mooretorque

My service advisor verified that the A/C light remains lit even if the compressor has cycled off.

willard west

In order for the viscous clutch to "stiffen" and provide a greater level of torque to the rear driveline it must be "heated" by the turbulence created by the disparate turning rates of the two sets of clutch plates. It typically takes something on the order of hundreds of milliseconds for this to happen.

If both front wheels begin to slip and TRAC were to quickly intervene then the VC would never have an opportunity to perform its task.

So my suspicion is that TRAC is used to prevent wheelspin laterally but not longitutnally.

Here is Lexus' "crafty" answer to that question...



Recently you submitted a question to the Lexus Customer Satisfaction Department.

Subject:
Fw: Trac


Dear Mr. West:

Thank you for contacting Lexus Customer Satisfaction.

In a limited traction situation, the viscous coupling is "hardware-controlled" power delivery, which helps get power to the end of the car with more traction.

The four-wheel TRAC system is "software controlled" power delivery. In limited traction situations, this helps get power to the individual wheel(s) of the vehicle.

The two systems work together to provide increased traction control.

Your Question:
----- Original Message -----
From: Willard West
To: Customer_Satisfaction_Inquiries@lexus.com
Sent: Tuesday, September 04, 2001 12:32 PM
Subject: Trac


I have a 2001 RX300.

My understanding of the Trac system is that it will automatically brake any wheel or wheels which lose traction and begin to turn faster. It is also my understanding of the AWD system that the nominal torque distribution front to rear is 70/30 and if the front wheels lose traction the differential turning rate causes the fluid in the viscous clutch coupling to "stiffen" which increases the torque coupling to the rear wheels. I understand that the torque distribution can be as high as 51/49 front to rear once the viscosity of the fluid is increased through this circumstance..

My question is this: If the Trac is used to "quickly" prevent wheelspin, how is it possible for the viscous clutch (with a much longer "time constant") to "sense" differential turning rates long enough for it to have any positive affects?

Willard West



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If you have any further concerns, you can also reach the Lexus Customer Satisfaction Department at 1-800-255-3987, Monday through Friday, 6:00 a.m. to 5:00 p.m., Pacific Time. Sincerely, Jessica Caldwell Customer Satisfaction Representative

vicpai

............I just HAD to say something here. LET ME GIVE YOU ONE GOOD SOUND REASON FOR STARTERS. When your "tractionless " RX 300 is pushing 400,000 TROUBLE FREE miles the UNRELIABLE, LOW-QUALITY, PIECE OF ****** Mercedes is probably going to be a useless heap of dust (That is IF it makes it the first 200 miles or so from the dealer's showroom without the engine catching on fire or the transmission blowing up. In fact in my HUMBLE opinion I just wonder about the IQ level of people today....and these are supposed to be intelligent people????????????????????.........How can they buy TRASH/GARBAGE like Mercedes, BMW etc. AND, TO BOOT, PAY MORE MONEY FOR IT when they can get a substantially better quality product (example: Lexus, Acura, Infinity) for less??????????......Boggles my mind!!!!

mooretorque

C'mon, Vic, open up. What are your REAL feelings on the subject?? Stop beating around the bush.........

RX300TC

You still don't get it, do you *****? Here's a clue: the VC is not what delivers the power to the rear wheels.

Maybe if you weren't so convinced that you know it all, you'd be able to think outside the box on this one, and finally get it.

I'll post more details when I have time to write up a long, detailed explanation.

For the rest of the RX owners: I've done my homework and I'm extremely happy that I purchased the 4WD Rex. Lexus engineering is pretty innovative, even if they do occasionally copy stuff from other manufacturers. But hey, isn't that what the Japanese manufacturers are best at?

wwest

Some of these replies make me wonder how Lexus ever sold anything back in 1990 before their vehicles proved to be so reliable....

I guess some of us just have more faith than others....

Or more willing to take a chance on a newcomer?

wwest

Send me your fax # and I sent you a blown up pictorial of the RX300 "transfer case".

RX300TC

No need, I already have it in front of me: page 64, CHASSIS, U140E-F Automatic Transaxle.

Sat down with the Lexus shop foreman for about 45 minutes going over the design (something you weren't willing to do). Plus he threw a car on lift so we could go underneath and point things out (really didn't help much becuse so much stuff is buried).

The problem is that the supplied pics do not show what is really going on. But of course you would have known that if you actually talked to someone at Lexus rather than come up with your own theories.

I'll say it one more time, the clues are there if you are willing to let go of your hard worn beliefs.

This is really getting amusing.

willard west

Maybe I haven't been plain enough...

Everything I can see or analyze, logically, indicates that the RX SHOULD distribute the engine torque fairly evenly, front vs rear, if the VC is properly configured.

As a practical matter everything I have actually seen and tested indicates that the majority of the engine torque ALWAYS goes to the front wheels. That was true of my 2000 RX300 AWD and the 2001 RX300 AWd tests out the very same way even with VSC and TRAC.

The last time I actually talked to a Lexus service manager it was about the throttle tip-in surging of my 2000 GS300. I had already been under the hood and taken all of the "back-lash" out of the throttle cable/pedal system that I could. When the service manager started telling me about how the E-throttle didn't allow me to do that since there was no cable to adjust I argued for a few minutes and then just gace up.

But since you seem to have developed something of a relationship with your service manager maybe you can ask him/her why the disparate final drive ratio between the front drive and the rear drive. What good does it do? what does it accomplish?

Part of the puzzle for me is that even if the VC is so lightly preloaded as to be mostly ineffectual that still doesn't explain how the front wheels get most of the engine torque in my testing, granted "shade-tree" testing.

But it (ineffectual VC) certainly does explain the Mercedes "trick" testing that shows the short-comings of the RX AWD setup vs the ML.

ObiDon

West, aren't you the same person that doesn’t believe in ABS either???

Looks to me like you are in the minority on most of the topics here, and you just clutter up the forum by repeating your gospel over and over. Why don't you just publish all of your "facts" on your WEB site and send us a link. That way if we happen to forget your opinon on something we can just go to your link to refresh ourselves as to your opinion.

wwest

I'm not against ABS I just think that now that lateral acceleration sensors (yaw detectors) are becoming inexpensive and somewhat commonplace the ABS should become active unless there is an actual need.

But yes, I have in the past disabled my ABS in the summertime when there is more likelihood that I will need to stop quickly without any threat of losing directional control.

That's what, ALL, ABS is about, prevention of loss of directional control during panic braking. Don't fool yourself into thinking it's there to help you stop quicker.

Actually I heard an argument recently that the reason ABS became so popular (with the manufacturers) suddenly was becuase of the advent of so many vehicles with FWD. The mechanical brake pressure proportioning valve didn't work very well with engine braking to the front wheels thrown into the equation, thus came the need to "actively" modulate the brake pressure.

wwest

40 Gigabytes = $120 these days.

My "clutter" costs $.000000000134

ObiDon

Argue with an idiot,
he will drag you down to his level,
then beat you with experience.
-from 'Dilbert'

......you win!

wwest

That was 'way too easy...

RX300TC

*****, *****, *****... you're a narrow minded 61 yo man aren't you? You haven't actually "read" one of my responses, have you? No, in fact all you are quick to do is fire off another message just so your lonely old voice can be heard.

I've practically given you the answer before I formally post it, albeit in clue form. I've given you every chance to redeem yourself. But you've not even tried. You can't get your mind around it, can you? Go back and read my previous message. Say the words out loud.

You must be a load of laughs at cocktail parties.