Changed rear diff fluid

[TheAutumnWind]

Question, been researching trying to find synthetic 80W90 gear oil and its like impossible to find in a local store. Best I found was a blend at O'Reilly. I wanted to go synethetic to improve chances of better gas mileage and better oil. Am I doing this right? What 80W90 do people use in synethetic? Everything I find locally is conventional and assuming I should not be touching the 75W140....

http://www.oreillyauto.com/site/c/detail/VAL3/280/N2367.oap?ck=Search_N2367_-1_-1&pt=N2367&ppt=C1985

IIRC 75w90 is now the recommended fill. Thats what I purchased.

 

[Meccanoble]

Where did you confirm this was the recommended fill? Much easier to get to but I'm hearing conflicting details. Unlike higher Dextron's that say they are compatible with Dexron VI devices, I dont know how to confirm 75w90 is same as 80w90. Assuming the bigger number makes it better for more aggressive use. Fearful to add a weaker fluid unless truly recommended

Can anyone else confirm this?

Also TheAutumnWind, how long have you had this fluid in your car?

 

[TheAutumnWind]

First off take note that I have an NBS, however IIRC they are the same.

Where did you confirm this was the recommended fill? Much easier to get to but I'm hearing conflicting details. Unlike higher Dextron's that say they are compatible with Dexron VI devices, I dont know how to confirm 75w90 is same as 80w90. Assuming the bigger number makes it better for more aggressive use. Fearful to add a weaker fluid unless truly recommended

Can anyone else confirm this?

Also TheAutumnWind, how long have you had this fluid in your car?

The bigger number makes it better for aggressive use? Think of it like oil.

http://www.driverstechnology.co.uk/oils.htm

VISCOSITY

Most oils on the shelves today are "Multigrades", which simply means that the oil falls into 2 viscosity grades (i.e. 10w-40 etc)

Multigrades were first developed some 50 years ago to avoid the old routine of using a thinner oil in winter and a thicker oil in summer.

In a 10w-40 for example the 10w bit (W = winter, not weight or watt or anything else for that matter) simply means that the oil must have a certain maximum viscosity/flow at low temperature. The lower the "W" number the better the oil's cold temperature/cold start performance.

The 40 in a 10w-40 simply means that the oil must fall within certain viscosity limits at 100°C. This is a fixed limit and all oils that end in 40 must achieve these limits. Once again the lower the number, the thinner the oil: a 30 oil is thinner than a 40 oil at 100°C etc. Your handbook will specify whether a 30, 40 or 50 etc is required.

http://www.tahoeyukonforum.com/threads/differential-oil-change-04-tahoe.57102/

 

[mizzouguy]

All the oreillys near me carry masterpro syn (house brand), lucas syn, castrol syn, and royal purple syn in stock in 75-90. There is no such thing as 80-90 syn that I've found. You can use 75-90 no issue. They can also order valvoline syn and mobil syn.

 

[MichaelSE]

It's true, I think I had to use non-synthetic 80W-90 for the front diff. For anyone else wanting to do this, here are fluid specs from my reference sheet. Note that I have the 14 bolt rear, most NNBS trucks have the 10 bolt, so the fluid capacity would be a bit less than 2.75 quarts.

Front axle 8.25"
1.42 liters
1.51 quarts
SAE 80W-90

Rear axle 9.5"
2.6 liters
2.75 quarts
SAE 75W-90

Transfer case
1.5 liters
1.6 quarts
DEXRON VI (2008+)
Auto-Trak II (2007)

 

[TheAutumnWind]

It's true, I think I had to use non-synthetic 80W-90 for the front diff. For anyone else wanting to do this, here are fluid specs from my reference sheet. Note that I have the 14 bolt rear, most NNBS trucks have the 10 bolt, so the fluid capacity would be a bit less than 2.75 quarts.

Front axle 8.25"
1.42 liters
1.51 quarts
SAE 80W-90

Rear axle 9.5"
2.6 liters
2.75 quarts
SAE 75W-90

Transfer case
1.5 liters
1.6 quarts
DEXRON VI (2008+)
Auto-Trak II (2007)

You can use 75-90 in the front.

 

[MichaelSE]

You absolutely can, and believe me, I thought about it for a while. But I think there's some merit to GM's decision to recommend 80W-90 for the front.

- The difference in cold viscosity between 75W-90 and 80W-90 does not become apparent until -10 degrees F, the point at which 80W-90 will yield lower fuel economy until warmed up. At operating temperature their viscosities are so similar (within 1 cSt of each other) that it will not be noticeable.
- Power delivery to the rear will always be more linear, and dampened by the longer driveshaft... power delivery to the front, when engaged, will be more varying, as the front wheels are more prone to slipping due to steering, and the pinion carrier gets more of a workout than it will in the rear. 80W-90, being conventional, theoretically has a different additive package that is more resistant to shearing under these circumstances.


I'm not a petroleum engineer at all, this is just from stuff I've read on the internet For 99% of drivers, there will probably be no noticeable difference at all, especially if you don't off road hard. So really, you can use either.

 

[ta07hoe]

Top is fill bottom is drain. There is a big nut welded to my fill plug since the previous owner stripped it and this was his way of fixing it lol. I use syn mobile 1 front and back. Is yours all wheel drive or selectable 4x4. It will make a difference on the fluid you will need.

 

[Meccanoble]

Mine is selectable AWD. I'm in South so I rarely see the cold conditions anymore. Moreso, I normally drive in 2WD, might do Auto in rain. Glad to hear 75w-90 synthetic will be fine.

BTW, my 10 bolt rear took a little less than 3 quarts.

 

[Meccanoble]

So i changed both transfer case fluid and front diff this weekend. Both fluids black but front diff was thick and disgusting at 130k miles. Drain bolt for both had metal shavings. Made sure not to over tighten. 18 size for all except front diff drain was like15 or 16. 24 lbs tq for front diff, 15 for rear.

I never really drove in 4x4 since owning but found few concerns unless this is normal?

1. In 4x4, moaning sound when taking turns. Straight has no issues.

2. Hard to move car when wheel turned. Car literally would stay in one spot even on a slight hill if no gas used.

3. If wheel turned all the way, can't do a circle or skater 8 without rough vibration.

4. Switching from4x4 to auto after some driving in4x4 causes a thump.

Mobil 1 75w90 synthetic put in front diff until dripping out. 2 qts

Valvoline red bottle dex 6 compatible synthetic trans fluid put in transfer case.

Btw added part num for rear diff gasket