Marc Ohmann

Popular thread I have here I guess lol Anyhow, I got the tcase back in today. The rain delayed things a bit. Overall it went pretty well considering I'm working out in the elements. The planetary was trashed so I'm guessing that was the loud motorcycle like noise we heard while driving and I'm guessing was also the reason for no reverse. Best I can figure, losing all the oil trashed clutch housing bearing which created enough driveline slop to mess with the planetary. It was an expensive rebuild with the new planetary, new pump, and new rear case half but at least I know what parts went into it and how the work was done. I also upgraded to the 6 planet planetary since it added minimally to the build cost. And for anyone keeping score at home, I did buy the J-44295 to set the clutch shim and after 200k miles, the original clutch pack was still in spec with the original shim -- even after being pulled apart and cleaned. Wishing I would have ordered new case bolts but I'm just gonna coat the outside of these with some lanolin. Also wish the rebuild kit came with all new clips. Seems pointless to risk a whole rebuild on one previously stressed clip failing. I'll be pulling the 246 on my '06 next to put a BRNY in before the rear case gives out. That one still holds oil for now.

Got a chance to tear into the tcase today. Chain is trashed so that must be the other clunk. Oil pump wore a hole through the back half so she didn't have much chance with no oil in her. If you own one with the NP246, do yourself a favor and tear into it to add a BRNY or similar while the repair is still cheap.

Yeah, "extensive cleaning"or "exhaustive cleaning" are probably more accurate. The crap just kept pouring out of those little seep holes in the baffle -- amazing how much was in there. At one time, I thought I had lifter noise but it's just the broken exhaust manifold bolts. I have 40-60psi now after replacing the o-ring so not too worried about replacing the pump yet. After having the oil pan off and seeing how clean everything was, I'm encouraged to maybe take on rocker panels and fenders next year and get her back to looking like new. I last did rockers on my '87 and that was a long time ago. I have a lot more patience for that type of work now and I think it'll actually be fun (or at least rewarding).

My turn. I have two. An '03 Yukon 5.3L flex NP246 with 190k on it and an '06 Sierra 5.3L NP246 with 220k. We've owned both since around 30k miles and they have both been incredible trucks. I've replaced front hubs in both and both are rusting in the usual spots and beginning to look their age. The Sierra is winning the race in returning to dust though. I replaced all fluids in the Sierra at 180k and feel terrible that I haven't in the Yukon yet. In the Sierra, I replaced the oil pump pickup o-ring, cleaned the new style PCV valve cover, replaced pitman arm, bank 2 sensor 1, oil pressure sending unit, and many pads/rotors -- not bad for that many miles. It needs rust repair on the driver's side crossmember at the lower control arm and exhaust manifold bolts replaced. It'll likely be getting plugs/wires and new power steering pump soon as well. The Yukon has also been a minimal maintenance truck. I replaced the alternator, drivers seat heater, blower control module, AC tensioner, encoder ring, many pads/rotors, and cleaned the driver's side chassis ground. Before winter I'll have to rebuild the NP246. Pretty sure it got tore up when the encoder ring started randomly locking her in 4HI and 4LO. Now it just becomes a game to see if I can get 400k out of them. We get -40F temps up here and both have no problem starting all winter and they sleep outside. Love these trucks. Just wish they weren't rusting out.

Thanks dna! The wife is leaving for a week with her truck so I'll have some time to research options. I'll probably even check the junk yards to see if I can get a temp one to throw in while I get parts and finish the rebuild.

My '06 Sierra with the 5.3L and 220k miles has been using 1-2qts oil between oil changes for years and recently started fogging the area in heavy blue smoke on startup. Until today. I pulled the driver's side valve cover to clean the PCV baffle and drill some new drain holes. After getting it off, I see it already had two additional drainage slots cut in so i just cleaned it excessively. The baffle was caked in tiny chunks of gunk. I ran a couple quarts of pressurized diesel through it with endless chunks draining from the tiny baffle holes until it was finally as clean as it was gonna get. One test drive with 4 starts and no smoke! Excellent! It even cleared the P0053 O2 sensor code it recently threw and it runs more smoothly at startup and shutdown. However it is better but still a little rough at idle. I'm guessing the original plugs could use a changing after all these years of oil consumption. If that doesn't do it maybe an intake gasket is in order. New oil pump pickup o-ring and now cleaned valve cover and she's almost a new engine ready for the next 200k.

