G80 locking diff questions

[Tbruz]

So I just discovered the original window stickers for my 1997 two door Tahoe.
Per the sticker and verified on the glovebox door I do have the G80 locking rear differential with 3.73 gears.

Original owner discussion and all paperwork received show no rear end service or repairs/issues with the truck before I got it.

Thinking I had just a regular open diff when I changed out the reaf diff lube about 8K miles ago I replaced it with Amsoil severe gear 75-90 synthetic EP lube.

1) Is this the correct lube for the G80?
If not how can I tell if I've done any damage/harm.

2) if I jack up rear of vehicle and spin a wheel, what direction should the other wheel spin? Same rotation or opposite rotation?
Basically how do I test the operation of a limited slip G80 rear end.
Thanks in advance
Tbruz

 

[SunlitComet]

Change it to the standard 80w-90 gl-5 stuff . No additives. If truck is just sitting there it will just act like an open differential. As long as you don't abuse it it should be fine.

---------- Post added at 09:29 PM ---------- Previous post was at 09:26 PM ----------

If you want to test it you need to slip one wheel with power on the drivetrain enough will get it to lock and start the opposite will. Just try to do it on slippery surfaces.

 

[Tbruz]

Thanks Sunlit,
I'll try to spin wheels on a slick surface and see what happens.

Does turning one wheel while the rear is lifted and observing what direction the opposite wheel turns indicate anything on this type of rear end?
Same direction = posi diff
opposite directions = open diff

Thanks,
Tbruz

 

[SunlitComet]

Like I said for the g80, spinning it by hand of the ground it should act like an open unit since it is not actually locked.

 

[_Dylan_]

It locks above a certain speed, IIRC around 15 mph. Find somewhere to get one of the back tires loose/off the ground. The tire should be sitting and spinning like an open diff, but if you give it some more gas it should lock and you will start moving.

 

[SunlitComet]

Oh that will be safe if off the ground.

---------- Post added at 01:40 AM ---------- Previous post was at 01:32 AM ----------

maybe some oil on a tire that you can clean later.

 

[_Dylan_]

You must be thinking of having it on a jack...I meant somewhere off road like a ditch or something.

 

[bowtiefreak]

worst case the g80 doesn;t work and you have an open diff.

I ran a G80 in mine for a long time with no problems (even with the 383!). The most common problem is stupidity. Spinning the tires and then one catching a little more than the other...BOOM. Drive like you like your truck and it should be fine.

 

[Tbruz]

Thanks to all for the input.
I was concerned because when I had it up in the air it did act like an open diff.
Now that I know it's supposed to act that way when not under power I have no more worries.
This truck was babied by the original owner and I only need 4wd to handle the NH weather. It does not go off roading so the freshly serviced G80 should be fine for my needs.
Tbruz

 

[WalterMitty]

Thanks to all for the input.
I was concerned because when I had it up in the air it did act like an open diff.
Now that I know it's supposed to act that way when not under power I have no more worries.
This truck was babied by the original owner and I only need 4wd to handle the NH weather. It does not go off roading so the freshly serviced G80 should be fine for my needs.
Tbruz

I check mine every year when it gets slick out. It's usually easy to put the right rear on a slick spot and the left rear on the dry. If it's on an incline it helps. Apply moderate power until the right rear slips, keep applying power until you get good lockup.

NOTE! If you haven't driven in the slick with a locker before, realize that the rear end will really come around on you if you're spinning while locked!

 

[bowtiefreak]

When used properly I rarely even use 4wd unless the family is in the truck

 

[SunlitComet]

well wheres the fun in that?

 

[WalterMitty]

I hit the 4X button every chance I get. If it's slick I use it. Easy on, easy off. Now, back in the days when I had to get out and lock and unlock hubs, I was as lazy as the rest. Today I consider it my civic duty to mitigate wash boarding on dirt roads and avoid polishing icy surfaces with unnecessary wheel spin.

 

[gpracer1]

Get on a dirt road. Turn the steering wheel slightly. Punch it. If you start getting sideways, it's working. Plus you can back up and see the peel out marks in the dirt.

I love the auto 4x4 button...... It will barely slip one rotation and go right into 4x4.

 

[Phone Man]

I'm jealous you have 3.73's. Most have 3.42.

 

[Tbruz]

What's the benefit of 3.73 over 3.42?

 

[noJeepshere]

What's the benefit of 3.73 over 3.42?

Greater torque applied to the rear wheels. The numbers indicate how many times the driveshaft turns for every revolution of the wheel. The higher the numbers, the more turns, thus more power applied.

 

[SunlitComet]

but go to far and mileage suffers really bad and power band to ground gets kinda weird. kinda of a balancing act. 3.42 to 3.73 would give you more towing capacity. with all other variables not changed.