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I was changing the transmission fluid and filter yesterday and noticed a small crack right below the drain plug on the back half of the transfer case. This is on my 2004 GMC 1/2 ton. It has the New Process 246 transfer case. This is the model with Autotrak.

The crack is about 3/4 of an inch long and clearly due to the drain plug being over tightened. I changed the fluid with GM Autotrak II fluid about 2 years ago right at 50,000 miles as recommended. When I changed it, I used teflon tape to seal the threads and tightend untill it was snug, but not tight. I've been under the truck dozens of times, checked the T case fluid at least 4 times since (truck now has 95,000 miles) and this is the first time I saw the crack. So it must have happened recently. How it happened and why now, I have now idea. I do all the service on it myself, and I haven't touched that plug in two years.

Now it appears that the area is not really stressed, so I think if I could seal it up and prevent the crack from expanding, it should be fine. Is there any repair that I can do, short of a new T case or ripping this down and replacing the cracked half? Or should I be looking for a used NP246? This truck is my daily driver, so I need to get up and running soon.
 

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I was changing the transmission fluid and filter yesterday and noticed a small crack right below the drain plug on the back half of the transfer case. This is on my 2004 GMC 1/2 ton. It has the New Process 246 transfer case. This is the model with Autotrak.

The crack is about 3/4 of an inch long and clearly due to the drain plug being over tightened. I changed the fluid with GM Autotrak II fluid about 2 years ago right at 50,000 miles as recommended. When I changed it, I used teflon tape to seal the threads and tightend untill it was snug, but not tight. I've been under the truck dozens of times, checked the T case fluid at least 4 times since (truck now has 95,000 miles) and this is the first time I saw the crack. So it must have happened recently. How it happened and why now, I have now idea. I do all the service on it myself, and I haven't touched that plug in two years.

Now it appears that the area is not really stressed, so I think if I could seal it up and prevent the crack from expanding, it should be fine. Is there any repair that I can do, short of a new T case or ripping this down and replacing the cracked half? Or should I be looking for a used NP246? This truck is my daily driver, so I need to get up and running soon.
I caution you about welding it. My understanding is the case is made of magnesium and if you do not weld it correctly you can start a magnesium fire which is very violent....
 

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Discussion Starter #3
Thanks, I didn't realize the case is magnesium. I thought it was aluminum.

My intial thought was to drain the fluid, clean the area really good, cut a notch like a V in a crack and fill with JB Weld putty. I don't know if JB Weld works on magnesium or not, but it was a start.

I have decided that if I can find a used transfer case, it would be much better. I've located one near home, and if it fits according to the VIN number I'll buy it and install it this weekend. I no longer plow commercially with this truck, but its still my daily driver, toy hauler, and farm truck. So reapiring correctly is more important than doing it on the cheap. I just hate to spend the money... :(

Anyone have any tips for R&R of a T case on a late model 1/2 ton? I've done them in older trucks and its relatively simple. But I've nver played around with the trucks with electronic shift.
 

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Are you familiar with GM pump rub?

Might or might not play a role, not enough information to tell.
 

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Discussion Starter #5
Thanks John!

I'm aware that people have had problems with the transfer case oil pumps wearing throught the case, but I thought it was only on the 3/4 and 1 tons.

No - this is definately a crack originating at the edge of the drain plug. A local used parts dealer (who has my new T case) told me that its common to crack the cases. He seems to think that I over tightened the drain plug and the crack started as a hairline crack.

I think this could be due to the teflon tape I used. I just couldn't get it to snug up. I should have used a thread locker instead.
 

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Discussion Starter #6
Weekend update!

The swap was not very difficult, but did not turn out the way I had hoped. The replacement transfer case looked good, had good seals and the install went well. I drove the truck to test the 4wd and it shifted well, no codes, and 4x4 worked well with no noise. I crawled under to check for leaks and found it dripping with oil. A very small hole, just large enough to get a peice of mechanics wire is the cause. Its right on the the housing, just below the tailshaft.

I don't know if this was caused by pump rub or impact or what. The case was supposed to have come out of a 2006 Chevy with 16,000 miles that was totaled. The truck parts recycler is being very good and working to get this resolved this week. He even offered to have a trans shop do the R&R for me.
Unfortunately, its in NY right now, on blocks at my father's shop.

I'll post pics when I finish next weekend.
 

