I got a decent mechanic. I am coming up on 100K for the 2007 GT. The manual says to use the proper weight fluid for the diff plus friction modifier, I believe 4 oz. Mechanic says I don't need the modifier. What say 'ye?
100K Mustang diff fluid. Need friction modifier?
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A lot probably depends on the fluid going in.
The only way you don't need the modifier is if the fluid be used already has it in there.
If Ford limited slips are anything like GM LS diffs, you'l be in a world of trouble if you don't use that modifier.
If Ford limited slips are anything like GM LS diffs, you'l be in a world of trouble if you don't use that modifier.
Why wouldn't you need it? More importantly, why wouldn't you just spend a couple bucks to be safe?
Some synthetic fluids claim you don't need it, but you know what? Those guys don't have the information about your vehicle that Ford has; they're guessing.
Some synthetic fluids claim you don't need it, but you know what? Those guys don't have the information about your vehicle that Ford has; they're guessing.
Look for a black square with the white letters "LS" on the label. If it's not there, you need to add FM separately. Motorcraft diff lubes needs the separate FM, but Valvoline and Mobil 1 do not...I'm sure there are others as well.
Your mechanic is correct. The majority of brand name gear oil suppliers contain an LSD additive from the factory, no need to add a supplement. I have always used QS and still do.
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Redline or Amsoil are my top recommendations
Most synthetic fluids don't require the additive. The rear end will chatter when turning tightly if you use a fluid without it. No harm, just noisy.
My dad lost the rear end in his F150 about 15 years ago because he changed it and didn't add a friction modifier.
I would refer to the FSM and go by that, mechanics are typically wrong in this area.
I would refer to the FSM and go by that, mechanics are typically wrong in this area.
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The few times I tried using Mobil 1 in a trac-lok (Ford's "posi") dif, it still required FM after some test driving.
The Ford fluid does not come with modifier already mixed in so it must be added. Your Mustang does have a clutch type limited slip, so you need to make sure that there is a modifier in there.
Someone else said it already, but your owner's manual should detail what spec the fluid needs to be. I would follow that.
Here's the manual for your car: http://www.fordservicecontent.com/Ford_Content/catalog/owner_guides/07musog1e.pdf
It does, in fact, specify a fluid spec and notes to add FM in some cases.
robert
Here's the manual for your car: http://www.fordservicecontent.com/Ford_Content/catalog/owner_guides/07musog1e.pdf
It does, in fact, specify a fluid spec and notes to add FM in some cases.
robert
I still remember the day when I learned to rebuild a diff. It was a '98 ranger with a LSD. When it was time to refill the rear end, I didn't have any 75w-140 which was specd for it so I filled it exclusively with Lucas HDOS. It worked without a hiccup for years.
I use royal purple in my differential and even though they say it has a friction modifier inside I still added a bottle of Mopar friction modifier to it. A whole $7 and no risk of chirping around or breaking any metal components inside. Just add it. Better safe then sorry.
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