4WD Test
12-05-01, 04:05 AM
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4WD Test
Finally had a chance to see if my AWD actually worked last night after reading all the negatives recently posted (by you know who). Coming home to about 3-4" of snow over slush, I waited in my slightly inclined driveway for my garage door to open. Decided to give it a little "juice" and break it loose going into the garage. Low and behold I had 4 identical spinning marks in the snow (each about 18" long). Guess the system transfers torque from front wheels to rear seamlessly. I'm ready for the flames!!!!
12-05-01, 11:23 AM
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AWD
Back in 95 when we had our last BIG snowstorm here in the Seattle eastside I tried your very same test with my 94 AWD Aerostar, except in a large open area in the company parking lot.
The Aerostar's normal torque distribution is 30/70 front/rear and is electronically switched to 50/50 if slippage is detected.
I made several runs in the parking lot in an attempt to determine if all four wheels were indeed "driving" when I accelerated hard in this snow and ice.
I couldn't readily determine either way but I can tell you that in trying quite hard to get the rear end to "step out", oversteer, I just simply wasn't able to make it happen. So my conclusion was that the Aerostar AWD setup was sure-footed enough that I had no worries from that direction.
Next time I'm in ice and snow conditions in the RX I'll try to take/have a video camera along to see if the rear wheels will actually "throw" snow on hard acceleration.
I sincerely doubt it but I'll wait for the video before I express any serious doubt.
The Aerostar's normal torque distribution is 30/70 front/rear and is electronically switched to 50/50 if slippage is detected.
I made several runs in the parking lot in an attempt to determine if all four wheels were indeed "driving" when I accelerated hard in this snow and ice.
I couldn't readily determine either way but I can tell you that in trying quite hard to get the rear end to "step out", oversteer, I just simply wasn't able to make it happen. So my conclusion was that the Aerostar AWD setup was sure-footed enough that I had no worries from that direction.
Next time I'm in ice and snow conditions in the RX I'll try to take/have a video camera along to see if the rear wheels will actually "throw" snow on hard acceleration.
I sincerely doubt it but I'll wait for the video before I express any serious doubt.
12-05-01, 02:44 PM
#3
Lexus Champion
Willard, as you know, I've followed the AWD saga with interest. Had forgotten, but MikeK's post reminded me of last winter's inclement conditions here.
And yes, my 99 AWD with LSD can spew from all 4; I'll have to do some cipherin' as to how to reconcile that with the the results you've obtained thru experimentation. Obviously, as has been proven with the MB rolling log test, there are situations where the Lexus system can be defeated.
Doctor Moore's axiom: The driver is the most important component in any drive system. (For those of you who don't read Autoweek, that's "driver" as in "controller of the vehicle regardless of circumstances" and as opposed to "wheel holder", aka "useless oxygen consumer holding onto steering wheel".)
And yes, my 99 AWD with LSD can spew from all 4; I'll have to do some cipherin' as to how to reconcile that with the the results you've obtained thru experimentation. Obviously, as has been proven with the MB rolling log test, there are situations where the Lexus system can be defeated.
Doctor Moore's axiom: The driver is the most important component in any drive system. (For those of you who don't read Autoweek, that's "driver" as in "controller of the vehicle regardless of circumstances" and as opposed to "wheel holder", aka "useless oxygen consumer holding onto steering wheel".)
Last edited by mooretorque; 12-05-01 at 02:46 PM.
12-06-01, 11:02 AM
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Suggestion
My I hazard a suggestion?
Factual points:
The RX300 has three "open" differentials with a viscous clutch coupling to the rear driveline.
Without the viscous clutch in the rear driveline when all four wheels have good traction but disparate turning rates front to rear, as would happen in a tight turn, you would experience severe driveline wind-up, tire scrubbing, and knuckle busting "feedback to the steering wheel. If you have ever driven a Jeep in part-time 4WD on dry pavement you will know what I mean.
So, the first, or primary purpose of the viscous clutch is to provide some reasonable level of "slippage" between the front driveline and the rear driveline in circumstances such as these. Otherwise the driveline would soon suffer significant mechanical damage, just as is warned in the Jeep owners manual in the aforementioned circumstance.
But now we have a trade-off, or compromise situation on our hands, to much "pre-load", latent coupling, in the viscous clutch and we might damage the driveline over time. Also, with "too much" pre-load, the feedback to the steering wheel would be too noticeable and discomforting to this "class" of owner/driver.
