I have a 2001 ZR2 Blazer I took out for the first time. Got stuck in sand. I was in 4 wheel high and while stuck only the back tires were spinning. I put in 4 wheel low and still only rear tires would spin. Is this normal or is there something wrong with the 4 wheel drive system? If there is something wrong, what should I check first?

Thanks for any help

Jon

 

To check this is what I do.

Raise up the right front wheel off the ground.
Start it up.
Put it in Park then shift into 4WD Hi.
Then go out to the right front wheel and see if it rotates a little then stops. If it stops, then your 4WD is working. If you can still rotate it, then the front actuator is not locking the front axle in.

The purpose of having the engine running is that the front actuator needs vacuum to pull on the cable to engage the front axle.

The transmission needs to be in Park so your vehicle does not move.

The 4WD HI needs to be pushed so the the transfer case applies torque to the front axle driveshaft.

If all this is done, then the front driveshaft will not turn, the rear driveshaft will not turn, and the right front wheel should turn a little then lock.

If any of this turns then you have a problem.

Bill

 

Yep, your 4wd is not working. There is a very good write up on diagnosing the 4wd system on here but as pointed out above, the actuator is the usual culprit but is only one part of the system.

 

I will be testing this weekend. The actuator is located under the battery tray correct?

Thanks again for the help

 

Yes, under the battery tray.

 

If everything works up to the front axle actuator, you could disconnect the cable from it that goes to the axle. Pull on it and see if it locks in. If not, the cable is bad. Could have gunk and dirt inside of it and it is frozen.

In my case, I just replaced the cable and the front actuator at the same time. It is not that hard to do and might save you downtime in the future.

The cable is not that expensive. Might as well do it if you are already replacing the actuator.

My 02 CrewCab had 200K miles on it when mine died. Replaced them both at the same time and now I know that it works.

Bill

 

I did the test, and whether is in 4 hi or low the front tires would spin. I pulled the cable from the actuator and it would not go into 4wd. I was able to find the actuator and cable on rock auto, but I was not able to find the shifter for the transfer case for the transfer case. None of the ones on rock auto looked like the right one to get.
https://onedrive.live.com/redir?resi...nt=photo%2cJPG

 

If what you conclude is true, then the front axle cable is not shifting the fork in the axles shaft housing into 4WD. If you CAN pull the cable, and the axle DOES NOT lock, then you have a fork to axle problem.

IF you CANNOT pull the cable, then most likely the cable is froze and should be replaced.

If you have a lot of miles on it, the actuator should be changed too. It can develop tears in the diaphragm and leak vacuum thereby not allowing the cable to pull the shift fork in the axle shaft housing.

Back to my previous post. No more expensive than these two items are, it would be best in the long run just to replace both of at the same time and be done with it.

You can obtain these parts at NAPA, Advance Auto Parts etc. I was able to buy both at NAPA from their store 2 blocks from my house and they had the parts in stock.

Good luck and keep up informed..

Bill

 

I replaced the actuator and cable. It defintly clicks in when selecting between 2wd, 4wh and 4wl. But I can still turn the tires when in park. I believe the problem may be a vacuum leak. Is there a part I should check first? Going through and testing the vacuum system is beyond me, and didnt want to have to take it to a shop.

 

As I stated earlier, if you can pull on the actuator cable and the front wheel locks in, it won't turn.

To check the vacuum actuator, when the engine is running, remove the battery and battery tray and watch the actuator while someone shifts in and out of 4wd. If you see the cable move in and out, then the actuator is getting vacuum. If not, then further investigation is needed to find out where the vacuum is and is not.