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Discussion Starter #1
My comments and thoughts are in bold italics. Any additional thoughts, comments and experiences will be greatly appreciated.
Information copied from sources is in plain text.

So I am on a quest to make my 2005 AWD Toyota Sienna XLE more off-road capable. I have experienced wheel spin twice in low traction situations.

I first turned to Siennachat.com a forum for Sienna owners.

I agree with the following post, as my Sienna has experienced wheel spin twice when off-road. The wheel spin made it obvious that the rear differential does not lock, rather it is an open differential; pretty conventional.

There is no way to lock all the differentials and force actual 4WD; at best you have one front and one rear wheel doing the work. And Sienna is a front-biased system, so the front wheels do most of the work.

The following post provided some information about the AWD setup on my 2005 Sienna. As I suspected, the ECU applies the brakes to the wheel that is without traction in an attempt to put power to the wheel that isn't spinning. Essentially this should require the differential to apply enough force to overcome the braking force, thus driving both wheels. This did not work when I experienced wheel spin.

#2 • March 23, 2010
The outgoing sienna (GM edit this is the 2004-2010 Second Generation Gen2) used the same AWD system as the highlander. The 2011 sienna uses the same system as the Venza and Rav4 from my understanding. Is it better? Correct me if I'm wrong but I believe that my '04 AWD sienna splits the torque 50/50 all the time. The traction control and stability assist programs actually apply the brakes to make corrections. Better AWD systems can vary the amount of torque to each wheel or front to back by large margins. I'm sure the number one reason for the change was cost.

The following post provides links to some Toyota Company training videos. The videos are pretty simple but describe the AWD system on the Sienna and contrast the system with other Toyota 4 wheel drive systems.

#20 • March 14, 2011
Second-generation Sienna (2004-2010) and first-generation Highlander non-hybrid (2000-2007) used the same system (as have some other Toyota and Lexus models): it is full-time using a centre differential, and is shown by the 2009-vintage online explanation (V5) for both Sienna and Highlander and by the current online explanation (V7.1) for the Highlander. This is a full-time system, always applying equal torque to each of the four halfshafts (before the intervention of any limited slip system that models other than the Sienna might have).

As indicated by the grouping in the current online explanation (V7.1), the Sienna has moved to an on-demand AWD system, shared with the Venza and current RAV4. I previously thought the Highlander had changed, too, but apparently I was mistaken. This system is fundamentally front-wheel-drive, and applies drive to the rear as well under some circumstances.

Some versions of the University of Toyota explanation:
Version 7.1
V5 (2009)
V4 (January 2008)
Since I only found V4 by guessing the URL, and I have not successfully guessed any other versions, I don't know what else might be available.

All forms of this explanation have some shortcomings:
  • they describe differentials as splitting power, but fail to mention that they distribute equal (or split in constant ratio, in the case of planetary centre differentials) torque; and,
  • the split of either torque or power in a locked differential or front/rear coupling is glossed over or misrepresented, as it is in essentially all descriptions (of any brand, from any source) for a non-technical audience.

The following post states that the pre-2010 Siennas use a Torsen system. The post does not state which of the three differentials (center, front, rear) are Torsen. My personal experience indicates that the rear differential is not a Torsen. The post also states that the 2006+ Rav4 uses a 4WD with a low range that locks the differential. Again it is not stated which of the three differentials are locked.

#27 • Apr 2, 2012
The 2011+ Sienna AWD uses a different setup than the pre-2010 Siennas, which use a Torsen AWD system (GM editorial comment -doubtful the rear is Torsen). The pre-2010 models use 50/50 FULL TIME AWD. BUT that does not mean the 2011+ models is terrible by any means, it's just a different system.

The 2011+ models use an Active Torque Control 4WD system. This is a very efficient, high performance, and sophisticated all wheel drive system. It DOES NOT use VISCOUS COUPLING unlike the pre 2006 RAV4, MATRIX, and Highlander 01-03 models. Those all use a VISCOUS COUPLING in the rear differential to engage the 2 wheels in the rear. That technology I would consider substantially inferior to the 2011+ models that use an ELECTROMAGNETIC CLUTCH COUPLING to engage the rear 2 wheels. The AWD ECU computer sends the electromagnetic clutch coupling signals to engage the rear wheels based on driving conditions. This is so you don't have to use 4WD when you don't have to so you save gas. In fact, 4WD is engaged when you move the car from a stand still. The AWD ECU will control the 4WD mode until you move steadily and conditions are not slippery and at steady speeds, it will move to a 2WD FWD system saving gas. It will also help with cornering at low speeds (by reducing rear wheel torque) where the full time 4WD systems will have some inefficiency doing so. Of course the new system (on the 2011+ Sienna AWD) you cannot LOCK the differential to lock all the wheels (4WD LO MODE) it runs in 4WD HI mode all the time WHEN it's needed. There are no actual specs on how much torque is distributed to the rear wheels but I'm going to guess it's 50/50.

