Originally Posted by timmiii

I'm not confusing ACD with AYC. If you jack up the car and run the car while holding (while the pump is not functioning or when the hand brake lever is pulled) the rear wheels you will notice no AWD in the system; the front wheels simply spin while the rear wheels stay perfectly stationary.

You are correct in stating that the center differential remains a 50/50 torque split however, the only way the torque is even transferred is by the friction created from the clutch pack within the transfer case due to the hydraulic pressure which the pump produces. The lack of pressure will result in the clutch pack's inability to mate and create friction thus not being able to transfer power to the rear under conditions which produce reactive forces from the rear wheels. In other words, if you produce non-uniform torque from the front and rear wheels the torque will not be transferred. Therefore the ACD pump is required to provide hydraulic pressure to the clutch pack to provide the possible transfer of torque.

Originally Posted by Raptord

Pulling the handbrake deactivates the ACD so that it doesn't go crazy trying to send power to the rear wheels. This had been known for a while now and is unrelated to the pump working or not working.

Originally Posted by timmiii

I'm not confusing ACD with AYC. If you jack up the car and run the car while holding (while the pump is not functioning or when the hand brake lever is pulled) the rear wheels you will notice no AWD in the system; the front wheels simply spin while the rear wheels stay perfectly stationary.

You are correct in stating that the center differential remains a 50/50 torque split however, the only way the torque is even transferred is by the friction created from the clutch pack within the transfer case due to the hydraulic pressure which the pump produces. The lack of pressure will result in the clutch pack's inability to mate and create friction thus not being able to transfer power to the rear under conditions which produce reactive forces from the rear wheels. In other words, if you produce non-uniform torque from the front and rear wheels the torque will not be transferred. Therefore the ACD pump is required to provide hydraulic pressure to the clutch pack to provide the possible transfer of torque.

Originally Posted by black95tt

I get what you are saying, but, have you actually tried that? I drove my evo IX for two winters with no ACD pump and I can assure you, it was still transferring torque to the rear wheels. It drove/felt exactly the same as when the pump worked.

Originally Posted by timmiii

Yes I have tried it. I was in the car when the two Mitsu Techs held the rear wheels in place. I remember last winter I tried getting up a hill infront of my house, the car wouldn't grip at all when set in Tarmac mode. Once I switched to Snow mode it gripped fine and I was able to get up the hill.

I do drive my car a bit hard on the street and take corners quicker than most, I definitely do feel a difference when my ACD did work.

Originally Posted by black95tt

Were you turning and going up that hill? There should be no difference between the modes if there is no steering input. That just doesn't make sense to me at all.

Originally Posted by asubennett

My ACD pump has recently become very very loud. Before it was not super noticeable and I always had one light as intended.

Now after start up and 1 minute on the road I get a very loud grumbling sound. Almost like bubbles popping. If this sound cuts off quickly (5 seconds or so it remains 1 light). If it does this sound for a minute or so then it cuts off and all three lights become illuminated.

Any ideas.

Originally Posted by black95tt

I get what you are saying, but, have you actually tried that? I drove my evo IX for two winters with no ACD pump and I can assure you, it was still transferring torque to the rear wheels. It drove/felt exactly the same as when the pump worked.

Originally Posted by TalonFiero

Normal driving you wouldn't notice much and to be honest when I drove with three red lights I can still get some torque to the back wheels in snowy conditions.

Then I tried launching the car this summer at the drag strip with the pump not working. Instant fail, there is video on youtube of my car just spinning the front wheels and smoking them. Car always ran 1.6x 60' but instead ran back to back 2.2 60' on the rev limiter entire time.

http://www.youtube.com/watch?v=trAp35U601U 2:22 in the video is a launch with a bad ACD pump.