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Old 11-14-2000, 06:49 PM   #1
Damon
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Question question on changing how car splits the power to wheels..

i know that the RS splits the power 90/10 (front/rear) and the wrxs split it 50/50. now i know how cornering transfers power to the approprate (sp?) wheels. is it possible to change the setup on the RS so that is splits it like the wrx? it seems to me that all it would involve is something in the computer, or maybe the actual center dif. (sp again?)?

lemme know guys thanks.
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Old 11-14-2000, 06:52 PM   #2
Eric SS
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Only the Automatic RS splits power 90/10 because of the electronic AWD. The Manual RS splits 50/50 using a Viscous Coupling.

Basicly the Viscous coupling uses a a liquid that turns a lot thicker when heated and transfers power to other wheels.

I'm sure someone else can explain it better.

Eric
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Old 11-14-2000, 06:58 PM   #3
Nanase
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knows how a clutch set up works? Basically the same, but instead of using pressure plate, it uses think fluids. (gear oil)
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Old 11-14-2000, 07:01 PM   #4
Eric SS
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It doesn't use gear oil. It uses some type of special fluid that instantly turns very viscous when heat is applied.

Eric
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Old 11-15-2000, 09:39 AM   #5
Dobes
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I can't recall what the fluid is, but it is NOT gear oil. Basically, there are two sets of teeth in a viscous coupling unit. One set on the input shaft and one on the output shaft. When one shaft is spinning at a different rate of speed than the other shaft, the teeth are rotating at different rates. This difference causes heat generation. Once the fluid in the coupling is subjected to a rise in heat, it solidifies, effectively locking the input and output shafts together. The fluid solidifies in less than one second if I remember correctly, so the locking force is almost immediate. I have an excellent article on four wheel drive systems in an old Performance Car magazine that I can scan and post if anyone is interested.

Torsen limited slips (most popularly found in Audis) work using a gearset to keep power flowing from input to output. I couldn't even begin to explain the operation of these, although from what everyone says they are superior to viscous systems, albeit more expensive. Torsen systems are more efficient and react instantaneous making power distribution more accurate.

BTW, The old WRX splits power 35F/65R - not sure about the new one.

JD

PS Feel free to correct me if I'm wrong. I haven't read up on this subject in a while.
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Old 11-15-2000, 10:04 AM   #6
ShaneW
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Saying that the 4EAT is 90/10 is almost unfair also. It is transfering torque all the time. So if you floor it, the 4EAT will not keep the 90/10. Only when crusing will it be 90/10.

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Old 11-15-2000, 10:34 AM   #7
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from what i've read, the EAT tranny will only give more than 10% to the rears only when the fronts are slipping, and not necessarily during acceleration
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Old 11-15-2000, 11:09 AM   #8
Damon
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[quote]from what i've read, the EAT tranny will only give more than 10% to the rears only when the fronts are slipping, and not necessarily during acceleration
[/qoute]
see, thats what ive read as well. thats why i brought the subject up. im not gonna say for sure im right and anyone is wrong here, so dont get me wrong any of u. i just remember reading in a issue of SCC i believe how the different split of power (the 90/10) when crusing could affect your cornering. that makes sense to me, seeing if your car was at 50/50 crusing v. 90/10. but once again, im no pro at soobies.. i come from a honda background so im not up to speed on all of this really.

new question.. does the RS come w/ LSD (not drug) in front and rear? if so, why the heck would you wanna go buy a new LSD from COBB tuning for right at 2 grand???
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Old 11-15-2000, 11:14 AM   #9
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see, the manual tranny RS is 50/50. the EAT tranny is 90/10. the only way to mess with it, is in the EAT, you can take out a fuse, and make it FWD. as for the LSD, i know the rear and center are LSD...but i don't know about the front, though. I think the reason for Cobb having their own is probably because it functions differently (ie, more performance oriented).
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Old 11-15-2000, 11:24 AM   #10
ColinL
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JD, they aren't teeth. They are clutches... plates moving over another, with little friction. Increase the viscosity and friction goes way up, clutch slippage goes down and the shafts are locked together. Other than that you've got it right.
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Old 11-15-2000, 11:27 AM   #11
oem
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this post was brought up back when this club started, i think that the (5spd) RS was about 65% front bias not 50% as hoped, as well they could not find out a way to change those figures.
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Old 11-15-2000, 04:57 PM   #12
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Ok, if the 4EAT is controlled by a computer, then shouldn't there be a not too difficult way to control it. I have no idea how it would be done, but can't you some how tap into it and control the distribution like the 22B's adjustable differential? Anyone have any clues on how or if this could be done.
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Old 11-15-2000, 06:04 PM   #13
CRZ_MSL
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Yes. Easy part was tapping in. Hard part was figuring out when/how to do what the computer would normally do by itself.
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Old 11-15-2000, 06:37 PM   #14
Damon
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Talking

sounds like a job for, DUN DUN DUN DUUUN!, Impreza Boy!

