New Truck Noises

[patsfan]

I bought my wife a 2011 regular cab sierra w/4.3L and G80 locking diff. For the first 600k there wasn't any noise but it seemed to develop a humming/vibration/grinding noise from the passenger rear. I brought it back to the dealer and they couldn't recreate the problem but noticed some noise in the exhaust. They dropped the diff fluid and couldn't find anything there either. It seems sporadic and the noise level is inconsistant. I also noticed on the dealer invoice there are 3 units of gear lube and 1 additive. My understanding from other posts is that no additive is required for G80 locking diffs. Also, one time when I took off on some ice the diff studdered before locking. Like it couldn't lock for 2-3 revolutions and sounded like a banging. Any ideas or suggestions are appreciated.

[bluArrow]

 

 

For the first 600k

You can tell it's a GM truck: "for the first 600,000 miles"

[patsfan]

I took it for a ride with the salesman on a straight highway and it seems the noise is from the exhaust upon acceleration @ 70-80 km/h. It's almost like the gears want to change from fourth to third but it stays in fourth and bogs down. If I punch it, it will downshift but not make the noise. I'm still unsure if the diff fluid should be changed again because of the additive?

[cliobogger]

pretty sure he was referencing kilomiters...i dont think its possible to drive 600,000 miles in a year...let alone since when the 11s were introduced. haha.

[patsfan]

For the first 600k

You can tell it's a GM truck: "for the first 600,000 miles"

 

 

 

first 600 km

[patsfan]

I took it for a ride with the salesman on a straight highway and it seems the noise is from the exhaust upon acceleration @ 70-80 km/h. It's almost like the gears want to change from fourth to third but it stays in fourth and bogs down. If I punch it, it will downshift but not make the noise. I'm still unsure if the diff fluid should be changed again because of the additive?

 

After speaking with the shop foreman at the dealership, I was told the best solution so far is the one I found on this site. They want to do the flex pipe bulletin #02-06-05-003E. Anyone have this done and what where your results? Also, from what I've read on here, the G80 diff doesn't require additive when changing the oil. Can anyone confirm this.

[Sir Dan]

I took it for a ride with the salesman on a straight highway and it seems the noise is from the exhaust upon acceleration @ 70-80 km/h. It's almost like the gears want to change from fourth to third but it stays in fourth and bogs down. If I punch it, it will downshift but not make the noise. I'm still unsure if the diff fluid should be changed again because of the additive?

 

After speaking with the shop foreman at the dealership, I was told the best solution so far is the one I found on this site. They want to do the flex pipe bulletin #02-06-05-003E. Anyone have this done and what where your results? Also, from what I've read on here, the G80 diff doesn't require additive when changing the oil. Can anyone confirm this.

 

It's my understanding that you are NEVER to use any additive in these G-80 rear ends. I hope everything turns out okay with your humming noise.

[cwendel4]

I would. The rear has clutch packs in side, it is not a true locker but a modified limited slip.

Now, if the dealer put in additive, save the invoice. If any type of additive can lead to failure of the diff, they will be holding the bag. Any body else have info on this?

[MaverickZ71]

Here is what the General says to use for 1500 rear difs:

 

 

 

Usage Fluid/Lubricant

 

Rear Axle

 

SAE 75W-90 Synthetic

 

Axle Lubricant

 

(GM Part No. U.S. 89021677,

 

in Canada 89021678) meeting

 

GM Specification 9986115.

 

 

 

 

Doesn't say anything different for G80 lockers or any other types, or refer to any special additives.

[patsfan]

Here is what the General says to use for 1500 rear difs:

 

 

 

Usage Fluid/Lubricant

 

Rear Axle

 

SAE 75W-90 Synthetic

 

Axle Lubricant

 

(GM Part No. U.S. 89021677,

 

in Canada 89021678) meeting

 

GM Specification 9986115.

 

 

 

 

Doesn't say anything different for G80 lockers or any other types, or refer to any special additives.

 

The invoice says...

 

Qty: 1

FP Number: 992694

Description: Additive Y 088000

 

Qty: 3

FP Number: 89021678

Description: Gear Lube Y 088000

[tanked_darren]

WELL WHICH IS IT?

 

I never put additive in mine, but some of the guys I work with say you need it, but they aren't GM mechanics.

 

I went to the dealer and the oil itself is all they said I need so thats what Im going with for it.

[rebelman06]

I am under the impression that you DO NOT add anything to the fluid for the gov-loc. The RPO code G80 is used in trucks and cars. It usually represents a limited slip diff in cars, which requires LS additives. The gov-lock does not need the friction modifier additive.

[patsfan]

WELL WHICH IS IT?

 

I never put additive in mine, but some of the guys I work with say you need it, but they aren't GM mechanics.

 

I went to the dealer and the oil itself is all they said I need so thats what Im going with for it.

 

From what I've read in this and other forums about 80% of people say no additive and some quote GM instructions to back it up. I would love to see this GM documentation to bring to the dealership.. anyone have a URL?

[cwendel4]

Check you manual. It should say what to refill the diff with and might even give you the part numbers as of the printing of the manual.

[patsfan]

Check you manual. It should say what to refill the diff with and might even give you the part numbers as of the printing of the manual.

 

 

Manual:

SAE 75W-90 Synthetic Axle Lubricant (GM Part No. U.S. 89021677, in Canada 89021678).

 

 

 

I talked to a friend of mine that works parts at a dealership and he said that he hasn't seen a bottle of additive used for a newer truck. I'm bringing him the invoice tommorow to see what exactly it is that was put in the diff.