When you start the car off on the 2011+ Sienna AWD, there is no torque steer and grip is always there! The car always moves in 4WD HI then gradually goes to 2WD FWD mode when it's necessary. This is a highly sophisticated system. Without the 4WD LO mode (locking the differential) like on the 2006+ RAV4, VENZA AWD, MATRIX AWD (09+) models, you may think it has a hard time getting out of a stuck situation. But you can simply turn off the VSC/TSC mode so you can get unstuck. I don't think the minivan was meant to be taken where an SUV would be better suited.


The following post states that the Gen2 Siennas do not have a locking center differential. This is consistent with my personal experience and post #2.

#29 • Apr 5, 2012
Just a note: the 2nd gen Sienna AWD uses a full time AWD system but has non-locking center differential. It locks each wheel slipping using braking, however (GM editorial comment - this is not Torsen if it uses brakes). The 3rd gen AWD system is highly efficient in fuel savings (whether or not it saves gas is dependent on the driver), weight, and is near instantaneous activation. Most of the new cars including the new 2013 Acura RDX will have this sort of system. It is not a wheel slip and grip system like a viscous coupling type AWD system. The 3rd Gen Sienna like the 09+ Venza, 06+ RAV4 have the same system minus the 4wd LO on the RAV4. In fact, if you disable the TCS and VSC (by holding the TCS button down longer), you can AWD drift till your heart's content. By disabling TCS, you can simulate (to an extent) a 4WD LO.


I am considering using a Miata Torsen LSD rear differential, as found on my Mazdaspeed Miata. Flyin' Miata's website stated that the OS Giken makes a substantially improved Torsen. Flyin' Miata uses it on one of their V8 Miatas (450 HP Chevy LS6). So I checked OS Giken's website. OS Giken actually makes one for the Sienna with the U660 transmission. Unfortunately for me the U660 transmission is used on the Gen3 Siennas, thus Giken's unit will not work on my Sienna.

I spoke with Giken directly. Giken developed the unit at the request of Toyota so a Sienna could be used in the Lap of America. Giken doesn’t expect much demand for a unit for the Gen2 Siennas and development would cost $20K or so.

I am also investigating using a Miata Torsen with the Giken upgrade for the rear differential in my Sienna.

OS Giken
OS SuperLock LSD for Toyota V6 Sienna
TY511-HA For the front differential
Toyota Sienna/Camry V6 U660 transmission
Regular price $1,450.00

Product Support:
Ph: (310) 986-6620
Hours: M-F 9AM - 5PM (PST)
2420 W. Carson Street, RM 145,
Torrance CA 90501

The following information on the transmission in 2004-2006 Siennas is taken from eBay postings and a Toyota parts website.

Automatic Transmission AWD Fits 2004-06 Toyota Sienna OEM
Manufacturer Part Number: 3050008021
Interchange Part Number: 400-61600
Stock #: 20D016
Used, from VIN #: 5TDBA22C26S063082
Transmission model U151E, U151F

eBay listing

Toyota Part Number: 305100802084
Supersession(s): 3050008020; 3050008021; 3050008022; 30510-08020-84

What this fits:
Sienna 3.3L AWD AT LE 7 Passenger. LE WAGON 2004, 2005, 2006
Sienna 3.3L AWD AT XLE 7 Passenger. XLE WAGON 2004, 2005, 2006
Sienna 3.3L AWD AT XLE Limited 7 Passenger XLE WAGON 2004, 2005, 2006

The following information on the transmission in 2011-2014 Siennas is taken from an eBay posting.

Automatic Transmission U660F 6 Cylinder AWD Fits 2011-14 Toyota Sienna
Manufacturer Part Number: 30500-45031
Interchange Part Number: 400-51898
Used, from VIN #: 5TDJK3DC2BS012140

eBay listing


The 2005 Sienna XLE AWD.
3.29 final axle ratio

There were other final axle ratios in 2005.
2005 Toyota Sienna XLE 7-Passenger - Passenger Minivan 3.3L V6 AWD auto
3.08 final axle ratio

Back to the Miata Torsen differential. Unfortunately the Miata differential has a 4.1 gear ratio while the Sienna differential has a 3.29 gear ratio. This will require further research.

In my quest I am also considering using a rear differential from a RAV4.
The following post from a RAV4 forum provides some preliminary information. Some RAV4s were sold with LSD differentials. These may be rare units.


