sleepybobcat

How does the RX300's 4WD work exactly?
I've been driving mine for over 10k miles and still
don't have a clue... Asked the service advisor yesterday
and he was almost clueless....

Does it mainly drive the front wheels and send some
power to the back wheels? (then send more power
to the rear wheels as needed) Or is it the other way
around?

Does each wheel get different amount of power
or is it distributed evenly between left/right wheels?

Also, is there an electronic brain that
determines this or is this done mechanically?

Thank you very much for any information!!!


Bob

1niceride

I thought RX's had AWD . In the case of 4wd , the rear wheels move the truck then when slippage is detected the front wheels get power and help move the truck.

I thought the salesman was supposed to show you how everything worked in your RX?

Also do you have a button to switch into 4wd mode or another shift lever? In my truck i have the lever and then i would have to shift it into 4wd mode. Then shift into high or low. If yours is a button then all you would have to do is push the button and your set.

I have a 4wd Tacoma and have only used it once when i got stuck in a hole. Switched it to 4wd mode and got out the hole . I only brought my truck because the 4wd looked much better than the 2wd.

mooretorque

The AWD in the RX is supplied in the form of a viscous coupling in the driveshaft between the front and rear wheels. Under ordinary conditons, the RX is front drive only; if the front wheels begin to spin, the fluid in the coupling is also spun, building heat, which markedly changes (thickens) it's viscosity. This essentially locks the rear driveshaft to the front, transferring power to the rear wheels (the one with the LEAST traction unless you get the LSD option.

Sounds timeconsuming, but in practice, it's essentially transparent and immediate. There is no seperate gearing for a low range although there could have been if Lexus had deemed it something that AWD owners would use. Not too many people offroad anything, much less a $40k sport ute, so they opted not to do so.

Hope this helps.

RX300TC

I know everyone is trying to be helpful, but this is how it really works.

The transmission in the 2001 four-wheel drive RX 300 features an integrated transfer case and a viscous center differential that provides a 50/50 front-to-rear power split. The system requires no activation by the driver. If slippage occurs at the front or the rear, the viscous center differential automatically and transparently directs power to the wheels with the most traction.

The traction control provides further "fine tuning" by sensing individual wheel rotation speeds and braking the appropiate wheel when necessary.

The fact that the 4wd system on the Rex is supplying torque to both axels all the time gives it superior handling characteristics to other so-called AWD systems where only one axel has torque until slipagge occurs. These are "reactive" systems, the Rex is a "proactive" system.

Hope this helps,
TC

mooretorque

oops.....forgot about VSC and TC........my wife's is a 99. TC was an option on FWD only and VSC didn't appear until 01.

But RX, torque transfer doesn't occur with a viscous coupling unless there is a speed differential between the front and rear shafts; therefore, our AWDs are FWDs until they slip. However, this occrus so quickly that it is essentially imperceptible. And it works GREAT!!!! Implicit in all this is that there can be no driver input; everything functions at the order of either microprocessors or physics.

RX300TC

I hate diasgaree, but that's not how the Rex's AWD system works. It's 50/50 normally. Here's a a couple of reference points:

Edmunds review: http://www.edmunds.com/reviews/roadt...2/article.html

Lexus Technology press release, 9/7/200:
http://www.lexus.com/about/news/pr_archive.html

Enjoy the miles,
TC

mooretorque

Arrrgghhh!!!!! RX, I bow to superior knowledge. Either my brain is fading, or I misread original material back in 99. Either way, my apologies to sleepybobcat (and all other readers) for misinformation.

I will go spank myself now.

RX300TC

Don't spank yourself when it's much more fun if a girlfriend or spouse does it.

The permanent 4WD is a big reason I chose the Rex and why it's foul weather handling is superior to many other vehicles out there, IMHO.

mooretorque

RX, certainly agree about bad weather handling. Wife's RX tracked like on rails while my 93 SC 5 speed couldn't decide which end wanted to go first even with new Dunlop SP8000s. Kinda fun at times, but you definitely had to stay in the game even when relaxation was the order of the day. The VSC in my 01 GS430 just ain't even in the same league as the RX AWD.

("Spank ME!!!" said the masochist. "NO." said the sadist.)

RX300TC

Sounds like you have multiple Lexii. While the Rex is great to drive, I do miss having a nice kick-*** performer to speed around in. The 4.3L engine must be nice in a vehicle that doesn't have all the extra weight like the Rex.

The new SC sure does look sweet. It's be nice if I had about $60k lying around

sleepybobcat

Thanks for all the replies. I'm still not completely
sure how it works. No matter, as long as it provides me
with trouble-free light winter driving. I'm very
impressed with my RX300's performace in snow. My
previous SUV was a MB ML430. It frequently got stuck
going my snow/ice-covered steep driveway.(because
the MB system brakes the wheels...)

Here's a hypothetical question, if I lift the RX300 off
the ground(all 4 wheels), start the engine and shift into
"D" drive, will all 4 wheels move?(provided VSC doesn't
kick in first....

Bob

RX300TC

My previous SUV was a MB ML430. It frequently got stuck going my snow/ice-covered steep driveway.(because the MB system brakes the wheels...)

I hate to tell you this, but that was the ESP and traction control kicking in on the ML, and the RX's system works pretty much the same way. In fact, a MB ML will be superior to a RX in foul weather because the ML has a true "4-lo" gear.

Here's a hypothetical question, if I lift the RX300 off
the ground(all 4 wheels), start the engine and shift into
"D" drive, will all 4 wheels move?(provided VSC doesn't
kick in first....

Don't do this! If you open up the hood and look under it and around the engine compartment, you'll see a warning sticker telling you no. You need a special set up to prevent parts of the system from burning out.

sleepybobcat

Thanks for the caution... I will not lift all 4 wheels off...



My driveway is rather steep, from 30 to 45 degrees.
My ML430 always had problem getting up when it's
ice covered... The RX300 never had this problem, it
just goes right up... even if I stop in the middle of the
uphilll and start again... The ML would just spin the
tires and then brake the wheels(untill the brake give
out the burn smell), and I had to back down the hill
and go back up in one swift motion...

Bob

RX300TC

Wow... I'm shocked Bob. I like both the ML and the RX, but I'm surprised the ML couldn't make it up and the RX could. Thanks for the feedback!

mooretorque

Bob, did the ML have LSD for rear wheels?? Does your RX?? If the RX does and the ML didn't, I could understand the driveway results........either that or we have to assume that the Goodyear Integritys which have been universally vilified have unguessed-at potential in icy conditions.

RX, yes, we are a dual-Lex family. God, how I love calling up all 325 lb-ft of torque in the GS!!!!!! Reminds me of the old days of the small block Chevys........but those are other stories!!!!!