I have a 97 Limited 4runner, V6 with automatic transmission. I have a push button on the shifter for 4HI. When the button is pushed, the dash light indicator comes on and 4WD feels like it is engaged.

The issue is when driving over ~30mph, the vehicle will randomly pull to the side, it seems like often the passenger side. It pulls hard enough where I feel it is safer to leave it in 2WD even on snowy roads. The issue is not present in 2WD. I’m not sure if what I am feeling is the front axle intermittently coming in and out of 4WD? Or if just one of the front tires is coming in and out of drive? At low speeds or in 4LO it may be happening but it is less noticeable. When disengaging from 4HI, there is a pretty noticeable “clunk” that I believe is coming from the ADD actuator, but this noise has been present for a few years. It is also possible that the pulling can be correlated to pushing on the accelerator, but I can’t say that for sure. I just can’t remember it jerking me around when I have been coasting.

What I have done:

- I pulled and tested the ADD switch on the front diff. I have continuity (<2 ohms) throughout the full stroke of the switch. I also don’t have any issues with the dash indicator light going out.

- With the vehicle idling in the cold, I “teed in” a vacuum gauge and found 16-16.5” Hg on one side of the ADD actuator, I then pushed the 4HI button, saw the vacuum switch and found 16-16.5” on the other side. For reference I had 17” Hg at the engine upstream of the Vsvs.

- I pulled 20” Hg on both lines that run from the Vsvs to the ADD actuator with a vacuum pump, then blocked in the lines to “leak check” the lines and ADD actuator. Both lines/sides of the ADD actuator held vacuum.

- Drained and refilled the front diff, it was full of gear oil as found and no shavings were observed.

- Verified that the front drive shaft locks in when in 4WD, it can be rotated by hand in 2WD. Also took an external battery and tested the transfer case actuator. It sounds like it should to the untrained ear and locks and unlocks the front drive shaft.

- Verified the transfer case fluid level is full, did not do a drain and refill.

The next thing I planned to do was pull the ADD actuator, look for damage and verify it fully strokes on the bench. If it was short-stroking, could that be the issue? Part of my problem is that I don’t have a great understanding of how the gears engage in the transfer case and front diff when switching into 4WD. Also, both CV axles have been recently replaced. Any suggestions or shared experience would be greatly appreciated!

Good job of diagnosing your issue I would also add.
Lift the front and check the front for bearing play also the cv axle is solid no play or movement. Uneven tire pressure upfront can also be a cause.

First, great job so far with checking/diagnosing things!

Can you elaborate on the ADD switch continuity a bit more? There should be part of the switch stroke that is open circuit (can't remember if it is fully out or in). If it is always shorted, the 4WD ECU will always think think 4WD is working even if the ADD is not engaged.

Even so, the ADD engaging and disengaging should not cause any jerking or other bad behaviors while driving. It should only really clunk or make noise if you happen to be turning a bit (wheels moving different speeds) while 4WD engages.

-Charlie

Thanks for the response, I went out and checked tire pressure and did find the driver's side tire to be overfilled, 5lbs above the passenger side.

I don't know much about the guts of the front diff, when you say check the front for bearing play, how would I go about doing this?

Hey Charlie I appreciate the response! The ADD switch was open until I started to push in the plunger. The switch then closed and I had a consistent ohm reading throughout the rest of the plunger stroke, and this was repeatable.

The only time I get noise is when I come out of 4WD, whether the vehicle is moving or not, I hear a clunk and then my 4WD dash light goes away. Sometimes there is a delay in coming out of 4WD, if I'm moving it may be immediate, or it may take 5-10 seconds to clunk out. If I'm parked, I have had to go back and forth between reverse and drive a couple times to get it to clunk out. If the ADD actuator was gunked up could it be sticking or failing to fully stroke, causing intermediate gear engagement?

I have a feeling that was the issue. Equalize the pressure in both front tires and test drive it.

I will test it out. My 4WD issues have been ongoing since November. The overfilled tire was installed after I had a flat a couple weeks ago. I can't tell you what pressure the old driver's side tire was at prior to going flat but I will definitely check to see if the problem still exists now that I equalized the pressures.

My personal experience is with the manually shifted transfer case. The front ADD actuation is much more like a soft click. I would expect the clunk you are hearing is actually the transfer case, since those are 'bigger' components moving and they are right under your butt.

Either one sounds pretty normal though (unless the clunk is really loud). It still doesn't really explain the pulling while 4WD is engaged.

-Charlie

With equal pressures in both front tires I still have the issue. I'm thinking my next window to wrench will be Saturday, I plan to check for cv axle play, are there any other checks I can do to prove out the bearings in my front diff?

Thanks for the info, I plan to do more troubleshooting this weekend, hopefully I find some sort of smoking gun

I am surprised that you didn't feel any diffrence in the truck pulling. Jack the front up and check play in the front wheel bearings. Rotate the tires to check if one of them has resistance to rotation even slightly.Check that brake calipers are functioning correctly and not dragging.

I was able to do some troubleshooting today and did not feel any play in the wheel bearings, and have not noticed any wheel bearing noise. Both front tires seem to have even resistance throughout their rotation. When I have the front jacked up in 4wd, I spin one tire and can watch the other tire rotate the opposite direction. There is a little "slop" when I change rotation directions- about 2.25" as measured on the outside tread of the tire. I do not know how much is normal.

I was able to wiggle the inner CV housing on both sides about the same amount with the front end jacked up and with the vehicle on the ground. I would say they didn't feel sloppy, but there was a little wiggle room.

The brake calipers do not seem to be hanging up, both rotors feel about the same temperature after driving, a little warm. If my caliper was hanging up, why would it only impact me in 4wd? Is it possible that my problems could be ABS related? My understanding was the ABS system relieved brake fluid pressure to a specific tire based on the speed sensor reading so I'm not sure how it would be my issue.

I did drain and refill the transfer case and did not see any metal shavings. I did another test drive today and the vehicle is really pulling hard towards the passenger side at times in 4wd, even at low speeds. It definitely seems like it pulls mostly to the passenger side. The system is also definitely more bogged down, when I coast I slow down much faster than in 2wd or past 4wd operation. What would cause the car to slow down much faster in 4wd, but not in 2wd?

I realized today that the ADD 4WD switch is actually integral to the actuator and the plunger is depressed by the actuator shaft. Since I don't have any issues with the 4wd indicator dash light, this seems to verify my ADD actuator is fully stroking and is not my problem.

From your description the Add system is good. The abs system in the 2000 and earlier models do not have vsc therefore the abs system is basically an advanced braking system to avoid wheel lockup and skidding If the alignment is good, I guess checking tierods, steering rack movement. Bushings etc. Swap the front wheels from left to right. or rear to front. Good luck.

Update: I rotated tires and the issue seems to have gone away, which points to a bad alignment. I plan to rotate them back, get it aligned, and verify this solves my problem, will update further once this is confirmed.

How does rotating the tires lead you to believe the alignment is the issue?