Transfer Case Issue - 99 Yukon with NP246 - Lots of Pics

[bulletpruf]

New speed sensors x 3 installed.

4WD still not working. The "Service 4WD" light isn't coming on anymore.

I pulled the actuator off the front axle and tested it. It seems to work just fine. It's not the thermal actuator and it engages immediately. Is there any way to determine if it's actually engaging the front diff?

Had someone shifting the truck in 4WD while I had my hand on the shift motor. It was doing something - some noise/vibration - so it's getting power.

Then got the truck off the ground - all 4 wheels in the air. In 2WD, the front driveshaft turns, as it should. In 4WD, nothing.

Hoping the issue is the shift motor; have a remanufactured one from Cardone on the way. If that doesn't work, I think it has to be something internal in the transfer case.

The dash switch is known to go bad, but if the actuator is working and the shift motor is shifting, I don't think the dash switch is bad.

Any ideas on what to check?

Thanks,

Scott

 

[SunlitComet]

In 4wd not shaft turning at all? Shift is incomplete or fault in the case gearing. Wait for the motor/encoder assembly and in the mean time double check life on the warning light in case it decided to quit working. When front axle is locked together, off the ground the front should act just like a rear axle diffy assembly. Hold drive shaft and spin a wheel, other should spin opposite. Hold one wheel spin other drive shaft should spin twice normal rate then when spinning both front wheels at the same time in the same direction. If axle does not work as such it is possible the locking collar or shift fork in axle is bad. At any rate if 4wd is manually selected and there is no front shaft output in sync with the rear you have a t-case issue.

 

[bulletpruf]

Ok, the issue was the front diff. Problem is the washer pictured below. It's kept in place by the end of the axle, which has a *** on the end. The axle *** fits in the hole in the middle of the washer. If you pull the axle out, like I did a few months ago when I replaced the axle seals, and don't pull the axle tube off to get everything back into place, the washer slips out of place and blocks the hole in the gear where the axle *** seats. Then you end up with an axle that won't fully seat his is what you end up with -- an axle that won't fully seat and a washer that's clearly been beaten to hell by some idiot (me!) trying to jam the axle in...



The washer is #9 below on the schematic.



To get the washer straightened out, I heated it up with a torch and pounded it into submission. Not quite as good as new, but not far from it.

To get the washer to stick to the gear while I was sliding the axle in, I was using grease, but this wasn't quite doing the trick. The washer kept sliding down the gear, and I couldn't get the axle seated fully. I ended up using a thin layer of RTV. With some gear oil and a little friction once I shift into 4x4, I'm sure the washer will release from the gear.

Speaking of RTV, I used a thin layer on the axle tube surface where it mates with the housing. It didn't have a gasket or any sealant when I disassembled it and it wasn't leaking, but it can't hurt.

One tip -- when reassembling, load up the parts into the axle tube, not the housing end. Only need the spring in the housing end. Then, with the axle inserted fully into the axle tube, get the axle *** through the washer and gear, and while holding it snug against the carrier, thread a few bolts and tighten up at least two. It helps if you have three arms and/or an extra hand. Then tap the axle in all the way; once it's flush, you know the end of the axle engaged the circlip that holds it in the gear.

Once it's assembled, using a screwdriver or a long finger, reach inside the actuator receptacle, press down, and make sure you can engage the front axle. Then you can reassemble.

Nice thing about getting this done today was the weather - it was freakin' gorgeous! About 36 degrees F, slight drizzle, a bit of wind! Awesome! At 6'4", I can't always fit under the truck, depending on what I'm working on, so the parts that were laying outside the truck benefitted from the freezing cold rain and wind! Sure do love being cold AND wet!



Appreciate all the input.

Scott

 

[HoS]

Nothing worse than fixing your own mistakes. But hey, we learn from out own mistakes.