Auto transfer case maintenance

[Moser97]

I originally posted here a few months ago with a blown transfer case in a '96 Bravada. I got a pile of good advice and got the Olds running right and sold it. Now I am driving a '99 Jimmy with the "Auto 4 WD" button to the left of the regular "4WD HI" button. Does this TC need the fluid swap program that was recommended for the AWD TC's? Mileage is at about 86 or 87K.

[tech1029]

Yes don't fall into the trap I did. The manual never mentoned the transfer case. Had I known I would have changed the fluid on the same schedule as the transmission. From what I understand this transfer case (New Process 236) uses a special fluid available only at the dealer. The original fluid was red now it is blue. Your manual will list the old part number. Expect to pay about $7.00 a quart or more you will need 3 quarts.
I got 96,000 on my Jimmy with the auto 4WD and now the thing is stuck in 2HI. I never serviced the transfer case even though the truck was dealer serviced every 3000 miles! The dealer never mentioned the transfer case and its not in the manual. I followed the heavy duty maintenance schedule to the letter. They wanted to clean my spark plugs every 36,000 though and thats not in the manual either!

[muddog321]

The light blue fluid is called AllTrack-II synthetic fluid P/N 12378508 and it should hold exactly 2 qts per my 01 owners manual and I did my 99 and it was 2 - but the 99 said Dextron III so after reading your post my searches turned up that GM printed the 99 manuals before AllTrack fluid came out and if I don't put it in (now at 120k) I'm probably screwed (already I bet)! The newer fluid has friction moderfiers in it due to the clutch packs in the Autotrac transfer case and GM was having problems with them - big surprise there! I've got a page on transfer case/4wd operations on 2nd gen Blazers almost written up that I will post soon so we all can understand the system and fluids - lots of wrong stuff out there but this forum has given more correct info than most other sites doing full google searches!

[MT-2500]

It depends on what transfer case.
136-236-246 transfer cases all call for the special fluid.
Figure out or check what transfer case you have and then check the owners manual or a good service manual.
MT

[Moser97]

My manual calls for Dexron.The dealer parts manager and my neighbor who is a retired Olds tech said to use the Alltrak ll. The parts guy said that if the vehicle has buttons on the dash they use blue stuff (Alltrak). If it has a handle on the floor it gets red stuff (Dexron). My neighbor says the blue was developed as a fix for sticky TC's in the early 2000 and newer cars, and service bulletins were sent out advising how to use it to fix binding problems. He says there were no bulletins for older cars because GM doesn't care about them. Since there is no warranty liability with older cars, GM would just as soon see you have to replace these TC's than get them working right. He said they used it in older cars to fix binding issues successfully. I'm swapping mine out for the blue tomorrow, before I get problems. I had the auto 4wd on the other night in the rain and when I dropped off the guy that rides with me the thing chattered pretty bad when I turned around in the semi-dry parking lot. My original post on the old Bravada describes these problems and has good advice for getting them straightened out. If I can find it I'll put up a link.

[Moser97]

http://www.automotiveforums.com/vbul...d.php?t=426615

This thread shows the problems I was having with the old Bravada. I paid $36 for 4 quarts of fluid at my local Chevy dealer. The outside of the bottle says something about using it in vehicles according to owners and service manuals and as described in various service bulletins. The guy says if it comes out blue just change it once and bring 2 back. I also found threads about bulletins on these TC's in the Astro Forum. They cover 99 thru 2003 TC's.

[MT-2500]

Originally Posted by Moser97

http://www.automotiveforums.com/vbul...d.php?t=426615

This thread shows the problems I was having with the old Bravada. I paid $36 for 4 quarts of fluid at my local Chevy dealer. The outside of the bottle says something about using it in vehicles according to owners and service manuals and as described in various service bulletins. The guy says if it comes out blue just change it once and bring 2 back. I also found threads about bulletins on these TC's in the Astro Forum. They cover 99 thru 2003 TC's.

