Changed the transmission fluid in my 06 Navigator with the ZF six speed (no dipstick), it was much easier than I had read about and thought I'd share my success.

Purchased 10 quarts of Mercon SP fluid from the dealership for about $65.00, six feet of clear plastic tubing 3/8 inner diameter, 1/2 inch outer diameter from Home Depot, and a 1 quart funnel that the clear plastic hose slid snugly inside.

Dropped the drain plug on the transmission and almost 5 quarts of fluid drained out, (90k miles and it was extremely dirty, so much for lifetime fill) and then took off the brass fill plug from the passenger side of the transmission. I ran several feet of hose down from the funnel placed inside the engine compartment where the trans dipstick would have normally been, being careful to run it outside heat shield of the catalytic converter and then fed about 1 inch of the end of the hose into the filler hole on the transmission.

Poured in about 4 quarts of new fluid before it started running out the fill hole, (figured why spend the money on a hard to use pump setup and have to lay on your back spilling fluid everywhere when you can just fill it from above and let gravity do the job...) then started up the Navigator and cycled it between drive and reverse a few times before putting it back in park for the final fill. It took about another quart before it started coming out the fill hole. (I did put a clean drain pan below the trans fill hole to catch the few ounces of new fluid that ran out during filling) The transmission is supposed to be warned up for 5 minutes or so to ensure the correct level so I let it run until the pan was warm to the touch (89 degrees according to my laser temp meter) and stopped adding fluid when it was slowly dripping out of the fill hole. One important tip I learned the hard way is you need to screw the filler plug back in while the engine is running as the hot fluid will leak out pretty quickly once you shut off the engine. I guess the fluid level must be higher in the pan with the engine off. (certainly makes sense, with the engine/pump running trans fluid level in the pan goes down)

After the first five quarts were replaced, and it was all buttoned up, I drove it for a few miles and repeated the procedure again. The second time it only took about 4 quarts but the 9 quarts I put in equaled the 9 quarts I drained out so the fluid level must be right. It shifts much better now, all the harsh shifts are gone and it's back to nice and smooth shifting again.

All in all, it was well worth the $70.00 and an hour of my time. Now that I know it's so easy to do, I'll change the fluid much more often, probably every 30k!

 

Just an update, last month I bought a new pan/filter assembly from Rock Auto for $120 and installed a Sonnax zip kit in the valve body that replaces the seals that had hardened and some plugs that had worn causing my firm downshifts when coasting to a stop in 2nd and 1st gear and harsh engagement into overdrive.

The original pan was clean, the two magnets were spotless, and the non-OEM filter/pan was of great quality.

The zip kit had about two dozen seals, plugs, and o-rings and took about 4 hours to put in. Nearly 9 quarts of fluid came out of the transmission after the valve body was pulled out so the torque converter was almost completely drained in the process.

The procedure was pretty straight forward and except for some incomplete instructions in the kit that required a little extra research to determine where the check ***** needed to go during reassembly and having to replace the valve body bonded separator plate (it came apart leaving some of the gasket material behind) the job was much easier than I had imagined.

Putting it all back in, and refilling using the hose and funnel from the engine compartment was very simple and the repair has worked very well.

 

Since no one else has replied I guess I will... Nice little write-up. My 06 navigator transmission is leaking from the back of the pan so I have been pondering this job myself. As I read your post though you mentioned something about an occasional hard downshift which mine does as well. Its been hard to describe and very random so getting it to reproduce is impossible.

I can do the fluid change no problem. I dont like screwing with transmissions beyond normal service unless its to completely remove. I think now I can better explain the symptoms to the tranny shop though. For that kudos to you.

Question- has the valve body repair held up in terms of reliability? Its stupid to do something if it is just gonna come apart again. It would also help if you could define 'zip kit' for me... I can't find this on rockauto. Thanks!

 

So Max, I think the reason you developed those issues with the harsh gear shifting is because the transmission had Pentosin fluid from the factory and you went with the Ford Motorcraft alternative of Mercon SP. I have an automatic ZF 6 speed transmission in my other vehicle (a BMW) and did the transmission flush at 75K miles with no adverse effects since and that's now been 5K miles.