Originally Posted by Derf00

Having learned a lot about the 5r55S last year when I did some light work on mine I'm going to suggest either replace the valve body with a remanufactured one or get a shift kit for the existing one.

A tune won't resolve the problem as Norm stated. It will be a temporary fix by increasing the tranny fluid pressure. I'll explain why below.

The valve body is in charge of directing fluid inside the transmission to get the gears shifted as directed by the Solenoid block which in turn is controlled by the PCM. It does this through a complex series of pathways machined into solid aluminum block. Each pathway contains a piston and spring(s) that rely(ies) on pressure to move the respective piston and initiate the shift or torque converter lockup.

The problem is these valve bodies are aluminum and the pistons are steel. So, when you have two surfaces that rub against each other constantly you get wear in that the valve body piston bores start to get slightly larger or out of round. This allows pressure to bleed by the piston thus preventing the transmission from shifting as expected (this could be in the form of how long the shift takes, how firm it is, whether it holds the gear properly or not and many others). The only way to truely address issues like that are to get a remanufacturered Valve Body, not new. New will have the same issues. Remaned fix the most common issues.

Also do not waste your time/money/effort on a used one. It will most likely have the same or worse problem than yours. If the aluminum is worn the valve body is toast. Yes you can use over bored pistons but without the proper jigging equipment to re-bore and/or sleeve the cylinder you will destroy your transmission with the micky-moused valve body.

One other thing, when was the lats time you changed fluid? I don't care what the manual says, 30K intervals is recommended to keep the 5r55s performing at it's best.

Start with the fluid, you can have a shop do a proper tranny diagnostic for about 100. This includes driving it with a pressure guage(s) installed to monitor the pressures as the transmission is driven. Each gear and shift must meet a specific range of pressure, over/under that range pinpoints the problem circuit in the valve body or in the shift process.

Originally Posted by jwog666

fyi the pressure tests now will only verify a large internal leak or low pump output, and arent useful for 99% of diagnosis as either of those concerns will result in major slippage. basically then line pressure and pc solenoid tests are done at idle. if they pass the rest will require removal of the valve body and air pressure tests using a special plate to take place of the valve body. this will cost alot more than $100 if its being done by a professional

Originally Posted by jwog666

ford only publishes warranty times, under the waranty time standards it calls for 2.0 to do the prelim scan tool and pinpoint diag, then another 2.0 to drop the pan and rand r the main control/valve body which is what you would have to claim for diag under warranty book times for the non warranty should be up to 1.5x as much