I wanted to ask a few questions since there are so many very well informed DIY'ers here. BTW, this site is awesome and I have learned much about diesels before buying one. Here I am now with a 2006 GMC LBZ CC 4x4 SB silver birch with about 4000 miles on it. It has been an awesome truck and we just came back from Lake Tahoe with it. It really boogies up the hills with 6 people and cargo in the truck.

I have changed my engine oil three times now and changed all the rest of the fluids (sans the transmission fluid) today after returning from the trip. I had a couple of comments about what I found and had some questions turn up along the way. Here they go:

1) How tight do you need to tighten the transmission filter (Allison)? I hand tightened as much as possible and that is usually what I do for my other cars.

2) For the transfer case, I used AMSOIL ATF Syn Dexron III - 2 quarts worth. Is this the proper oil to use? It was recommended by the guy at lubrication specialists.

3) In the front and rear diff I replaced the oils with Amsoil 75-90w EP gear lube. It was really easy. The front I removed about 2 quarts and the oil was UGLY. It was yellow and looked like it was mixed with mustard streaks. The magnetic definitely had some small amounts of metal shavings on it. Has anyone else found this to be the case?

4) In the rear diff the oil was black and streaky. I removed about 3 quarts and placed in just the side of 4 quarts into it. There was no magnet on the plugs so I couldn't see if there were any metal shavings. Is it wise to replace the plug with one containing a magnetic? Can anyone recommend one?

5) In the transmission, is it true that we need a Dexron VI to top it off?

6) On a side note. I also changed the shocks to bilsteins and it made an incredible difference. Much recommended upgrade.


Thanks in advance to all of you,

Doug

On any spin on filter, I tighten as much as I can by hand, then go another 1/2 turn. All you are accomplishing by making it any tighter is a crushed gasket, and a tough job getting it off the next time. I have never had a leak from the filter in almost 40 years.

IIRC, the spin on alley filter has a very tall seal and overtightning it will cause a leak. I would say spin it on easy, then go 1/4 turn. I also expect MikeL will give you the real story on all of it.:)

On any spin on filter, I tighten as much as I can by hand, then go another 1/2 turn. All you are accomplishing by making it any tighter is a crushed gasket, and a tough job getting it off the next time. I have never had a leak from the filter in almost 40 years.

:exactly:

maybe not 40 years for me but just the same..

1) How tight do you need to tighten the transmission filter (Allison)? I hand tightened as much as possible and that is usually what I do for my other cars.
As tight as you can get it by hand. Use a latex glove and you can easily get a full turn after gasket contact, which is all you need.
2) For the transfer case, I used AMSOIL ATF Syn Dexron III - 2 quarts worth. Is this the proper oil to use?
Synthetic Dex-III is good stuff for the case.
3) In the front and rear diff I replaced the oils with Amsoil 75-90w EP gear lube. It was really easy. The front I removed about 2 quarts and the oil was UGLY. It was yellow and looked like it was mixed with mustard streaks. The magnetic definitely had some small amounts of metal shavings on it. Has anyone else found this to be the case?
Normal. The stock fluid is not synthetic, and it has a glow-in-the-dark additive that is used to check gear mesh. Actually, the material is applied to the gears and then checked. For some reason, GM's vendor does not drain and refill the diff after the initial run-in, while the rear fluid IS changed prior to delivery.
4) In the rear diff the oil was black and streaky. I removed about 3 quarts and placed in just the side of 4 quarts into it. There was no magnet on the plugs so I couldn't see if there were any metal shavings. Is it wise to replace the plug with one containing a magnetic? Can anyone recommend one?
Should have been a magnet on the drain plug. Did you pull the cover, or the drain plug? The plug is on the bottom of the casting on the passenger side of the ring gear... remove with a square-drive ratchet.
Frequent reports of underfilled rear diffs from the factory... as much as 2 quarts low.
5) In the transmission, is it true that we need a Dexron VI to top it off?
Factory fill is Dex-VI. Dex-III is just as good (and will no longer be available/licensed after q4 '06), synthetic Dex-III is better, but it is strongly recommended to flush and replace the stock fluid with Castrol TranSynd, Citgo QuatraSynd, or Amsoil TorqueDrive.

Good info Rich! :) Would Torquedrive work in the transfer case?

Good info Rich! :) Would Torquedrive work in the transfer case?
Sure.... it's designed to match TranSynd, but AFAIK, it is still a Dex-III approved fluid.

It's overkill, but if you're changing the trans, you'll have between 1 and 2 quarts left over so it's no biggie.
Personally, I use Mobil-1 ATF in the 'case because it's readily available in quarts and saved my remaining TorqueDrive to top off the spin-on.
TorqueDrive is available in nothing less than a gallon, and what's left from the flush should last the 50k for spin-on changes until it's time to drop the pan again, when I'll buy a 10qt jug and use 7.5 of it.

Rich - thanks for the very informative response. Regarding the magnet on the rear diff drain plug, I didn't see a magnet like on the front diff drain plug. Is it incorporated into the plug, or should it be sitting on top of the end like on the front plug? Maybe I should buy a new one before the next change...

Doug

It's definitely there... it MAY have had so much crap on it that it blended in with the threaded portion. Mine looked pretty "solid" until I pressed on it and it "bent".