General questin on 3rd gen transfer cases

[norrisbiker]

It's complicated, lol. I'll try to explain how the '01 - '02 works.

The front diff doesn't actually lock, it's an open diff. I assume by lock you just meant engage the drive shaft.

In 2WD mode the front driveshaft doesn't spin at all. It's disconnected from the front diff and the transfer case. When you push the 4WD button the front driveshaft is connected at both ends and you're in what is technically AWD. The front and rear diffs, and the transfer case, are open at this point. You can drive like this on dry pavement, no problems.

There is a system called ATRAC that is always active, that makes the rear and front (if you're in 4WD) sort of like a locked diff. It uses the ABS sensors to detect wheel spin and then applies brakes to the wheel that has lost traction, effectively transferring power back to the other wheel. It works ok, not as good as a locked diff, but better than nothing.

I believe some 3rd gen models came with a locking rear diff, but I'm not sure how common that was. I'm thinking there aren't many of them. However, it's a popular mod for people who do serious off-roading.

There's a button on the dash that will lock the transfer case, giving you a true 50/50 power split between the front and rear diffs. Aside from testing it in a gravel lot I've never had to use it.

And then you can manually shift the transfer case into a lower gearing. Which again, I've never had use for other than to test it out.

For normal on road driving, in pretty much any condition, just pushing the 4WD button is all you need to do. Locking the transfer case, and/or shifting into low gear, is for off road.

WallyWest, Thanks for the reply and very clear explanation.

Without seeing an exploded diagram of the front diff and transfer, I would assume the engagement for the front driveshaft would just be a sliding collar that connects two splined shafts, one in the diff and one in the transfer case.. A very simple but efficient and strong way to do it.

So from your explanation, once you "lock" the transfer case, it no longer functions as an open diff type, but now works as the old "part time" transfer cases did. So if I wanted to just get AWD (wet/snow/etc) then pushing the 4WD button will get me there without "locking" the transfer case.

Appreciate immensely, Tom

 

[WallyWest]

So from your explanation, once you "lock" the transfer case, it no longer functions as an open diff type, but now works as the old "part time" transfer cases did.

I think we have a few crossed wires with respect to the terminology. This is just how I understand it, I could be wrong.

A locked differential, or transfer case, means it's splitting power 50/50 no matter what. So both wheels, or both axles, are turning at exactly the same speed all the time. That will cause binding, wheels to hop, stuff like that if you use it on pavement, and it's really hard on the differential. So it's just for off road, very slippery conditions.

An open differential will let the two sides spin at different rates. For 4WD keeping all the diffs open allows it to stay on all the time, like on a full time AWD vehicle.

The 4Runner's transfer case can go either way, which is why they call it multi-mode. And yes, it's also what some call a part time 4WD since it can operate in a 2WD mode as well. So it can go from 2WD to open diff AWD to locked 4WD. Again, being super picky about the terminology, some people wouldn't consider it to be in "real" 4WD until you lock it.

So if I wanted to just get AWD (wet/snow/etc) then pushing the 4WD button will get me there without "locking" the transfer case.

Yep.

 

[amalik]

'96-'98 Limited models.

'99-'00 Limited models had a multi-mode T-case, which had a unique engagement method for those two model years.

'01-'02 SR5 and Limited models used the same multi-mode t-case, and method of engagement.

Sorry, can you clarify something for me?

So the multi mode t case for say, the 99 limited allows 4H or 4L all the time if desired.. I.e. dry pavement? Wouldn't you need a center differential for that like the torsen center differential in some 4th and 5th gens?

 

[nvestor88]

What's the part #'s for the 2 sensors on top of the transfer case?

 

[johnbyebye]

Sorry, can you clarify something for me?

So the multi mode t case for say, the 99 limited allows 4H or 4L all the time if desired.. I.e. dry pavement? Wouldn't you need a center differential for that like the torsen center differential in some 4th and 5th gens?

It's only 4HI with the option of the transfer case "center differential" unlocked. In 4LO the transfer case is locked. There's an extra planetary gearset in the transfer case that acts like a center differential when it's unlocked. So when referring to AWD/4HI unlocked it's this extra planetary gearset that is allowed to turn. It's not a typical differential that we think of with spider gears, a ring gear, etc, but it accomplishes the same task.

 

[amalik]

It's only 4HI with the option of the transfer case "center differential" unlocked. In 4LO the transfer case is locked. There's an extra planetary gearset in the transfer case that acts like a center differential when it's unlocked. So when referring to AWD/4HI unlocked it's this extra planetary gearset that is allowed to turn. It's not a typical differential that we think of with spider gears, a ring gear, etc, but it accomplishes the same task.

Thanks. I get what you mean. My only confusion at the time I posted that was that I didn't know that some 3rd gens had that functionality to be able to go 4H (Same as some 4th/5th gens).

Pretty impressive!