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Old 08-09-2015, 12:25 PM   #1  
Urambo Tauro
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Default Gear Oil and Friction Modifier

I'm rebuilding the 8.8 on my 1995 GT, and was trying to decide what lube to fill it back up with. The FRPP carbon Traction-Lok kit I'm installing specifies the use of synthetic oil and XL-3 friction modifier.

I was thinking about going with Royal Purple, Mobil 1, or maybe Valvoline. But many of the newer formulas claim to already have friction modifier in the mix. Since there are multiple kinds of friction modifier, is it even a good idea to trust a "one-size-fits-all" solution?

I figured I was probably overthinking all this, and have already decided to use Motorcraft oil and modifier. Can't go wrong with that.

But I'm still curious about the use of friction modifier with oils that claim to already have it. Another thing that I found odd was that Ford's instructions (which cover both IRS and solid axles) call for 4oz of modifier either way. If you have IRS, its 3.5qt capacity gets 4oz of modifier. If you have solid axle, its 5.5qt capacity also gets 4oz of modifier (I would have expected 6oz to maintain the ratio).

What are your thoughts?
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Old 08-20-2015, 11:50 AM   #2  
mjr46
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you can buy the synthetics such as Valvoline with the modifier already in it and be fine...however we always add the ford modifier on top to reduce any possibility of chatter...and when I rebuild T-LOK...YOU NEED the modifier to soak the clutch packs in for 20 min before assembly and after that I just use a suction gun and suck it out of the container I used for soaking and put the rest into the rear end.
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Old 08-20-2015, 10:17 PM   #3  
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I can't figure out why Ford's instructions say to dispose of the friction bath after soaking. Seems like a waste of (perfectly good?) modifier, that could be added to the pumpkin.
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Old 09-10-2015, 01:17 PM   #4  
movielover40
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I was at the oil change place and they wanted to replace my gear oil and charge me quite a bit for it.

Is there a mileage limit on when to change it?
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Old 09-10-2015, 01:39 PM   #5  
Urambo Tauro
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On my '95 it's good for 100,000 miles.
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Old 09-10-2015, 02:03 PM   #6  
movielover40
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Thanks for the info Urambo. I don't have near that many miles. The guy tried to tell me you should change it every 30k.
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Old 12-08-2015, 08:03 PM   #7  
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You should change your gear oil every 30k, its not that expensive and if you drive it normally you'll do it once every 3 years.
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Old 12-10-2017, 11:47 AM   #8  
Buck Sergeant
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Default Gear Oil and friction Modifier

Urambo Tauro, I have the Ford Performance Differential Cover for added oil cooling when pushing the 60 foot barrier. I use Ford Full Synthetic 75w-140 , and the 4oz friction modifier additive. After two years of questionable use of this 2014 GT Premium, with everything American Muscle can sell me, I am completely satisfied/confident. As far as soaking the Carbon Fiber clutches, mjr 46 is right on the money. The friction modifier draws out contaminants, and prepares the clutch pack for your 50 foot burn out as soon as you take your ride off the lift. DON'T use the modifier used to soak those clutch plates. Yes, for our type of driving, change the differential fluid every 30,000 miles. Yes, the 100,000 mile change if for "normal" driving habits. Need I say more.
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Old 12-10-2017, 12:58 PM   #9  
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Thanks for the input, Buck. My apologies for not updating this thread. Motorcraft 75w-140 is indeed exactly what I ended up going with, plus 4 oz of Motorcraft friction modifier. My axle has been quiet and trouble-free for the past two years now.

I ultimately decided that it was simpler to just use the factory recommended fluid + modifier, instead of agonizing over whether the modifier already included in aftermarket fluids would be sufficient, or if the extra additive would have any ill effect. Oh, and I did end up using fresh friction modifier (not the clutch-bath stuff) for final fill, in the quantity recommended by Ford.

I'm still not sure why solid axles like mine are supposed to get a lesser concentration of modifier in the fluid, as opposed to IRS diffs. It's hard to imagine that the modifier would stay in the diff housing alone while the rest of the extra gear oil moves around the axle tubes. But I guess that's just a matter of curiosity now. It's obviously enough to keep mine from chattering.
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Old 12-11-2017, 07:16 AM   #10  
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Default Gear Oil and Friction Modifier

Urambo, great news. Glad everything worked out for you.
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