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Old 05-15-2014, 07:12 PM   #1
jawknee5
 
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Default High mileage differential oil change...

Howdy folks. I'm needing a little help on my high milage 1998 mustang gt.

It's got 200k miles on it. But then engine only has maybe 100k. So it runs like a champ still. My brother owned it before me so I didn't know what had done to it maintenence wise.

Well I found out recently he has never changed the differential fluid! Wtf?

So obviously I should change it asap, right?

What oil though? I see a lot of people using royal purple 75/140 or whatever it may be. Is this good for a high milage differential? Or should I select one without friction modifiers in it and add my own?

It doesn't seem to make noise, maybe a bit but nothing terrible. It could also be coming from something else back there. I don't know really. The dmn car is so loud I can't really hear anything but rumble. But I love it. I figure changing old diff oil would be a good first step?

Thoughts?
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Old 05-15-2014, 08:32 PM   #2
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You only need friction modifier if you have a limited slip differential.
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Old 05-16-2014, 08:57 PM   #3
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I just changed mine out with amsoil. A lot of times you won't need the friction modifier and it's a bit cheaper than royal purple.
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Old 05-17-2014, 08:43 AM   #4
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You can check to see if you have a limited slip rear by checking the body tag axle code in the driver door jam area, the tag on the axle, or you can jack up both rear wheels. If, when you spin one wheel, the other spins in the SAME DIRECTION, you have a limited slip. If the other wheel spins in the OPPOSITE DIRECTION, you have an open differential.
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Old 05-17-2014, 12:11 PM   #5
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It's easier than that, all '96 through '04 GTs have Traction-lock...
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Old 05-17-2014, 12:22 PM   #6
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Quote:
Originally Posted by cliffyk View Post
It's easier than that, all '96 through '04 GTs have Traction-lock...
I'm not entirely sure that's correct....

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Old 05-17-2014, 12:42 PM   #7
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Quote:
Originally Posted by VTX1800N1 View Post
I'm not entirely sure that's correct....

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If there is one guy on this board that could be called a master, it's Cliffyk. And he is correct, all of the GT's came with traction lok.
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Old 05-17-2014, 01:04 PM   #8
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Quote:
Originally Posted by JC316 View Post

If there is one guy on this board that could be called a master, it's Cliffyk. And he is correct, all of the GT's came with traction lok.
Could very well be. Thought I read somewhere about that being a factory option for GTs rather than standard.

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Old 05-17-2014, 01:27 PM   #9
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If you use a synthetic oil you don't need the friction modifier.

If you use the friction modifier get the Ford one but be careful, its some of the stinkiest stuff on the planet. One drop on your shoe will make people think something is very wrong with you.
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Old 05-17-2014, 01:31 PM   #10
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Quote:
Originally Posted by CalBoy101 View Post
If you use a synthetic oil you don't need the friction modifier.

If you use the friction modifier get the Ford one but be careful, its some of the stinkiest stuff on the planet. One drop on your shoe will make people think something is very wrong with you.
Wrong. You need the friction modifier either way.

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Old 05-17-2014, 01:31 PM
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