Can’t shift into L4 normally

!!Read Slowly!! It’s confusing. So to start off my diff lock doesn’t work hasn’t worked for a while. So this morning I took the actuator off to look at it and I just determined to get a new one to replace it because this one is very rusty. So after i put the old one back on I went to go see if the diff lock would work just because. I went up to a gravel patch up by my house and put the 4wd shifter to 4H then I put the regular shifter to N then the 4wd shifter to N. So both shifters are in Nuetral. I’m trying to engage L4. Now that both are in N. I go to shift the 4wd shifter into L4 and it grinds and won’t go in. I try again slower and I can feel the gears touching and grinding. I go back to neutral and try to get out of neutral back to 4H. It grinds just like trying to go into 4L. At this point I am on a hill stuck in Nuetral in both shifters. I call my dad he says to turn the engine off. I turn it off and now can shift back to 4H and Drive on the gear shifter and it drives just fine in 4H and 2H. I can reverse put it in park and everything else just fine.

What is the problem here. Did I do something weird with the actuator that I wasn’t supposed to? Is my transmission cooked? Why can it turn to 4H but not 4L? What’s up? 4L has worked in the past year and there were no problems with it earlier.
Any help would be greatly appreciated.

 

Year make and model, automatic or manual trans and does she have the 2-4 selector or not?

 

2001 3.4L v6 automatic what’s the 2-4 selector.

 

Thanks for the detailed description — it really helps. Based on what you've described with your 2001 Toyota Tacoma 3.4L V6 automatic 4x4, this sounds like a transfer case engagement issue rather than a transmission problem, and likely not related to the actuator directly — especially since you're talking about grinding while shifting into 4L (which is a mechanical function, not electronic in this case).

Here’s a breakdown of what likely happened and what’s going on:

What likely caused the grinding:

1. Misalignment in the transfer case gears: When you tried to shift into 4L with the engine running and both shifters in Neutral, the transfer case gears were still spinning slightly. Unlike modern electronically shifted systems, your Tacoma’s transfer case is mechanically actuated and requires very precise conditions for the low-range gears to mesh cleanly.
   
   
2. Transfer case gears not synchronized: 4L in these trucks doesn’t use synchros like a transmission does. It relies on gears stopping or lining up naturally. If they're spinning even a little (due to driveline windup or friction), it will grind.
   
   
3. Truck not fully stopped / slight wheel movement: Even on a slight incline, if your wheels were rolling a bit, that small movement is enough to keep pressure on the gearset, making engagement into 4L difficult or impossible (and cause grinding).
   

✅ Why it worked after turning the engine off:

• Turning the engine off stopped any rotation in the drivetrain, letting the gears in the transfer case settle. Once everything stopped moving, you were able to shift back out of Neutral into 4H without grinding — that’s normal for this style of part-time 4WD.
  

No, your transmission is not cooked.

• Your transmission is fine. It shifts, drives, and reverses in 2H and 4H, so it’s functioning. The issue is isolated to the transfer case, not the automatic transmission.
  

Why it won’t go into 4L now (but worked before):
A few possibilities:

1. Drivetrain bind or pressure due to not being on a flat surface.
   
   
2. Transfer case linkage is slightly out of adjustment or getting worn (common in older trucks).
   
   
3. Gears slightly out of alignment internally — again, because this isn’t a synchro gear, it sometimes just takes a little finesse or patience to line up.
   

️ Suggestions / Fixes:

1. Always shift to 4L with the vehicle fully stopped, foot on brake, transmission in Neutral, and ideally with engine off or idling on a flat surface.
   
   
2. Try gently rocking the truck back and forth (with someone inside pressing brake lightly) while you attempt to shift into 4L — it helps align internal gears.
   
   
3. Check the transfer case shifter linkage under the truck. The bushings or joints may be worn or rusty, making it harder to get full engagement into 4L.
   
   
4. Flush or check the transfer case fluid if it's never been done — old or low fluid can contribute to sluggish shifting or internal drag.
   

❓Was the actuator connected to the rear diff lock only?
Yes — your rear diff lock actuator is separate from the transfer case. Removing or messing with it should not affect your ability to shift into 4L, unless some electrical issue is causing interference (unlikely unless wiring was disturbed).

 

Oh my thank you so much. What a reply. Um it still has a problem on flat ground I will try having someone rock it back and forth while it try. Transfer case could definitely use some new fluid. What is the transfer case linkage. And where would I find specifically rather than just under the truck. Thanks again.

 

This is just generic info pulled from the internet to somewhat point you in the right direction so take it with a grain of salt.

What is the Transfer Case Linkage?
The transfer case linkage is the mechanical connection between your 4WD floor shifter inside the cab and the transfer case bolted to the back of your transmission. When you move the 4WD shifter (2H → 4H → N → 4L), you're moving that linkage — it translates your motion into movement inside the transfer case to engage gears.

Over time, this linkage:

• Gets rusty
  
  
• The bushings wear out
  
  
• Or the alignment gets slightly off, making full gear engagement harder (especially into 4L, which has the most throw).
  

Where exactly is it located?
To locate the transfer case linkage on your Tacoma:

1. Crawl under the truck, ideally with it parked on flat ground, parking brake on, and wheels chocked.
   
   
2. Follow the back of the transmission, and you’ll see the transfer case — a roughly football-sized component bolted to it.
   
   
3. On the driver's side of the transfer case, near the top or side, you’ll see a small rod or lever with a metal linkage going up toward the cab — that’s your transfer case shift linkage.
   
   
4. It’ll have a pivot point, clevis pins, and maybe some rubber bushings or grommets. If they’re worn or rusted, that can cause vague or stiff shifting.
   

What to Look For / Do:

• Check for rust or corrosion at the linkage joints.
  
  
• Move the 4WD shifter inside the cab (with the truck off and safely parked) and watch the linkage move underneath — see if it moves freely or binds.
  
  
• Spray the joints with penetrating oil (like PB Blaster or Liquid Wrench) to loosen it up if it’s sticking.
  
  
• If there’s slop or play, or the linkage doesn't fully move when you shift, the bushings might be toast — there are replacement kits available (or you can fabricate with new bushings/washers).
  

Optional Upgrade:
Some people upgrade to Aftermarket Transfer Case Shifter Bushing Kits (like from All-Pro Off-Road or Marlin Crawler) for a tighter shift feel. Cheap fix, and makes a big difference.

 

The 2-4 selector is nothing more than an electronic motor that moves the sliding gear inside the transfer case. IMHO, the manual lever is the way to go.