fwd based awd?

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fwd based awd?

Postby FLASHBACK » Tue Dec 14, 2010 6:42 am

i was wondering, is the celica's alltrac system fwd based awd?

because i remember reading up on it before, and if i remember right, the celica is fwd until the computer thinks that it's slipping (just the front?), then it turns on the center diff and becomes awd

also, is the awd system just front back split, or does it differ the power depending on the individual wheel, like if youre back passenger wheel starts slipping more, will it send more power there?

i would assume so, but im not too sure
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Re: fwd based awd?

Postby aus jd 2703 » Tue Dec 14, 2010 11:02 am

Computer?? What computer? Transmission is a permanent 50:50 drive split with a viscous coupling centre diff. Front diff open rear canbe torsen.
No electronics all mechanical
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Re: fwd based awd?

Postby klue » Tue Dec 14, 2010 4:31 pm

the celica is FWD until the back slips, all mechanical coupling systems.

In contrast something like the skylines are RWD first then spit to AWD
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Re: fwd based awd?

Postby CMS-GT4 » Tue Dec 14, 2010 5:11 pm

The alltrac awd system is 50/50 split at all times. The center dif is open with a viscous coupler (VC). If there is any change in speed front to rear the VC will lock maintaining the 50/50 split. The VC only locks during speed change, which is why it will burn out if you run different diameter tires on any side of the car. Front dif is open, and rear is optional torsen. Most US models that have participated in being checked appear to not come standard with a rear lsd.
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Re: fwd based awd?

Postby klue » Wed Dec 15, 2010 12:00 am

Yea when I reread my post its the opposite, in my videos i see the front wheel spin first
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Re: fwd based awd?

Postby GTFOURST205guy » Fri Dec 17, 2010 6:25 pm

i don't think any awd system would give more power to the wheel that's slipping. if you were in a fwd car
and you were taking a corner and the wheels started slipping, would you start flooring it to get more traction?
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Re: fwd based awd?

Postby FLASHBACK » Fri Dec 17, 2010 10:03 pm

GTFOURST205guy wrote:i don't think any awd system would give more power to the wheel that's slipping. if you were in a fwd car
and you were taking a corner and the wheels started slipping, would you start flooring it to get more traction?


i know that on the prelude, i think like 3rd or 4th gen, they had a system where even though it was FWD, it had a weird traction bar system that if one wheel starts coming up and spinning, it will do something with the power to help it regain balance

http://www.preludepower.com/forums/show ... p?t=306108

unless im reading it wrong
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Re: fwd based awd?

Postby FLASHBACK » Fri Dec 17, 2010 10:05 pm

CMS-GT4 wrote:The alltrac awd system is 50/50 split at all times. The center dif is open with a viscous coupler (VC). If there is any change in speed front to rear the VC will lock maintaining the 50/50 split. The VC only locks during speed change, which is why it will burn out if you run different diameter tires on any side of the car. Front dif is open, and rear is optional torsen. Most US models that have participated in being checked appear to not come standard with a rear lsd.


its impossible for it to be split 50/50 at all times. even though i hear stuff like oh, celicas have true awd, etc etc

if we had all wheels powered, all the time, we would have almost literally no torque from splitting up so much of the power
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Re: fwd based awd?

Postby klue » Sat Dec 18, 2010 12:43 am

Yes it is a 50/50 split.
Torque is applied in equal amounts to every wheel. If you have 4 wheel drive and every wheel has traction then every wheel is recieving the full toruqe of the engineX gearingX final drive.

So if you have 200 ftlbs engine every wheel is receiving maximum torque, it is not divided or split 100 front 100 rear.
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Re: fwd based awd?

Postby CMS-GT4 » Sat Dec 18, 2010 5:19 am

FLASHBACK wrote:
its impossible for it to be split 50/50 at all times. even though i hear stuff like oh, celicas have true awd, etc etc

if we had all wheels powered, all the time, we would have almost literally no torque from splitting up so much of the power


The front to rear IS split 50/50. A viscous coupler locks the distribution. Left to right has turning variables when turning since they are operating differentials. There is some variation from front to rear, but its mostly due to the delay of the viscous locker. Once the fluid heats up from the different in speeds it locks. So the outside wheel will turn faster than the inside wheel. See below info on viscous couplings. Different types of difs react in different ways, as there are multiple types of viscous difs, but the one used in the alltrac is indeed designed to lock. The front dif is open, and serves its serves its purpose as a regular dif but has proven to produce inside wheel spin on hard driving. Rear is optional torsen, but a clutch type can be fitted as well.

You can read about the alltrac dif and gearbox here.
http://bgbonline.celicatech.com/90alltrac/MT/MT.htm

http://www.awdwiki.com/viscous.html
In this case, all wheels are powered at all times. Viscous coupling is integrated into the center differential. Central differential distributes power to all wheels and lets them turn at different speeds while cornering. When excessive wheelspin occurs on one of the axles, viscous coupling locks the differential and equalizes the speeds of both axles. Torque is transferred to wheels that have traction. This is a full-time all wheel drive system.


You might want to read up more on the concept or look at the lsd faqs.
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Re: fwd based awd?