seroiusly, any of the guys out there in R&D this would be a GREAT project to look into, and im sure any and all of us would buy this product if you produced it.
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Old 11-15-2000, 09:15 PM   #15
AKGC8
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Well from what you guys have described, an automatic transmition works in the same sort of way, and AT fluid does just that(solidifies when heated). So I don't know what would be different between ATF and differential fluid.
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Old 11-16-2000, 12:06 AM   #16
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I don't have any technical information to add to this, but the fluid you all speak of is ATF automatic transmition fluid.
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Old 11-16-2000, 12:09 AM   #17
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no it's not. much different in the viscous differential
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Old 11-16-2000, 12:29 AM   #18
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Here's some good info on viscous couplings: http://www.howstuffworks.com/differential7.htm
and here: http://www.eskimo.com/~eliot/awd.html
According to an email I received from Subaru in '98, the defaults are 50/50 (5-speed) and
90/10 (auto). The 5-speed can vary anywhere from 90/10-10/90 and the auto maxes at 50/50.
Some Japanese models have adjustable center diff. (STi?)
Dennis


[This message has been edited by bluesubie (edited November 15, 2000).]
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Old 11-16-2000, 06:56 AM   #19
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According to the link I posted above, it's a silicone fluid. Is a ATF or gear oil silicone? This is in the center diff (VC), not the where the ATF or gear oil goes in the front or rear.
..."First on the scene was the viscous coupling (VC for short) which used a silicone liquid in a casing designed so that minor speed differences were allowed between the two axles but increased slip would lead to a rapid increase in the viscosity of the fluid which would then lock up the coupling."
and more info:
."In yet another twist, Subaru has for many years been quietly offering radically different AWD systems in the same car, depending on the transmission choice. The manual transmission Legacies and Imprezas use a full time system that is split 50-50 with viscous couplings for limiting slip. In the automatic transmission versions, however, the system is a part time, computer controlled, automatically engaging system in some models and a full time uneven torque split with computer controlled locking in other models."
And check this out:
"Subaru deserves mention here because in the automatic version of the Legacy and Impreza (including the Outback variants), it uses a computer controlled system much like those found in the Mercedes 4Matic, automatic Audi A8/V8 and the earlier Porsches. Subaru has been offering this sophisticated system for a long time in a relatively inexpensive car."
Dennis

[This message has been edited by bluesubie (edited November 16, 2000).]

[This message has been edited by bluesubie (edited November 16, 2000).]
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Old 11-16-2000, 08:12 AM   #20
Eric SS
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The 98-99 RS didn't have a LSD in the rear. MY00-01 do have one. That's why Trey sells them.

Eric
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Old 11-16-2000, 09:31 AM   #21
Ken S
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Talking

Actually, the 4EAT varies it's torque split under non-slip conditions based on what gear it's in. In 1st, 2nd and Reverse, it's split 50/50. In 3rd and 4th, it defaults to 90/10. When wheel spin is detected, it will transfer torque between the two settings regardless of which gear you are in.

BTW, if you have 4EAT and are driving in very slow and slick road conditions, keep it in 2nd. The tranny will not only start in 2nd but it will try and keep torque at 50/50.

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Old 11-17-2000, 12:14 AM   #22
cakagan
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Question

I contacted my dealership for prices on changing the diff fluids and tranny fluid on my manual '98 RS (too damn cold to do it myself!). According to the service guy I made the appointment with, they do the front diff and tranny together since it has the same fluid, and the rear diff seperately because it has a different type of fluid.

No mention about the center diff. Can someone clear that up? I'm foncused...

Thanks,
-Chris
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Old 11-17-2000, 12:20 AM   #23
bluesubie
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Chris,
The viscous coupling fluid isn't changed. It's zero maintenance.
Dennis
From subaru.com
In vehicles with the 5-speed manual transmission, the All-Wheel Drive uses a viscous coupling in a center differential inside the transaxle case. It contains a series of opposing discs attached to the front and rear output shafts, surrounded by a type of silicone fluid. In normal operation, power is distributed equally between the front and rear wheels (50/50 power split). Slippage at the front or rear wheels causes a rotational difference between the front and rear discs in the viscous unit, which then shears the fluid.

The shearing action heats the fluid, causing it to thicken. As the fluid thickens, power transfers from the slipping wheels to the wheels with the best traction. When the slippage ceases, all the discs turn at the same speed, restoring the 50/50 power split. The process is quick and unnoticeable to the driver and passengers.



[This message has been edited by bluesubie (edited November 16, 2000).]
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