How Does the 2020 SR5 4WD System Operate ?
 

Im considering a 2020 SR5 Premium with a sunroof. Ive looked at the drawings on the Toyota parts site and I want to understand what happens when you engage and disengage part time 4 wheel drive.

There are 2 motors, one on the transfer case and one the front differential.

When put into 2 wheel high the front drive shaft is disconnected from the transfer case by the first motor.

The second motor disconnects the right wheel drive shaft from the front differential. The left wheel remains connected and when the vehicle moves the front differential will rotate and the front drive shaft (to the transfer case) will also rotate.

Is this correct?

Yes. I believe only part of the differential ends up spinning (the outside gear, maybe?). That's why Toyota recommends shifting into 4 once a month - to exercise the rest of the gears and get them coated in diff fluid.

Driver side axle is directly connected to the wheel so the spider gears are always turning and the passenger side shaft section before the ADD turns the opposite direction but the ring & pinion and front prop shaft don't move.

Engaging 4wd moves the collar from the diff side of the passenger shaft over the rest of the shaft.

Ok. Thank you very much.

I just recently found that out, about using 4WD once a month. I've had my 2019 TRD OR for 2 months now and didn't know that.

Your conversation is very insightful. I'm considering buying a 5th Gen with part time 4WD to flat tow behind a Motor Home.

Toyota doesn't recommend doing so. Is that more likely because the front drive system is still turning even though your disconnected at the Transfer case?

Were to put front tires on a dolly, would that alleviate front end concerns.

The rear-end to transfer case would then be all that's turning. As long as there is no differential lock on rear-end, I can't see there being a problem.

Anyone care to comment?

The reason Toyota doesn't recommend flat towing is because the pump in the transmission is driven off of the input shaft. So if the engine isn't running, neither is the pump. If the pump isn't running, the transmission isn't being lubricated properly. Without lubrication... things tend to go south.

Most automakers don't recommend flat towing anything with an automatic transmission. I think Jeep says it's safe if the transfer case is put in neutral... not 100% positive. Anyway, Fiat Chrysler not being known as the kings of vehicle longevity, take that advice with a grain of salt.

Trans Case & Towing
 

I was considering a model that had a manual (with shifter) Transfer case, so as to shift it into neutral. I would also leave the auto Trans in Park.

Its a great vehicle for everything I want to do, so I'm exploring this option as deep as I can.

Thanks for your comments.

Oh man, this thread might get good...

The manual is helpful regarding the exercising of the system - frequency and steps for enabling, but not with the level of detail about the how it works.

:pop2:

:doh:

I'm not sure that is a great idea??:behindsofa:

I think whether its a KNOB or Gear shifter, the transfer case still engages 4WD with an electronic actuator.

Oh here we go...

Trans Case & Towing
 

Since my question about towing with a T-case, I spoke to a service manager and read a couple articles reviewing the Part time 4WD drive on the 5th Gen TRD Off-Road. What is clear is the T-Case with manual lever shifted into neutral disengages the front wheel drive completely. Also it disengages T-case from the output shaft. Thereby isolating the drive axle aft to the Rear Differential and rear wheels. With out the rear diff being locked you have the needed sleep between rear tires while cornering etc.

Its my understanding that 5th Gen Toyota transmissions require a pump to circulate oil while running oiling moving parts. Without power no oiling, which is no dough why Toyo doesn't recommend flat towing. The transfer case would appear to depend on oil slinging for lubrication. Which would occur if rear wheels on the ground are turning the drive train up to the Transfer Case.

So in my infinite lack of wisdom, if front wheels of 4Runner are on a Dolly, Transmission is in Park with engine off, and Transfer case is in Neutral. You are basically free wheeling the rear drive train and oil T-case....just don't break something or I'm sure Toyota will not honer your warranty.

Any one care to tell me where my logic is faulty?

Front tires in 2wd are perfectly fine to flat tow. So no need for a dolly there. If you can lock the steering wheel and put the rear tires on the dolly - that's probably okay if it tows straight. In 2wd the front drive system is essentially freewheeling and flat towing should be perfectly fine - for the front drive line (but not the rear).

This is a summary from Marlin with some clarifying edits so not a direct quote, but mostly plagiarized. It explains why you should not flat tow a 4Runner with the rear tires on the ground.

The problem with a chain drive transfer case like the VF2A is that if you tow with the rear wheels on the ground and transfer case in neutral the transfer case output shaft will turn and it will not be lubricated. The gear oil lives at the bottom of the transfer case and needs to be moved by some mechanism to the top of the case where the output shaft bearings are. On Toyota the chain driven cases, the input shaft turns the planetary housing which drives the oil pump. You must have the transfer case input shaft spinning to lube the output shaft and rear seal of the t/case.

In short: you need to either put a dolly under the rear tires and pull backwards with the front tires on the ground (no problem there) or you need to disconnect the rear drive shaft. There is no combination of transfer case and transmission shift positions that will lubricate all of the moving shafts while flat towing. It's very likely that there is enough residual oil on the bearings that they would last a reasonable amount of time flat towing without more gear lube being brought up from the lower case. If you could modify the shift linkage to engage 4x4 (engage the chain drive and therfore front output) you could likely rely on the chain to adequately lubricate the rear output shaft and seal. I suspect this is why you can get away with flat towing a MT version of the FJ Cruiser or possibly even a Limited 4Runner where you can't flat tow other models without some risk of rear output bearing and/or seals running dry. I think transfer case in Neutral (I assume it has that position) in a Limited 4Runner would work.

Hope that helps.

Good luck!

From the Grand Cherokee owner's manual for 4wd vehicles with 4lo.

Recreational Towing — Quadra–Trac II/Quadra–Drive II Four-Wheel Drive ModelsThe transfer case must be shifted into NEUTRAL (N) and the transmission must be in PARK (P) for recreational towing. The NEUTRAL selection button is adjacent to the transfer case selector switch. Shifts into and out of transfer case NEUTRAL can take place with the selector switch in any mode position.

CAUTION!DO NOT dolly tow any 4WD vehicle. Towing with only one set of wheels on the ground (front or rear) will cause severe transmission and/or transfer case damage. Tow with all four wheels either ON the ground, or OFF the ground (using a vehicle trailer).

And the Toyota 4Runner manual says...

Dinghy towing
Your vehicle is not designed to be dinghy towed (with 4 wheels on the ground) behind a motor home.

!NOTICE
To avoid serious damage to your vehicle
Do not tow your vehicle with four wheels on the ground.

We're both on the same page. I was just commenting on the somewhat unintuitive part about putting the transmission in Park.

There is no good way of towing a 4R with all the wheels on the ground.