Pulling off the Perfect NP246 Transfer Case Rebuild

[AngryFish]

What year is your truck? I have a 2001. My transfer case control buttons don't do a LED self check.

I actually have no issues with my transfer case right now. Just bought a spare one to rebuild so I have a fresh transfer case. Well I have ONE issue, when I put it in 4wd, the LED doesn't illuminate in the instrument cluster. I cannot figure out why. The instrument panel is good, I took it out and probed the LED.

Thanks for tip on encoder! I will add that to original post / parts list. Very helpful.

Also the gasket, I forgot to put it on the parts list. I'll add that too.

My truck is a 2003. Showing some age but still moving along.

The switch module should start up right away and do a self-check just like the dash. All the LED's should light just like all the lights on the dash cluster so you can see if they are burnt out.

Each LED is on its own wire, with a transistor on the common/ground side. Could be a wire thing, could be a transistor failure. Easiest way is to find someone with a scanner or beg, borrow, or steal (or purchase) your own bi-di scanner. They can turn on the LED's individually. It is also possible for the LED itself to fail, so you can check to see if the resistance to ground through the transistor changes when the light is on (positive lead of the meter on the wire and common on the ground or it may not work). This is a very low current circuit, so don't use a standard test light or you will likely have to replace a transistor.

More commonly is a broken solder joint on either a pin for the switch module or on the board for the LED or resistor. I had a similar issue with most of the modules in the dash. Once I reflowed the solder joints, I was able to get it working again. The lead-free solder is very bad about fractures due to the brittle nature of the lead-free solder failing due to the vibration of the car. I've fixed several similar issues on other vehicles, too, with just re-soldering the pins.

 

[rockola1971]

Interesting what GM did there. Each switch mode has a resistor in series with each switch.(built into switch module) Each one of the resistors would have to be a different value atleast 25% lower or higher than the next one. The 5volt reference(supplied from Tcase module) comes in across the switch that is pressed and voltage is dropped from the reference 5volts. Dropped voltage of course depends on the value of respective resistor. The final value is sensed within the Tcase control module at the A6C1 terminal which is marked "Switch signal". The module works its magic inside and closes what is likely an electronic switch (transistor) and that closing gives the respective switch position led a ground to show that you are now in that 4wd/2wd mode.
The switch assembly has an internal connection for the 5 volt reference and the outgoing signal form the respective resistors also. Each one of those legs is common to ALL switch positions. If either one of those becomes electrically open then the switch module is useless until repaired or replaced.

 

[Matthew Jeschke]

I'm trying to figure out where to get a decent deal on the tool to setup the clutch clearance. Kind of hate to buy a one time use tool.

 

[rockola1971]

I'm trying to figure out where to get a decent deal on the tool to setup the clutch clearance. Kind of hate to buy a one time use tool.

You dont need a special tool. All you need is a caliper to measure your clutch stack and compare to specs. Measure your old stack for comparison.

 

[Matthew Jeschke]

see next post...

 

[Matthew Jeschke]

I've got all the parts ordered minus few incidentals; encoder, clutches, vent, etc. Actually not sure where to order factory clutches from... Rock auto didn't have them, ebay does but I never fully trust eBay.

You dont need a special tool. All you need is a caliper to measure your clutch stack and compare to specs. Measure your old stack for comparison.

You have convinced me What you mention is how I did it in my 4L60E build (more or less). I'm really perplexed as to why they do it differently for the drum on the NP246 with that stupid complex tool. For the 4L60E build I put a feeler gauge between the pressure plate an the top clutch and checked the gap met spec in my book.

The only question, and I'm sure you're accounting for this... They don't give me a spec for gap, only for using that stupid tool. So if I spec off the old clutch pack height, won't there be wear to account for? I've 250,000 miles on that transfer case. Do clutches wear much? idk...

Practically fell apart, really easy to work on except for those double seals. Came with 6 pinion planet already.

 

[rockola1971]

@Matthew Jeschke Give me the thickness measurement of your new and your old stack and I will dig around for the numbers you seek. During tranny clutch loaded measurement most shops just hit the drum with a air hose and measure the gap of the pack when air is released. Hit it with air a couple times and take multiple measurements to make sure around the gap.

If you hit that gap in 3 different places around the drum and you get .002", .005" and .010" using new steels and clutches...well you just measured the gap of a warped drum that got too hot and is JUNK! Not likely to happen in a Tcase but very probable in a tranny.

Dont forget to let auto clutches soak in Autotrac fluid before installing them! I let mine soak overnight.

Get your caliper and feeler gauges out and blow off the dust!

 

[Matthew Jeschke]

@Matthew Jeschke Give me the thickness measurement of your new and your old stack and I will dig around for the numbers you seek. During tranny clutch loaded measurement most shops just hit the drum with a air hose and measure the gap of the pack when air is released. Hit it with air a couple times and take multiple measurements to make sure around the gap.

If you hit that gap in 3 different places around the drum and you get .002", .005" and .010" using new steels and clutches...well you just measured the gap of a warped drum that got too hot and is JUNK! Not likely to happen in a Tcase but very probable in a tranny.

Dont forget to let auto clutches soak in Autotrac fluid before installing them! I let mine soak overnight.

Get your caliper and feeler gauges out and blow off the dust!

Awesome! I'll try to get into the drum tonight after work and measure thickness of the original clutch stack-up.

Curious, I have LOTS of dextron VI. The parts store now says to use Dextron VI in the NP246 tcase. However, that seems highly disputed online. I've no clue haha can I use the NP 246? I can no longer find Auto Track II. Some say to use Dextron III but I would prefer to use what I already have... Any tips there?

 

[rockola1971]

Awesome! I'll try to get into the drum tonight after work and measure thickness of the original clutch stack-up.

Curious, I have LOTS of dextron VI. The parts store now says to use Dextron VI in the NP246 tcase. However, that seems highly disputed online. I've no clue haha can I use the NP 246? I can no longer find Auto Track II. Some say to use Dextron III but I would prefer to use what I already have... Any tips there?

If you have the auto4wd then you need auto trak fluid. Its blue.

Amazon.com : acdelco auto trak 2 transfer case fluid

 

[Matthew Jeschke]

Clutch hub and drum was immaculate. Some wobble in the needle bearing though at neck of drum. no abnormal wear on the shaft or anywhere. Maybe is typical.

I measured the clutch pack including the apply plate and spacer. Measured in three places was and pretty uniform. When measuring I held clutch pack with one hand in a fist to squeeze it together, while I measured with dial caliper next to my hand. I measured all the clutches and steels as well. They were pretty uniform. Rough dimensions below:

Ten clutches ~ 0.086" each
Nine steels ~ 0.067" each
One spacer = 0.071"
One pressure Plate = 0.252"

Stack up ~ 1.803"