Sorry for the lengthy post, but I wanted to include some details of my problem. I have a 2005 Mustang with the 4.0 V6 and automatic transmission. A few days ago, I took it out for a brief spin due to having nice weather finally. Prior to that, it had sat thru most of the winter and all the snow and ice we've been having. After going about a quarter mile, I turned onto a road with an upward grade. Before it had a chance to shift thru all the gears, it flared into neutral. Thankfully no cars were behind me, so I was able to engage it into reverse and back down to the intersection and at that point, the forward gears engaged again I was able to drive it back to the house with no issues. I live on a dead-end road so I drove it back and forth for a few minutes to see if it would flare into neutral again and it never did, either in forward or reverse.

I bought the car a little over a year ago and it has 214K on it. The Carfax showed the previous owner had a $1800 transmission repair done at just shy of 170K. Since I have owned it, it shifts great...kinda feels like it has a shift kit in it. It hits each gear solidly, not mushy at all. I presume it is the 5R55S trans but haven't confirmed that. What I do know it has no dipstick. Since I was on an upward slope when it slipped out of gear, I considered the fluid level may be low enough that just that slight grade might have caused a bit of fluid starvation to the clutch packs. I have noticed evidence of transmission fluid leakage around the front of the pan. I went thru the process to check the fluid level. I jacked it up and got it perfectly level with jack stands all around, started it up and ran it until the trans fluid temp was 100 degrees. While it was running, I shifted it through the gears several times. When I got the temp between the 80 to 120 degree range, I pulled the torx head screw out of the big drain plug and let the fluid drip into a pan. I kept the engine running during this time. I was expecting no fluid to come out at all, assuming the level to be low, but it was just the opposite. The fluid came out with great force for quite a while and when it finally got to just steady small drips, I had drained nearly a gallon of ATF! So, I thought my problem must be that it was overfilled by a good bit rather than underfilled. According to the ford manual, the method I used should have the fluid at the perfect level. Then, I was more than surprised when I put the plug back in and started it up only to discover the transmission would not engage at all! It seemed to engage fine before when it was "overfilled", but now it would not engage forward or reverse. So, what gives? Anyone have thoughts on this? Could the fill tube that the little torx plug threads into be damaged somehow? I had to go out of town for a week right after that, but when I get back this weekend, I guess I could pull the bigger drain plug out and should be able to check that tube then I guess, right? So, if nothing looks screwed up, what do I do, put the same amount of fluid back in it that I drained? That's probably gonna be hard to do because the fluid is gonna want to keep draining back out on me. Did I overlook something here? Thanks for any ideas on this.

 

All automatic mustangs from 05-2009 are 5r55s. You performed the leveling correctly. I've done a lot of maintenance and some performance work on mine before my 08 got totaled after 14 years of owbership.

Drop your pan, check the transmission filter for having either two orings (old one +newer one) or none at all where it goes into the valve body.

There is a thread on the forum with a similar problem from a few years ago. The guy had dropped the pan to replace the filter and upon refill he was getting what seemed like an underfill situation. Yet he had put in roughly a gallon more than he pulled out.Same as what you found.

His problem turned out to be that when he removed the old filter, he failed to notice that the rubber oring that seals it into the valve body got left behind. When he put the new filter with its oring on top of the old one it caused a bad seal and air to get pulled in to the transmission pump because the two orings interfered with each other. So, the transmission couldn't build pressure to engage or shift properly. Same would happen with no oring. No seal.

When he overfilled, the level of the fluid reached the valvebody essentially sealing the leak but, caued other issues.

drop your pan, check the filter oring. You'll have to remove 1 or 2, 8mm or 10 bolts.

 

Thank you for the reply. Your theory about the o-rings is certainly a possibility. I will check that this weekend when I get back home.

 

Never have I wanted to find something screwed up as I did with this transmission filter and the orings. I truly hoped to find them messed up as you suggested as a possibility, for the main reason, it would have revealed my problem and secondly, it would have been a quick, easy fix. However, both orings were in place and neither was boogered up, they were in the exact place they should be and were not doubled up or anything weird.

What I have drained is close to 6 quarts. I guess after I change the filter and put the pan back on, I will pump about 4 quarts in before starting the process all over again. Four quarts ought to be enough for it to engage the gears, wouldn't you think? I'm still perplexed as to why so much fluid drained out after reaching the required temperature and going thru the gears a few times. The drain plug and tube looks fine as does everything else inside the pan. Pretty much normal residue on the magnet and the fluid looked fine, red in color and no burnt smell or anything.

 

so only 1 oring per fitting that attached to the valve body?

 

Thanks for your input and suggestions. I changed the filter and installed the pan and close to 6 quarts and that likely because it drained for a long time as I had the pan and filter off of it for a couple days while I was called away. Everything went as it should. I had to use a suction gun to fill it and that took some time to complete. I noticed when I got to just a little over 3 quarts in it, fluid started draining out the nipple fitting when I pulled the hose off to reload the suction gun. That required me to unscrew the nipple and put the torx head bolt back in each time as it would drain out on me while reloading the suction gun. It requires you to work fast and with ATF soaked fingers, hopefully not drop the little torx screw into the pan I had underneath! After I got it a little over 4 quarts, I started the engine. Right after that, it quit draining out on me between each suction gun load, I guess some of the fluid had circulated throughout the transmission, lines and TC so the fluid level dropped. I can definitely see why a machine like Brian uses is much preferred and quite a bit easier and faster. When I was at about 5.5 quarts, the fluid started dripping out of the nipple just a little bit and the temp was between 110 and 115. When I was close to 5 quarts, the transmission would engage just as you had pointed out. I haven't driven it yet as I still have it up on jacks as I have some other work I'm doing to the car before I put it back on the ground. I think the trans will be okay though, seemed to shift normally while I was running it on the jack stands. The auto adjust feature Brian talked about worked fine on the fill side, I just don't know what happened on the drain side for me as it had me drain nearly 3 quarts out of it before the nipple stopped dripping and by then the transmission would no longer engage. And that was at a temp of about 100 degrees and the car perfectly level. Anyway, thanks again for your help, much appreciated!

 

Only check it while it's running. Make sure you've manually shifted through all gears including reverse before before trying to level it. The reverse servo itself can use up to a full quart to fill itself and fluid circuit.

Another thought, if the previous person removed the valve body and didn't replace the separator plate gaskets, you could have leaks in the valve body fluid paths. You need two gaskets. An upper and lower foot the plate. One goes on the valve body to plate. The other goes plate to transmission.

 

Yes, I have run it extensively. In fact. I've had to shut it down a couple times and let it cool down so I could get the trans temp back within the test range just to double and triple check the fluid level. Each time I have run it thru all the gears multiple times. The good thing is, with the temp in the range, the ATF is just barely trickling out just like the ford tech makuloco indicated. So far, there has been no hesitation when engaging forward or reverse and shift points are all hitting nicely. When I finish the other repairs, I'll probably run it again before dropping it down just to make sure everything is still all good. I'm very encouraged at this point, and thanks for the heads up about the valve body gaskets. That is good info to know.

 

Glad it sounds like you got it figured out.