I know that this has been seen before, I did a search on it. I don't have an answer though.
My truck started this the last time I changed the filter. I put the filter back on same as always and filled with fluid. The thing that is different is that now I have bubbles on the stick with the truck running. I have a modified valve body so my truck pumps fluid in Park now, but it doesn't matter whether it is in park or N. When it is cold, the fluid is about a 1/4" below MIN on the stick. When it is warm after driving for about 10 miles, it is 1/4" above F mark. But it always has bubbles in it like a froth. I don't have any shifting problems though. ANy suggestions as to what to do. I am thinking about changing the filter and fluid again, but don't really think that will solve anything.
Chris

 

Check your filter to be certain it is tight to the valve body. Any looseness will pull air and give you exactly the symptoms you have.

 

I don’t know much about transmissions but I am a hydraulic engineer. Transmissions have there own hydraulic “circuit” so the principals are the same.

Foam bubbles mean air in the system and seeing as you just changed your filter maybe you are sucking air where the plastic filter meets the tranny or perhaps you have a crack in the plastic. If the filter meets the tranny above the normal fluid level you could be getting air bound there?

Try adding more fluid to get the fluid level above that seam.

Good luck!

 

Well, I went on and changed the filter and fluid again. Seems to have fixed it afterall. Don't know where the problem was. Maybe the filter was defective and had a crack in it, I just don't know. It has been about 1500 miles like that, do you think I hurt anything? This tranny has been the source of many sleepless nights and worries for me. I want it to last as long as possible. It did have a few very fine shiny particles in the pan. Is this normal or something to worry about? Looked like aluminum since it wasn't stuck to the magnet.
Chris

 

yea, you had a bad seal between the filter and the housing, could even be around the torx screw?

i'm not too sure on the tranny end of things but hydraulics systems and cavitation do not get along.

I cut and pasted this info from another site

Cavitation -- 'cancer' of the hydraulic system
A client recently asked me to advise them on the possibility of repairing a large spool-type directional control valve off a 400 ton hydraulic excavator, used in open-cut mining.

The valve in question had been badly damaged as a result of cavitation, which had occurred over a long period in service.

What is cavitation?
Cavitation occurs when the volume of fluid demanded by any part of a hydraulic circuit exceeds the volume of fluid being supplied.

This causes the absolute pressure in that part of the circuit to fall below the vapor pressure of the hydraulic fluid. This results in the formation of vapor bubbles within the fluid, which implode when compressed.

Cavitation causes metal erosion, which damages hydraulic components and contaminates the hydraulic fluid. In extreme cases, cavitation can result in major mechanical failure of pumps and motors.

While cavitation commonly occurs at the pump, it can occur just about anywhere within a hydraulic circuit.

In the directional valve described above, the metal erosion in the body of the valve was so severe that the valve was no longer serviceable. The valve had literally been eaten away from the inside, as a result of chronic cavitation - a kind of 'cancer' of the hydraulic system.

In this particular case the cause of the cavitation was faulty anti-cavitation valves, which are designed to prevent this type of damage from occuring.

 

Ahh, you mean impingement

 

A thin shiny film in the bottom of the pan is normal for an auto trans from everything I've ever heard or seen. They all do it. As long as the amount of that material doesn't suddenly increase, or start having larger chunks in it, it should be fine.

 

I always have a line pressure gauge inside the cab of my truck.I use to keep the fluid level on the high side of the stick,until I started watching the line pressure.As the fluid heats up the moving components start frothing the fluid whem this happens the line pressure starts oscillating wildly.When I keep the level in the center of the cross hatch,pressure is rock solid.

 

It has been a few days now since I replaced the filter, and everything seems to be fine. No more bubbles. Still makes me wonder though, where the leak was or what was causing it to foam. I set the level the same and everything. It had to be a bad seal between the valve body and filter. I did tow my trailer some during that time. Man I hope I didn't cause cavitation damage. I have seen what cavitation does to the impeller of a 10K dollar fire pump Sure would hate to know my tranny pump suffered that. Maybe I didn't cause any damage since I really didn't notice any shifting problems.
Chris