So I removed the encoder motor TCM module and left the transfer case in high range.Modified the firewall mounted vacuum module with a dash mounted illuminated switch.Now if I need 4wd I can just flip the switch,engaging the front axle and shut it off when done.I never use lo range or the auto 4wd anyways. Anybody see any issues with this? Thanks.

 

eh, not really, maybe a little bit more wear on parts or slightly worse gas mileage. probably hear the transfercase chain spinning around at higher speeds, which i dont know if that would be a issue if you drive fast i ran a vacuum switch inside my 83 for the front axle when i was younger. got sick of wondering if my 4x4 was gonna work when i need it

 

I was told that on my model, that the front driveshaft is always engaged in hi range 2wd or 4wd and that the only thing different when shifting to 4wd is that the front axle vacuum switch engages the front axle.

 

What year?
What model? (Blazer, Jimmy, Bravada, or pick up)
3 button or 4 button switch on the dash?

The front drive shaft turns when the vehicle is in motion, this is what allows "shift on the fly". When you're moving, everything is meshed and turning, but power is not applied to the front differential. Much like the forward gears in a synchronized manual transmission; always meshed, but not all are powered. When you select 4WD, it all gets connected and power is applied to the front differential.

 

It's a 99 Blazer with the 4 button dash switch.So if what you say is in fact the way it works,what engages the TC to get 4wd? I have another S10 with the same setup that actually works (yeah,I tried swapping parts) and don't hear any shifting going on when I go from 2wd to 4wd,looked like just the vacuum solenoid to the front axle opened up.Is there a vacuum switch on the tc? Thanks-Chuck.

 

In 2WD, the front drive shaft is driven by the left front wheel so it's turning whenever the vehicle is in motion. When 4WD is selected: the encoder motor shifts the transfer case to apply power to the front drive shaft. The TCCM activates a vacuum switch on the firewall that applies vacuum to the axle actuator under the battery tray. The actuator pulls a cable that operates a clutch mechanism that engages the right axle shaft with the differential. When the axle is fully engaged, it activates a switch on the axle housing and the 4WD light comes on.

 

OK so it sounds like my plan is a no go because the encoder motor must be activating the clutch inside the tc that actually directs power to the front driveshaft instead of just spinning it to speed for the shift on the fly.Too bad it wasn't as simple as engaging the front axle and getting the 4wd.Thanks for your help.