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?

I got a chance to test the front actuator and it shifted just fine when adding/removing ground from the signal terminal. I also attempted to test the t-case encoder but the directions I shared above don't seem to match up color-wise to my harness. I did get 1ohm to ground as the lowest reading on any pin so I'm assuming that's the ground. It was the second pin to the right when looking at the truck connector with the clip oriented down. In the same orientation, I had a constant 12vdc on the second pin from the left in the top row. So assuming that is the ground and not some short, 1 ohm seems good to me. Now I need a good way to test the TCCM and I still have no idea how we could temporarily lose reverse the other day. I did have the TREC fuse out to keep the truck from randomly shifting the t-case when we lost R the other day. The fuse had been out for days though and we still didn't have reverse even after I replaced it. Any ideas?

ok, found this pinout for the front actuator also. That should be an easy test tomorrow. That'll help with the 'Service 4WD' message but still no idea how we could temporarily lose reverse...

I'll plan to follow these steps to check the signals coming out of the TCCM at the t-case actuator but something similar for the front axel actuator would help as well.

My wife's '03 Yukon (VIN:1gkek13z03j140424) with 180k miles has had the 'Service 4WD' message for about 6 months now. When it originally appeared, I pulled codes CO306, CO327, CO379, and BO790. The issue the truck had then was only that it would be in a random t-case gear after startup and sometimes we couldn't shift out of it. Not usually an issue except when stuck in 4LO. I traced the issue then to a broken ground wire on the frame under the drivers door. I soldered in a new wire, cleaned the frame connections and applied dielectric grease. That solved the problem for about 3 months. Then later last winter, it started getting stuck in 4 and 4LO with what felt like the front end fully locked in. Later it became a clunking sound as if the t-case or front-end wasn't fully engaging. We've kept the truck in 2HI since then and all has been fine. I was planning on digging into it once bug season dies down since I work outside on a gravel driveway lol Then today we started hearing what sounded like an electric motor/fan revving while we drove at 60 mph. The noise had no effect on power to the wheels and didn't seem to be effected by engine speed or wheel speed -- the truck seemed to operate just fine when it was happening. The first time it happened, we thought a motorcycle was passing us -- that's how loud it was. The noise lasted only a minute or so as we drove and then was gone. We pulled over to check things out and visually all looked ok. I then put the truck in R to back out of our parking spot and could hear the loud motor sound. It seemed to be an actuator on the t-case or transmission. Shifting back into P stopped the sound and shifting back into R brought the noise back. The truck also had no reverse like the transmission was in neutral and not able to shift into R. All forward gears worked fine. I pushed the truck out of the parking spot and we drove home without incident. After the truck sat for an hour, all gears including R work just fine with no noise. That seems to tell me the issue is electric and not mechanical but what do I know. Could it be the transfer case was shifting into N when we tried to shift the transmission to R? I'm just thinking a ground issue could cause weird behavior across all these things. And I can't think of what could make that revving sound while we're cruising down the road... So my questions: - Any thoughts or recommended diagnostic steps on what could cause the revving sound when shifting into R? And why would this noise happen when cruising along at 60mph in D? - Any thoughts or recommended diagnostic steps on the Service 4WD message and diagnosing the t-case actuator, TCCM or maybe even the front diff actuator? I'd like to pin all of these (t-case actuator, TCCM, and front actuator) out to see if I could have another ground or wiring issue. Anyone have diagrams? I have two of these trucks. The other is an '06 Sierra. They both have had similar t-case shifting issues. The funny thing is that the '06 Sierra only has the issue when temps are below 0F. Thanks in advance for any help