Even in full-time 4WD (viscous clutch in the loop) the Jeep's steering wheel would still provide substantial driveline windup feedback in a tight accelerating turn.
Now the guessing part, my guessing.
Part of my assumptions here are based on the fact that the Chrysler T&C AWD has an over-running clutch and a dog-clutch combination in their AWD setup. The purpose of the over-running clutch is to allow the T&C's viscous clutch to be by-passed in severe braking situations, otherwise the harder braking slower turning front wheels would "dictate" the turning rate of the rear wheels via the "tight" viscous clutch coupling.
According to Chrysler this over-running clutch is a safety benefit, it is there solely to prevent the rear wheels from being unduly influenced by the turning rate of the front wheels during heavy braking situations.
This is Chrysler, remember?
And then they go on to add a "dog-clutch" used to by-pass the over-running clutch when the vehicle is in reverse so the vehicle still has 4WD capability even in reverse.
Again, Chrysler ??? !!!
The RX300 has neither of these features. So my conclusion would be that, one, Lexus doesn't give a damn about the safe operation of the vehicle in severe braking situations, or, two, the RX300 viscous clutch has such a low "pre-load", latent coupling coefficient, that the front wheel braking "rate" is not coupled to the rear driveline in severe braking circumstances.
I can't accept that Lexus has so little concern for our safety.
So, how do we account for the fact that the rearl wheels will "throw" snow under "hard" acceleration.
Then we must ask ourselves just how much of the engine torque is needed for the rear wheels to "throw" snow when all four wheels have approximately equal but fairly low levels of roadbed traction.
Then that takes us back to the example with all four wheels off the ground. None of the wheels had any resistance to turning and so all four did exactly that until I would apply friction pressure to any one tire.
I guess its sorta like thinking about having the RX on an ice rink, sure, all four wheels will turn, but how much engine torque is being wasted if you floor the accelerator.
What are we missing here? I dunno...
Was the torque level I measured at the rear wheels, 40 ft/lbs, the viscous clutch "breakaway torque level? I have a vague memory that the Ford LSD "breakaway" torque was something around 70 ft/lbs.
Factual points:
The RX300 has three "open" differentials with a viscous clutch coupling to the rear driveline.
Without the viscous clutch in the rear driveline when all four wheels have good traction but disparate turning rates front to rear, as would happen in a tight turn, you would experience severe driveline wind-up, tire scrubbing, and knuckle busting "feedback to the steering wheel. If you have ever driven a Jeep in part-time 4WD on dry pavement you will know what I mean.
So, the first, or primary purpose of the viscous clutch is to provide some reasonable level of "slippage" between the front driveline and the rear driveline in circumstances such as these. Otherwise the driveline would soon suffer significant mechanical damage, just as is warned in the Jeep owners manual in the aforementioned circumstance.
But now we have a trade-off, or compromise situation on our hands, to much "pre-load", latent coupling, in the viscous clutch and we might damage the driveline over time. Also, with "too much" pre-load, the feedback to the steering wheel would be too noticeable and discomforting to this "class" of owner/driver.
Even in full-time 4WD (viscous clutch in the loop) the Jeep's steering wheel would still provide substantial driveline windup feedback in a tight accelerating turn.
Now the guessing part, my guessing.
Part of my assumptions here are based on the fact that the Chrysler T&C AWD has an over-running clutch and a dog-clutch combination in their AWD setup. The purpose of the over-running clutch is to allow the T&C's viscous clutch to be by-passed in severe braking situations, otherwise the harder braking slower turning front wheels would "dictate" the turning rate of the rear wheels via the "tight" viscous clutch coupling.
According to Chrysler this over-running clutch is a safety benefit, it is there solely to prevent the rear wheels from being unduly influenced by the turning rate of the front wheels during heavy braking situations.
This is Chrysler, remember?
And then they go on to add a "dog-clutch" used to by-pass the over-running clutch when the vehicle is in reverse so the vehicle still has 4WD capability even in reverse.
Again, Chrysler ??? !!!
The RX300 has neither of these features. So my conclusion would be that, one, Lexus doesn't give a damn about the safe operation of the vehicle in severe braking situations, or, two, the RX300 viscous clutch has such a low "pre-load", latent coupling coefficient, that the front wheel braking "rate" is not coupled to the rear driveline in severe braking circumstances.
