Full-time 4wd/AWD Driveshaft Mod Possibilities?

I really wish my Tacoma had full time 4wd. I don’t do any real off road driving, just fire roads and the occasional questionable dirt track. I do tend to park in precarious places when camping, hiking, biking, or other outdoor shenanigans. I also really like having 4wd for bad road conditions like greasy freshly wet pavement, patchy snow, and really wet fire roads. I would also love to have low range when backing up my toy trailer, so I’ve been looking for options that would allow me to have this truck do everything I want.

An ideal solution would be the transfer case from a manual transmission FJ Cruiser, but I haven’t found a thread where someone actually completed that swap. From what I’ve read it seems that even if you go through getting new driveshafts, modifying the front ADD, and cutting holes in the transmission tunnel, you still would have a nightmare of a time getting the computer to cooperate in order to retain A-Ttrac and rear locker activation. I have read about possibilities of using 4-Runner full time cases, but haven’t seen where anyone has successfully completed that either.

I had another idea for a possible solution and was wondering if anyone has seen this done before?

I’m thinking about a front drive shaft modified to allow some slip and give the ability to use 4wd in situations where a part time locked transfer case would otherwise have problems?

The advantages would be:

• Easy modification just bolt in the new drive shaft.

•Easily reversible if you want normal part time 4wd functionality.

•Could be relatively inexpensive compared to a full time transfer case swap. I’m guessing a driveshaft might be fabricated for around 1K to 1500 bucks or so depending on the parts used.

Challenges would be:

• Space. It looks like there’s only about 6 inches or so of safe clearance around the front drive shaft so the mechanism would need to be relatively small diameter. The current drive shaft appears to be about 3 inches in diameter.

• Weight. It’s possible that if this ends up being heavy it could cause increased wear on the transfer case output and/or differential input bearings. Since we're able to turn it on or off by switching to 2H, could help mitigate this wear though.

• Could be very expensive if substantial fabrication is needed to build one.


I’ve thought of two possible ways to do this.

Put a viscous coupling in the drive shaft.

This would effectively make the truck work like a rear biased AWD vehicle. This is similar to how some of the older Jeeps and Chevys worked with a viscous coupling in the transfer case connecting the front drive shaft that was engaged when you selected auto 4wd.

This would be less effective on really loose surfaces or largish rocks, but would probably work very well on sketchy pavement and make low range available most any time you want it for technical towing situations.

Big challenge would be finding a coupling in the correct size that would handle the torque and lock up as desired. Most I’ve found seem to be over 8 inches in diameter, but there is one Volvo used that might be around the correct size. I also saw some used for the output on inboard V8 boat engines that were close in size, so maybe something is out there. Managing vibration on this could also be a challenge due to the weight of the coupling.

Another option is a torque limiting coupling.

This would be something like a ball detent coupling that would slip once a specified torque is reached, sort of like a ratcheting mechanism. I’ve seen these able to hold up to 1400 ftlbs of torque, so I figure if it was set near 1000, that would be half of what most transfer cases are rated for and would still put about 4000 ftlbs at the front wheels of a manual Tacoma with the 4:33 stock differential.

This would allow the truck to drive like it normally would in 4wd, but if you happen to forget to shift out and bind up the driveline, the coupling should slip before anything is damaged. I think this coupling would work better on very loose surfaces, but the handling dynamics on slick pavement won’t be ideal. It will still behave like a locked center diff causing push when cornering, and if the coupling slips while cornering it could create a serious pucker moment.

If you were bored enough or interested enough to read all the way to here, thank you. I’m curious as to what you think about these ideas.

However, if you just want to respond with how stupid this idea is, that I should go buy a Subaru, that “if you need 4wd you’re driving too fast for conditions”, or the dozen or so other negative responses that show up in every thread about using 4wd on road,… feel free, but you’ll most likely be ignored unless you’re really creative and entertaining.

 

Start looking for Limited 4Runners in the local wrecking yards as they have a torsen center diff and are full time 4wd.

 

Trade in for another truck

 

What's the fun in that Cut up a perfectly good truck to make it what you want.

 

Other options to consider: Landcruiser, 4th gen 4runner, 5th gen limited 4runner, Lexus GX...

 

I fantasize about this all the time. Had a 4Runner before and the AWD was great in light snow and mixed conditions.

For the Tacoma's ATRAC to work, you will need to signal to the computer that it's in AWD/4WD. I think it only operates in 4Lo in the OR. Slipable front shaft *might* confuse the system as wheel speeds would not be the same as it would if it were locked. Would be curious to know for sure.

I would look at the threads where people have adapted the FJ and 4th T4R T-case to the second gen and go from there. I think I saw one thread that adapted a landcruiser case. If you can't use the controller from the donor, you would likely need to have a build a separate control for the lockable center diff and engage that for 4L.

 

Thinking about this more, you could probably wire up everything so AWD modes are the default, and then the center diff lock is a prerequisite to engage ATRAC.

