Please explain SR5 4-wheel drive system

[36bound]

Hi all, I'm new to this forum. I've been a Jeep Wrangler owner for years, but I'm about to place an order for a 2012 SR5. Remarkably, not one of the salespeople I have dealt with (or a service writer) was able to answer a few questions that I had about the SR5's part-time 4-wheel drive system. As we are aware, most "4-wheel drive" systems are not actually true 4-wheel drive systems. Even in the Jeep Wrangler line- with the exception of the Rubicon which permits both differentials to be locked-in.

In the 2012 SR5 model, a locking rear differential is NOT available as an option (nor is it standard). This was a bit of a let down to me, but not a deal breaker. But this state of affairs does give rise to the following three questions about the SR5's drivetrain/4-wheel drive system.

1. When in normal drive mode (i.e. not in 4-high or 4-low) which wheel(s) is predominantly driving the vehicle? Is it the right rear? Both rear?

2. When in 4-HIGH which wheel or wheels are predominantly driving the vehicle? Is it the left front & right rear? Right front and right rear? All four wheels?

3. When in 4-LOW which wheel or wheels are predominantly driving the vehicle? Both front wheels only? Both front wheels and the right rear? All four wheels?

Remember, the SR5 is NOT available with a locking rear differential. One would think that a salesperson would be able to explain something as fundamental as how the part-time 4-wheel drive system works on a $38,000 rig.

Your valued insight would be greatly appreciated!

 

[dekeman]

:snacker:

 

[DizzyV6P]

For $38k (out the door or w/o taxes?, why don't you spring for a Trail? If you can find a 2011 Limited you get the nice full-time 4wd for about $39k w/o taxes, tags, destination.
:snacker:

 

[Jeremy556]

Your understanding of differentials is a little off. Normally, power is applied to both sides of an axle with an open differential. In the case where one wheel loses traction, it then in affect becomes 1 wheel drive as power is not sent to the wheel with traction.

So, with a stock SR5 in 2HI, both rear wheels are driven. If one wheel loses traction, the traction control will apply brakes to the spinning wheel to transfer power to the wheel with grip.

In 4BOTH, power goes to all 4 wheels. If a wheel on either axle loses grip, power is going to the 2 wheels on the opposite axle, and traction control will again try to brake the spinning wheel.

With a locker, the differential basically works like a spool, both wheels turn at the same rate. Good for traction, bad for driving on pavement and turning.

 

[4ShoreRunner]

Yeah...I really gotta ask why you're paying that much for an SR5....I paid less out the door for my new trail back in 2010.

 

[scanny]

If you need locking rear differential you can install ARB one. I think it costs about $1500 but you'll get onboard air compressor with it and it's still cheaper than TE. By the way I haven't seen a car salesperson who know much about cars, I guess it's a requirement to get a job.

 

[Intruder]

Yeah...I really gotta ask why you're paying that much for an SR5....I paid less out the door for my new trail back in 2010.

If the OP is in Canada I believe that's an accurate price for an SR5.

This should answer the part-time 4WD question:
4WD Simplified Version 4.0

 

[homeyclaus]

Hi all, I'm new to this forum. I've been a Jeep Wrangler owner for years, but I'm about to place an order for a 2012 SR5. Remarkably, not one of the salespeople I have dealt with (or a service writer) was able to answer a few questions that I had about the SR5's part-time 4-wheel drive system. As we are aware, most "4-wheel drive" systems are not actually true 4-wheel drive systems. Even in the Jeep Wrangler line- with the exception of the Rubicon which permits both differentials to be locked-in.

I tend to get more reliable technical information about the vehicle I am buying from the rock in my pocket than a dealership employee. At least the rock does not make **** up.

In the 2012 SR5 model, a locking rear differential is NOT available as an option (nor is it standard). This was a bit of a let down to me, but not a deal breaker. But this state of affairs does give rise to the following three questions about the SR5's drivetrain/4-wheel drive system.

ARB makes air lockers for the 5th gen IIRC, so if you want that option, it's available. Air lockers are more reliable than electric ones anyways, says the the interwebz.

ETA: Unless you're doing specific things, they're really no advantage. I assume you know that.

1. When in normal drive mode (i.e. not in 4-high or 4-low) which wheel(s) is predominantly driving the vehicle? Is it the right rear? Both rear?

In 2WD the rear wheels power the vehicle. The front drive shaft is decoupled from the rear one, and there is an electronic device that disengages the axleshafts from the front differential, akin to the 80's automatic hubs, except you don't have to drive backwards while singing the right song for them to disengage.