I can't accept that Lexus has so little concern for our safety.
So, how do we account for the fact that the rearl wheels will "throw" snow under "hard" acceleration.
Then we must ask ourselves just how much of the engine torque is needed for the rear wheels to "throw" snow when all four wheels have approximately equal but fairly low levels of roadbed traction.
Then that takes us back to the example with all four wheels off the ground. None of the wheels had any resistance to turning and so all four did exactly that until I would apply friction pressure to any one tire.
I guess its sorta like thinking about having the RX on an ice rink, sure, all four wheels will turn, but how much engine torque is being wasted if you floor the accelerator.
What are we missing here? I dunno...
Was the torque level I measured at the rear wheels, 40 ft/lbs, the viscous clutch "breakaway torque level? I have a vague memory that the Ford LSD "breakaway" torque was something around 70 ft/lbs.
Last edited by willard west; 12-06-01 at 11:07 AM.
12-06-01, 01:51 PM
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dialog
The best dialog/dissertation on this subject I have found on the internet is at:
http://www.difflock.com/offroad/4x4explained.shtml
Don't let the title fool you, it does apply.
But for a quick read or anyone with a short attention span:
http://www.difflock.com/offroad/difflocks.shtml
Start at the tenth paragraph down:
"The VC's rotational sensing characteristic..."
"The easiest hack...."
THE EASIEST HACK? HACK? LEXUS?
http://www.difflock.com/offroad/4x4explained.shtml
Don't let the title fool you, it does apply.
But for a quick read or anyone with a short attention span:
http://www.difflock.com/offroad/difflocks.shtml
Start at the tenth paragraph down:
"The VC's rotational sensing characteristic..."
"The easiest hack...."
THE EASIEST HACK? HACK? LEXUS?
Last edited by willard west; 12-06-01 at 04:58 PM.
12-08-01, 09:15 PM
#6
You're just plain wrong *****. I've been offline for a while researching and corresponding with folks regarding the 4WD setup on the RX. Expect a lenghty explanation soon regarding how the 4WD setup REALLY works.
The question is will you be man enough to admit you're wrong? I doubt it, because you've made yourself out to be blowhard with your redundant postings. Oh well, should be fun soon...
P.S. Never had a fogging problem with my RX. I suspect you have "other" issues.
The question is will you be man enough to admit you're wrong? I doubt it, because you've made yourself out to be blowhard with your redundant postings. Oh well, should be fun soon...
P.S. Never had a fogging problem with my RX. I suspect you have "other" issues.
12-09-01, 10:32 AM
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TC
"Never had a fogging problem with my RX."
It begins to sound to me that if you owned a Ford Explorer and never experienced its "rollover" problem you would be saying it doesn't exist.
Just because you haven't experienced a problem or circumstance doesn't mean that it doesn't exist. Look around you, just within this forum!
It begins to sound to me that if you owned a Ford Explorer and never experienced its "rollover" problem you would be saying it doesn't exist.
Just because you haven't experienced a problem or circumstance doesn't mean that it doesn't exist. Look around you, just within this forum!
Trending Topics
12-09-01, 12:38 PM
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communications
TC:
It occurs to me that maybe we are talking at cross purposes.
I just went out and checked and with my RX300 AWD in gear at idle with all four wheels "blocked" I used a torque wrench to measure the energy it takes to move each wheel, in turn, against the engine torque. The measurement was about 140 ft/lbs all around.
For the rear wheels this seemed to hold true up to about 2000 RPM, a point which I was reluctant to test beyond. At anything above idle I wasn't able to bring either of the front wheels to a stop in order to make the measurement.
Now, this could have been the "stall" point of the torque converter, or the "shearing" of the viscous clutch, I can't be certain of which. But it does seem to me that the "stalling" point of the torque converter would have increased with engine RPM, and my measurements did not.
So, Lexus is technically correct, approximately EQUAL engine torque is delivered to all four wheels AS LONG AS ALL FOUR WHEELS HAVE GOOD TRACTION WITH THE ROADBED.
But in the case cited above I was able to use the palm of my hand against the side of the spinning tire in order to stop it for the torque measurement.
What this means to you and me is that if any one wheel, or wheels lose roadbed traction then ALL OF THE AVAILABLE ENGINE TORQUE WILL GO TO THE WHEEL(S) WITH LEAST TRACTION.