The kit I was looking at is chain, bearings, pump, seals and clutch steel https://www.rigidaxle.com/products/gm-np246-transtar-transfer-case-rebuild-kit-w-bearing-chain-pump-clutches-steel?currency=USD&variant=7475189317660&msclkid=bc0019cca20b11c520c67b0489f70728 I guess there unknowns are pinholes around the pump in the rear housing and wear on the chain drives

Thanks for the info Richard! A chain skipping seems to make sense. I guess I have to tear into it first to find out what parts it'll need. I can't think of any way to ensure it's the tcase but seems high enough probability so I should just drop it and dig into it I guess. Looks like $350 for a rebuild kit without gears or case parts.

I'll add that when it clunks, it only does it under load and I don't notice any slippage -- the truck just keeps powering forward. But it is a repetitive clunk like a slipping and catching. Or it could even sound like the driveshaft hitting something as it spins but for that to happen only under load, the tcase would have to move and that doesn't seem likely.

So replaced the front hubs and that took care of one clunk but now I can hear another clunk from the tcase area. I'm starting a new thread for that issue to be more on topic. I'm considering this issue resolved. I think pulling the TREC fuse somehow screwed up our ability to shift into reverse. It hasn't happened again since I replaced the fuse and the Service 4wd message was fixed by the new encoder ring.

My wife's '03 Yukon has a clunking or skipping noise coming from the transfer case area when in 4WD and under load. It happens in both 4hi and 4lo but not in 2wd. I just replaced both front hubs and that eliminated a separate clunk from the front but this is definitely coming more from the tcase area. The encoder ring went bad last winter and I'm guessing the random shifts into 4hi and 4lo from that may have caused some transfercase issues. When I did the encoder ring, the front u-joints and splines looked fine. Ujoints are original. Does clunking under load sound like a tcase issue? To me it makes sense. Or is there anything else I should check?

I couldn't wait so I went out and checked the frontend tonight. The clunking sounded too much like front hubs and with almost 200k on the originals, they've probably seen their best days. Anyhow I got just a little play in them when wiggling the wheel so I ordered a pair of Timkens. Hopefully that gets her back to working 4wd.

I got the encoder ring installed today and we also still haven't seen the issue with no reverse appear again. I'm now wondering if it was somehow related to me having the TREC fuse out. The problem persisted even after replacing the fuse but has been gone after every restart since replacing the fuse. So hopefully the computer just needed a shutdown/restart reset with the fuse in and all is good... The encoder ring was a pretty easy job even on the gravel driveway without a lift. It only took two hours and that was with stopping regularly to swat/cuss mosquitoes. The install was a partial success as it got rid of the 'Service 4WD' message, the t-case shifts into any gear we choose, and so far it hasn't randomly chosen a new gear after startup. But we still have a problem with the front end clunking when in 4HI or 4LO under power and when turning either direction. I did test that front encoder and it shifts but it seems for some reason it's maybe not engaging all the way. I'll jack up the front end tomorrow to check the CVs and hubs. Any ideas or other tests I can do?

So ordered a new encoder ring. Seems worth a try at $80. Right now I'm guessing the t-case was shifting into neutral and that's how we lost reverse but still no idea if that's realistic or why it would happen. Again all forward gears worked fine and all gears have worked fine for days now.

Still can't find a good pinout for the encoder plug but I pulled some voltages with the key in run position. Following the same orientation with the clip pointed down, I got 5vdc signal on the lower left pin, 1.7v on the top-left pint, 1.3v on the lower-right pin, and the same 12vdc on the second pin from the left in the top row. I have an OBDII MX+ reader. From what I see, it doesn't look like I can get PID (is that the right term) values from the encoder. Do I need a Tech 2 to test the TCCM or is there someway I can do it with my reader?