Gear Oil Recommendation for '05 Suburban Z-71

[Islandvic]

2005 Suburban Z-71 88k miles w/ Original Diff and T-Case Fluids.

Rear diff 10-bolt w/ Eaton G80 locker and 3.42 gears.

The front diff calls for 80-90w and rear 75-90 Synthetic.

I need to spend $10/quart or under.

I have seen M1 and Castrol Syntec 75-90 under $10/quart.

Can I put 75-90 in the front or stick with the recommended 80-90w?

For rear diff should I use a Fel-Pro gasket or RTV Sealant?

Your thoughts, recommendations and experieneces please.

Thanks

 

[Greg L]

If you insist on using synthetic for your transmission, I suggest Redline MT-90...which is 75w90 gear oil for trannies.

Goes for about $11 or $12 bucks, depending where you buy it. I think Napa sells it for twelve.


I switched to it last year in my GMC with manual tranny, and it is great stuff. Smooth shifting.

My 2 cents.


GL

 

[unDummy]

You can use either the M1 or the Syntec 75w90 in both diffs. No need to worry about the 80w90. 75w90 will work fine.

 

[dave1251]

+1

 

[Islandvic]

Greg L, I am asking about my differentials, not my transmission.

GM specs synthetic for the rear diff, I am not insisting.

Looking at your signature, how did you get a manual trans with the 5.7? Is it a 2500 or 3500 series?

Thanks.

The owner's manual doesnt specify GL4 or GL5 for the diffs.

 

[Greg L]

Sorry...I misunderstood. Disregard.

My jimmy is an older one, with a manual 4-speed installed by the previous owner.

 

[TC33]

I just changed both the front and rear differential fluids on our 03 Suburban yesterday. This is the second time I have changed fluids and have run the fluids between 40K and 50K miles each time. I used Mobil 1 75-90 both times with no regrets. I used the Fel-Pro gasket and a bit of Permatex ultra black to help hold the gasket in place during re-assembly with good results. I also added a 4oz container of limited slip additive to hopefully prevent any unwanted chatter/locking.

 

[Greg L]

Island:

The diff. in my 1996 GMC was filled with Pennzoil 75w90 last year. I have Valvoline DuraBlend at home for the next diff change.

No issues or leaks, works great.


GL

 

[gmctodd]

M1 75-90in for my diffs too. Mine also has the G80 locker. I would NOT add any FM to it

 

[Islandvic]

yep GMCtod, I have also heard not to add friction modifier additivesto the G80.

TC33, yeah I prob do same thing with fel pro gasket and RTV black.

thanks for everyone's input!

 

[3311]

I use M1 75w90 in every diff I own, even my 7500. Unless you have long high speed runs in 4wd, I would use dino though in my front axle to save some coin. +1 on Valvoline dino or durablend being good stuff.