rear and front axle fluids

[the winemaker]

I know there has been lots of questions in regard to different types of axle and diff fluids,however perhaps you could answer this dumb question for me...I recently changed my rear axle fuid,,2000 gmc 2500 4/44drextcab..using castrol syn axle fuid[gl5]as dealer wanted 28 dollars plus tax for gm product..can I use same type in front axle[it calls for 80-90 gear lub not syn] or should I stick with as owner manual states a 80-90 straight gear lube...with thanks
the winemaker,truro nova scotia canada

 

[Bret Chase]

If I recall correctly, in order to use synthetic in early models (99-01)
of the current generation trucks, you need to replace the front axle vent as it is incompatible with synthetic oil. I think there's a TSB out on it.

-Bret

 

[Rat407]

I own an 02 Silverado and changed the front axle out to AMSOIL 75w-90 over 36k ago with no problems and I didn't change out the vent tube.

There is a TSB out in extreme cold weather climate conditions where the dealer will change out the fluid to synthetic, to keep the front axle from damage due to the cold conventional oil not being fluid enough. I would imagine they change out the vent tube at the time since it is a dealer change.

I know of several others on another board that have changed out to synthetic and didn't change the vent tube and have had no problems.

 

[heyjay]

Yes, the TSB warns that the regular production black vent may not be compatible with all synthetic gear oils, and seepage may occur if you retain this vent.

The new vent grommet and tube is white.

I have a 2000 GMC Sierra and did the initial axle service at 1,000km, then a follow-up at 2,000km. For the front axle I run a commercial gear oil: Mobil MobilLube SHC 75W-90.

At 63,000km my front axle is dry, no seepage evident. In temps down to -42 my front axle engages quickly.

I'm not sure why GM specifies an 80W-90 in the front axle, as most other makes run a regular 75W-90. GM could have prevented a LOT of their cold weather front axle failures if they had specified a regular 75W-90 in front.

You only gain about 27 F in high temp protection running an 80W-90 over a regular 75W-90. A regular 80W-90 is frozen at -15 F.

This issue has been discussed at the GM Truck forum. Go there and do a quick search on "front axle" in the LD forum or the HD forum:

http://www.gm-trucks.com/forums

There are a lot of advantages to running a synthetic in the front axle: better cold temp operation and better hot temp protection.

Isn't that GM Goodwrench stuff expensive?? They must think we're BMW drivers the way they charge for some parts.

Jerry

 

[Ken2]

quote:

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Originally posted by the winemaker:
I know there has been lots of questions in regard to different types of axle and diff fluids,however perhaps you could answer this dumb question for me...I recently changed my rear axle fuid,,2000 gmc 2500 4/44drextcab..using castrol syn axle fuid[gl5]as dealer wanted 28 dollars plus tax for gm product..can I use same type in front axle[it calls for 80-90 gear lub not syn] or should I stick with as owner manual states a 80-90 straight gear lube...with thanks
the winemaker,truro nova scotia canada

---

I'm not sure that ordinary synthetic GL-5 gear oils are suitable for those GM differentials which use the high priced synthetic that smells like grape juice. Schaeffer recommends their #741 synthetic gear oil which meets the Eaton 750,000 warranty requirement as the only gear oil in their line which meets the GM spec. Unfortunately this is only available in 40# pails--but the price is much lower than the GM stuff.


Ken

 

[heyjay]

I would have to urge caution trying to run an Eaton Dana E500-certified gear oil in the GM rear axle.

If the rear axle has the factory G80 "locker" the additive package in commercial HD gear oils E500-certified are usually not compatible with the clutches inside the G80.

I found out the hard way in my 2000 GMC Sierra and almost glazed the clutches. It would slip and chatter like crazy.

That's why I run Mobil MobilLube SHC 75W-90 in the front axle and Mobil 1 Gear Oil 75W-90 (Claims suitable for Limited Slip service) in the rear axle. No problems with the G80 if I run Mobil 1 Gear Oil.

Jerry