Postby FLASHBACK » Sat Dec 18, 2010 9:20 am

CMS-GT4 wrote:
FLASHBACK wrote:
its impossible for it to be split 50/50 at all times. even though i hear stuff like oh, celicas have true awd, etc etc

if we had all wheels powered, all the time, we would have almost literally no torque from splitting up so much of the power


The front to rear IS split 50/50. A viscous coupler locks the distribution. Left to right has turning variables when turning since they are operating differentials. There is some variation from front to rear, but its mostly due to the delay of the viscous locker. Once the fluid heats up from the different in speeds it locks. So the outside wheel will turn faster than the inside wheel. See below info on viscous couplings. Different types of difs react in different ways, as there are multiple types of viscous difs, but the one used in the alltrac is indeed designed to lock. The front dif is open, and serves its serves its purpose as a regular dif but has proven to produce inside wheel spin on hard driving. Rear is optional torsen, but a clutch type can be fitted as well.

You can read about the alltrac dif and gearbox here.
http://bgbonline.celicatech.com/90alltrac/MT/MT.htm

http://www.awdwiki.com/viscous.html
In this case, all wheels are powered at all times. Viscous coupling is integrated into the center differential. Central differential distributes power to all wheels and lets them turn at different speeds while cornering. When excessive wheelspin occurs on one of the axles, viscous coupling locks the differential and equalizes the speeds of both axles. Torque is transferred to wheels that have traction. This is a full-time all wheel drive system.


You might want to read up more on the concept or look at the lsd faqs.


interesting. i read up on the FAQ a bit, but i dunno, something about this just confuses me

wait so some people agree its FWD based AWD, but now youre saying its always FULL 50/50? as in its always driving with 4 wheels instead of FWD until the front starts slipping?

and if so, doesnt that mean it just has better traction than normal, but because it cannot variate lets say:

back starts slipping, front gets more power to pull it out (70/30), and then once it normalizes it becomes 50/50 again?
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Re: fwd based awd?

Postby Nitro_Alltrac » Thu Dec 23, 2010 12:09 am

You have to remember that the system in our cars is purely mechanical. There are NO electronics involved like on new AWD cars. The torque split isn't going to change because you have spillage on the rear wheels. I know that some of the new AWD cars, like Subaru, advertise an intelligent system that will send torque to what ever wheel has traction or vary the torque from front to back. The system in our cars doesn't.
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Re: fwd based awd?

Postby MWP » Fri Dec 24, 2010 2:30 am

CMS-GT4 wrote:The front to rear IS split 50/50. A viscous coupler locks the distribution.


Hmm, thats not correct in quite a few ways unfortunately :(
Wish it was.

#1 - The VC will never "lock" distribution of power at 50:50. It just doesnt work that way.

#2 - The front wheels WILL always loose traction first, and once the VC fluid has thickened up, the VC will transfer more power to the rear. The bigger the speed difference, the more power will be transfered until the ideal 50:50 split, but itll very rarely get to a 50:50 split because....

#3 - The VC unit is quite small and has its limits. There is no way itll hold a 50:50 (or close) split at full, or even half engine power on a firm surface. It just cant move that much power. On a snow/dirt surface, itll do a better job at equalizing wheel speeds front to back.
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Re: fwd based awd?

Postby CMS-GT4 » Fri Dec 24, 2010 4:42 am

MWP wrote:
CMS-GT4 wrote:The front to rear IS split 50/50. A viscous coupler locks the distribution.


Hmm, thats not correct in quite a few ways unfortunately :(
Wish it was.

#1 - The VC will never "lock" distribution of power at 50:50. It just doesnt work that way.

#2 - The front wheels WILL always loose traction first, and once the VC fluid has thickened up, the VC will transfer more power to the rear. The bigger the speed difference, the more power will be transfered until the ideal 50:50 split, but itll very rarely get to a 50:50 split because....

#3 - The VC unit is quite small and has its limits. There is no way itll hold a 50:50 (or close) split at full, or even half engine power on a firm surface. It just cant move that much power. On a snow/dirt surface, itll do a better job at equalizing wheel speeds front to back.



What sources do you have to back up your claims? From what I have read is the gtfour has a viscous coupling lock, which works to maintain a minimum of speed difference between the front and rear. It tries to maintain the power split rather than transfer the split like a standard Viscous coupling unit.

When the VC is tied to a differential, then the power is normally split between front and rear axles equally. Without the differential, and only using the VC, power normally goes to only one end of the car and the other end just floats along with the VC absorbing any speed differences


As you see above, the characteristics of one linked to a diff is meant to keep a constant speed being a true full time 4wd compared to the other part time unit. I used to think that our center diff system was meant to transfer power as well, but as I did more and more research into the system trying to find out how to replace it, I found more and more data claiming it was a fixed setup. If you have evidence otherwise please post it up so we can unravel the mystery of the gtfour diff system.

http://bgbonline.celicatech.com/90alltrac/MT/MT-2.jpg
http://www.awdwiki.com/viscous.html
http://www.syncro.org/VCTest.html
http://www.autozine.org/technical_schoo ... _4wd_2.htm
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Re: fwd based awd?

Postby celicat93 » Fri Dec 24, 2010 6:31 am

Real World Demonstration of Viscous Coupling AWD

http://www.youtube.com/watch?v=FSZVoBHv-vM

So why don't I have the problems with torque steer (especially from a standing start) and spinning tires like I do with my FWD GT? Why do I feel a more positive acceleration from the rear? Or is it just in my head? When I had my GT, I would often have my front tires break loose, even when I wasn't trying to get on it (and yes, the tire tread was very good, pressure maintained, etc.), I've never had that problem with an All-Trac, with 65 more HP and lbs of torque.
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