I currently have the ADD shift on the fly system.I want to switch to the manual hubs.What I am confused about is what exactly happens.I dont care about locking or unlocking the hubs.What I want is the axle to not turn when I'm not in four wheel drive.Do I still have to do anything with the differential?

 

Nope. Slap the hubs on. I did this on my t100, which has the aADD system. Usually what I do is leave the hubs locked in adverse weather (snow and ice) then use the 4wd as needed, then unlock them when I don't need 4wd.

 

So the only reason to mess with the differential after manual hub conversion would be to have "shift on the fly"?

 

With ADD, there is a vacuum driven sleeve that disconnects the driver side axle shaft from the differential (for 2WD) or connects the two (for 4WD). On trucks that originally did not have ADD (had manual hubs from the factory) the driver side axle is permanently connected to the differential.

One drawback to the ADD differential is that if you develop a vacuum leak in either of the vacuum lines going to the ADD actuator you could lose the ability to slide that sleeve on or off; effectively keeping you from engaging 4WD. I think its because of this, that most guys will replace the whole differential too.

For me, I simply swapped the drive flanges (with ADD) for the manual hubs. With the hubs locked, the truck operates and drives exactly the same as if it still had the drive flange (the flanges act the same as the hub permanently locked). The manual hubs allow me to completely disengage the front CV shafts from the hubs.

And to be honest, I'm not sure how or where shift on the fly comes into the picture (whether its in the differential or in the transfer case).

 

As long as you have your hubs locked, you can shift on the fly. If they are unlocked and you shift to 4WD, the shafts will turn, but the tires won't because they're disconnected.

There is one mod you can do to the differential where you put a hose clamp around the shaft so the ADD collar is always set in the connected position. You won't have to worry about whether or not the shafts will connect with the ADD actuator. Try searching for it. It's not necessary, but it's extra assurance. With this mod, you'll definitely need the manual locking hubs.

EDIT: Sac beat me to it. He must have posted while I was typing.

 

Wait wait wait. . . We can really shift on the fly? I always stop to engage 4WD. I have in the past slowed down below 15MPH, shifted into neutral and then engage it but I don't remember it sounding so good. .

 

You can shift into/out of 4-hi up to 55mph (even though I have done it at higher speeds)

DO NOT shift into 4lo over 5mph. You can shift OUT of 4-low at any speed under 55mph (but good luck achieving 55mph in 4-low

 

I really wanted to do this when I replaced my CV's earlier last year but didn't have the time or $ to do it. One day....

I'll be able to lock in my hubs when I hit the woods and retain shift on the fly and when I hit the highway again I unlock and no spin on the CV's.

 

I wonder why they did'nt offer this as an option from the factory?

 

They did offer manual locking hubs from the factory. After '88 it seemed like ADD slowly took over. ADD was mostly offered on V6 SR5 pickups and all 4Runners. Manual locking hubs were offered on base model and DLX trucks with the 22R-E or some of the V6 models. Someone please correct me if I'm wrong.

 

I have always had a beeping sound when I tried to shift on the fly with the green light flashing. If I stop it still wouldn't shift either! Then I switch it off (to 2wd) again, and when I switch it back on (4wd) THEN it engages! I had a 91 V6 Surf 2 door auto and changed the engine to 95 3.0lt td auto. Same story!

 

My add switches in and out as smooth as glass, I still going to convert to manual though.