Torsen Cent Diff & Frame Question - Design

[anthonym]

Hello Everyone,

My wife and are seriously looking at the 2003 4Runner SR5 to purchase. When I think of 4WD, I think of my 1983 Ford Ranger 4X4 with a tranny, transfer case, and drive-shafts to front/rear differentials.

How/where does the Torsen Center Differential fit into the mix? I am very familiar with the viscous coupling used on the Escape/Tribute and am not too thrilled with it as it does not come close to the 4WD on the Ranger.

I looked for diagrams of this system and found none. Any help to the physical implementation of this unit would be greatly appreciated.

In addition, the dealer said the 4Runner has a composite frame and not a truck type rail frame. Can anyone give my the quick and dirty explanation? Good/Bad?

Finally, the 4Runner is the best SUV we looked at. We also drove the Explorer, Pathfinder, Durango, Xterra, Discovery etc... and by far the Toyota was the best in our view.

Anthony

 

[Thai]

Anthony,

Welcome. Here are few links first to start with:

Link: All you need to know about 2003-2004 4runners!

Link: All you need to know about 4runner's 4wd system

Now, to answer your questions quickly:

4runner's system is similar to your old truck's system...but, it is far more advanced (and just as capable). 4runners do have a separate transfer case for 4-HI and 4-LO ranges. 4-Lo is for torque multiplication at low speed (off-roading). The good thing about the 4runner is that you can put it in 4wd on ANY surface without fear of binding (as would happen on your old truck).

Of course, 4runners also come with stability control (prevents oversteer/understeer...aka losing control) and brake assist.

4runners have an independent front suspension and a rear live axle.

4runners have a body-on-frame design. I am not sure what "composite" means. You're either a UNIBODY or a BODY-ON-FRAME. 4runners have two fully-boxed frame rails running from front to rear. In addition, it has 9 crossmembers to support the frame. It is an extremely strong frame (probably strongest in it's class by far). The frame is made from high-strength steel/alloy. Most of the crossmembers are boxed also.

Torsen center differential is superior to viscous coupling and clutch packs seen on other SUVs. Torsen is GEAR-based. This has three main benefits:

1. It lasts longer...much less wear and tear (as compared to clutch packs). Less maintenance (due to less wear-tear). Stronger.

2. Quicker acting. It is faster at responding to slippage than viscous coupling or clutch packs.

3. With Torsen in 4runners, it varies the amount of power being distributed depending on traction. However, it ALWAYS sends power to both axles ALL THE TIME. This is a key point. Because of this "full-time" function, it is a PROACTIVE system...in that, it does not wait for slippage to send power to one axle (it just varies the AMOUNT). Power is ALWAYS available to both axles. No lag time. No reaction time.

In many viscous coupling systems (including Highlander/RX300), only one axle gets the power. When slippage occurs, it THEN sends power to the other axle. This is a REACTIVE system. It REACTS to slippage. Therefore, there is a LAG TIME before power goes to the other axle.

Hope this helps.

P.S.: i agree with your last statement.

 

[Swaro]

Anthony:

I'll give you my 2 cents, but do a search on this forum...Thai and others have extensively talked about the various 4wd/awd configurations. In my limited view, the big difference with the Torsen and standard truck transfer case 4wd is, the Torsen allows power to be shifted front to back and vice versa. This makes the vehicle FAR more effective on a snow covered road over standard truck 4wd. (I've driven both through the same snowstorm.) I can't speak for off-road, but being able to lock the center diff (Torsen), should make it pretty effective. The Torsen is an American designed product; I'm not sure where it is manufactured. It has been used in most awd Audi's for at least 20 years. And Audi's drivetrain has been considered one of the best if not the best forever. The torsen is mechanical in that it is all gears. I understand it is much more expensive to manufac than say a viscous coupling diff. They are bulletproof, I've never heard of one failing in an Audi. Good thing, too, I hear they are 4-6 thousand dollars, but I could be wrong on that. I was initially attracted to the new 4runner when I saw that it had a Torsen.

First off, learn to question everthing most car salesman tell you; most of them don't have a clue, but being salesmen, they will give you an answer whether they know or not. I think it must be in the car salesman's creed that you never say. "I don't know".

I believe the 4runner is a truck type, boxed rail, ladder frame. I never heard of this composite business. I vaguely remember reading something where Toyota bonded the frame to the body in places???? I might be totally wrong on that.

Hope this helps. My '03 V8 SR5 has been very good.


Swaro

 

[Thai]

Swaro is right. Audi's have had this Torsen for a long time. In addition, the new Range Rover uses Torsen...and that thing is pretty capable!

The "body" of the 4runner is welded together...it is then attached to the "frame" via body mounts. If you peak the underside of the 4runner, then you can see these mounts.

 

[anthonym]

Thia and Swaro,

Many thanks for your input! After reviewing your posts and the below document:

http://uhaweb.hartford.edu/htruong/2003_4Runner.pdf

All of my questions have been more than answered. I think at this point I just have to pick the color!

Anthony
Seattle, WA