Eaton posi trac and diff fluid

Messages
109
Location
Allentown Pa
I had a Eaton posi trac installed on my 2009 Ranger 3.55 gears 28 spline 8.8 diff. 80w-90. Eaton recommends mineral oil so I tried 80w-90 Motorcraft and added friction modifier. It lasted 5k before chatter started. Then tried Valvoline 80w-90 with and added friction mofidier and it lasted 5k and started to chatter. So called Eaton techs, one said to try 75w-140 syn and don't add any FM . Another said 75w-140 would be not good for Pa winters try 80w-90 syn with FM . Both tech recommend Mobil1. So question is , can I use 75w-140 in Pa in the winter ? Also, can you mix say 80w-90 and 75w-140 Mobil1 ? and what exactly is chatter and how bad is it for the diff ? And if anybody uses a Eaton posi please give a recommendation for rear diff gear oil. Thanks.
 

BlueBird

Thread starter
Messages
109
Location
Allentown Pa
Originally Posted By: Bottom_Feeder
Strange that one of their techs would recommend you try not using FM for a clutch-type LS diff.
My mistake , didn't communicate right, tech said don't use additional FM , just what was in the lube already .
 
Messages
2,377
Location
Paradise of Florida
Don't blindly use FM. Use as little needed to prevent chatter and add more if there is chatter. Try Lubegard LSD additive. http://www.lubegard.com/~/C-268/LUBEGARD+Limited+Slip+Supplement Don't fear a double dose on your new diff. Use any full synth 75w90 and add as much additive as needed.
 
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24,432
Location
Dallas,Tx USA
If you want heavier than an 80W90 but lighter than a 75W140,how about something like Amsoil SVG 75W110? They also make the additive as well if needed (Slip Lock?).
 
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3,637
Location
Occupied Virginia
Found on the Moser Engineering website. For what it's worth:
Quote:
Eaton Posi What kind of oil should I use? Can I use synthetics? Do I need a friction additive/modifier? Eaton Posi units perform best when using GL4 (or better) mineral/petroleum based gear oil. A four ounce bottle of friction additive/modifier is also necessary for optimum performance.
EDIT: And that looks like it's been taken right from Eaton's site.
 
Messages
2,377
Location
Paradise of Florida
Is that 4 ounce dose perfor my 1 quart diff, or my 4 quart diff? One day they'll understand dose per sump size, and that not all LSD additives are bottled to the same concentration level. Let's not even get into the conventional vs synth debate here, especially when there are many full synth filled 75w85, 75w90, or 75w140 from the automaker where conventional isn't an option. And we trust those diff manufacturers and their engineers??? Since you used the Motorcrapht gear oil, it's only fair to give the GM DexronLS a try.
 

BlueBird

Thread starter
Messages
109
Location
Allentown Pa
Originally Posted By: Greasymechtech
Since you used the Motorcrapht gear oil, it's only fair to give the GM DexronLS a try.
Yes , the tech at Eaton said to try DexronLS too but I got the Mobil1 . They recommend mineral based fluid but that doesn't seem to last but 5k miles. So if that fails I guess the recomd trying synthetic or different weight. Is it ok to mix different weights gear fluid from the same manufacture , say 80w-90 syn M1 and 75w-140 syn M1 ?
 

BlueBird

Thread starter
Messages
109
Location
Allentown Pa
Well, Mobil1 synthetic 80w-90 with or without adding FM does not work. Chatter city ! Don't know whats left to try except going to a heavier gear oil.
 
Messages
1,686
Location
VA
This seems like a question for Jim Allen or Molakule. I have no experience with your setup, but some questions come to mind that might help you find an answer: When chatter started with the oils that DID work for awhile, did you try adding a little more Friction Modifier? Or did you just change the fluid? Are you using Ford's FM? It usually gets recommended in these differential threads. Maybe your issue is not the oil, but the FM breaking down. Is this the style of limited slip that would have come in your axle from the factory? If so, what fluid was recommended by Ford? Since an Eaton tech already suggested synthetic, contrary to the FAQ, a call to Redline could be worthwhile. They'll probably recommend their product, but they might also have some insight about why.
 
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9,614
Location
Pennsylbammyvania
I have the same exact Posi in my car, save for the smaller carrier, since it is a 7.65" ring gear vs. your 8.8. The Millers I had in there was very good, but my current fill of Valvoline Synpower 75W-140 (I'm also in Pa., and I've ALWAYS used a synthetic 75W-140 with NO problems in the dead of winter wink ), is the absolute quietest this very noisy rear axle has ever been. I use the heavier gear oil because of the overload of power/torque this relatively, and therefore weak, small ring and pinion has to deal with, (shock loading and otherwise) and it's noise due to improper initial set up. It must have had enough limited slip FM already in it, since I did not have to add ANY of my usual Motorcraft XL-3 additive, and had NO low speed chatter/groaning what so ever, also a first for me. Best of all, it was only $11.49 a quart on sale at NAPA. grin2 I have paid up to $30.00/qt. for various gear oils in the past, so this was a refreshing break!
 
Messages
2,377
Location
Paradise of Florida
Mobil-1 is a 75w90. Mobil 80w90 is conventional, and the last bottle I looked at had no LS additive. After every gear oil change, you need to work it into the diff by practicing the parking lot figure eights. What LS additive are you using and exactly how much? Not enough details and since you're not following any recommendations, good luck.
 

BlueBird

Thread starter
Messages
109
Location
Allentown Pa
well the M1 75w-90 synthetic with or without the FM did not work. It chattered so much I didn't want to drive it. Mineral 80w-90 with FM added is ok but doesn't last but 5k then its starts to chatter. Did this for 2 changes . The shop mech is adding the FM. Don't know exactly how much, im sure its ford product though. Next is to try 75w-140 gear oil. It's in the shop right now. The shop installed 3 of these units for customers, my Ranger , a Crown Vic and another pick-up .... all chatter on mineral after 4k - 6k miles so this, 75w-140 might be the way to go . DailyDriver - thanks for the tip !
 
Messages
772
Location
Ohio
I've typically seen the recommendation to add more FM to address chatter. I would be tempted to try that first. I've also seen the recommendation to drive in several tight figure 8 patterns after a change to better distribute the FM. Not saying any of this will work for you, but I've had a few of the limited slip diffs and this has been my practice. Never had any chatter issues.
 
Messages
772
Location
Ohio
You shouldn't need to add it every 5K. May just need a little more than the initial amount. Once the correct amount has been added, no additional should be required until the next lube change. At that point, you're basically starting over. Otherwise, I'd say something else is wrong.
 

BlueBird

Thread starter
Messages
109
Location
Allentown Pa
The 75w-140 Valvoline syn did not work without or with after adding 4oz FM . Drove to a parking lot and did the figure 8's real slow like , no good. Im sure they are the stock springs that came with the unit. Unless Eaton sent the wrong unit.
 
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