It all depends on what transfer case you have.
What transfer case do you have?
MT

[Moser97]

NP 236 CM, don't hold me to the CM the tag is banged up. It had red in it, and a tag calling for Dexron lll. I filled it with blue, drove around for a half hour, drained it and refilled with blue. It still chirps in a tight turn with the Auto 4wd on. I guess I'll do the differentials with synthetic gear lube next.

[ZL1power69]

heres another one of my dumb questions , what is the difference between the regular transfer case and the auto transfer case? Is it all wheel drive when u hit the auto 4wd button? im a little confused i ask because im thinking about getting a newer blazer/jimmy, silverado/sierra, or tahoe/yukon. most of the pickups or tahoes/yukons that are 4x4 have this button and i just wanted to know more about it.

[MT-2500]

Originally Posted by Moser97

NP 236 CM, don't hold me to the CM the tag is banged up. It had red in it, and a tag calling for Dexron lll. I filled it with blue, drove around for a half hour, drained it and refilled with blue. It still chirps in a tight turn with the Auto 4wd on. I guess I'll do the differentials with synthetic gear lube next.

The 99 gmc jimmy 236 calls for the blue gm fluid.
In auto mode the front axels/drive shaft should not engage unless the rear wheels are slipping.
You may need to drive it a while for the blue fluid to start working.
Are you sure the transfer case has not been replaced or switched?
If it keeps on doing it get a good scanner on it and check out the transfer case operation. If it has any problems it should show pp on a good scanner that can read transmission/transfer case and body codes and data.
Also most good scanners have some test you can run on it.
If it shows any B or C codes post back code no.
MT

[MT-2500]

Originally Posted by ZL1power69

heres another one of my dumb questions , what is the difference between the regular transfer case and the auto transfer case? Is it all wheel drive when u hit the auto 4wd button? im a little confused i ask because im thinking about getting a newer blazer/jimmy, silverado/sierra, or tahoe/yukon. most of the pickups or tahoes/yukons that are 4x4 have this button and i just wanted to know more about it.

The 236 auto transfer case is a automatic/electronic controled 4 wheel drive in auto mode.
In auto mode it only pulls on rear wheels unless they start slipping then it applies power to the front wheels as needed.
The old floor shift ones are manual shifted in or out of 4 wheel.
Then you have the all wheel drive jobs. 4 wheel all time.
On them the pull is mosty but not all together on rear wheels and if rear wheels start slipping they transfer more power to front wheels.
Kinda of a variable 4 wheel drive. All done with a viscious clutch inside the transfer case
MT

[ZL1power69]

so its basically like all wheel drive on demand. alright thanks for clearing that up MT.

[MT-2500]

Originally Posted by ZL1power69

so its basically like all wheel drive on demand. alright thanks for clearing that up MT.

You are welcome.
And 10-4 on the 4 wheel on demand. It just kicks in when you need it.
Which is a good deal as long as it works right and be sure to use the blue GM fluid to keep it working right.
MT

[Moser97]

The manual calls for GM Part # 12378396. A tag on the TC says NP 236, and a seperate tag calls for the same product to be used in the transfer case. That part number is Dexron lll. The TC has a manufacture date of 1998. The vehicle went into service in Oct. 1998. I have to assume this is the original TC. I used GM part no. 12375808. I can't put my finger on an official document from GM saying I should have done this, but everything I've heard or read indicates that these TC's need to have this fluid in them. I think the point of this whole discussion is that if your automatic transfer case does not have this improved fluid in it you should get it in ASAP. I've read Bulletins calling for this fluid exchange on Asrtos, Caddies, Bravadas and other vehicles from model year 1999 to 2003. I think I've done the right thing. MT do you agree?

[muddog321]

The manuals were printed before GM came out with the blue fluid to fix the AWD and Autotrac transfer cases failing in 99 (mainly in AWD due to always on). The dealers are kinda clueless on this - the improved fluid should be able to be run in any case would be my opinion. This blue syn fluid was to solve clutch binding and wear and added friction modifiers per GM. The only risk I have read about on all syn fluids is long term RTV breakdown and this mainly applies to rear ends with no gasket, only RTV.