http://media.gm.com/division/powertrain/products/transmission/2004/2004Allison.doc


In this article it says:


"MODULATED OIL PUMP PRESSURE REDUCES NOISE / INCREASES COOLER FLOW: A modulator valve body and external wiring harness to control the modulator were added to modulate the main oil pump pressure. This reduces oil pump pressure at engine idle speed and therefore lowers the operating noise level of the transmission and substantially increases transmission cooler flow at idle."I need a better understanding of how this trans flows. Can anyone explain how lower pressure at idle equals better flow? I must be misunderstanding.

that change was made for the 04 MY trans, uses the new solonoid to reduce fluid overage, allows all fluid to go through cooler at lower pressure, high pressure would not allow all fluid to go to cooler, dumping some back in pan...

Is it modulation that diverts more flow to the cooler than before (at idle)? Thus permitting lower "system" pressures?

yes in a sense, drops line pressure at idle which aids in cooling and keeps down pump noise on the gassers.

So is the pressure in the LLY cooler line (at idle) MORE than the LB7 number?


Just trying to be sure I understand, because to flow more oil, more pressure (not less) must be present (if line size remains constant). The article says there is an increase in cooler flow, to me that means more pressure or bigger lines, we know the lines are the same.Edited by: masterp2

in this case, the cooler pressure should remain the same or even a bit less. the line pressure gets dropped to allow more fluid to go through the cooler. when the pressure is high the fluid can only go so fast and the rest is called 'overage' fluid and just gets sent back to the pan. By dropping the pressure at idle, when its not needed, this keeps that pump noise down some as it dont work as hard, (yes, i know the pump dont make pressure differences) but according to Allison, this all works, even if it dont make sense..http://www.dieselplace.com/forum/smileys/Confused.gif. I guess I am not the best one to explain it, I just have to believe what my sources at Allison tell me...http://www.dieselplace.com/forum/smileys/Cool.gif

My thinking is like this, Put your thumb over the end of a garden hose pressure goes up and flow goes down, correct? Remove your thumb pressure goes down and flow goes up.


Does that sound correct? Just a thought

Here is a little fluid dynamics. When you increase preassure in smaller lines you increase the friction loss of the fluid. You can really loose good flow with to much preassure in the line. Allison has reduced flow pressure to reduce friction loss thus allowing more fluid to pass smoothly through the lines. An example of this would be to take an 1 1/2 inch line 100 feet long, pumping 100 psi at one end would get you around 55psi at the end of the line due to friction in the line. Don't want to get to technical, but that is the reasoning behind their flow preassure reduction.

Here is a little fluid dynamics. When you increase preassure in smaller lines you increase the friction loss of the fluid. You can really loose good flow with to much preassure in the line.


That was hysterical! You might have been in my class.http://www.dieselplace.com/forum/smileys/Big Smile.gif


.... the additional friction would be a result of what, the fluid going "slower"?

My thinking is like this, Put your thumb over the end of a garden hose pressure goes up and flow goes down, correct? Remove your thumb pressure goes down and flow goes up.


Does that sound correct? Just a thought exactlyhttp://www.dieselplace.com/forum/smileys/Clap.gif

...and that works to describe what happens when you, say, decrease line size, the thumb is like any restriction. But line size didn't change. if all things being equal, all that was done was to increase pressure (bigger pump for example) then flow (and fluid velocity) will ALWAYS increase, along with it the pressure loss in the line. There is no change in this relationship until you get to transonic fluid velocities. If this weren't the case, we would all be getting better (not worse) MPG at 100 MPH.


So maybe what they are saying is that a larger proportion of the fluid is modulated to the cooler line per a schedule, so that pump pressure can be lower across the board. I don't know, but lower pressure in a line does not get you greater flow. Otherwise, I (big pump) wouldn't be able to finish my Mcdonalds shake before my son (little pump)http://www.dieselplace.com/forum/smileys/Big Smile.gif