rear axle questions

[stutaeng]

Well, maybe I'm wrong on my previous post then? I should have been more specific on the G80 ON THE GMT 400s. I thought it was a locker based on what I read here some time ago. The axles are not locked together then when engaged? It was my understanding the axles do get locked together or at least they both spin at the same exact rate.

And remember some of the early GMT400s had a Dana 70. They too got the G80 RPO code, I think. Not sure that was in them.

 

[Schurkey]

GM advertises it as a locking differential.

GM certainly does not want excess "posi" friction-modifier in the gear lube, which does promote slippage.

I think the idea is that the carbon-based clutches aren't intended to slip, (much) they're intended to be engaged/disengaged by the added clockwork of the speed-sensing "governor".

In real life...they're a clutch-type "posi" with "added features", whereas aftermarket "lockers" really do LOCK. Even Detroit Lockers have a harsh "ratchet" when one wheel turns faster than the other. The TrueTrac has no clutches, it's got some variation of the Torsen-patent worm-gear system.
www.youtube.com/watch?v=lZmsY2YvVsc

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So in the same way that light is both a wave and a particle, the G80 Gov-Lock is both a "locker" and a "slipper".

But that's just my opinion. And I've been wrong before. And maybe mine is just worn-out. Lord knows it took a "vacation" when I filled it with Amsoil gear lube having friction modifier already mixed-in. (Seems to have come back to life with two changes of no-additive gear lube.)

 

[stutaeng]

Um...I think all my G80s are like a light switch; when they engage, I can feel it as I gain traction; somewhat harsh, but I don't expect it to be buttery smooth... LOL.

I have a G80 in a 99 NBS 2wd 10 bolt/8.6", 00 K3500 14 bolt/10.5", 06 2wd 14 bolt/9.5" and 04 4x4 14 bolt/9.5". Combined, close to 850k miles together. Only truck that I've driven the most was the 10 bolt, as I bought the rest with high miles. I was always "careful" if I ever off-roaded though.

So we definitely confused the OP! What are we telling him? I think he'll be okay/happy with the Detroit TruTrac...

I was looking at getting "something" for my swapped 14 bolt/9.5" axle recently for my 99, and was eye-ing that differential...it turned out it already had the G80, so I decided to keep it...

 

[sewlow]

According to Miss Mona Lisa Vito..."What is Positrction? It's a limited slip differential which distributes power equally to both the right & left tires. The '64 Skylark had a regular differential, which, anyone who's been stuck in the mud in Alabama knows, you step on the gas, one tire spins, the other tire does nothing."
Just because she wore that Cat-Suit, I believe her.

'Positraction' or 'Posi' is a GM coined term first used in '57.
Pontiac called theirs 'Safe-T-Trac'.

 

[Schurkey]

Total edit, removed crummy video and replaced it with this one.

www.youtube.com/watch?v=tTGZOJQQBeE

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[stutaeng]

...so it's a LSD, UNTIL it detects slippage, then it becomes a locker??? I think that's what I understood watching that like 3 times, LOL.

Or did I get that wrong?

 

[Schurkey]

No, theoretically it's an "open" until it detects slippage. Then the flyweights fly, and the gears move, and SHAZAM! the clutches lock.


Unless they don't lock. Then they slip.

 

[eran tomer]

back to the full float swap...
i read contradictory opinions on whether the yoke fits or not the driveshaft.
btw my car has the 13" drums.

 

[RichLo]

Do you mean if it takes the same U-Joint? No need to swap yokes when changing axles. If its a different size you can buy conversion u-joints that have two different size caps to fit both your factory driveshaft and swapped axle.

 

[Schurkey]

back to the full float swap...
i read contradictory opinions on whether the yoke fits or not the driveshaft.

Going from 9.5" ring gear axle to 10.5" ring gear axle, you'd not only need to verify the U-joint, you'll also have to verify how much farther the yoke is from the axle centerline.

When changing an 8.5 to a 9.5, the 9.5 yoke is about 3/8" farther from the axle centerline. Ideally, the driveshaft should be shortened ~3/8", but no-one does--they just cram it farther into the tailshaft housing.

And that works. That's what I did, years ago.

But I don't know how much bigger the 10.5 housing is from the 9.5 housing. I have a suspicion that it's enough bigger to require shortening the driveshaft. This is only a suspicion. Supposed to have thunderstorms starting any minute, and lasting all day tomorrow; and I'll be gone for the weekend. Remind me, and I'll take a measurement or two when I get back.

btw my car has the 13" drums.

There's at least three different versions of the "13" drums".

13" semi-float, drums slide right off the axle shafts.
13" X 2.5" full-float, have to remove hubs and bearings to get the drums off.
13" X 3.5" full-float, drums may slide off the hubs--I have contradictory info on them.