Can I pick your brain on a transfer case rebuild?

[Silverado2910]

Backstory- I have an 04 silverado2500HD The transfer case required is an MT1, about 1k for a pulled TC.  Its been rattling, random gear grinding, random reverse not working.  So, 6/20 we pulled the TC case off and the mode fork was toast.  Ground down to nothing, filter and magnet full, fluid was dirty.  We tore apart an NP261 and used the mode and range fork, slide and oil pump from that into the TC pulled off of the truck.  The part numbers were the same, looked like the only difference between mine and the 261 was the drive shaft and the chain.  Both are larger on mine.  After we rebuilt the truck ran beautifully.  Smooth and better control.  on 6/27 I set off across the state, was about 20 min from home coming off the bottom of the mountain and the truck would not accelerate.  I coasted to a stop on the shoulder, tried shifting, no movement at all.  Engine would rev but nothing.  Could not shift into park without gears grinding.  I ended up in neutral with the parking brake on waiting for a tow.  We got it home and after playing with it was able to get gears caught between 4l and neutral then drove it into the garage.  Tore the TC open and the mode fork was practically melted.  End busted off, pad in pieces, filter and magnet full.  

 

Ive found an updated version of the mode fork that comes in a kit with a slide and fork pads.  

 

Now, WHY was the mode fork destroyed?  The part was brand new.  No way to tell if the rest of it was new or just really clean but the 261 case shifted nice and mine did as well before we installed it.  We used transmission fluid in the TC, 2 quarts.  No driving issues at all until it failed a week later.  Im currently waiting on parts to rebuild the TC again.  But any clue why it failed?  And how do I keep it from failing again?

 

 

Edited June 29, 2020 by Silverado2910

[David89GMC]

There are two Range Forks. Might you have a 263 because of the larger chain?

 

 

Are the springs intact and not damaged?

[Silverado2910]

There was only one spring, at the top of the guide rod.  The spring looked good, not damaged.  

 

The part number stamped on the range shift fork in both cases was 17833.  

 

[Silverado2910]

Also, the 263 range fork doesnt look the same.  Both cases fit in a plate.  The range fork with the 263 doesnt fit into that plate, it slides onto the rod but shifts different.  I believe the 261 is not an HD and is why the chain is smaller.  

[davester]

263's are the electric shift models, which use different parts for shifting gears.  He'll have a NP261HD if he has a 6.0 (along with a 4l80e) or an NP261XHD with an allison if he has a diesel or the 8.1l gas engine.

 

Maybe you didn't get everything together quite right, so the fork was constantly being pressed against by the side of the groove it rides in?

 

I know when I rebuilt my NP261HD, the guy initially sold me some "updated" parts, which didn't work, and I returned them, brought in the original fork and then he got in a new matching fork, which worked fine for me.

 

And don't forget to install a pump rub fix, I would suggest the cheap pressed-metal plate, it's the cheapest fix and it works.

 

And I guess I got lucky with finding a TC, a local junkyard had one I could pull, and it was only $300 or so.

[Silverado2910]

It'd be a NP261HD since the truck is gas.  6.0 4L80E.  Its a floor shift, so def not a 263 then.  

 

We had the plate in it but it wouldnt shift with it installed.  Just locked up like it didnt have enough room.  I wonder if thats the issue, we just didnt have it together right.  I ordered an original arm AND the arm with the update and new slide.  Im trying to find someone local that could help put it back together to make sure we have it right.  

 

[davester]

I referenced this video when I rebuilt mine:

 

as well as an exploded-view parts diagram.  And then when assembled, made sure I could shift it by hand through all the gears.

 

And don't put too much sealant on the mating surfaces when you assemble it.  Everything that oozes out the outside, also oozes out on the inside, and it all eventually falls off and clogs the oil pickup tube...

[Silverado2910]

Thats the same video we watched.  Makes sense about the sealant.  I wasnt over generous with it but did have some oozing.  Ive got a couple calls made trying to find someone local that can either put it together or at least double check us.  Hoping we can get someone to look it over.  Im a little worried that its going to jam up and fail yet again.  At least I wasnt pulling anything this time...  

[davester]

You can test fit it together (without sealant), and make sure it shifts through all the 4 modes relatively easily.

[Silverado2910]

we did, and before we installed it we checked that it moved thru all gears.  I drove the truck for a week after, shifted into 4H a couple times to get to the farm and it shifted great.  It failed driving down the interstate in 2H.