I am also having a problem with my 2000 Chevy Blazer ZR2. When I press the 4 Hi button, I can hear the transfer case engage, it locks the axle for about 2 seconds, then disengages and goes back to 2 WD. I was having problems last year with it not going into 4wd and I ended up replacing the vacuum switch under the battery tray and then the switch that sits on top of the transfer case. Then the 4 wd worked fine after that. Now its acting up again. I had a friend go under the truck as I press the 4 Hi, and he heard the gears engage and felt the axle lock up, but then after a couple seconds, the axle was free and the indicator switch had 2 Wd lit again.

 

4 button Auto 4X4 switch on the dash?

 

welcome to my world...lol...


didn't the 2000 models have the vacuum switch on the case and not the firewall?

 

The 3 button NV233, (2 speed selectable) has a vacuum switch on the transfer case. The 4 button NV236, (Auto 4WD) uses an electro vacuum switch on the firewall.

 

This is the 3 button selector switch mounted to the right of the steering wheel (2wd, 4hi, 4lo)
Last year I replaced the vacuum switch under the battery plate and the switch that screws into the top of the transfer case with the three vacuum lines come out of it.

 

Suggest watching the vacuum actuator located under the battery to see if the cable that locks the front diff is pulled when 4HI is selected but does not stay. This would be a small vacuum leak...somewhere. If you have not replaced all the vacuum lines under the hood in awhile...do so.

 

When your friend "felt the axle lock up" are you referring to the right front axle from the differential to the right front wheel, or the front driveshaft from the transfer case to the front differential?


Raise only the right front wheel off the ground, engine at idle, transmission in park or neutral, select 4WD HI. The right front wheel should not turn by hand. Post your results.

 

It was the driveshaft from the transfer case to the front diff. that locked, then released.


I will check on the right front wheel to see if it turns.

 

You guys are geniuses! !!
Not sure what I did but got 4wd working today! !
Might have been the cleaning of the tccm connectors. But after I did it, same thing. Today did what Cpt Hook said in above step and now everything is working as advertised! !
Next on my list is complete fluid change. But when I went to Auto Zone for the cover, he said they are 3 different ones depending on what gears u have...

Thanks to everyone! !

 

The 3 button NV233, (2 speed selectable) uses (red) DexronVI fluid, (any auto parts store).


The 4 button NV236, (Auto 4WD) uses (blue) Auto-TrakII fluid, (Dealer only).












They both hold just under 3 quarts, and the change interval for both, to be on the safe side, is 36K miles, not to exceed 50K miles. Very important on the NV236 as there is a pump and clutch packs inside. Easy way to remember, is change transfer case & transmission fluid at the same time.