Ford transfer case

Messages
3,297
Location
West Michigan
At 20k miles since my last transfer case fluid change in the 2011 and need to get the factory fill out of the 2018. Both are now rated for Mercon LV in the transfer case, so that may, potentially, simply some things. What I'm concerned about is the 2011, though. Historically this truck has demonstrated spline slip bump refractory to all interventions. This is the transfer case slip yoke splines as it is a one piece driveshaft. After trying all types of different greases and pastes including NLGI 2 with moly, moly paste and two different Ford/Motorcraft teflon/ptfe greases the most ever got was a few thousand miles (like 6k MAX usually just a couple hundred) before it returned. Eventually I hit the 100k service and drained the transfer case which undoubtedly came out silver/grey/black. No other mechanical symptoms so maybe its lube contamination from the greases but I doubt it (which is one reason I will be changing the 2018 early). Well anyways at 100k miles I drained it and refilled with Amsoil universal ATF- not the LV version. Sure enough, slip bump disappeared! Now I'm 20k miles down the road and still silky smooth off the line.

Given the above, I am due for my not exactly annual trans pan drain and fill. Great time to replace the transfer case, though for the most part I'm just curious how the fluid is looking. Interestingly it looks like Ford has canceled the XL-12 (aka Dex/Merc) spec and back spec'd Mercon LV for this transfer case. Not entirely a bad thing as the lower viscosity can only help in winter, which is 99% f my 4WD use, and shouldn't hurt mileage either. Modern synthetics, I have no real concern about wear issues or heat either - especially in a low demand application like a chain drive, part time transfer case. What I am trying to decide on is if it makes more sense to switch to LV at this point or stick with the tranditional Amsoil universal ATF? The main benefit of going LV is economy in that I could just buy two jugs of MaxLife ATF (not to start an arguement but that is my choice for ATF in this application) and not have to worry about any extra shopping.

Now the specs of all three (Maxlife, Mercon LV, Amsoil ATL) are extremely similar and Amsoil ATF is, of course slightly more viscous. What I am wondering is, will that make a HOOT of difference to my transfer case slip yoke splines? As described above it would certainly appear that the primary factor in lubrication is the transfer case fluid. Thick = better? Thinner = better? Or too close to matter and base oils, additives, etc make more difference? The viscosity range in cst at 100C for LV is 5.9 for Maxlife, 6.0 Motorcraft and 6.3 Amsoil ATL with the ATF running 7.5. Semi interestingly, despite the thinner fluid at operating temp the brookfield is lower for the Amsoil ATL making me wonder if its a higher quality fluid. While the price difference as a percentage is significant in reality its only a few dollars more so I don't mind running the premium option if there is actually a benefit.

MaxLife Datasheet
Amsoil ATL and ATF datasheet
Mercon LV Datasheet
 
Messages
2,380
Location
Paradise of Florida
Bump could be internal to the transfer case and not necessarily the slip joint. Harmonic or shake give the slip a vibration workout???

I would never take a gearbox to 100k on the factory fill. I hope that you've learned your lesson. Don't wait to 'hit' the manufacturer interval for ANY fluid service. 3years/30k miles should be consider a limit on long term ownership for diffs/transmission/transfercase/PTO's/PTU's.

Synthetic can help with winter when compared to the conventional fluids. I would use a full synthetic Dexron/Mercon like Mobil1 or the Valvoline transfer case fluid. Skip the xl12, merconLV....

You won't notice an MPG difference when comparing a synthetic LV 6 cst fluid to a synthetic 7cst fluid. That is not even worth mentioning on a F-150.
 
Messages
1,431
Location
Missouri
I doubt the fluid used will make any difference whatsoever to your transfer case. You're the first I've heard say that any fluid change in the transfer case made a difference for the slip yoke bump. Which is kind of interesting. Before Ford came out with the Smurf blood grease to put on those I was putting CV joint grease on them and having good luck with it as it was the tackiest grease I could easily source at the time.

If you want an improved fluid I would take a look at BG synchro shift. I have that in the T case of my F150 as that's what the previous dealership I worked for used. Never an issue out of it in any T case and by looking online it is supposedly a very robust fluid. Might be worth looking into.
 

buck91

Thread starter
Messages
3,297
Location
West Michigan
Aren't the slip yoke splines external to the transfer case? I'm thinking there'd be no difference.

I cannot guess how the bump vanished after your 100K fluid change.

I have the one piece driveshaft so the splines are on the yolk like in other rwd Ford’s (think panther 4r70w). Can’t tell you the exact reasons but nothing else worked very long. 20k on fresh t-case atf and still no return of the slip bump.
 
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