Valvoline SynPower limited slip 75w140

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Ramping up to service the rear diff on my ‘11 FX4. Has factory fill in it, 111k miles so it’s going to happen real soon. I have Valvoline SynPower LS 75w140 on hand for the job. Will this be high enough quality to replace the original fill Motorcraft stuff? For the price of the Motorcraft stuff it must be good!
I know, I know, I should have done this a long time ago but life keeps getting in the way, I hope I don’t have to surrender my bitog card because of my negligence.
Thanks
 
From the 2011 Ford F-150 owners manual the recommended rear diff fluid is 70-140 synthetic fluid. However, your title of your posting says limited slip. The Synpower will be fine but you need to figure out if you need a friction modifier for the limited slip feature. A GM diff would need this. Any Ford experts out there?

SF
 
I used 75W90 Synpower in the tiny rear end in a WRX I owned. Bought it new, sold with 136K on it. Always used that for the rear end with zero issues.
Used Supertech 75W90 semi synthetic for the five speed manual. The WRX sent 50% of the power to the rear, but also consider a stick is harder on a rear end than a slushbox.
 
Originally Posted By: Snagglefoot
From the 2011 Ford F-150 owners manual the recommended rear diff fluid is 70-140 synthetic fluid. However, your title of your posting says limited slip. The Synpower will be fine but you need to figure out if you need a friction modifier for the limited slip feature. A GM diff would need this. Any Ford experts out there?

SF


I believe some diff/gear oils exist where a friction modifier isn't required as there is enough of whatever that good stuff is already in their oil.
I think Mobil is one, but that may depend on what weight it is? I want to try Pennzoil in my diffs but may just use Mobil again if a a friction modifier is req'd?
 
Just checked the Valvoline website. Both the 70-140 and the 70-90 have the limited slip additive. Check the Valvoline gear oil website to confirm. I’d stick with your original plan for the 70-140 because it’s what Ford recommends. They always use heavier gear oil than the others.

SF
 
That’s what I can’t figure out. To lock the diff I have to pull out the knob on the 4WD selector, which makes me think it’s just an open rear end until, somehow it gets locked at the pull of the switch. The SynPower bottles says it already has friction modifiers and no additives need to be added, presumably for a clutch pack type of diff. I just want to make sure this stuff will cover the lube requirements of the diff ie it’s not a low quality product. It is cheaper than Mobil 1 diff oil.
 
If you have the locking diff, no need for additional FM (unless it also has a LS in it as well?).
If you had a limited slip, you would need more FM than what comes in the bottles (the Ford stuff is a great FM, but stinks something horrible)
 
Try use your VIN to confirm your equipment. The Ford trade name of a limited slip differential for 2011 is Traction-lok or Trac Lok.
It requires 4 oz of Additive Friction Modifier XL-3. This is from page 418 of your owners manual.

What's not clear is if the locking diff is used with the Trac Lok or it it's an open diff when the locking diff is ordered.

Trak Lok and a locking diff are two different things.
 
It's very unlikely for the differential to have both a locking mechanism and clutch packs for limited slip operation. Simply not enough room in the carrier. Nevertheless Valvoline SynPower 75-140 is, in my opinion, the very best you can get for a Ford axle. It has perfectly sufficient and effective amounts of friction modifier included, and if it has a mechanical locker, this doesn't even matter.

Ford originally spec'd 80-90 conventional for the diff in my '03 Marauder, and later published a TSB due to "soft axles" failing where the rear axle bearings ride, due to poor heat treating. Mine ate it's axles up at 105k, I put new aftermarket axles and bearings in it, and after a thorough cleaning and inspection replaced the fluid with SynPower 75-140, obeying the TSB. My 3.73 Traction-Lok has been quieter, chatter free and performs flawlessly ever since. I drag race the car a few times a year and beat the snot out of it when I drive it.

In conclusion, I highly recommend SynPower in any Ford axle. This car uses Valvoline Synthetic products exclusively. Not a Valvoline fanboy, just happy with my results. I use Mobil 1 products exclusively in my wife's cars, including gear lube. Her AWD Hyundai Santa Fe has 178k trouble free miles with Mobil 1 in the rear diff and X-fer case. Only because she is a Mobil 1 fan, and stubborn. She's a gear head too. I think her affinity for Mobil 1 comes from being a Mopar girl, and SRT cars are Mobil 1 factory filled. (She's had a couple of Challengers...)
 
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For what it’s worth I looked at an owners manual for a 2018 Ford F-150 and both the locking diff and non locking diff took the same synthetic fluid. No mention of friction modifiers. I’d go ahead with the Syntech 70-140 and not add any friction modifier. You already have some in the fluid and you could always add some if you get chatter.

SF
 
Went through this … had a quart of MC … needed two. It was ridiculous …
Mobil 1 was twice as much for 140 -vs- 90 …
Came home with Valvoline SynPower …(2013 Charger)
 
Originally Posted By: Snagglefoot
From the 2011 Ford F-150 owners manual the recommended rear diff fluid is 70-140 synthetic fluid. However, your title of your posting says limited slip. The Synpower will be fine but you need to figure out if you need a friction modifier for the limited slip feature. A GM diff would need this. Any Ford experts out there?

SF

YES! If it's a L/S add the required L/S additive.
How I do it is, add a little bit of the gear fluid then add the additive to said gear lube bottle. Shake it, add to differential. After adding the required lube, take the truck to an empty parking lot and do a series of figure 8's (about 8-10) to circulate the lube/additive.
I have been doing this for YEARS with no problems, YET!
Also, I ALWAYS use a gasket on my differential cover.
A lonnnnnnnnnnng time ago (1987), a tech at ALANS GEAR WORKS (http://www.agearworks.com) told me no matter how much a L/S gear lube bottle reads NO ADDITIVE NEEDED, add it anyway!
 
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A lonnnnnnnnnnng time ago (1987), a tech at ALANS GEAR WORKS (http://www.agearworks.com) told me no matter how much a L/S gear lube bottle reads NO ADDITIVE NEEDED, add it anyway!


This is a safe bet. However, I decided to go with the advice of the Royal Purple rep, who stated that additional LS additive is not required for MaxGear 75w90 in my limited slip cadillac. I was skeptical at first, and cautiously tested it by slowly making sharp turns in a parking lot. No issues then, or in the 2 yrs since.
 
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