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Mod to lock auto trans into AWD?


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11 replies to this topic

#1 Ratpick

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Posted 05 July 2014 - 12:45 PM

I know I saw a thread about this a while back, but can't find it now. If I remember it was a fairly simple hack into tcu or something and then you'd install a switch that would engage "full time four wheel drive" for off-roading and such. Just trying to do my research. (Will this mod be usable on-road, or tear stuff up?)

Sorry if this thread is somewhat unnecessary but search function and scrolling through random pages just isn't working.

#2 CNY_Dave

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Posted 07 July 2014 - 11:08 AM

It's pretty simple, a switch disconnects the trans from the TCU, and switches the TCU to a resistor to keep the TCU from thinkiing something has gone wrong.

 

I temporarily had to use a switch ('04 trans AWD solenoid uses the opposite signal from all before that, and of course I put an '04 trans in my '03), and I can say if your AWD is working properly, there will be very little gain to adding the switch.

 

And yes, locked on a hard surface would be bad, bad, bad.

 

One real negative of locking it is down a slick hill, the rear wheels will slide because of the braking forces transmitted to them via the front wheels. Found that out going down a slick snowy hill...



#3 grossgary

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Posted 07 July 2014 - 02:00 PM

yep, just cut the Duty C solenoid wire. 

 

install a switch - with the circuit "cut"  - it's "locked". 

 

with the circuit complete it's just like normal.  this is how you normally drive. 

 

good to have a light or something to remind you it's on in case someone or something (a pet) accidentally flips it.



#4 CNY_Dave

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Posted 07 July 2014 - 05:35 PM

And as far as I can tell, dumping to the resistor is optional.

 

There is some discussion out there that you will kill the TCU if that connection isn't wired to *something* but it's just a solenoid driver, and also as soon as the AT Temnp light starts flashing the TCU stops trying to drive the solenoid.

 

You do need to shut the key off to get it back to normal mode after disconnecting the solenoid.

 

In fact, you could probably use a momentary-off switch in the circuit, push the button long enough to set the fault, then release and it probably won't try to use the solenoid again (unless it defaults to 'front wheel drive')..



#5 Fairtax4me

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Posted 07 July 2014 - 11:52 PM

Isn't there a way to trigger that without confusing the TCU? I thought there was a pin on the TCU that could be powered or grounded and the TCU would command full lock of the AWD clutch?

The FWD fuse works that way as far as I know. Just commands full unlock instead. I've never checked to see if this is reversible without cycling the key.

#6 CNY_Dave

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Posted 08 July 2014 - 10:35 AM

I've never come across what you describe, just the fuse which grounds a pin which tells the tcu to release the AWD.

 

If the ATF Temp light isn't flashing, it haSN'T latched into a fault state.



#7 Fairtax4me

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Posted 08 July 2014 - 06:14 PM

I was thinking of the Power mode switch on the older models.
But it does seem like there should be a way to command the duty C to full lock of the AWD clutch without freaking out the TCU.

#8 johnceggleston

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Posted 08 July 2014 - 07:29 PM

the way to create AWD locked,

is to cut the power to the duty c.

this has been covered.

 

all the info about resistors and the switch

is simply a way to avoid a flashing AT Temp light.

 

and the wrong combination of resistors and switch will eventually burn out.

 

but there is a plus to having the AT Temp light flash at start up.

it acts as a reminder to check and see if you are AWD locked.

AWD locked on dry pavement can cause excessive wear and tear on the drive train.

 

so if a flashing light at start up reminds you to turn OFF the AWD locked switch,

all the better.



#9 Ratpick

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Posted 09 July 2014 - 12:25 AM

Thanks. But I was kind of hoping to find where this has been covered, so I can put together correct combo of resistors and switch. But simply cutting power to duty C solenoid will achieve full-four wheel drive? I'm getting close... ;)

#10 johnceggleston

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Posted 09 July 2014 - 05:20 AM

the TCU is looking for resistance on the wire.

if you put 17omhs, i think, on it the TCU will be happy.

 

do a search and read up.

tcu* pinout

AWD* switch*

AWD* switch* resistor

AWD* locked mod*

AWD* duty locked switch* mod*

 

disconnecting the wire going to the duty c is simple.

cut the power and you will get awd locked all the time.

just like when the duty C solenoid fails.

 

but the transfer clutch sending power to the rear wheels was designed to ''slip'' for a reason.


Edited by johnceggleston, 09 July 2014 - 05:23 AM.


#11 Corvid

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Posted 09 July 2014 - 11:35 AM

Do a google search for "torquemada lite".

Pages of conversation and pictures.

And to ruin the ending for you, I don't think they ever do the handbrake mod.



#12 CNY_Dave

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Posted 09 July 2014 - 11:47 AM

During my experiments, I recall you can go as high as 100 or several hundred ohms, maybe even 1kohm.

 

Higher resistance limits the power dissipation, I had my dumping resistor inside the box with my pulse-inversion circuitry.






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