in inventory at any given time! What a shame. When I get this rear-end out I'll pull that ring and pinion and take better pics. Probably go on my customer states shelf lol!

that's what happens when it gets ran bone dry! that was the first clue

 

[strutaeng]

H*O-Lee Chit Batman!

Regarding 4.10s, I have heard/read they did come with them, but pretty rare for sure.

For the front differential, I think you can also include Silverados (not the rear because those had leaf springs for a direct built-in.)

 

[HoeLuvr]

H*O-Lee Chit Batman!

Regarding 4.10s, I have heard/read they did come with them, but pretty rare for sure.

For the front differential, I think you can also include Silverados (not the rear because those had lead springs for a direct built-in.)

That's actually the only info I can dig up is for Silverados. I'm sure I'll end up with 3.73's which is fine for now. I have a set of Dana 60's that I have considered swapping in. But I actually like the thought of a prerunner build for this Tahoe. Want to get this on the road for now so I can address any other mechanical issues it might have.

 

[Doubeleive]

That's actually the only info I can dig up is for Silverados. I'm sure I'll end up with 3.73's which is fine for now. I have a set of Dana 60's that I have considered swapping in. But I actually like the thought of a prerunner build for this Tahoe. Want to get this on the road for now so I can address any other mechanical issues it might have.

inside the glove box is a sticker/label on there is a list of RPO codes, those codes will tell you the axle ratio, when you go to the junkyard just match it up
you are looking for a GU code so like gu6 i.e. 3.42 (most common) but could be gu5, etc...

 

[89Suburban]

H*O-Lee Chit Batman!

Haha you took the words right out of my mouth

 

[Fless]

Adding to what @Doubeleive said.

 

[HoeLuvr]

Yes, these are from my tahoe.

I know the GT4 is 3.73 and the G80 is Positrac, what's the G63 in between them? I can't find it on any RPO codes list. I thought it might be the front diff code, but again can't find that anywhere.

View attachment 433953

Adding to what @Doubeleive said.

And thank you for that. That is what I found also.

Does anyone know if a 3/4 ton front diff and rear axle assembley will bolt right in to my 1/2 ton tahoe? Can't seem to find any definitive answer. I know axles, wheel bolt pattern, knuckles, and brakes would have to change. But front diff carrier specifically. Are the mounting points the same?

Just pondering different options. Thanks again for everyone's input.

 

[strutaeng]

Yes, these are from my tahoe.View attachment 434004
I know the GT4 is 3.73 and the G80 is Positrac, what's the G63 in between them? I can't find it on any RPO codes list. I thought it might be the front diff code, but again can't find that anywhere.

And thank you for that. That is what I found also.

Does anyone know if a 3/4 ton front diff and rear axle assembley will bolt right in to my 1/2 ton tahoe? Can't seem to find any definitive answer. I know axles, wheel bolt pattern, knuckles, and brakes would have to change. But front diff carrier specifically. Are the mounting points the same?

Just pondering different options. Thanks again for everyone's input.

Unfortunately, neither 8 lug axles are direct swaps. They'll both require extensive modifications ( IDK what though) to make them work. I'm sure there's someone that has done it. A welder and some fabrication and enough time you can do it.

However, the "AXN" rear axle that was available on some of the high performance SUVs is a direct swap if you want something stronger. It's still 6 lug like your rear axle.

 

[Fless]

G63 is a Roof Luggage Carrier.

 

[HoeLuvr]

Unfortunately, neither 8 lug axles are direct swaps. They'll both require extensive modifications ( IDK what though) to make them work. I'm sure there's someone that has done it. A welder and some fabrication and enough time you can do it.

However, the "AXN" rear axle that was available on some of the high performance SUVs is a direct swap if you want something stronger. It's still 6 lug like your rear axle.

So instead of AXP on the glove box sticker it would have AXN? Is this still a positrac? Is it better?

G63 is a Roof Luggage Carrier.

Thank you. I see your a mile high! I lived in Grand county, for 23 years. Sure do miss those mountains!

 

[strutaeng]

So instead of AXP on the glove box sticker it would have AXN? Is this still a positrac? Is it better?

Thank you. I see your a mile high! I lived in Grand county, for 23 years. Sure do miss those mountains!

The AXN is a 14 bolt, 9.5" semi float axle vs your original 10 bolt, 8.6" semi float axle. Obviously, the larger ring gear of the 14 bolt is much stronger. I don't know all the other details such as shaft diameters, etc.

The differential locker (what you are calling "positrac"?) is independent of the axle; any axle may be open differential or could be optioned with a locker. But needless to say, a 9.5" G80 LOCKER is also stronger than a 8.6" G80 LOCKER. Neither are a Limited Slip Differential (LSD) or also called "positrac", at least not on the full sized GM vehicles.

I hope this makes sense.

There's a member here swapping an AXN into his GMT900 SUV, but I can't remember who it is now...