So, to beat this dead horse...I have read many contradicting post regarding whether to use the Synthetic ATF/MERCON/MERCON V in the 4R100. I do not do a lot of towing and my transmission is stock (for now). What do you experienced 4R100 users recommend I use that wont break the bank. I do not plan on doing a complete flush (not sure how even after reading, I am a visual aid kinda guy) but maybe just do shorter interval changes to cycle out the old fluid. I just ordered a filter and the rubber metal/gasket combo from BearLake Ford. Any recommendations will truly help.

 

I used Ford XT-5-5QM MERCON-V from Amazon.com... A 5 quart jug is 32.30 right now.

 

Assuming you read thru the tech folder? No need to buy the reusable gasket.

https://www.ford-trucks.com/forums/1...l#post12824085

 

1975stroppebaja also has some visuals on Mark K's flush method. His page is linked near the bottom of the tech folder.

 

Mercon V for the transmission. Dino or synth is your choice.

Motorcraft XL-12 for the transfer case.

Stewart

 

Been running Valvoline's synthetic Mercon V for over a year in my rebuild, zero issues. Synthetics might have a higher thermal degradation temperature than conventional, but the comparisons, benefits, etc between the two are all over the place.

Personally I'd just swap it all out at once, I don't see the point in trying to cycle out old fluid. It's just going to mix and merge once it goes in, a full swap is the only way I see it being efficient and financially sensible. It's not like the old fluid is going to up and separate and move out when you pull the drain plug...

 

Ok did some further looking around. Thanks for the visuals on Mark K's flush method, like I said I am a visual aid kinda guy (this one has way more pictures) After reading it a couple times I feel confident on the process. >drain the pan, change the filter, and button her up>refill what was drained>connect tubing and secure it to the cooler line>start the truck (engine running) and watch the flow--once the flow ends, stop the engine and replace what was drained>repeat the process until your bucket has 19-20 quarts! Chime in if I am jacked up! I found some Valvoline Mercon V FS at Napa for less than 5.00 per quart I am going to give it a shot and reserved 20 ea. My next question to you pros, how to remove the crossmember in order to access the rear tranny pan bolts. Seems like a PITA trying to work around it. I would rather remove or move the crossmember to get good access and good seal when buttoning her up.

 

It's really not that difficult, let me try to get you a 'photo' for your visual .

 

Sweet, sorry I am a Strong Ranger!

 

Update: the process of completely flushing the transmission wasn't that bad at all. I had to finagle my way around the crossmember and it wasn't as bad as I thought it would be. Once I removed the harmonic dampener for NVH attached to the bottom of the crossmember it gave me easy access to the rear pan bolts. I ended up using 20 qts of Valvoline Mercon V. I did notice smoother shifting; however my temps read 10 degrees higher than normal. I normally calculate using the ambient temp + a variable of 75. I am normally 10 below, now I read right at the mark. I am calculating the math properly? Is there another method? I felt good about the flush so I ended up changing the fluid in the transfer case with 2 qts XL-12 probably could use a bit more but only had 2 qts on hand and I even flushed the steering system using 2 qt of Mercon V as well My tool box of knowledge grows everyday using FTE. Thanks.