It occurs to me that maybe we are talking at cross purposes.
I just went out and checked and with my RX300 AWD in gear at idle with all four wheels "blocked" I used a torque wrench to measure the energy it takes to move each wheel, in turn, against the engine torque. The measurement was about 140 ft/lbs all around.
For the rear wheels this seemed to hold true up to about 2000 RPM, a point which I was reluctant to test beyond. At anything above idle I wasn't able to bring either of the front wheels to a stop in order to make the measurement.
Now, this could have been the "stall" point of the torque converter, or the "shearing" of the viscous clutch, I can't be certain of which. But it does seem to me that the "stalling" point of the torque converter would have increased with engine RPM, and my measurements did not.
So, Lexus is technically correct, approximately EQUAL engine torque is delivered to all four wheels AS LONG AS ALL FOUR WHEELS HAVE GOOD TRACTION WITH THE ROADBED.
But in the case cited above I was able to use the palm of my hand against the side of the spinning tire in order to stop it for the torque measurement.
What this means to you and me is that if any one wheel, or wheels lose roadbed traction then ALL OF THE AVAILABLE ENGINE TORQUE WILL GO TO THE WHEEL(S) WITH LEAST TRACTION.
Last edited by wwest; 12-09-01 at 12:58 PM.
12-09-01, 02:28 PM
#9
Re: communications
Originally posted by wwest
What this means to you and me is that if any one wheel, or wheels lose roadbed traction then ALL OF THE AVAILABLE ENGINE TORQUE WILL GO TO THE WHEEL(S) WITH LEAST TRACTION.
What this means to you and me is that if any one wheel, or wheels lose roadbed traction then ALL OF THE AVAILABLE ENGINE TORQUE WILL GO TO THE WHEEL(S) WITH LEAST TRACTION.
Let's see if you can figure the rest out before I/you make a complete fool of yourself. Your day is coming...
12-10-01, 11:16 AM
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LSD
The ML series, unlike the RX, has a CONSTANT 50/50 front/rear torque split. The RX, once you reach the shear point of the VC, doesn't route any greater torque to the rear wheels.
I studied the differential and transfer case gearing and setup for hours last evening and I cannot see how the RX "favors" driving the front wheels over the rear the way I am absolutely sure it does.
With the rear wheels elevated and spinning freely the front wheels were most definitely still trying to climb over the chocks, and no brake modulation was noted or heard, nor was there any indication of such. In the opposite configuration it was quite clear to me that virtually no torque was being delivered to the rear wheels.
TRAC. It is my personal belief that this feature is used left to right or right to left but never front to rear. I have even grown suspicious about the use of Trac on the front differential as a substitute for LSD.
As anyone ever heard of an LSD in the front differentail?
It seems to me that using the front brakes in this manner might result in a potentially hazardous driving situation. Having Trac de-throttle the engine if the front wheel(s) begin to slip I can understand, but appling only one of the front brakes?
Is THIS a possible explanation?
With an open differential and both rear wheels spinning freely if I use my hand to stop one rear wheel the other wheel will spin twice as fast (or more?).
The same should be true of the center differential. If the VC has reached its shear point and the rear wheels ar "stalled", not rotating, the rear drive input shaft to the VC is still experiencing some level (the VC shear level) of traction, will that level of traction be multiplied by the center differential and "sent" to the front wheels?
I studied the differential and transfer case gearing and setup for hours last evening and I cannot see how the RX "favors" driving the front wheels over the rear the way I am absolutely sure it does.
With the rear wheels elevated and spinning freely the front wheels were most definitely still trying to climb over the chocks, and no brake modulation was noted or heard, nor was there any indication of such. In the opposite configuration it was quite clear to me that virtually no torque was being delivered to the rear wheels.
TRAC. It is my personal belief that this feature is used left to right or right to left but never front to rear. I have even grown suspicious about the use of Trac on the front differential as a substitute for LSD.
As anyone ever heard of an LSD in the front differentail?
It seems to me that using the front brakes in this manner might result in a potentially hazardous driving situation. Having Trac de-throttle the engine if the front wheel(s) begin to slip I can understand, but appling only one of the front brakes?
Is THIS a possible explanation?
With an open differential and both rear wheels spinning freely if I use my hand to stop one rear wheel the other wheel will spin twice as fast (or more?).