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LetsTalkSnow.com - Travel & Bar Consultant
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Ahh....the dreaded GM new process "case rub" issue. Its like a rash
on the GM truck forums !
These guys have the cure (they say):
The Problem;
http://www.adaptacase.com/TC236CBRNY.html
outside look

Inside look:


The fix:

With pump in place:


These guys also sell a replacement case 1/2 for $250 bucks
 

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Discussion Starter #9
Thats the hole!!!!!!

Thats the exact spot that the blue fluid was spewing out of. But I thought this problem is only common among the NV 263 transfer cases in the 2500 HD and 3500 trucks? Mine is a 1/2 ton with the NV 246 transfer case. So I was kindas assuming it wouldn't happen to the light trucks. Maybe they share the same housing.

I returned the case with the hole in it this morning. I'll post again and let you guys know if that is the definate problem. Sure looks it from the last two pictures that you posted sonjaab.

Thanks!
 

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LetsTalkSnow.com - Travel & Bar Consultant
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The ad sez it happens to these models:
TC236C BRNY Transfer Case Repair for 236, 246 and 263 N.P.

So I guess the 1/2 ton case is the same design/size etc.........

And I will mention again the rear part of the case cost $250
from them guys. Not sure if its a OEM replacement or aftermarket
piece.

Heres some instructions/pics from the diesel place on that kit install.
http://www.thedieselpage.com/reviews/tcase.htm

Theres a pic of the cheap POS clip that they install at the factory to
prevent the pump rub problem at that link.
Of course they only use ONE of the slips instead of 4.
 

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Discussion Starter #12
Now shifting issues!

This past week I got both transfer cases repaired and installed the one that previously had the hole in it. The shop that repaird this one added a steel plate in the pump housing to keep it from wear through again.

The original case was welded up, but the guy who welded (another shop completely) it thinks that the threads may still leak slighty, so he warned me that plenty of silicone would be needed to keep it sealed. Thats why I optd to install the repaired replacement. Its getting kinda complicated isn't it?!?!

So a week ago, when I installed the replacement case, it shifted and operated perfectly. This time, after it was disassembled and repaired (heated and welded) the case will not shift. The trucks stuck in two wheel drive. If I press a button (Auto, 4Hi, 4Lo) it flashes for a few seconds and remains in 2 wheel drive. When driving I get "Service 4WD" on the message center.

So I plugged in my code reader, and since its not a generic code, the code reader finds nothing wrong. Would a GM dealer be able to isolate the problem by pluggin in their computers? I'd rather not start throwing parts at it. BTW - I tried reconnecting the battery and all connections.

Any help would be greatly appreciated and I must thank you guys for all the help so far!

Leo
 

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Discussion Starter #13
Another Update.

The "Service 4wd" light was on all week, even after changeing out the encoder motor. So I took it to the dealer and they found a trouble code C-0300 - Faulty Tailshaft Sensor. They updated the transfer case software, which didn't seem to do anything. So I went home and I changed out both tail shaft sensors with the two on my old case. I also cleaned the ground at the cab mount as recommended by the tech at the dealer. He said that a lot of the code and shifting troubles come from the ground here.

Well, no more "Service 4wd" message, 4wd works in Auto and in 4Lo. But 4Hi flashes the light on the button and then activates Auto. However, I can feel the bind of regular 4wd. So something funky is going on. Tomorrow I'm going to replace the dash switch and see what comes of that.

I'll attache pics when I resize them.
 

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Discussion Starter #14
Pics

1st picture is of the hole in the replacement transfer case.
2nd is my truck in my father's unfinished garage. Yep - working in the dirt!
3rd is the encoder motor from my original t case. This is a very easy part to change. Three bolts, reusable gasket and a unique type of input shaft that only allows installation in the correct position.
 

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Discussion Starter #15
More Pics

4th pic is the mounting place of the encoder motor on the T case.
5th is my orginal T case that was welded by a friend. Its a spare now.
 

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Discussion Starter #16
I never really closed the loop here.

It turns out the replacement T case was re-assembled incorrectly and a set of clutches would not release. So my used parts vendor gave me another t-case with more miles on it.

All is well and I've put about 10K miles on it as well as plowed my driveway and a few others this year with it. I'll probably re-build my original T-case when I get the chance to.

Thanks to all who have helped me and hopefully this sticky will help others with transfer case and pump rub issues!
 
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