ETA: The rear end (actually, so is the front) is an open differential with traction control. In reality this means the wheel with the least traction gets more power, with some bias to the rear right. Traction control will pulse the brake on the slipping side causing the clutch in the diff to engage and transfer power to the non-slipping side.

2. When in 4-HIGH which wheel or wheels are predominantly driving the vehicle? Is it the left front & right rear? Right front and right rear? All four wheels?

The transfer case locks both output shafts together, so it's a forced 50/50 distribution.

From there, it's up to the front and rear differentials. And A-TRAC traction control.

3. When in 4-LOW which wheel or wheels are predominantly driving the vehicle? Both front wheels only? Both front wheels and the right rear? All four wheels?

Same as 4Hi, but a mechanical advantage in gearing.

Remember, the SR5 is NOT available with a locking rear differential. One would think that a salesperson would be able to explain something as fundamental as how the part-time 4-wheel drive system works on a $38,000 rig.

Your valued insight would be greatly appreciated!

(Sorry for the late post, I had all this typed up and then I had to jump on some issues at work.)

 

[1engineer]

Hi all, I'm new to this forum. I've been a Jeep Wrangler owner for years, but I'm about to place an order for a 2012 SR5. Remarkably, not one of the salespeople I have dealt with (or a service writer) was able to answer a few questions that I had about the SR5's part-time 4-wheel drive system. As we are aware, most "4-wheel drive" systems are not actually true 4-wheel drive systems. Even in the Jeep Wrangler line- with the exception of the Rubicon which permits both differentials to be locked-in.

In the 2012 SR5 model, a locking rear differential is NOT available as an option (nor is it standard). This was a bit of a let down to me, but not a deal breaker. But this state of affairs does give rise to the following three questions about the SR5's drivetrain/4-wheel drive system.

1. When in normal drive mode (i.e. not in 4-high or 4-low) which wheel(s) is predominantly driving the vehicle? Is it the right rear? Both rear?

2. When in 4-HIGH which wheel or wheels are predominantly driving the vehicle? Is it the left front & right rear? Right front and right rear? All four wheels?

3. When in 4-LOW which wheel or wheels are predominantly driving the vehicle? Both front wheels only? Both front wheels and the right rear? All four wheels?

Remember, the SR5 is NOT available with a locking rear differential. One would think that a salesperson would be able to explain something as fundamental as how the part-time 4-wheel drive system works on a $38,000 rig.

Your valued insight would be greatly appreciated!

I do not know what information you are really looking for. The video linked by intruder above is very good basic info. With that said, here is a little more information I think will help:

Toyota has some pretty smart engineers. Sure, you can't buy a 4Runner with 1960's technology that had straight front axles and everything locked but Toyota does some things that I think are better and more suited for everyday driving.

The SR5 is part time 4WD. I will not go through it's operation as it is explained above. What is important to know though is Toyota uses some electronics to aid in low traction conditions. In addition to Vehicle Stability Assist (VSC) on the SR5 you can also engage ATrac which imitates a locked differential. After driving in many slick environments like snow, mud, etc I can assure you that the 4Runner, in stock form, will go most places. If you are looking to hard core off road you of course would need to make adjustments in suspension and drivetrain. With regards to your questions about "which wheel" is providing tractive effort in different modes the answer is all of them - as various electronics are determining wheel slip and providing effort to the other, all in a few milliseconds. Hope this helps.

 

[Arterisk]

My advice is or you go with the SR5, or you go with the limited, but in Canada, the Trail is not the optimal choice given 42k sticker price. The full-time 4WD is worth much more in Canada than the KDSS of the Trail.

Part-time 4WD driving after one winter seems to me to be like driving a manual car, but without the clutch. Let's say you're parked on ice, you engage 4wd to get out, but once you're out of the ice and acquired momentum, you switch back to 2WD. On the highway, you will need to switch between 4WD and 2WD depending of the snow patchs. It's not that bad, but if you're lazy it could bother you.

N.B. : I'm from canada and dealed my SR5 for 34.5k. Invoice is about 33.5k in canada and but most deader won't go that low.

 

[Jeremy556]

On the highway, you will need to switch between 4WD and 2WD depending of the snow patchs. It's not that bad, but if you're lazy it could bother you.

You only need to switch to 2WD if you are taking tight turns on dry pavement. You won't get any binding going straight.

 

[Barry694]

Sr5

If he had the SR5 with the premium package(which is about $2800), the MSRP would be about $37,200. Depending on state taxes and license, $38,000 would be too much to be paying. I hardly haggled and got mine for $34500, including all fees. The fees can vary greatly from state to state. So when quoting prices online should stick with just the cost minus fees. In that case mine would have been $33,400. I live in a sales tax free state, but we do have a 3.75% transfer tax, four years license plate fee of $160, Title and registration is around $50. Dealer also tries to slide in the $100 processing fee, which is BS. I also got environmental plates which added another $35, and I got the OEM mudguards at their cost with installation.

