The ST165/ST185/ST205 4WD systems are really FWD? Weigh in!

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The ST165/ST185/ST205 4WD systems are really FWD? Weigh in!

Postby Redrkt01 » Tue Sep 25, 2012 6:13 pm

So I'm having a discussion with a guy about the original ST165 4WD systems regarding how they function. We covered the original E50F1 system (driver controlled pneumatic center diff lock) that was released on the original JDM GT-Four and the E50F2 system (viscous coupling center diff lock) that was released to the rest of the world in 1988-1989.

Long story short he claims that both the original system and the worldwide system are basically FWD until wheel slip occurs. I don't think he's right. I think both systems are full-time 4WD with power distribution being 50/50 front and back. I think the only time that distribution changes is during wheelslip, but at a minimum it is always 50/50 front and back.

Here is some reference material:
Original Toyota Canada training video for the introduction of the Celica and Camry "Full Time 4WD Manual Transaxle". Shows exactly how both the mechanical and viscous controlled center differentials work.

Part 1:
http://smg.photobucket.com/albums/v287/YerRand0/?action=view&current=diff1.mp4

Part 2:
http://smg.photobucket.com/albums/v287/YerRand0/?action=view&current=Diff2.mp4

Part 3:
http://smg.photobucket.com/albums/v287/YerRand0/?action=view&current=diff3.mp4

I think we should have a healthy discussion here. Please don't post unless you have FACTS that you can BACK UP or have REFERENCE MATERIAL. I'm trying to make sure this thread doesn't get clouded with BS.

Talk among yourselves.....
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Re: The ST165/ST185/ST205 4WD systems are really FWD? Weigh

Postby Rpz123isme » Tue Sep 25, 2012 7:20 pm

Put front end on stands and leave the back on the ground. Get in and fire it up and put it in gear and let go of the clutch at 6k with your buddy in front of the car. And if he is right then no harm done. If he is high as a kite then he will learn a lesson......lol :D
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Re: The ST165/ST185/ST205 4WD systems are really FWD? Weigh

Postby Redrkt01 » Tue Sep 25, 2012 7:30 pm

Rpz123isme wrote:Put front end on stands and leave the back on the ground. Get in and fire it up and put it in gear and let go of the clutch at 6k with your buddy in front of the car. And if he is right then no harm done. If he is high as a kite then he will learn a lesson......lol :D


I'm looking for serious contributions here. I get your point, but that wouldn't prove anything anyway. In the event that the car is really only FWD until wheel slip you'd be demonstrating that with your example. You would be simulating front wheel slip and then the viswcous coupling would transfer power to the rear. So in both potential designs (FWD and 4WD) my buddy would get run over, proving nothing.
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Re: The ST165/ST185/ST205 4WD systems are really FWD? Weigh

Postby CMS-GT4 » Tue Sep 25, 2012 8:01 pm

I am in the hospital now posting from my phone but there is a thread here on this very subject. Short answer: system is a 50/50 split full time with a viscous coupler locker. The center LSD's goal is to maintain this 50/50 split. If you can find the thread there should be links to the bgb description of the transfer operation as well as links to explain the locker type of the viscous coupler.
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Re: The ST165/ST185/ST205 4WD systems are really FWD? Weigh

Postby Redrkt01 » Tue Sep 25, 2012 8:27 pm

Thanks Josh, I'll look. Get well and post more when you can.
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Re: The ST165/ST185/ST205 4WD systems are really FWD? Weigh

Postby Killtodie » Tue Sep 25, 2012 8:46 pm

Any transverse front mounted engine in a 4wd system will always have front wheel bias.

some good videos
http://www.youtube.com/watch?v=2OzK-oRPCbs
http://www.youtube.com/watch?v=nKnxM9Ymw-c
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Re: The ST165/ST185/ST205 4WD systems are really FWD? Weigh

Postby Redrkt01 » Tue Sep 25, 2012 9:00 pm

Killtodie wrote:Any transverse front mounted engine in a 4wd system will always have front wheel bias.

some good videos
http://www.youtube.com/watch?v=2OzK-oRPCbs
http://www.youtube.com/watch?v=nKnxM9Ymw-c


The Highlander in the video is probably using the same system we're used to, but I'm wondering if the decreased weight of the Celica would improve upon the slip scenarios Suburu was demonstrating.