#3 • Sep 1, 2011
Rav4's did have a rear Limited Slip Differential optionally fitted. It was a pricey option though, and I am under the impression that it didn't sell well.
AW111, to determine if yours had this option fitted, try to replicate a low traction situation by putting three wheels on a slippery surface and leaving only a rear one on a high traction surface, then lock the centre differential (assuming you have a manual).

Now, the power will be split between front and rear axles, and the front wheels will waste their share due to slippery ground.
If you do have a rear LSD, it will divert part of the engine's torque to the wheel placed on the high traction surface allowing the car to limp forward.
If however the high traction wheel remains stationary while the opposite rear wheel spins due to low traction surface you are not equipped with a rear LSD.

The following post reiterates that some RAV4s did have LSD differentials. The post states that the rear differential LSD was available on 1996 & 1997 manual transmission RAV4s. Based on post #3 above, the LSD was an option in 1996 & 1997.

The following post also states that starting in 1998, the rear LSD was available on all 4WD RAV4s. I assume that the LSD was an option, but I have not confirmed this. The 1998+ RAV4 LSD is supposed to be a Torsen.


RAV4 info

Discussion Starter • #5 • Sep 6, 2011
Subject: 3.1.3) How does the Four Wheel Drive (4WD) system work?
Very well. Actually, it depends on your choice of transmission, and whether you have the Limited-Slip Differential (LSD) option.
If you have a 2-Wheel-Drive RAV4, then it is powered by the front wheels only.

If you have 4WD, a full-time system puts power down to all four wheels at all times. Some refer to this as an "all-wheel drive" system, rather than 4WD, but AWD usually refers to "reactive" systems that delay transfer of power until after slip is detected. The RAV4 drive system is most correctly called "Full-time 4 wheel drive." It is reported that 25% of the engine power is normally sent to each wheel.

- For automatic transmissions, there is a center coupling that
detects wheel slip and gradually locks the front and rear axles as
the slip increases. There are no driver controls for this feature.

- For manual transmissions, there is a center differential lock button
on the dashboard that manually locks the front and rear axles. When
engaging, an amber "C. Diff Lock" indicator lights on the dashboard.
When disengaging, there will be a beeping sound until the center
differential is fully disengaged; it may beep just once, or may
beep for as much as a full minute (seems to beep longer when cold).
Toyota recommends that it only be used only in difficult situations,
and that the center differential can be damaged if used improperly.

- For 4WD vehicles, there is an optional rear LSD available. In 1996
and 1997 model year, it was available only on standard transmission
models, but starting in 1998, the rear LSD is available in all 4WD models.
This device is called a "Torsen-type" LSD by Toyota, and is one of
the most sophisticated and effective types available. It automatically
detects wheel slip by either rear wheel and redirects the most power
to the wheel that is slipping the least. There are no driver controls
required for this device.

The following post provides some information about part #s and gear ratios for the RAV4 differentials, along with some prices in Euros. The rear LSD has a 2.928 ratio.

RAV4 info
#10 • Sep 9, 2011 (Edited)
This is what I found on toyodiy:
41110 carrier assy, differential, rear
41110-42011 final gear ratio=41:14=2.928 1 € 2,110.35
41110-42031 final gear ratio=41:14=2.928, w(lsd) 1 € 3,461.99

41309a shaft sub-assy, rear differential side gear
41309-32020 2 € 120.94
41309-42010 w(lsd) 2 € 178.48

41334d ring, shaft snap (for rear differential side gear shaft)
90520-22012 2 € 2.37
90521-28004 w(lsd) 2 € 0.99

As far as I can see, these three parts are the only ones that differ between the open differential and the LSD. The pictures posted by toyodiy don't show any visual difference.

On another forum, one member claimed that recently (2010, February) he was quoted by Toyota "only" 2500 pounds in order to have an LSD fitted.
And to (possibly) answer the question of the original poster, on yet another forum it is stated that the Rav4 lsd and the Celica equivalent do not share the same part number. (contradicting info alert):


The following is some information on prices for the RAV4 rear LSD.

ToyoDIY 8/3/20
2005 TOYOTA RAV4
CARRIER ASSY, DIFFERENTIAL, REAR
Toyota part # 41110-42031
41110-42031 *FGR=41:14=2.928, W(LSD) 1 $3,877.43

Conicelli Toyota 8/3/20
1580 Alan Wood Rd
Conshohocken, PA 19428
800-825-7128 ext. 5

Drive Axle Assembly - Toyota (41110-42031)
Sale Price: $2,020.11

RAV4 1998-2005 8/3/20
Rear LSD differential
Out of stock $2,207.29
mpn 4669766920 incorrect on Carid site. Actual Toyota part # 41110-42031
more details on - Toyota OE 4111042031 - Rear Drive Axle Assembly

The following post states that the 4.2 RAV4s also have the rear LSD. I am not sure which years are 4.2 RAV4s.