 

[Arterisk]

You only need to switch to 2WD if you are taking tight turns on dry pavement. You won't get any binding going straight.

Yep that I get this, but let's say I'm on the highway and it looks like this :

Can I keep in 4wd on long distances (hundred of miles) without any problem, even when there's curves on the road? Can light slush allow the wheel to slip enough without damaging the drivetrain?

 

[1engineer]

Yep that I get this, but let's say I'm on the highway and it looks like this :

Can I keep in 4wd on long distances (hundred of miles) without any problem, even when there's curves on the road? Can light slush allow the wheel to slip enough without damaging the drivetrain?

Sure you can. Too many people worry about this unnecessarily. What you do NOT want to do is put it in 4WD on a beautiful July day and go out in a parking lot, turn your wheels to full lock and start doing circles. That is not good. Normal driving with highway curve radius is fine. Any road condition (dirt, rain, snow) that reduces the coefficient of adhesion lower than rubber on macadam is fine.

 

[scanny]

Can I keep in 4wd on long distances (hundred of miles) without any problem, even when there's curves on the road? Can light slush allow the wheel to slip enough without damaging the drivetrain?

I would normally turn off 4x4 in this situation when slush is over and there is dry asphalt for some time and I don't expect anything wet.

The manual says that we should use 4hi when we need extra traction and we definetely need it on the higway from your picture : )

 

[M1911]

The 5th Gen SR5 has a part-time 4WD system with open front and rear differentials. When in 2WD, the rear wheels are driven.

When in 4WD (both hi and lo), both the front and rear driveshafts turn at the same speed. However, since the diffs are open, if you have a front and rear wheel without traction, you may get stuck.

If you want to avoid that situation, buy a TE (which comes with a locking rear diff) or put an ARB rear diff in an SR5.

 

[Intruder]

My advice is or you go with the SR5, or you go with the limited, but in Canada, the Trail is not the optimal choice given 42k sticker price. The full-time 4WD is worth much more in Canada than the KDSS of the Trail.

Depends on what you're going to do with it. I preferred having the locker and KDSS and knew I was going to take it off road A LOT so the TE was worth it to me.

Part-time 4WD driving after one winter seems to me to be like driving a manual car, but without the clutch. Let's say you're parked on ice, you engage 4wd to get out, but once you're out of the ice and acquired momentum, you switch back to 2WD. On the highway, you will need to switch between 4WD and 2WD depending of the snow patchs. It's not that bad, but if you're lazy it could bother you.

We got a lot of snow in Calgary last night. I only used 4HI to get out of my residential neighbourhood then switched it back into 2HI. For most on road conditions you only need 2HI with good tires and let VSC and all the other electronics do their job (and drive appropriately to the conditions). Either that or I guess that coming from driving stick all my life I'm just not too lazy to switch back and forth between 2HI and 4HI.

 

[JB.]

Can I keep in 4wd on long distances (hundred of miles) without any problem, even when there's curves on the road?

A qualified yes, but why would you want to? (even though the binding issue is milder than it's often made out to be -- see 1engineer's post)

The rule of thumb to use 4WD when traction is necessary pretty much takes care of everything.

Using 2WD will help avoid going too fast for conditions (4WD doesn't help you stop). Going to 4WD can decrease safe operating speed all by itself by inducing understeer in corners and presumably reducing the effectiveness of VSC and ABS by eliminating the ability to completely isolate the effect to individual wheels.

 

[KidVermicious]

Using 2WD will help avoid going too fast for conditions (4WD doesn't help you stop).

This this this, a thousand times this. If the roads are bad enough that you're considering 4wd, you shouldn't be going over 30 anyway.

 

[whodat]

This this this, a thousand times this. If the roads are bad enough that you're considering 4wd, you shouldn't be going over 30 anyway.

I agree with you. 4wd does not make people invincible in the snow. I like to put it in 4wd mainly to quickly get out of the way from cars sliding towards my rear.

I've posted before about driving in 4wd on the interstate hauling a car on a dolly from TX to IA, the car on the dolly was swaying left and right too much, so I put it in 4wd and I felt like I had more control. I went up to 65mph. At a gas station I even had it fully locked turning and heard some thump yhump thump, which is not good and i'm sure it's what 1E was talking about. But as of now, no issues that I know of. 4Running fine.