Lock, Stock, and 2Wheel Low (3rd Gen DIY Mod)

So i didn't need to spend the extra money on a 4x4?

 

Lol! I mean at least with 4wd you get the third drive wheel. The concept of a strictly RWD truck with a locked rear makes me chuckle, though.

 

So if the relay fails in a rather unlikely manner, you COULD be stuck without 4wd. To properly assess this would require a formal FMEA analysis, some data in the service manual, and a bunch of data from Toyota and the relay manufacturer that we don't have. So we will never so that, so we will just have to rely on anecdotal evidence. Well right now anecdotal evidence is for just one truck. So until we get more data, all I can say is don't drive where 4wd is needed to live with this mod. Make sense? I will describe it a bit more tonight

 

Understand...guess I'll be waiting on this for a while then.

 

you've never seen it then

 

Thanks OP!!! I gotta find the thread I started on this with links to the various other discussions. Great job Op!!!!

 

So the pdf says to go back to 2hi you are supposed to hit the new switch and then cycle back to 2lo. Say you are cruising around Moab and you want to stay in 2Lo for casual slow paced cruising and then occasionally engage the front end to get over something. Can you go back and forth from 4lo to 2lo just by using the switch, or do you have to run through the whole cycle every time?

I had 2lo on my old doge with the posi lock cable and absolutely loved it. This would be a huge plus if the scenario described above would work!

 

I go back to the days of having 3 sticks in the floor and locking hubs. It was certainly possible to engage lo range in 2wd back in the day. The owners manuals specifically warned you not to do so too. I've seen U-joints snapped from this. They aren't designed for that much torque going to a single axle.

Newer trucks are designed to prevent you from doing this for a reason. But it's your truck.

 

So in actual developing this mod, it makes you understand just how 'delicate' the 4wd system. 'Delicate' not that it is necessarily easily broken, more that the computer is programmed to monitor so many variables and when any unexpected signals are detected from the sensors, the system goes to fail-safe mode. In this particular system (from anecdotal evidence), that usually means the mode changes are cancelled and you are locked into the current mode. I am sure that for 99% of the users and 99% of the time this is exactly the best course of action to protect the truck from any further damage to itself.

So what does that mean for this particular mod? For now I will assume only relay failures.
If the relay fails completely in the power off position (guessing this is the most likely failure), then all normal (non 2Lo) modes are available, low criticality failure.
If the relay fails completely in the power on position, then all 4wd functions are lost if currently in 2wd.
If the relay fails some bad connections, then likely all 4wd functions could be lost if currently in 2wd.

The workarounds are:
The relay can be accessed and removed, and all 4wd functions are returned. But accessing the relay is difficult with interior in.
The front ADD can be manually activated using a few pieces of wire and a couple of flashlight batteries (I did it about 20 times with 3AA while troubleshooting the mod), but accessing the ADD connector on the belly sucks with skids on.
If the truck is placed in 4hi or 4lo before heading into no-man's-land, then any failure of the relay will have zero impact on 4wd modes, however when the truck is power cycled a relay failure will cause the 4wd system to fail-safe to the current status.

All this being said, how often will a relay like this fail after a few hundred or 1000 cycles, when stored away from water etc, probably not often. Much more likely I would guess would be failures due to poor wiring methods, routing, wire chafing.

 

No, not the way this mod is designed. I based mine off the 2nd gen designs, which had the same limitation. This method requires the 4wd ECU to approve of mode changes. We could force the transfer case actuator to engage any time the button is pressed, but if you are doing 60 and engage it= BAAAD.
The alternative to doing the mod as I did it, but with some level of safety is to make a much more complex system that monitored speed to decide if you can safely activate the transfer case.

Or we could apply power to the ADD actuator ourselves and use the ADD sensors for feedback. But we loose alot of the monitoring the ECU does, checking current and timing on the ADD actuator.

In the end, every other option I came up with seemed much more difficult, or much higher risk to the truck.

 

I didn’t even think about accidental button presses. Yes, that would suck. But the thought still sounds nice. Maybe with a shielded switch? I could feel better that way.

I have been anxious for someone to come up with a trick a 2wd locker option but now this is very intriguing as well. The combination of the two though, perfection!

 

Yeah, people keep begging for anytime locker mod design.
Looking at the schematics I haven't come up with a design I really like. Based on the schematic it seems like the rear locker electro-mechanically has changed significantly. It appears the 2nd gen design that when locked, you cut power to the diff lock actuator. Now it appears power must be maintained to keep it locked.

Can anybody validate on the 2nd gen diff lock vs 3rd gen. Did it significantly change in mode of operation?

 

What about an external power supply. If it needs power to engage and stay that way, can it get it from somewhere other than the ECU? I have spent 0 time looking at this. Just disecting your statement and wondering...

 

Yes, I think that is possible, but I don't know what the ECU is supplying yet with what feedback. Need to go hook up techstream next and play with it. Just not as excited to put in the effort, as I don't think I will use anytime rear lock that often. Also, it will be harder to incorporate using the existing overhead switch with a circuit that supplies power (at least in my head). Not impossible, just harder.

So techstream data lists include
Locker target current, <0.1A unlocked, 1A-8A locked
Locker actual current, <0.1A unlocked, 1A-8A locked
Locker voltage, <3.5V unlocked, >3.5V locked
Locker duty cycle, 0% unlocked, 0%-100% locked

So that looks like PWM controller variables to me. And what is up with variable target current?

Sigh, I should probably start a development thread for this. Just not excited about it.

 

Nice job. I played around with the add by the diff manually switching it back and forth while truck was on but gave up at the relay stage .

You should sell the 4wd cards to Toyota, your is easy to read and understand!

The link to the switch isn’t working in the first post.

 

Thanks
Looks like https://www.aironboard.com/ was down, seems back up now...

Looking at the reference card again, I think maybe I should more strongly word DO NOT USE 4Hi on hard dry pavement... so many posts on here of 'why is my truck trying to commit suicide, I only tried to move my boat in the parking lot in 4Hi?' Not that it will help...

 

Ok
I am going to do a bit more work on anytime rear lock, but i am going to want help. If people really want it, then be willing to step up and do some help/testing

https://www.tacomaworld.com/threads/rear-diff-lock-anytime-mod-3rd-gen-development.537810/

 

@BigWhiteTRD why is there a power resistor in-line with the motor? Why does that need to be added?

 

@bradshawnh
The ECU checks the resistance on the line (antecdotally) at startup, and mode change, so I put a resistor on the line.

It doesn't have to be a high power resistor, just a little milliwatt resistor. However, during failure modes (operator or equipment) there can be large wattage. If you change dash selector back to 2hi with the added 2lo switch active, then the ECU will apply 12v for 30 seconds or something before it error codes. If that happens, I don' want any high temp shit happening up under the dash on my resistor. So easy solution seemed to be put a huge power resistor with big thermal mass, to absorb until ECU errors out and kills power.

After the failure, just return 2Lo switch to normal and power cycle the truck. Will clear current error, it will be stored long term as a 4wd mode change fail in techstream

 

Be excited. Be very excited.

I am willing to help. I dont have the skillset that you do for the breaking down of schematics, but Im pretty ok with doing what Im told.