I really like the push button feature to change from 4WD HI to 2WD and vis versa for my 1999 LS. My question is should I be at speeds less than 35 MPH to change to 4WD to 2WD? The book says at any speed and the tag behind the sun visor says under 35 MPH. Any comments?

 

Stop and change it. How long can it take? Not very.

If its in poor traction conditions and shifting from 4 to 2 then youre not going too far too fast anyway.

Never trust old systems to work as well as when new.

 

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This

It's too easy to just stop the vehicle and push the button. Very simple way to ensure that you don't break anything in the driveline.

I can't imagine any scenario where any one would be going even just 15+ mph and suddenly need to change from 2wd to 4wd or vise-versa, and are in such a hurry that you can't just stop for a second...

 

4HI to 2HI can actually be changed at any time and speed. Just make sure you switch from 4HI to 2HI or vice-versa on a straight stretch of road, especially the engagement from 2HI to 4HI.

What many do not realize is that if you change even at very low speed but under load it may not disengage until later when it gets unloaded for a short while. It usually engages immediately as it is pushed into gear the same as a manual gearbox. I can hear and feel my 4x4 being engaged or not and just give it a little bit of accelerator to release the pedal again to create this unloading of the drivetrain and it usually disengages.

 

I am confident that you mean 2HI in all of those situations above. 1) I do not believe that there is a 2LO and 2) to switch in and out of 4LO, you need to be stopped and in neutral. I am new to this Blazer so I don''t know it all too well but in my '91 S-15 Jimmy with a manual transfer case I can go back and forth between 2HI and 4HI at any speed as long as 'wheel is not spinning' (loss of traction). Same in my F-250 with electronic shift on the fly (ESOF) 4X4.

 

Geee - you're absolutely right. Correcting right away!

The transfer case is an unsynchronised gear set similar to the ones used in a manual transmission. It needs standstill to be shifted and the transmission in neutral. The electronic transfer cases usually will not switch to 4LO until the transmission is in neutral and the vehicle speed below a certain threshold (usually lower than 5mph), while later vehicles even require it to be in standstill.