I got bored today and figured this out. I remember people discussing this, bu wasn't sure if anything was brought from it.
What will this work for?
-ADD equipped vehicles, with Open front diff
-I have J-shifter, not sure if it matters
Caution: Do not Engage/Disengage ADD while moving to prevent damage to unit. Try this at YOUR OWN RISK!
Now on to what it is. On the ADD trucks the 4wd switch in the transfer case is what tells the Transmission Control Relay to actuate the ADD differential for 4wd. Now I don't need this as bad since I have manual hubs, but some of you may make use of it. Naturally I would recomend a "twin-stick" option for better performance and less wear and tear on components, but this will work for now. Pin #7 on the Transmission Control Relay box is the input from the transfer case. When put in 4wd this circuit is closed telling the TCR it is in 4wd. To get 2 low you would put the transfer case is 4low and open this circuit. The white/black stripe wire on pin #7 is what you want to install a switch onto. In 2wd the switch won't do anything. In 4wd Hi and Lo the switch in closed position will be 4wd. When switched to "open" the switch will turn off the 4wd indicator on the dash and disengage the ADD differential.
Now, I'm going to go pick up a switch and wired it in and jack up the front to confirm all of this. I did confirm that cutting the white/black wire in 4wd will turn off the 4wd indicator. Now be careful there are two white/black wires. Refer to pictures for pin #7. You have to take off the plastic at bottom of door opening, then pull the kick panel. From there you can access the Transmission Control Relay and then get to the white/black wire.
I'm trying to figure out what you're doing... are you disengaging the ADD to completely open the front diff so that you have 2-LO with the front driveshaft spinning?
Basically. T-Case is engaged, but ADD is disconnected. Useful if you need lowrange and not 4x4. I use my truck to move stuff around the shop alot and the low range in 2wd is useful so I don't have to ride the clutch pulling stuff around the parking lot or moving the 26' trailer.
gotcha! I use my Sammi in 2-lo to move trailers around the backyard...Sammi turns much tighter than the 'Duty or Taco... just looks funny moving a travel trailer around with a Sammi all flat on the bump stops
this is useful in bad stop-and-go traffic, especially uphill. I have factory manual hubs, so sometimes I just shift into 4lo with hubs unlocked and it keeps my clutch leg from getting tired..
Has anyone tried switching from 2low to 2high while moving with an auto? I heard a few guys being able to do it wtih a 5 speed. I just thought it would be good for towing from a dead stop (lights on the freeway onramp, ect.)?
Has anyone tried switching from 2low to 2high while moving with an auto? I heard a few guys being able to do it wtih a 5 speed. I just thought it would be good for towing from a dead stop (lights on the freeway onramp, ect.)?
CajunTaco, did you ever get a chance to jack your truck up? I have been researching this mod, and read a couple of posts that said this was not a true 2-lo mod; that the front drivers side tire is still driven. Is this the case?
The deal with an open diff is that it sends power down the path of least resistance. With the ADD open, the path of least resistance is into the open shaft. There is a small amount of "torque bias", due to friction and the viscosity of the oil in the diff, but there is so little power getting to the drivers side wheel that you could hold it with one finger. If you want to feel how much, jack up one front wheel with the ADD open, and turn it by hand to feel how much friction there is. If you want to see the action with your own eyes, put it into 4WD without the engine running (so it doesn't engage the ADD), and take a look underneath to see the driveshaft held in place while you are turning the wheel. Or just grab a hold of the driveshaft to hold it still while you turn the wheel. Or turn the driveshaft (by hand in 2WD) while you hold the wheel still.
Go look in tech/FAQ, find the factory service manual for your truck, look at the wiring diagram, there are many ways of doing this mod. On my '99 manual with j-shift (no push button), I got at the wires at the blue 2-pin connector on the passenger side of the gearbox.
I forgot about this thread. I put the truck on a lift and let it run in 2 low. Drivers front wheel spins, but really slow so I grabbed it and it stopped.
You get a 2wd ish by the power being wasted to the passenger axle shaft which is disconnected.
Front drive shaft spins ring and pinion but open diff dumps it. IF you have a locker this will not work!!!
I forgot about this thread. I put the truck on a lift and let it run in 2 low. Drivers front wheel spins, but really slow so I grabbed it and it stopped.
You get a 2wd ish by the power being wasted to the passenger axle shaft which is disconnected.
Front drive shaft spins ring and pinion but open diff dumps it. IF you have a locker this will not work!!!
Figured I should confirm that yes, this does work for J-shift trucks to get 2lo. I put a latching pushbutton switch in series with the transfer case switch by cutting and splicing into the wires shown in the OP's post. My truck is an 01 v6 manual with the J-shift. The front driveshaft is still spun by the transfer case, but the ADD is dissconnected so the power goes no where. It's great for backing trailers into tight spots or up hills.
This mod will not work if you have a lunchbox locker in the front diff, but a stock open diff it works great.
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