Quick diff fluid change question - Ford Mustang Forum
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post #1 of 3 (permalink) Old 09-12-2017 Thread Starter
PonyBoyW's Avatar
Joined: Sep 2017
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Quick diff fluid change question

I have a 09 v6 with a 7.5 rear end. Gonna change the rear bearings and the fluid is of course replaced also. The fluid I bought is royal purple 75W-140 with friction modifier addictive. Just wondering if I need to put my own friction modifier in also or is what's made with the fluid enough?

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post #2 of 3 (permalink) Old 09-12-2017
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Does the rear end even have a limited slip differential? If it doesn't you don't need friction modifier at all. If it does just use the fluid you bought. If the rear end chatters going around corners then you need to add some more friction modifier, if it doesn't you are good to go.

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post #3 of 3 (permalink) Old 09-13-2017
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Why did you by 75W140? That's too heavy for a street car. All you need is 75W90. Unless someone has installed a limited slip differential you don't need any additive at all.

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