transfer case and front/rear diff oil change recommendations

GrandChien14 · December 23, 2019

Thanks, up in Canada, I saw a sign around one road, might look him up ?

txab · December 24, 2019

Eaton only advises using added friction modifier to their posi rear end, which the G80 is not. Also their Truetrac does not require any friction modifier

NomadicCPO · December 26, 2019

Just did all three of mine recently. Went with Supertech full synthetic 75w-90 front and rear for the differentials. I realize that it’s not what the manual calls for in the rear, but it’s my opinion that the -85 it calls for is more a consideration of fuel economy than longevity and protection. Also, the Supertech does have some friction modifier, but not enough to affect locker operation as far as I can tell. Definitely don’t add additional friction modifier.

The fluid pump I had on hand was garbage, so I ended up using a long clear plastic tube attached to the bottle’s cap and squeezed it in. Duct tape the end of the tube into the filler hole to avoid it falling out and making a smelly mess on your garage floor.

The transfer case was pretty straight forward. Used Supertech Dexron VI. Was pretty shocked at the amount of metal shavings and fuzz on the magnetic plug. I hear that’s typical though.

Plan on changing all three fluids every 45k miles as per the severe service schedule. Not knocking Amsoil, but at this short interval, it would be expensive overkill in my humble opinion.

davester · December 26, 2019

39 minutes ago, NomadicCPO said:

Just did all three of mine recently. Went with Supertech full synthetic 75w-90 front and rear for the differentials. I realize that it’s not what the manual calls for in the rear, but it’s my opinion that the -85 it calls for is more a consideration of fuel economy than longevity and protection. Also, the Supertech does have some friction modifier, but not enough to affect locker operation as far as I can tell. Definitely don’t add additional friction modifier.

The fluid pump I had on hand was garbage, so I ended up using a long clear plastic tube attached to the bottle’s cap and squeezed it in. Duct tape the end of the tube into the filler hole to avoid it falling out and making a smelly mess on your garage floor.

The transfer case was pretty straight forward. Used Supertech Dexron VI. Was pretty shocked at the amount of metal shavings and fuzz on the magnetic plug. I hear that’s typical though.

Plan on changing all three fluids every 45k miles as per the severe service schedule. Not knocking Amsoil, but at this short interval, it would be expensive overkill in my humble opinion.

What vehicle do you have? If it's a GMT800, you may find that the transfer case seals might leak due to using DexVI. I know for '06, GM was still recommending using DexIII in the TC, while the transmission could get DexVI.

RedGirl · December 26, 2019

I Have a 2018 Escalade. I really want to do the rear differential, but it is soo ridiculous that you can't just drain and fill. At least in my husband's Colorado there's a drain and a fill plug. Completely awesome and logical. It takes all of 15 minutes to drain and fill. The Escalade has no drain plug so tale the whole plate off. I might try sucking the fluid out by means of a suction system that I saw a guy uses on YOU TUBE, and refill it. Since my truck still has low mileage I'm not in a hurry. I've done all those fluid changes on our old Nissan Xterra and our Durango and all are straight forward, but some of the larger GMC trucks really tend to be much more labor intensive. I do agree with you that probably using the Amsoil is kind of overkill, but my son and my husband are pretty tough drivers so I figure I'll spend the extra in hopes that it will help.

davester · December 26, 2019

26 minutes ago, RedGirl said:

I Have a 2018 Escalade. I really want to do the rear differential, but it is soo ridiculous that you can't just drain and fill. At least in my husband's Colorado there's a drain and a fill plug. Completely awesome and logical. It takes all of 15 minutes to drain and fill. The Escalade has no drain plug so tale the whole plate off. I might try sucking the fluid out by means of a suction system that I saw a guy uses on YOU TUBE, and refill it. Since my truck still has low mileage I'm not in a hurry. I've done all those fluid changes on our old Nissan Xterra and our Durango and all are straight forward, but some of the larger GMC trucks really tend to be much more labor intensive. I do agree with you that probably using the Amsoil is kind of overkill, but my son and my husband are pretty tough drivers so I figure I'll spend the extra in hopes that it will help.

I would suggest pulling the pan vs trying to suck the fluid out via the fill port, so you can get more of the fluid out, and also look at and feel what has built up on the bottom of the diff, if there is any sign of metal bits or lots of paste from the clutch plates (if your diff has them).

Inacanyon · December 27, 2019

My take on the 75w85. The Silverado 4.3l(75w85) has 25% more fluid than a Colorado(75w90) and the Colorado sports a slightly higher tow rating. The Silverado rear fluid capacity increases as they increase the tow rating with each engine and package. You obviously can run 75w90 but the extra capacity and temps are likely considered.

also does the pan have a magnet block on it. I’d wipe that off. Colorado has a magnetic plug.

GrandChien14 · December 27, 2019

18 hours ago, davester said:

What vehicle do you have? If it's a GMT800, you may find that the transfer case seals might leak due to using DexVI. I know for '06, GM was still recommending using DexIII in the TC, while the transmission could get DexVI.

She's a 2016 2500 HD ( gaser) . Love this truck !!

