'98 Qx4 T-case problems

[The_Q]

Hello everyone! I moved to Michigan in late February this year. I had a commute to work that was up to an hour in the snow. I have the Mile Marker manual hubs. When I locked the hubs and flipped my switch to 4auto or 4high, the front wheels would engage normally and without problem. However, there was at least 3-4 different occasions where I would engage 4auto at the start of my commute, but after 40-45 minutes the vehicle would kick me out of 4wd and start flashing the 4wd light. This would go away after a few minutes (longest was ~10 minutes), and it would allow me to switch back into 4auto. Restarting the vehicle did not reset this if it appeared. This was a bit scary the first couple of times this happened (I'm from California lol). The flashing 4wd light makes me think this could be related to the manual hubs because when driving highway speeds with the hubs unlocked, the 4wd light flashes the same way. 

 

some background mechanical info for those who may be wondering:

-mile marker manual hubs. 

-VG33E with the Qx4 Transfer case, which is different from the VG pathy T-case. For those who are unaware, the Qx4 has an auto transfer case. The shifter only has 4hi, N, and 4Lo. There is a switch on the center console when in 4high to switch between 2wd, 4auto (center diff unlocked), and 4high (center diff locked).

-This has had new Tcase seals and fluids from early 2022. I've been off-road several times with it and not ever had T-case issues. 

 

 

If anyone has any idea what could have been going on, or has also experienced this before, please let me know! I will add that before I added the manual hubs, I had been in 4auto for long durations without any issues. 

If the issue is the Mile Marker hubs, I have 2 options

-gamble some $$$ and buy Warn hubs and pray they work better

-swap back to OEM hub setup (sad to lose the up to 2 MPG extra)

[Slartibartfast]

If the hubs are locked, they should be functionally identical to the drive flanges the truck came with, or to any other brand of hub. I have heard of the auto-transfer-equipped trucks complaining when the hubs aren't locked--near as I can work out, this is because some of the auto transfer trucks read front wheel speed from a sensor at the front output of the transfer, rather than the ABS wheel speed sensors, so they get understandably confused when the front driveshaft isn't spinning--but this is the first I've heard of one complaining when the hubs are locked.

 

The first thing I would do is confirm that the hubs are actually locked in. The Mile Marker hubs on mine (which I assume are the same 435s you're running) move the collar using springs, which allows you to turn the dial whether the innards can move or not (they'll pop in or out when the splines line up or when they're not under load). If the innards are bound up, maybe one of your hubs was stuck in the unlocked position--though this would only make sense if you locked the hub before going on the drive where it acted up, rather than leaving it locked from a previous day when it did not act up. I would take the hubs apart, check that the collar that locks the CV to the hub moves freely, and look for evidence of dirt, corrosion, or water (ice) that could've bound up the mechanism. The hub should not be packed with grease, but a little grease on the surfaces that slide may do it good. I added a little grease to mine when I installed them.

 

Other than that, I would have a stare at the TF section of the '98 service manual, specifically the diagnostics. You may be able to get a code out of it the next time it acts up. I haven't looked through the troubleshooting for the ATX14A in a while, but I would not be surprised a wiring issue or sensor crapping out would give the same flashing, especially during winter. I had a failing ABS sensor on mine act up only in winter, presumably when it got wet.