[alb9110]

hey

just have a question about changing the diff fluid. i have an 2002 silverado Z71 and was wondering if i needed to add any additives because some people say that i do and some say i dont. any info is great.

 

[silveradotrailblazer]

'02 Z-71's had limited slip rear ends so you need a additive. Starting in '04 the Z-71's came with a true locker.

 

[Crawdaddy]

Pretty much you only need the additives if you have a G80 locking rear differential. It won't hurt anything if you put the additives in and you don't have the G80, but if you do have it and don't put the additives in it can mess up the clutch pack.

 

[alb9110]

alright thanks ill go get a bottle today. also does matter who makes it and how much should i put in

 

[silveradotrailblazer]

If you go to your GM dealer they have small bottles of the additive and just add the bottle.

 

[Crawdaddy]

I think you can also get it from AutoZone and the like in the single-use bottles.

 

[jreagan]

'02 Z-71's had limited slip rear ends so you need a additive. Starting in '04 the Z-71's came with a true locker.

Pretty much you only need the additives if you have a G80 locking rear differential. It won't hurt anything if you put the additives in and you don't have the G80, but if you do have it and don't put the additives in it can mess up the clutch pack.

This is a very confusing topic. If you hop over to the Powertrain subforum and read the sticky thread at the top, you'll see folks with trucks prior to 04 that claim they have lockers. Are they wrong?

And my understanding is that the lockers don't need friction additives. Only the limited-slips in the Corvettes, etc. (ie, not lockers) need the friction modifier. Yes there are clutch packs in the G80, but they don't do the same thing as the clutch packs in the Corvette limited slip.

The real confusing part is that GM calls them all G80 in the RPO label.

 

[2COR517]

My 97 K2500 had a G80, and it was a full locker. It worked perfectly too, on 80W90 no additive. The G80 works like an open diff, until a significant difference in wheel speed occurs. The actual difference has been rumored to be anyway from 10 RPM to 100 MPH, either way, it doesn't matter. Once this difference is reached, a flyweight moves and instantly locks both axle shafts together. At this point you have a full locker, power is transmitted equally to both sides. On paper and in theory it's a perfect setup. No effect on street handling, but a full locker when you need it. In practice, however, there are some issues. The primary problem being the sudden lock and transfer of power. This can create quite a shock load on the carrier, often resulting in a broken carrier at the passenger side of the bearing. GM further magnified this weakness when they "upgraded" the 10 bolt from a 28 spline axle shaft to a larger diameter 31 spline shaft. Rather than redesign the carrier to maintain strength at the bearing area, which would have required modifying the carrier bearing and possibly the housing, they simply took more meat out of the carrier.

Regardless, a quality synthetic gear lube like Mobil 1 is all you need.