NomadicCPO · December 28, 2019

On 12/26/2019 at 4:16 PM, davester said:

What vehicle do you have? If it's a GMT800, you may find that the transfer case seals might leak due to using DexVI. I know for '06, GM was still recommending using DexIII in the TC, while the transmission could get DexVI.

As this is posted in the 14-19 K2 forum, I don’t have a GMT800, but thanks for looking out.

Mike GMC · January 4, 2020

Just did my 18 the other day. Both diffs and the t-case. Whole job took about 1 hour. I used the Amsoil severe gear 75w-90 front and rear and signature series ATF in the t-case. Filled the tank and drove it the last few days. It may be a fluke, but my gas mileage seems to be up about 1 mpg. The t-case fluid was dirty and the magnet look like it had a ZZ top beard. Glad that crap is out of the case. The diffs looked pretty good yet, but now that they are changed, they should be good for quite some time. Oil is cheap compared to parts, even Amsoil, so I tend to change it early, particularly the first change to get any break in wear material out. Truck has about 20k on it now. I'll probably do the next change at 60k now that I have good fluid in it and the break in junk out.

Doublebase · January 4, 2020

I have 44,000 miles on my truck now, I think I've done my rear diff twice (once with Mobil1 and the other with a mixture of Mobil1 and Redline because I ran out of one). I've done my transfer case once, my front diff once. I'll probably do the front diff and transfer case after the winter again.

I've done a couple services to my transmission...I exchanged 4 quarts (in and out of the dipstick tube) at 22,000 miles, then I did a pan drop filter replacement at 40,000 miles. Magnet looked good - probably won't do anything but simple fluid exchanges through the dipstick tube from here till 100,000 plus.

My rule of thumb has always been change all of these fluids between 20,000-30,000 miles and you may not ever have a problem. Then again you might. Lol. Or you can let it ride 50,000-100,000 and have problems. Or maybe not. Haha.

Doublebase · January 4, 2020

10 hours ago, Mike GMC said:

Just did my 18 the other day. Both diffs and the t-case. Whole job took about 1 hour. I used the Amsoil severe gear 75w-90 front and rear and signature series ATF in the t-case. Filled the tank and drove it the last few days. It may be a fluke, but my gas mileage seems to be up about 1 mpg. The t-case fluid was dirty and the magnet look like it had a ZZ top beard. Glad that crap is out of the case. The diffs looked pretty good yet, but now that they are changed, they should be good for quite some time. Oil is cheap compared to parts, even Amsoil, so I tend to change it early, particularly the first change to get any break in wear material out. Truck has about 20k on it now. I'll probably do the next change at 60k now that I have good fluid in it and the break in junk out.

I think all of us can say the same thing about our first transfer case fluid change...most of us had the metal on that magnet and the fluid discoloration. It's normal break-in stuff.

I changed mine out at around the same mileage point. My first year of owning my truck I only used 4wd a handful of times (easy winter). But this winter has been a different story - we're barley into January and I've already had to use the 4wd ten times - just last week I found myself in a 2 hour commute through a snow storm...4wd the entire time. Cars all over the road. I'm getting my money's worth out of that transfer case fluid change this year. Haha.

RedGirl · January 4, 2020

Hey Mike, Was this service you just did on your Silverado? I'm kind of wondering if you removed the cover and installed a new gasket? Or is the Silverado like the Colorado which has a super convenient drain plug and a fill plug. Genius design in my book! I'm just at 13,000 miles so I still have a little time, but As soon as I get a warm weather day I'm going to jump in and do it. From the design of my truck it looks like I will have absolutely no other option than to remove the cover, at least on the rear differential. I have a feeling the same will be applicable on the front differential. I've been looking for YouTube videos on the subject but no one has posted too much on the 2018 Escalade. Some guy posted a full flush on an Escalade, but everything I've investigated on flushes is that they are really not recommended. As I understand it the reason is that the flush may force minute particles into tiny places and could cause problems that are way worse. That the best is to change your fluids while they are still in good shape since fluids are cheap compared to components. Essentially what you say.

Mike GMC · January 5, 2020

Yep, I did the 18 Silverado. The front is easy, has a drain and fill plug as does the t-case. I always remove the fill plug first. I've had them get stuck before. There is no worse feeling than having just drained a case and not being able to remove the fill plug. The rear required a cover removal. Very easy to do and factory gasket is reusable. It's a rubber covered metal gasket. Just be careful not to damage or bend it when you clean it. And yes, make sure you thoroughly clean the cover and mating surfaces. The cover bolts have red loctite from the factory, so they come out kinda stiff all the way out, do not clean this off. It helps the bolt stay in and not rattle loose. You will also notice they are pretty tight and should be reinstalled that way.

RedGirl · January 5, 2020

Thank You Mike. In that case I might go ahead and start with the front. Much less intimidating with a drain plug. Also since its so new if I do the rear I might not order the cover gasket. It does make me a little nervous not having one on hand in case something goes wrong. I'm also assuming that the front diff and the transfer case are almost identical to the Escalade, it seems like GM doesn't change that stuff too much from truck to truck. Except like I mentioned, the drain and fill plugs on the Colorado in the rear diff. I'll drop you a line when I get it done.