Ford 5R55N/S/W Transmission Fluid Level/Change

Well, guys, I’m back after a week of wrenching on The Millennium Falcon. I’m trying to get the old bird drivable soon, so look for some upcoming Falcon Friday posts! Anyway, on to this week’s In the Shop post!

The Ford 5R55N/S/W transmission has no dipstick, no fill/check plug, and really no easy way to check the transmission fluid. If you’ve been under the hood of a Ford, Lincoln, or Mercury trying to check the transmission fluid lately and you haven’t been able to locate a dipstick, there’s a decent chance you could be dealing with one of these transmissions or one of its variants. The 5R55 series was used in a wide range of FoMoCo (Ford Motor Company) vehicles from about 1999-2010.

While reviewing a common procedure used to fill the transmission fluid in these transmissions, I thought I might have a better solution than buying a ridiculous $120 tool just for this procedure. Sure I’d like to have one for future projects, but I needed this vehicle done tonight!

I’ll save you the steps for puling the transmission pan and filter for now, so we’ll pick up the procedure assuming I’ve already drained the fluid, changed the filter, cleaned the pan, and we’re ready to go back on the vehicle with the pan.

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You’re supposed to use a little tool like this inserted into the fill plug hole like so and hook up the fluid transporter as outlined in the procedureIMG_1713

Instead of using that whole contraption, I just inserted the fill plug using a T40 (I think) Torx bit and turned the transmission pan right side up.IMG_1716

The theory behind the aforementioned procedure is this: you install the pan, pump some fluid in with the special tool, run the vehicle until the transmission is at operating temp (more on that in a bit), remove the tool and filler adapter, and let the fluid run out until it is a small stream or a drip. Instead of going through all that, I figured the pan was deep enough to hold the specified amount of fluid for the 2005 Mercury Mountaineer I was servicing, then I could just bolt the pan on full of fluid.
IMG_1717

I was right! I think it held right around 4-5 quarts of Mercon V transmission fluid and I was able to put the pan on full of fluid with some help (shoutout to Jeff!).IMG_1718

After tightening the bolts on the pan with it full of fluid I let it run until the trans reached operating temperature (red circle). I have a Snap On Modis that showed this information, but if you don’t have any way to read trans temp, just let it idle for 10-15 minutes and it should be about right.
IMG_1721Back under the car (engine running), I removed the fill plug and….

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Perfect! It was barely dripping with the transmission at operating temp, meaning I had exactly the right amount of fluid in it.

I’ll probably still buy that tool sometime in the future because this little trick won’t work if the fluid is just low. You have to remove the pan and fill it up to the proper level for this to work. Also, it probably won’t work on a lot of other transmissions with shallower pans, but they usually have a dipstick to check the fluid levels.

I hope this helps someone who is changing the transmission fluid and filter on one of these goofy Ford transmissions. Check back Monday for another installment of Mopar Monday!

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