02 S10 ZR2 Pickup 233C transfer case problems

Hi, I have a 02 S10 ZR2 Pickup with a 233C transfer case. It has 2wd, 4hi and 4low three button setting on dash. It will not always shift into 4hi or 4lo, sometimes makes a growling or winding noise when trying to shift into 4hi. All lights indicate shift was successful, front axle is locking and encoder motor is making a successful shift, but no power to front drive shaft upon most tries.

I already replaced encoder motor, front axle actuator, and three prong vac switch on case. When you start truck all lights flash once and then the position I’m in stays lit. No codes are stored in TCCM when grounding pin 13 on OBD port. All systems function properly including vacuum locking front axles. When you select 4hi or 4low the encoder switches, the light switches to the new position and light stays on, the front axles are locked, but the transfer case is not connecting to the front drive shaft, it still spins freely. Sometimes it will work if you are moving forward at a certain speed, other times it will not ever work no matter what speed you try it at. Sometimes when you are lucky enough to get in in 4hi it will clunk and slip out of 4hi, lights don’t change, axles still locked but transfer case is not sending power to front drive shaft. Other S10 trucks will engage 4hi at full stop in neutral and at any speed, not this one you have to be moving at an exact speed around 5-10 mph or it will never work. What part in the transfer case would be at fault, or is it a sensor or what?

A sensor failure would likely result in an error code. It is more likely that the clutch pack may not be engaging fully, either from wear of the cam plate/ slider fork mechanism, wear of the guide pads/pucks, clutch plate wear, or contamination.

Has the xfer case been drained/refilled at regular intervals? Has it been flushed? Contamination from chain and case wear can impede the full travel of the slider forks or stack up between clutch plates and the spline and prevent full engagement. If the unit has never been serviced, it is possible that a flush and refill might help. It is also just as possible that the flush could liberate contaminants and damage a bearing, so there is some risk involved if the unit has never been properly maintained.

The fluid was flushed, looked fine, no grindings. This is the three button system without awd and don't believe it has any clutch packs. Think it is the mode fork or it's plastic tabs or synchronizer gear or something.