Bias is one thing; FWD is another.

I understand what happens under slip conditions. What I want to know is what the power distribution ratio is during normal non-slip driving conditions. Willpower distribution be 100% in front and 0% in the rear while on dry pavement driving stright-line with all wheels moving at the same speed?
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Re: The ST165/ST185/ST205 4WD systems are really FWD? Weigh

Postby klue » Tue Sep 25, 2012 10:15 pm

the celica is FWD system until slip activated the VC, then power is sent to the rear.
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Re: The ST165/ST185/ST205 4WD systems are really FWD? Weigh

Postby CMS-GT4 » Tue Sep 25, 2012 11:29 pm

Redrkt01 wrote:Thanks Josh, I'll look. Get well and post more when you can.

Thanks, Not sick. Just had a baby this morn.

Killtodie wrote:Any transverse front mounted engine in a 4wd system will always have front wheel bias.

some good videos
http://www.youtube.com/watch?v=2OzK-oRPCbs
http://www.youtube.com/watch?v=nKnxM9Ymw-c


Not true. If a system has an electronically controlled center diff or a custom output center diff then that can be rear bias. The TTA active center diff for the gtfour can have a rear bias. The there is an aftermarket center VC diff for the 3000gt that gives it a 40/60 split. Transverse has nothing to do with the wheel bias.
The alltrac is 50/50 split. It has a center open diff with vc locker. Its bias changes like any open diff. The end that spins the fastest will get the most bias. What fights this is the center vc locker. It attempts to maintain the 50/50 split. The reason it suffers from any bias is the slower reaction time of the viscous design.

klue wrote:the celica is FWD system until slip activated the VC, then power is sent to the rear.

No. It is full time awd 50/50 split. Power is only transfered overly front or rear due to delay in the VCL system, but is corrected when locked.

Here you can compared VC to VC lock.
http://www.autozine.org/technical_schoo ... _4wd_2.htm

BGB explination of dif. Mentions 50/50 split.
http://bgbonline.celicatech.com/90alltrac/MT/MT-2.jpg

Bottom of article explains when power is sent to wheels at all times then a VCL is used.
http://www.awdwiki.com/en/viscous+coupling/

If you think about how an open diff works, then think of how a VCL would attempt to keep it from doing what open diffs do.
http://auto.howstuffworks.com/differential2.htm

EDIT: Just look at this official toyota 4wd video thread. It even explains it.
viewtopic.php?f=43&t=44912

The first video explains things pretty much how I said.
http://smg.photobucket.com/albums/v287/ ... =diff1.mp4
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Re: The ST165/ST185/ST205 4WD systems are really FWD? Weigh

Postby athousandleaves » Tue Sep 25, 2012 11:55 pm

^^Josh pretty much summed it up and beat me to posting... but here's how I understand it.

The way people are using term 'slip' here isn't quite right and your friend may be confusing the differences of AWD vs 4WD.

The manually locking 4WD system in the early 165's was like a 4X4 offroad lock where if one set of wheels was moving faster than the others then you would end up with drivetrain binding and either a toasted front or rear diff. The viscous coupler was the solution to this problem of being able to have full time 4WD without having to worry about drivetrain binding.

My understanding is that with the case of the transmissions equipped with the viscous coupler center differential is that the viscous unit senses the bias between front and rear wheel speed and seeks to minimize it at all times.

One of the main differences in the 4WD system in the alltrac family vs others is where the power is sent first from the transmission.
When the car is accelerating at from a standstill the power is sent from the transmission into the center differential first and then split based on the conditions sensed in the center diff up to 50% torque to the front and 50% torque to the rear. The front and rear wheels will see equal power until the car is at cruising speed because the viscous unit will have to exert equal force on either set of wheels to put the car in motion.
Once the car is rolling at speed the rear wheels are techincally being dragged by the fronts and the fronts are being pushed by the rears so you could say that the viscous center is locked. When one of the sets of wheels slips while crusing the other set will be unaffected and still continue to receive power.

The change in the viscous unit from being "unlocked" to "locked" occurs very rapidly unlike the viscous system in other AWD cars see: http://www.youtube.com/watch?v=FSZVoBHv-vM&t=00m25s because they apply power to their front differential first it takes time for the viscous unit to actually lock up and work.

