Installed my Mag-Hytec today

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Just to follow up, I sent a note to Mag Hytec to see what they said. They confirmed you need to fill above the stock oil plug line and to go ahead and add the full six qts.

I'm going to add at least one more and see where it falls on the dip stick.
 
Originally Posted By: Onug
Just to follow up, I sent a note to Mag Hytec to see what they said. They confirmed you need to fill above the stock oil plug line and to go ahead and add the full six qts.

I'm going to add at least one more and see where it falls on the dip stick.

Is it 6QTs or 5? I bought 5QTs and used about 4.5 to fill it a little above the halfway mark on the dipstick. I would imagine that another 1.5QTs would put the level quite a bit above the full mark on the dipstick.

I will be checking this post to see how it goes...
 
When you drive, some will go up the tubes in some axles and stay there, so after you drive a bit go back and check the level. The other option is to jack up the truck from one side of the axle and let oil run down to the opposite hub. Then jack the other side, let the oil settle a while and recheck. I do this after I've rebuilt an axle to make sure the bearings have been lubed well.

As to six quarts vs five, I know I would NOT fill over the upper line on the dipstick. In fact, I have always been skeptical of Jerry's (the owner and engineer at Mag-Hytec) stance on the oil levels. I have had it pounded into my head by various engineering contacts that an overfull diff is bad news. I have to revisit this with some of them when I get a chance. Like 2010_FX4, I hedged my bets and didn't go to the full mark. Even at that the oil level is about 3/4 inch above the factory fill line and oil is flowing freely up the tubes. That part might be a good thing in terms of wheel bearing life but my biggest worry is oil foaming/aeration... something that increases the oxidation rate of the oil. When you talk to Jerry, he makes a good case and claims to have thoroughly tested his method. He COULD be right but it's not proven to my satisfaction. Anecdotally, I have thousands of miles in two trucks with the diffs ostensibly "overfull" and nothing untoward has happened. I guess my research could be said to be "ongoing."
 
About the overfilling

While I wouldnt overfill one of my differentials, I doubt it hurts anything from a longevity standpoint. Almost all of these modern differentials and axle bearings are already bulletproof. It would only reduce efficiency and driven power.

I have been water wheeling many times where the differentials become completely full of a water and oil mix. When they are completly full, they will definately leak from every seal. I would say that as long as the seals are not leaking, you are fine.
 
I got some time today to work on my truck, so after some thinking I decided to go ahead and top off my differential per Mag-Hytec's instructions. I added another full qt of oil before reaching the top of the fill line. I have about 5qts of oil in there, plus the FM. Next time around, I'm going to to use oil with the FM already added so I don't have to mess with the two fluids (hopefully).

Stay tuned…I'll let everyone know if I have any problems.

Don't forget to re-torque the nuts. I had one move slightly when I rechecked everything today.
 
Originally Posted By: Onug
I got some time today to work on my truck, so after some thinking I decided to go ahead and top off my differential per Mag-Hytec's instructions. I added another full qt of oil before reaching the top of the fill line. I have about 5qts of oil in there, plus the FM. Next time around, I'm going to to use oil with the FM already added so I don't have to mess with the two fluids (hopefully).

Stay tuned…I'll let everyone know if I have any problems.

Don't forget to re-torque the nuts. I had one move slightly when I rechecked everything today.

I added the FM, but did not need it, but I am sure that 5QTs would have me at the full mark. I recently had to ford some deep water so I have to check for water in it anyway. The front axle and transfer case are due for an OC so I will just dump them and refill.
 
The Ford 9.75" Diff doesn't have the traditional "S" spring in the center as other ford Traclocs did. Its actually very hard to spot the plates in one of these diffs because they are well hidden on the ring gear side under the case. I've re-geared both the 9.75 diffs in my 05 FX4 and my 01, both had lockers according to the diff tag but I couldn't see it until I removed the carrier.
 
Originally Posted By: racin4ds
The Ford 9.75" Diff doesn't have the traditional "S" spring in the center as other ford Traclocs did. Its actually very hard to spot the plates in one of these diffs because they are well hidden on the ring gear side under the case. I've re-geared both the 9.75 diffs in my 05 FX4 and my 01, both had lockers according to the diff tag but I couldn't see it until I removed the carrier.

My axle is an Electronic Locking Differential (not sure if the 2001 and 2005 were electronic or not?). Jim Allen was kind enough to decode the tag numbers and informed me that FM is not needed in my axle as it not like a traditional locker and has no clutch plates, but uses electronically activated cam rings to lock the differential. I do not plan to use FM on the next OC (which may be sooner than I planned due to the high water that I recently drove through).
 
Originally Posted By: Jeff_in_VABch
Wouldnt you guys think that overfilling the diff would cause more drag/pumping losses as the ring and pinion are deeper in the oil and pull a larger ring of oil around the ring gear/carrier?




Once the ring gear starts to move, most of the oil is not in contact with it: The oil get thrown to the back and side of the housing. I think at highway speeds most of the lubing is done by splash lubrication.
 
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