 

Do you know of another pickup truck that has full time 4wd, crew cab, and three pedals? I'd be interested. It needs to be somewhat modern and reliable. I don't know of any since chain driven transfer cases became popular back in the late seventies. I've heard that dodge and chevy used to do something like that back then, but it seems like the combination of those three things is a unicorn. Also, having owned dodge, chevy, and ford, I'm not keen on the amount of work I had to do on them. They weren't terrible, just required more work then I liked. I considered a manual trans FJ Cruiser, but carry around too much useless crap and they're kinda short on space. I considered 4 Runners and Land Cruisers, but they don't have enough pedals. A manual transmission is the most important requirement for me and Toyota was one of the very few options for that.... Compromise is a part of life, I'm just wondering if it's possible to get closer to what I want.

 

I wonder if the VSC system would kick in at random times if the front wheels are not turning at the same speed as the back wheels wheels?

 

Worth watching:
https://www.tacomaworld.com/threads/transfer-case-swap-multi-mode-2wd-awd-vf3am-vf4am.627123/

 

4th Gen 4Runner V8 models are full time AWD with selectable 4WD.

The V6 models have selectable 2WD, AWD, and 4x4.

Good luck modifying something with so much electronics. I’m assuming it’ll interfere.

 

Maybe a Subaru Baja?

 

I would suggest just learning how to drive your current truck within its factory configuration options.

You might be surprised how well it performs in most situations.

With the manual trans you have the added ability to push the clutch in from slightly to completely to reduce traction/friction between the engine and drivetrain whenever you feel the need.

 

Thanks, yeah, I'm watching that one too. I really hope he succeeds.

If I were able to build a solution using a viscous coupling, I would probably give up on using A-Trac with that drive shaft. I would switch back to the OEM drive shaft when I went anywhere that technical.
I think if it were a torque limited shaft, A-trac should still work, and if I bound it up enough to slip it might be an indicator that it's time to back up and try something else?

This is a very good point. I don't know how active the VSC is when 4Hi is engaged. I guess it could either get really upset that axle speeds don't match, or maybe it stops monitoring axle speeds in 4Hi and only reads side to side wheel speeds as it normally would never see different axle speeds with the part time transfer case.. This is one of the many electronic complications that concerns me when I think about swapping the transfer case.. It would suck to spend a bunch of money on some weirdo front driveshaft and then find out I couldn't use it, but not as much as it would suck to spend a ton of money on a case, driveshafts, and then cut up my floor pan to then find out the electronic gremlins could never be defeated.. I find the traction technology on this truck impressive, but also very intimidating.

 

be careful of what you wish. Why do you want mommy 4x4?

 

They never offered one in the states with a MT. Would have really been a hoot if they had!

 

I think what you should be searching the forum for are "good all weather tires."

Good luck with your mod. Seems like a bit of an effort for a truck that tends to handle all weather conditions pretty well!

 

I considered it, but it's a bit too small, I don't really like the way it looks, they're rather old with high mileage, and I have a close friend who's had a couple of Subarus and didn't have great luck with their reliability.

I appreciate the suggestion. I'm rather familiar with how this truck works. I had a ford ranger stx back in the day that was a manual with part time 4wd and the new (at the time) push button transfer case. I put about 250K miles on that truck and really enjoyed it until it started having so many mechanical and electrical issues that it was time to let it go.
The drive train on that truck was a bit tighter than the Tacoma and it would bind up pretty quick if the tires couldn't slip. You could only use 4wd in the dirt or in a really straight line. On wet pavement or patchy snow it would still bind in a gentle turn. I didn't end up using 4wd very often and with the auto locking hubs, if you waited until you needed it, the truck wouldn't roll for the hubs to engage so it wouldn't give 4wd.
The auto hubs on the 83 chevy K10 I had before this truck had the same issue, but once I swapped manual hubs I could just leave the hubs locked if I thought I might need 4wd and pull the transfer case lever when I wanted to engage the front axle. I would have kept the K10 but it needed constant work and had an auto trans, so I went for something newer with a manual..
The Tacoma has a similar issue to the auto hubs with the ADD system. It doesn't usually want to engage unless the truck can roll a bit, but if you're at a point where you need the front axle to pull, it's probably too late to get it to engage. I suppose it could be worth looking into some sort of manual ADD engagement, but I don't know what sort of sensor/dash light issues that might cause.
The drive train has a lot more play in the Tacoma than my old ranger did, and it doesn't seem to bind up as quickly on wet or snowy pavement. I still don't like risking forgetting to disengage it when I make a sharp turn. A manual transmission can't help with driveline bind. I need something that would allow the front axle to turn at a different rate than the rear.

(?)... OK,... thank you?...

 

Not a good idea. Put the truck in 4wd when you need it. Spending $$$$$ and being without your truck for months is not worth it when you just hit a button to go into 4wd.

 

It doesn't fit OP's requirements, but it most certainly was available with a manual transmission in the states; there was even a turbo version available with the manual.