[Sandpiper]

Simple question. Does it turn all the time or just when the 4 wheel drive is engaged? Or, when its put into low 4wheel drive?

[Sandpiper]

Surely someone out there can answer this.

[Jtraskell]

Originally Posted by Sandpiper

Simple question. Does it turn all the time or just when the 4 wheel drive is engaged? Or, when its put into low 4wheel drive?

Somebody said that the manual suggests we put it in 4wd once a month for about 10 miles, that would lead me to believe that the gears in the transfer case do not move unless 4wd is engaged. The 10 miles per month is apparently for the purpose of proper lubrication of the gears, seals etc. Is there really a Chain in there?

[Froggy]

Originally Posted by Jtraskell

. . . Is there really a Chain in there?

Sure is — in both versions.

[Jtraskell]

Originally Posted by Froggy

Sure is — in both versions.

Love this forum. Learn something new everyday! Thanks Froggy. I always though it was just "toothed" gears similar to the rear and front end diff. Never saw a transfer case opened up, just assumed! Thanks again. Be safe.

[Fuzzylogic]

OK...I'll try to answer all questions...If I miss one, let me know.

Yes, the transfer case is chain driven. Most modern light/medium duty tranfer cases are (I believe all major 4WD brands in the US are). You have to go back to 1970's vintage vehicles like the old matchbox Ford Broncos (which had an NP205...or NP204...can't remember the number), International Scouts, certain Jeeps, and some early Toyota Landcruisers and Nissan Commandos to find "Gear Driven" transfer cases (SUVs...There are a lot of older trucks from the same time period that have gear driven cases, like Fords through 1979).

The transfer case in the SR5 4 runner does not turn when in 2wd (speaking for the SR5, part time 4wd here...not the Limited with the full time 4wd). I'm not sure if the case rotates in the Limited and Trail in normal driving...If it is like my old Expedition, it only engages when it detects rear wheel spin.

All above information is from my feable memory...so...someone might correct me (which is appreciated). I haven't visited these topics in a while.

By the way...There's nothing wrong with having chain driven transfer case. Take care of them...and they will last indefinately. It's not a bycicle chain...it is much more robust than that. Abuse them...and they will crater like anything else. But, the Toyota transfer case can take on a lot of challenges.

It's good practice to "excercise" your 4wd system. I don't hit the 10 mile a month goal. But, I do get 3 or 4 in driving back and forth to the river each month.

[JB.]

Originally Posted by Fuzzylogic

I'm not sure if the case rotates in the Limited and Trail in normal driving.

It does in the Limited, for sure, as it's full-time 4WD.

[Sandpiper]

Thanks for the answer. I had heard nearly all light four wheel drives use the chain system because it is so much quieter than gear on gear. I could not imagine it turning all the time but then some engines use a timing chain that runs all the time. As sort of a gear head I still don't understand why they suggest running the four wheel drive once a month or so. Its not like it will rust or something but then it might just keep the linkage freed up.

[dpdsurf]

What does it mean by the t-case is being "locked" when you switch the Limited into 4H or 4L? Its engaging something that normally isn't. But I guess you're right that something has to be moving in there with AWD.

[homeyclaus]

Originally Posted by Sandpiper

Thanks for the answer. I had heard nearly all light four wheel drives use the chain system because it is so much quieter than gear on gear. I could not imagine it turning all the time but then some engines use a timing chain that runs all the time. As sort of a gear head I still don't understand why they suggest running the four wheel drive once a month or so. Its not like it will rust or something but then it might just keep the linkage freed up.

The front differential and the front drive shaft u joints don't turn when the system is in 2WD. The front diff is about 1/3 of the way full, exposing the top of the gears, bearings, and so on. Leave them in place a few weeks, any lubricant with its corrosion inhibitors will eventually run off those components. They are then exposed (potentially) to corrosion.

There is an electric actuator that effectively locks the front hubs on the front diff, and this also needs to be moved.

Originally Posted by dpdsurf

What does it mean by the t-case is being "locked" when you switch the Limited into 4H or 4L? Its engaging something that normally isn't. But I guess you're right that something has to be moving in there with AWD.

It locks the torsen differential in the transfer case to lock 4H, which has the same effect as engaging 4H in the part time system.

There is the other reason to use a chain the transfer case - it's the weakest link, and when you overstress the 4WD linkage by, say engaging 4H on a dry road and doing a bunch of turns, the chain will fail. Ostensibly the system is designed correctly and will leave you with RWD only when this happens. On gear-driven transfer cases, the actual transfer case housing will fail, and you'll lose all drive, and get to call a tow truck.

[Slag]

Originally Posted by homeyclaus

There is the other reason to use a chain the transfer case - it's the weakest link, and when you overstress the 4WD linkage by, say engaging 4H on a dry road and doing a bunch of turns, the chain will fail. Ostensibly the system is designed correctly and will leave you with RWD only when this happens. On gear-driven transfer cases, the actual transfer case housing will fail, and you'll lose all drive, and get to call a tow truck.

Shouldn't the u-joints in the system be the weakest links as they are the easiest and cheapest components to replace?

[homeyclaus]

Originally Posted by Slag

Shouldn't the u-joints in the system be the weakest links as they are the easiest and cheapest components to replace?

In a perfect world, yes. The reality of u-joints is that they're subject to non-linear stresses, at varying angles - the drive shaft turns, and the drive shaft articulates as the suspension compresses and decompresses. It's really, really hard to make a part that'll sacrifice itself, at the right time, to protect other parts under those circumstances.

[M1911]

Originally Posted by dpdsurf

What does it mean by the t-case is being "locked" when you switch the Limited into 4H or 4L? Its engaging something that normally isn't. But I guess you're right that something has to be moving in there with AWD.

When you lock the center diff in the Limited, that causes the front and rear differentials to turn at the same speed, thus behaving just like a part-time 4WD system in 4WD.

[jworth]

Sorry, I'm new and can't make a new post. I have a 2012 limited with the full time 4wd transfer case. Looks like the fluid got low as I had to put about 400ml in to top it off. Apparently that caused pretty excessive wear on the chain. I can move it quite large amount with a screwdriver through the fill hole. I think it's so bad it's jumping teeth. Apparently this is pretty rare as several searches turned up nothing. Rock Auto doesn't even carry the parts. Has anyone done this? I've done it on an old XJ Cherokee (NP231), but I'm sure this one is significantly more complicated. Any tips would be appreciated.

[fkheath]

Originally Posted by jworth

Sorry, I'm new and can't make a new post. I have a 2012 limited with the full time 4wd transfer case. Looks like the fluid got low as I had to put about 400ml in to top it off. Apparently that caused pretty excessive wear on the chain. I can move it quite large amount with a screwdriver through the fill hole. I think it's so bad it's jumping teeth. Apparently this is pretty rare as several searches turned up nothing. Rock Auto doesn't even carry the parts. Has anyone done this? I've done it on an old XJ Cherokee (NP231), but I'm sure this one is significantly more complicated. Any tips would be appreciated.

Suggest you start with the repair manual. It shows how to do most repairs. Even though this version is different years, not that much has changed throughout the 5th generation production:
TOYOTA 2016-2019 4Runner Repair Manual RM27F0U