athousandleaves
New member
Luke, as RedCelicaTRD said; when launching your front right tire is experiencing a lack of traction and due to your front differential being open you are sending most of the 50% of the front axles torque to that wheel. The rear wheels are still receiving 50% of engine torque and you will continue to move forward because of this. With regard to esracing's launch he was able to break traction on all four wheels with half engine torque to the front and half to the rear. Even though all four wheels were slipping they were all gripping an equal amount and all received identical power.
I took my car to my friends shop tonight and we tried a few tests to see how the 4WD system reacted. Ideally we would have reproduced the test used in the ramp video but we didn't have such a nice ramp available to play with and opted instead to try and duplicate this test: http://www.youtube.com/watch?v=9B0ANOI3GcM using these positioning jacks and another test up on the lift.
Before commencing these tests my car sat outside in ~6°C weather for over 3 hours so everything was completely cold. Also to my knowledge my car is equipped with all stock differentials, open front, viscous center, open rear.
Firstly when the car was put on the lift and then put in first gear with all wheels receiving 0 traction; all 4 wheels moved in the same direction simultaneously. No detectable delay in the rears catching up.
We tried the lift test with the e-brake on (by accident) and when dropping the car into gear only the front wheels moved but the engine was beginning to stall as the power being sent to the rears wasn't being used and therefore the bias on the viscous coupler caused engine braking.
We then propped the front wheels up on the jacks to simulate slipping across the entire front axle. Unfortunately the jacks acted more like an e-brake for the front wheels as they weren’t really designed for being driven on however when the wheels did get rolling the jacks would meander and the car would start to push them out, bringing the test to a halt.
Initially when put on the jacks and driven in reverse the car began driving backwards with only the rear wheels moving!
The car acted in a similarly to when the e-brake was engaged up on the lift, it wanted to stall.
Eventually with some more driving in reverse the car did manage to briefly spin the wheels on the jacks as well as the wheels in the rear however they spun at different velocities, the rear's were constantly turning whilst the fronts only got a quarter turn in before stopping again.
We then tried driving forward with the front wheels on the jacks and managed to get all four wheels moving. The rears were getting the power out much more easily with the fronts once again struggling to put the power down because of the jacks refusing to roll fluidly.
I took some videos while completing all these tests so if anyone REALLY wants to see them I can put them on youtube when I have time.
As a result of these tests I stand by my conclusion that the viscous coupler is a limited slip type differential that has the ability to mechanically sense the front and rear axle speed/grip and apportion up to 50% of engine torque to the wheels on those axles. Furthermore, the alltrac's 4WD system is not FWD until slip occurs it is a full time 50/50 4WD system with the ability for a limited difference in front and rear axle speeds.
Again, the reason our system is not FWD based 4WD is because of where the transmission is putting the power first.
The Viscous coupling connects the left side gear and right side gear of the center differential. When there is a bias of rotation on either side of the unit it will 'lock up' and put the car in full 4WD mode until equilibrium is achieved again.
I took my car to my friends shop tonight and we tried a few tests to see how the 4WD system reacted. Ideally we would have reproduced the test used in the ramp video but we didn't have such a nice ramp available to play with and opted instead to try and duplicate this test: http://www.youtube.com/watch?v=9B0ANOI3GcM using these positioning jacks and another test up on the lift.
Before commencing these tests my car sat outside in ~6°C weather for over 3 hours so everything was completely cold. Also to my knowledge my car is equipped with all stock differentials, open front, viscous center, open rear.
Firstly when the car was put on the lift and then put in first gear with all wheels receiving 0 traction; all 4 wheels moved in the same direction simultaneously. No detectable delay in the rears catching up.
We tried the lift test with the e-brake on (by accident) and when dropping the car into gear only the front wheels moved but the engine was beginning to stall as the power being sent to the rears wasn't being used and therefore the bias on the viscous coupler caused engine braking.
We then propped the front wheels up on the jacks to simulate slipping across the entire front axle. Unfortunately the jacks acted more like an e-brake for the front wheels as they weren’t really designed for being driven on however when the wheels did get rolling the jacks would meander and the car would start to push them out, bringing the test to a halt.
Initially when put on the jacks and driven in reverse the car began driving backwards with only the rear wheels moving!
The car acted in a similarly to when the e-brake was engaged up on the lift, it wanted to stall.
Eventually with some more driving in reverse the car did manage to briefly spin the wheels on the jacks as well as the wheels in the rear however they spun at different velocities, the rear's were constantly turning whilst the fronts only got a quarter turn in before stopping again.
We then tried driving forward with the front wheels on the jacks and managed to get all four wheels moving. The rears were getting the power out much more easily with the fronts once again struggling to put the power down because of the jacks refusing to roll fluidly.
I took some videos while completing all these tests so if anyone REALLY wants to see them I can put them on youtube when I have time.
As a result of these tests I stand by my conclusion that the viscous coupler is a limited slip type differential that has the ability to mechanically sense the front and rear axle speed/grip and apportion up to 50% of engine torque to the wheels on those axles. Furthermore, the alltrac's 4WD system is not FWD until slip occurs it is a full time 50/50 4WD system with the ability for a limited difference in front and rear axle speeds.
Again, the reason our system is not FWD based 4WD is because of where the transmission is putting the power first.
- The transmission directly drives the center differential.
- The left side gear of the center differential drives the front differential
- The right side gear of the center differential drives the rear wheels via the transfercase
- The amount of power sent to either the front or the rear is decided by the center diff via the driving conditions mechanically sensed.
The Viscous coupling connects the left side gear and right side gear of the center differential. When there is a bias of rotation on either side of the unit it will 'lock up' and put the car in full 4WD mode until equilibrium is achieved again.