4Hi won't engage but 4Lo will

Have been dealing with this issue for the past few months, I feel it's the result of not running 4wd every now and then to free things up. I have the manual trans, 4wd w/switch configuration. A bit new to the understanding of what's going on, but the truck has no issue with being manually engaged into 4Lo. That being said, does that mean this is likely a transfer case actuator issue if it won't go into 4Hi with the push button? Just want to start ruling things out. Mainly trying to get an understanding of what the two actuator's jobs are (the front one vs. transfer case one) Green light for 4wd (either Lo or Hi) doesn't come on at all. Thanks!

 

I don't see how this is possible. Are you SURE it's not in 4 hi. And are you SURE you're actually in 4lo. It could be a glitch where the light isn't coming on correctly.


If it were an issue of not engaging due to non-use you wouldn't go into 4lo or 4hi. When that happens the transfer case will usually engage but the hubs don't lock because the lubricants in the hubs have dried up and won't let them engage.

 

You could very well be right that I might be in 4Hi. I know for a fact it engages in 4Lo (can feel that strong pull from the front end and tougher to turn). I'll have to test out how it feels on the road to truly know. It would make sense that the light doesn't come on for either. To note, I can distinctly hear the actuator doing something when the button is pressed, but I don't get the *clang* that I'm used to hearing which is throwing me off.

Just want to clarify that the 4Lo is mechanical (moving the 4wheel shifter full front) and 4Hi is the button, and both are essentially operating the same actuators?

 

Try taking a tight turn in 4Hi. If you feel some resistance/difference compared to in 2WD your 4Hi is working.

 

A couple things to add. You can engage either 4Hi/4Lo and then have someone watch underneath (carefully), as you crawl forward a couple feet. If they see the front driveshaft spin, then the transfer case actuator is working properly.

If that checks out, then it may be worth putting the truck up on 4 jackstands (all 4 wheels in the air) and seeing if the front wheels spin once you accelerate in either 4Hi or 4Lo.

If that checks out, then it's simply an issue of the light not working (which would point to either the bulb being burned out, or the transfer indicator position switch on the ADD actuator being defective).

Edit: with the first check I mentioned, of the front driveshaft you'll rule out the possibility of your truck being in 2Lo when you try and engage 4Lo. If the transfer case actuator isn't working it's possible you can get the Lo part of 4Lo without the front drivesaft (4) part of the equation working. Just feeling that increased torque of 4Lo doesn't necessarily mean that you're in 4Lo and not in 2Lo

 

Re: engagement sound / "clang"...

FWIW: I only get a slight noise with engagement of 4H on my truck. Engaging 4L gives a subdued/dull metallic clunk noise (which also can be felt) which is what I would expect from the front fork engagement and moving into place. If I repeat the cycle a second time soon after, the 4L engagement is much quieter.