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Rear Locker + ATRAC - Write up

69832 Views 65 Replies 41 Participants Last post by  ShowStop
The TRD edition has this working already from the factory.

Seems all the newer FJ's released after the TRD edition now have it working without the modification.

Also, here's a nice write up on doing the mod anotherway without cutting the wire in the engine compartment.

**End Updates***

Ok, it's been finaly done!

A BIG BIG BIG thanks to Alex H., he did all the study and theory behind it, working with the elec diagrams and logic flow of the FJ's systems - and he doesn't even have an FJ!! . I'm just the lab rat who was crazy enough to try it first. So yes, I now can have both the ATRAC system and the rear locker on at the same time, or just ATRAC, or just rear locker, or none of the above. :D

Ok, on to how to do it!!.. First off, do this at your own risk, yes this could void your warranty, no don't do it if you have no idea what you are doing, and nobody is responsable if you screw it up or anything else!! But if you want to use the rear locker and ATRAC at the same time, read on!

This is the master cylinder, with the VSC computer on the side of it. For those with service manuals and/or electrical diagrams for the FJ, the large connector with all the wires is A4, the smaller one is A5.

This is the wire you are looking for - it's the SMALL blue/yellow. It's pin 26 on the connector, in the electrical diagrams it's terminal EXI3.

You want to cut the blue/yellow, leaving a good amount of length. You then want to take the connector side of the blue/yellow, and using a T-junction or tap, connect it to the Black/orange wire on connector A5 (pin 1). You do not want to cut the black/orange, just tap into it. The remaining blue/yellow in the wire harness just tie away inside the harness, do not ground it or connect it to anything.

That's it! You now can use ATRAC with the rear locker. Damn that was simple wasn't it?

Ok, the theory behind it (all via Alex). The blue/yellow wire is a signal wire from the rear locker (actualy it's from the dash light circut). When the locker is off, this wire has +12v, telling the VSC computer that the locker is off and it can use ATRAC. When the locker is locked, this wire has 0v, telling the system the locker is locked and then it won't let ATRAC turn on. All we have done is take the wire, and tap it into the 12V acc power on connector A5. This tells the VSC computer that the locker isn't on, all the time, even when the locker is on. This doesn't affect the locker light or any of the other lights or system. It just fools the VSC computer into thinking the locker is off all the time.

In Alex's honor, for all his work on this, I think we should call this the Alex hack!
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Very cool mod. When are you going to test it on the trails? Do you have any concerns about ATRAC trying to apply the brakes to one wheel on a locked axle? I wish we knew more detail about how ATRAC works.
sbechtold said:
Very cool mod. When are you going to test it on the trails? Do you have any concerns about ATRAC trying to apply the brakes to one wheel on a locked axle? I wish we knew more detail about how ATRAC works.
ATRAC works by sensing wheel spin on each axle. If it senses one wheel on an axle spining faster than the other, it applies brake to that wheel to lock it and transfer the power to the other wheel. Since the rear is locked, one wheel on that axle can't spin at a diffrent speed than the other, so the ATRAC system never activates on that axle, it ignores it. It will then only activate on the front if it senses one wheel spining up there.

Toyota ran an FJ on the Rubi with a simular mod, and rumor has it they may enable this on the 08's
For some background history of how this mod came about, it orginated on the mud board:

Alex I already personaly knew from wheeling with him as part of The Trail Crew. We e-mailed back and forth the details of trying this mod, including wiring and electrical diagrams.
In the FJ cummunity this is like the second coming of Christ.

Hats off and a decent bow to the electrical wizards whom can look at scematics and figure this stuff out. IRL I am a plumbing contractor, Union
trained, 15 years old to 48 years old, I need no more practice, I have always held men whom can grasp scemantics of electrical systems and design to the highest level of intelligence. When it comes to electricity, I RUN, and dam fast at that! :eek: I am 99.9% sure that if I were to do this w/ the warranty policy I purchased, that covers much of the electronics on the vehicle, basically I bought (some will say threw away big money) a 1600 $ or so policy covering dam near everything. Oh well, I am very impressed w/ your skills though. Congrats!
treknwil said:
In the FJ cummunity this is like the second coming of Christ.
Donations can be sent via pay-pal to vaud "at" :D I need a set of 17" Mojave Teflons so I can fit 34's. LOL..
Ok, it's been tested on an MT and works on them too, make sure your taps into the black/orange are good! Same person also took it off-road and verifed the ATRAC and locker are working with no problems.
Posted this on the FJ Cruiser Forum ;)

PROOF that this mod is a BIG advantage.

Chris has the mod on his FJ, tackling this hill was not the easiest thing with our stock FJ's but Chris's did it alot easier than mine. I had to stop and keep switching between ATRAC and the locked rear diff. The process was repeated many times while Chris just gave it gas on the same climb and made it to the top on the first go run. I did too, but after alot of switching around. Can't wait to do this mod.


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I did it. Works great. It only takes 5 minutes. It's not worth it Not to do it IMO.
Tankota and a few guys from 2 other forums gave the mod a major workout yesterday at Rowher Flats, and came away all smiles and thumbs up.
as they said, it works perfectly, giving you a locker in the rear and a computerized limited slip in the front. doesn't get better than that.
Looking at the picture above, does he have stock tires? It looks like just Dueler HTs. I was just wondering.
I went up Miller's Truck Trail yesterday, a-trac and rear locked. The tractions was great and it patched worked great all day LOOOOOOOng.
yoshiboy said:
Looking at the picture above, does he have stock tires? It looks like just Dueler HTs. I was just wondering.
Yes, he was running stock wheels/tires.
The combination of TRAC and rear locker is awesome. The 2000+ Land Cruisers have TRAC and run this combination with a rear ARB. Very nice to have options such as this and I'm not surprised to see Tankota leading the way. Sweet.
Well finally had the chance to try out the mod this weekend and I'm going to have to give it a big thumbs up! At the crest of this climb was a nasty drop off to the left. Since the conditions were muddy and slippery the vehicle would naturally slide down to the left towards some trees. On the right side the front right tire would catch some big roots which meant there was not grip to be had.

Well after some careful manuevering back and forth I was able to shimmy outta the bind. With the rear locker locked and A-TRAC off the front tires would spin with no grip. As soon as I enable A-TRAC I was able to progress forward enough that I could change my approach angle and get out of that tight bind. Once I was facing the direction I wanted to go I turned off the A-TRAC. I wanted some tire spin and a bit more speed to get out...worked like a champ.
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I really want to do this mod, but at the same time I am affraid to cut into the wire.
Did it, works great. Good lookin out Tankota and all affiliated!
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