Dave, It's not the filter which causes the problem, it's the restriction it creates in flow which causes the problem. If you took an engine which required a 1/2" fuel line to properly feed it and installed a 1/4" filter in this line, even tho the filter was brand new, you would still hurt the engines performance by restricting the flow to it. It's the same with the tranny filter. Like you said, the tranny operates on fluid flow and when you restrict this flow, you hurt the performance. And I'm not talking about old, dirty filters, I'm talking about brand new tranny filters being restrictive to the point of causing a performance loss. We're not directly increasing the performance of the tranny, only allowing it to perform better thru less restriction. Now someone just needs to come up with a tranny filter which allows this to happen. As far as running a tranny without a filter. Again, like you said, a tranny is a closed system. By being a closed system, it is far less prone to being contaminated then an open system, such as a fuel system, where you are constantly adding fuel and /or whatever to it from an outside source. Thus a tranny filter is cleaning the same fluid over and over again. You are correct, a tranny thru normal operation does create it's own internal contaminates thru clutch slippage, etc, and these contaminates will cause wear to other internal parts. But so will restricting / starving the system for fluid flow cause transmission wear. Again, running the tranny without a filter is a trade off with a risk involved. You must decide for yourself what to do. Marty In a message dated 9/11/00 4:13:03 PM Central Daylight Time, jtrealty@xxxx writes: << You wouldn't try running without a fuel filter and that isn't a closed system. David Teitelbaum >>