The same should be true of the center differential. If the VC has reached its shear point and the rear wheels ar "stalled", not rotating, the rear drive input shaft to the VC is still experiencing some level (the VC shear level) of traction, will that level of traction be multiplied by the center differential and "sent" to the front wheels?
12-12-01, 01:23 PM
#11
Good news Gene, things will change 
Just came back from a meeting with the shop foreman at my Lexus dealer. We had a 45 minute discussion of how the RX300 4WD actually works. We poured through dozens of manuals on his shelf in the office.
I'll combine that with my other research to write a long FAQ of how the 4WD really works, rather than what ***** wants everyone to believe.
I would never devote this much time to a project that I really don't have time for, but when somebody is so bombastic and full of themselves, they deserve to eat some crow.
And hopefully he'll buy that ML320 and go annoy folks on the MB forums. Better yet, why doesn't ClubLexus just give him his money back and kick him out.
Just came back from a meeting with the shop foreman at my Lexus dealer. We had a 45 minute discussion of how the RX300 4WD actually works. We poured through dozens of manuals on his shelf in the office.
I'll combine that with my other research to write a long FAQ of how the 4WD really works, rather than what ***** wants everyone to believe.
I would never devote this much time to a project that I really don't have time for, but when somebody is so bombastic and full of themselves, they deserve to eat some crow.
And hopefully he'll buy that ML320 and go annoy folks on the MB forums. Better yet, why doesn't ClubLexus just give him his money back and kick him out.
12-12-01, 02:56 PM
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eating crow
I'll gladly eat all the crow you can dish out if you can give me good sound (well-founded) reasons to keep my RX300 rather than trade it for an ML320.
All of the testing I have done indicates that when the chips are down, ice and snow, low roadbed traction conditions, the RX300 has a definite front wheel drive torque bias and I haven't been able as yet to get the TRAC system to intervene, at least not in any way that I could see.
All of the testing I have done indicates that when the chips are down, ice and snow, low roadbed traction conditions, the RX300 has a definite front wheel drive torque bias and I haven't been able as yet to get the TRAC system to intervene, at least not in any way that I could see.
12-12-01, 06:30 PM
#13
Don't keep the RX, please, please get the ML320. You obviously have buyer's remorse and you are trying to rationalize that remorse in your mind. Do yourself and all of us a favor, you'll feel better. Hopefully.
12-12-01, 06:31 PM
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Willard:
Take a ride this weekend to SLC. We're expecting 6"-10" here at my home on the bench. Got the VSC to kick in this morning with about 2" of new powder on the street in front of my home. It kicked a a tail out condition almost immediately...just like my Z06 active handling. So far, I'm quite pleased by the way this vehicle is handling snow. The braking has been exceptional. By the way, it appears that my AC compressor is still operating at 25 degrees as it was this AM on the way to work...at least the AC light stayed lit.
Take a ride this weekend to SLC. We're expecting 6"-10" here at my home on the bench. Got the VSC to kick in this morning with about 2" of new powder on the street in front of my home. It kicked a a tail out condition almost immediately...just like my Z06 active handling. So far, I'm quite pleased by the way this vehicle is handling snow. The braking has been exceptional. By the way, it appears that my AC compressor is still operating at 25 degrees as it was this AM on the way to work...at least the AC light stayed lit.
12-12-01, 08:11 PM
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VSC
I've had the VSC kick in twice that I'm relatively sure of, first time the VSC "sound" made me think I had hit something in the road so I went back to look.
I'm used to the sound and feel of ABS now here I am with another "sound" I have to get used to.
ALL automotive A/C systems are designed to NEVER chill the evaporator surfaces below freezing so I would guess that the light was on but the compressor wasn't. Unless the system automatically put itsself in recirculate.
On my 92 LS the indicator goes out below 35F OAT but you can turn it back on but the compressor still doesn't run. Doesn't make a lot of sense.
I'm used to the sound and feel of ABS now here I am with another "sound" I have to get used to.
ALL automotive A/C systems are designed to NEVER chill the evaporator surfaces below freezing so I would guess that the light was on but the compressor wasn't. Unless the system automatically put itsself in recirculate.
On my 92 LS the indicator goes out below 35F OAT but you can turn it back on but the compressor still doesn't run. Doesn't make a lot of sense.