The owners / shop manuals call for Mercon in the front differential of my 95 4.0 AWD. I've searched and found that some folks believe this to be a misprint and we should use gear oil.

Has anyone filled with Mercon? Any problems? Thoughts?

Thanks,

Gary

 

Our resident differential drivetrain engineer type recommends 75w70 diff. gear oil which has far more antiwear and friction modifiers than Mercon ATF...hypoid diff gear sets are hard on any oil.....not a owners manual misprint, Ford eng. spec'd Mercon so there would be fluid continuity between front diff., tranny and transfer case.....

the Dana 28 in all other apps specs 75w90....Dana specs 75w90....
i run 75w90 Severe Gear extreme duty Amsoil 75w90 synthetic in mine...runs lower temps...no longer fry fingers on case in summer
such a small volume of oil that cost is not factor....wear and part life is....

 

96_4wdr, that makes sense to me. I assume it was originally filled with Mercon so I have a _lot_ of miles on that ...

BTW, I noticed that Dana corporation has filed Chapter 11. What will become of our warranty

Gary

 

If Ford said that the front axle can run in ATF, then they must have validated it as such. But that still don't make it right! What I keep coming back to is that the front axle still contains a hypoid ring and pinion gear set. Hypoid gears really ought to be run in hypoid gear oil, which is typically of the 75W-90 or so variety.

It may be that the Mercon they specified had hypoid additives in it. However, ATF usually doesn't because a lot (although not all) of those additives attack bronze components in a transmission (such as syncro rings). So without knowing what was specifically blended into the oil Ford called out, I don't think its safe to dump any old ATF in there. I think it's best to default to what is known to work in (and is blended for) axle applications.

 

The only reason mercon is recomended is that it causes less friction and hurts fuel mileage less.

Best anti wear properties are definitely with gear oil.

It is not uncommon to lose 10% of transmited power to frictional heat in a differential. If you doubt this notice on the next rainey day the differential of the car in front of you. They are always dead dry from the heat generated.

Ken

 

Some silly trivia - most of the heat generated comes from the ring and pinion, not the differential. The differential actually only contributes a small amount to it, a little more if it's an LSD. But the gearing within the diff is static (relative to the diff case and ring gear) most of the time, and only turning slowly the majority of the time it is dynamic. On a normal day, the oil in the axle will be in the 150 degree ballpark. Warm, sure, but not super-hot compared to other things in cars... Now, if you get into a prolonged differentiation condition, such as running a minispare down the highway all day, then the diff can add significant heat to the oil, and can double its temp. But that isn't a normal operating condition.

Oh, BTW, ATF may have less drag on components spinning in it, due to its lower viscosity compared to gear oil, but that doesn't necessarily make it low friction. In fact, gears operating in ATF will generate a bit more friction in their meshing then gears operating in gear oil. The more viscous oil leaves a heavier film of oil on the gear teeth, which provides better lubrication then ATF can. I've also seen this backed up in dyno testing - a differential's torque bias ratio can increase as much as 25% (IIRC) if its running in ATF rather then 80W90. TBR is a way to characterize the amount of friction being generated will differentiation occurs, the higher it is, the more friction there is. Under those conditions (especially in the minispare example), ATF will allow greater heat build up to occur then gear oil will.

 

Thanks for all this scientific/engineering discussion regarding friction coefficients and fluid-n-dynamic drag. But what I want to know is...

Most of the discussion focused on AWD applications -- should I use the gear oil recommended in this thread for my rear-wheel drive 4.0L Aero??

 

Torsen Rick, ken1mod, 96_4wdr, are you guys running gear oil in your front differential? I wonder if I should pump mine out and replace it. Can I just pump it out through the filler hole, or would there be a problem if a little Mercon is left in there and mixes with the gear oil.

LTCPipkin, the rear differential is spec'd for gear oil.

Gary

 

the Aero rear end specs 75w90 or 80w90....i would use the 75w90 in cooler climates....

i run 75w90 Amsoil Extreme pressure synthetic in the front axle....can drain with drill driven rotary pump from marine store and small 3/16" semi stiff tube for suction end with reducer to match pump....most come with a stiff tube to fit down dipstick which works well

 

Well this is a drag...I just replaced the ATF in my front diff with new Mercon, since I had it out. The old fluid, while not the clear rosy color of fresh ATF, was only slightly darkened, after 120k miles. My feeling is that the front diff does not get a lot of driving load under normal circumstances. (All its parts are so small.) I like the idea of better protection with the gear lube, but I don't know if I'm up to sucking out the fluid through that little hole. Would gear lube and Mercon mix well?

I understand about the torque bias ratio; that's how the Torsen (and Quaife) works. They must get pretty hot if you turn a lot.

One of the most inefficient, but strongest, differentials is the Ford 9". Its pinion engages tangentially to the ring at the lower edge so its nose can be supported by a third bearing. It makes the pinion very strong, but that engagement creates a lost more friction than the more common design where the pinion engages the ring normally at the front. It is known to run hotter than other diffs, so a good synth gear lube will be very helpful there.

 

LTC:

Yes, the rear differential definitely requires gear oil. I just put Mobil I synthetic gear oil in the rear differential and forget all about additives for limited slips. My understanding is that using synthetic gear oil would negate the requirements for additives in the LS differentials. So, to make a long story short, just put synthetic gear oil in there and sleep well.

XLT:

I would just leave the Mercon in there. Don't sweat it. Boy! Aren't we a bunch of hypochondriacs!

 

The last time I worked with Mobil 1 gear lube, it smelled like it had the friction modifier already. Similarly, it seemed like the Dexron III/Mercon ATF smelled like it had the same friction modifier.

On a slightly different note, I just changed the PS fluid in my most recent operations. I think I had used semi-synth Quaker State ATF before (Dexron III/Mercon/Mercon V rated). Now that I know that it's supposed to be Type F, that's what I put in (non-synth). But now it's really noisy when I turn. I'm wondering if I should have conctinued to use the multi-purpose synthetic ATF.

 

A lot of synthetic gear oils are blended with modifiers already. So it really isn't necessary to add more unless there's a specific issue, such as getting excessive clutch chatter in the LSD during turns. But if you aren't then you don't need extra modifier. Of course, if you aren't it could also mean that your Traction Lok (if you have one) is worn out as well... However, I never have that issue with the Torsen in my van

 

Was thinking about getting this drill pump to suck the front diff fluid out, With the fittings on this unit what reducer would I use which would be compatible with the pump and the 3/16" semi stiff tubing to couple to the one end? Hopefully a link for a setup I could use without breaking the bank to just drain the liter of fluid out and replace it. TIA, BRGDS,

p.

http://www.ebay.com/itm/Draper-18937-Drill-Powered-Pump/121515802958?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D30251%26meid%3Dd0c33d99a8d24c3db10b920a14145ea7%26pid%3D100005%26rk%3D1%26rkt%3D6%26sd%3D351384782263&rt=nc