RAV4 info
#11 • Sep 9, 2011 (Edited)
Interestingly, on this site, these part numbers apply to the 4.2 Rav4's as well (?!?!):
Rear axle housing & differential for Toyota RAV4 ACA21W - -INF
Toyodiy confirms this as well.
So, we could widen our search in the junkyards to include both generations of the Rav4. We might get lucky.


I spent some time looking for other Torsen differentials, OS Giken offers upgrades for some.

VehicleGear ratio
2005 RAV42.928
GM 7.5" & 7.625" 10 Bolt Strange Engineering3.23
BMW Series - E36 M3 Coupe manual3.23
Ford 8.8 axle3.27
2005 Sienna XLE AWD3.29
Toyota AE86 Corolla. Part # 41201-294063.308
Ford 8.8 IRS from Strange Engineering3.31
Ford 8.8 axle3.31
Grannas Racing 8.8 inch Ford3.31
Nissan Z34 370Z automatic3.357
Datsun 280Z, 280ZX, 300ZX3.36
Datsun 280Z, 280ZX, 300ZX3.54
Nissan Z34 370Z manual3.692
Honda S20003.9
Datsun 280Z, 280ZX, 300ZX3.90
2006 Lexus GSE21 IS3504.08
MSM Miata 2004, 20054.1
Honda S20004.1
BRZ/FRS4.1
2020 Toyota FA20A GT864.1
Integra DC2 Type R4.4

The Ford 8.8 axle was used on 1980s and 1990s four-liter Aerostar vans, Bronco and Explorer SUVs, four-liter compact Ranger pickups, full-size F-150 and F-250 pickups and Mercury Capris and Cougars. Contemporary F-Series and Rangers continue to use the 8.8-inch differential.

The 7 1/2-inch differential works just fine on any powertrain rated less than 225hp, but for anything larger than that, the 8.8-inch differential should be considered. The 8.8-inch is 30% stronger than the 7 1/2-inch and can be used reliably in 300hp or better vehicles.

New leads from TundraSolutions forum.
Kazuma/TRD LSD in 2002 Tundra
Auburn Gear makes an LSD for 2nd Generation Tundras

I am still looking for a reasonable way to convert my 2005 Sienna. I may wind up purchasing a second gen Sienna, installing the OS Giken torsen conversion, putting in the 3.5 inch JourneysOffRoad lift kit, putting on A/T tires and converting the inside to a camper set up as I have done to my 2005. I lot of time and money.
 

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just sell the van and buy a jeep and be happy with it.....you have the wrong vehicle, With all the effort and money spent it will still not be a real 4wheel drive. you need 3.73 or 4.88 gearings to actually get the desired torque to the ground.....any way Goodluck your money your time....

Javvy
 
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Discussion Starter #4
WrenchRunner,

tdlr? I don't know this one.

Remember DUA (Don't Use Acronyms).
 

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Discussion Starter #5
Javvy,

I already have a Tundra 4X4, but it doesn't have the features of the Sienna - sliding doors on each side, lots of headroom for sleeping, and so forth. If I could graft the Sienna body on the Tundra that would be a great combination for me. The Sienna is lifted and has A/T tires so I can get about 90% of the places I want to go off-road that the Tundra gets me to.
 

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Javvy,

I already have a Tundra 4X4, but it doesn't have the features of the Sienna - sliding doors on each side, lots of headroom for sleeping, and so forth. If I could graft the Sienna body on the Tundra that would be a great combination for me. The Sienna is lifted and has A/T tires so I can get about 90% of the places I want to go off-road that the Tundra gets me to.
Funny, but as I read it, my entire line of thought was that it would be cheaper and easier to get a 4x4 truck frame/chassis and graft a Sienna body on top. With all the 4x4 trucks ever made, you should be able to find something which will support the surgery.
 

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Discussion Starter #8
Funny, but as I read it, my entire line of thought was that it would be cheaper and easier to get a 4x4 truck frame/chassis and graft a Sienna body on top. With all the 4x4 trucks ever made, you should be able to find something which will support the surgery.
BillG,

I have definitely thought about grafting a Sienna body on the Tundra, but the cost would fund a bodacious road trip.
 

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BillG,

I have definitely thought about grafting a Sienna body on the Tundra, but the cost would fund a bodacious road trip.
I've taken my FWD, bone stock van many places, but it's not an off-roading, rock-crawling sled. If I want to go someplace like that, I park as close as I can and start hiking. When the kids are out of the house in a decade or so, I might change my mind. More likely, I'll make the van-life conversion and hit the road with the wife. Things get so much easier when you only have to provide bedding for two instead of 5!
 
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