Another complication is with the automatic alltrac's, like my camry.
They received computer controlled clutch type center diffs that monitored the bias between the front and rear wheels.


PS. Congrats on the baby Josh!
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Re: The ST165/ST185/ST205 4WD systems are really FWD? Weigh

Postby Redrkt01 » Wed Sep 26, 2012 2:09 am

Josh, congrats on the new addition! I have only one concern about all that you posted above. At the end of your post you reference the first video and how it pretty much restates what you said. In the first video the narrator is talking about the mechanical/pneumatic system that is used on the 1986-87 JDM ST165 E50F1 (and the later Camry systems). Being that we're using a VC system, how does video #1 back you up? Did you mean to reference one of the other videos?

Andrew thanks for following up on Josh's post. So let me clarify: Upon acceleration from a full stop the power distribution is 50/50. Then once the car reaches cruise the front drag the rears and the rears push the front; The center diff is effectively locked. To me this sounds like cruise speed is still a 50/50 power distribution. Am I wrong?
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Re: The ST165/ST185/ST205 4WD systems are really FWD? Weigh

Postby phattyduck » Wed Sep 26, 2012 5:08 pm

Killtodie wrote:Any transverse front mounted engine in a 4wd system will always have front wheel bias.

some good videos
http://www.youtube.com/watch?v=2OzK-oRPCbs
http://www.youtube.com/watch?v=nKnxM9Ymw-c
As others have said, this is not true.

These videos show cars (the non-Subarus) with all open differentials (or a very weak clutch action in the case at least the Honda). Traction is then moved around via individual wheel braking and throttle reduction. This is a very inefficient way of doing it and thus the lack of motive power up the ramps.

The Subarus shown a torque biasing center diff with locking capabilities. This reduces the need for individual wheel braking and engine power reduction, allowing them to get up the ramp. Funny enough, a manual transmission version of those Subarus would probably fail those tests, other than an STi (with the clutch-type rear diff) because they lack the active center diff.

An Alltrac would pass the first set of tests (ramp, front or rear without power), but not the second set (only one wheel with power) because of the lack of locking F/R diffs and/or traction control.

Take out the viscous coupler for the center diff, and the Alltrac would be just as much 4WD as a normal car is 2WD - each wheel will be able to put down as much power as the wheel with the least traction (thus a 50/50 split). Add the viscous coupler and power can be transferred from front to rear or rear to front depending on slip.

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Re: The ST165/ST185/ST205 4WD systems are really FWD? Weigh

Postby athousandleaves » Wed Sep 26, 2012 6:19 pm

phattyduck wrote:An Alltrac would pass the first set of tests (ramp, front or rear without power), but not the second set (only one wheel with power) because of the lack of locking F/R diffs and/or traction control.

For arguments sake would an Alltrac with front and rear torsens not be capable of climbing with one wheel grip?
I feel that it would be able to as 50% of the power will be lost on the slipping front or rear axle while the other axle with one wheel having grip will receive up to 75% of the 50% of power into that one wheel depending on the bias for the torsen (approximately 37.5% of total engine power).
I guess it would depend on the amount of power you need to actually move the vehicle up the ramp so power to weight is more of a concern once grip is available.


Also the viscous unit does not detect slip! It's a purely mechanical device that minimizes the differential of angular velocity/rotational speed on either side so that both sides are rotating at the same speed at all times. Read the BGB page: http://bgbonline.celicatech.com/90alltrac/MT/MT-2.jpg It isn't a true LSD however it does function as one in that some difference in output shaft speed is allowed.
Last edited by athousandleaves on Wed Sep 26, 2012 6:41 pm, edited 1 time in total.
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Re: The ST165/ST185/ST205 4WD systems are really FWD? Weigh

Postby Redrkt01 » Wed Sep 26, 2012 6:37 pm

This is all good stuff. Keep it going.....
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Re: The ST165/ST185/ST205 4WD systems are really FWD? Weigh

Postby klue » Wed Sep 26, 2012 9:08 pm

Its all great in theory, and yes I agree you guys are technically right, and eloquently put at that .
But Maybe this VC works on some sort of duty cycle, or frequency hard to explain but for instance:

launching my car under boost, spins the front passenger wheel consistently even though the car is accelerating. You can hear it squeel, but still peel :)

anyone else have a similar real time situation?
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