You are correct in your thinking. The fluid has to be flowing from the pump or nothing would work. I think you have a stuck valve in the valve body or a stuck solenoid, if your mechanic diagnosed the electrical correctly.

 

Well all he dose is transmissions. An he dose good work. But I just can’t see why he has to pull the transmission. He is saying that in order to find an fix blockage he has to pull an go into the transmission. But only reason I know of to pull transmission is if the blockage was in the pump. But like I said, I can’t see that being the it shifts from 1st to 2nd just fine. I’m thinking that he is not sure where the blockage is. He pulled valve body and said there was a spring put in backwards and there was a little bit of metal in the pan but the valve body looked good. An his scanner is saying all is good electronically with everything. So I’m think that IF everything is good with valve body then the blockage almost has to be in that screen on the tip of the B solenoid. But then I’m not sure where the fluid gos when it leaves the B solenoid. Haven’t been able to find any videos that explains how the fluid makes the tranny shift after passing through B solenoid. I’m gonna call him an talk to him Monday an see if he has pulled B solenoid an checked the screen on tip. He also said that there was a hole drilled in some plate in there. An he couldn’t see why anybody would drill a hole in that plate. Not sure what plate he is referring to though. An he said it looks like somebody may have tried to modify the transmission or something. Idk. I just can’t see why he has to pull tranny an go into it if all is good in pump. Which I think it is bc obviously fluid is getting into valve body bc it dose shift 1-2. We will see what he says Monday. I really appreciate all y’all’s info. If anybody knows how the fluid causes tranny to shift after passing through B solenoid please explain. I would be greatly appreciative

 

Transmissions is all that Aamco do also but that doesn't mean they know what they are doing. I have seen them rebuild a trans for an elderly lady and after the rebuild it was doing the same. I replaced a $30 TCC solenoid, and the problem is gone. What I am saying here is a lot of shops out there that are good at your normal rebuilds but if something out of the ordinary comes in they are lost.

I ask if your guy disassembled the valve body or just poked at it with a small screwdriver and said all is well. Something is stopping the valve body from shifting, a stuck valve, stuck solenoid or an electrical problem not turning the solenoid off.

An ATSG Transmission Repair Manual for a 4L60E would help you.