Rear diff lube question

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Dec 29, 2005 | 05:13 PM

t_b

Thread Starter

Mountain Pass

Joined: Jun 2005

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Rear diff lube question

I'm swapping out the rear differential cover this weekend and bought Royal Purple synthetic gear oil. It mentions that it already has limited slip additive in it. Will it be ok to use this lube all by itself, or would it be prudent to add some friction modifier?

Thanks!

Dec 29, 2005 | 05:16 PM

ford390gashog

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Joined: Jan 2004

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From: Brentwood,CA

do you have a l/s? make sure to use 75w140 lube and 4 oz friction modifier.

Dec 29, 2005 | 05:30 PM

t_b

Thread Starter

Mountain Pass

Joined: Jun 2005

Posts: 152

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I guess it would have helped to mention that I have a limited slip rear.

390 - I am all set with the R.P. 75W-140 and a couple of 4 oz. bottles of friction modifier (one bottle per three quarts of lube, I believe) - I am just wondering if the "limited slip additive" that R.P. includes in their product makes the addition of extra friction modifier unnecessary.

Dec 30, 2005 | 09:24 AM

bterry

Elder User

Joined: Feb 2005

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If you put in too much, your LS won't work as designed. When there is not enough, the rear will 'grab' too much and you'll get a shudder in the rear when making low speed tight turns. The modifier is what lets it slip a little. You can always add more, but taking it out is harder (and more expensive). Before adding more be sure to try it after the rear gets warm for driving. Heat in the rear will make it grab more.

Dec 30, 2005 | 09:37 AM

Ralph Reeves

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Hi .I have a 2003 f150 with 373 Ls .It has vib at low speed what would be the best thing to start with .

Dec 30, 2005 | 11:05 AM

slc10844

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Joined: Oct 2003

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From: Baltimore

Quote:

Originally Posted by t_b

I am just wondering if the "limited slip additive" that R.P. includes in their product makes the addition of extra friction modifier unnecessary.

If the lube has it in already you shouldn't need to any more.

Dec 30, 2005 | 02:31 PM

biz4two

Lead Driver

Joined: Sep 2003

Posts: 5,844

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From: Albuquerque

I agree with slc...

R.P. already has the modifier included...thus no additional or separate modifier is necessary. R.P. has you covered.

t_b -- What brand cover are you installing? (curious...cause I am looking for a rear cover). Thanks!

biz

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Dec 30, 2005 | 03:16 PM

t_b

Thread Starter

Mountain Pass

Joined: Jun 2005

Posts: 152

Likes: 4

Quote:

You can always add more, but taking it out is harder (and more expensive).

A very good point, bterry - thanks!

I guess that I'll go with just the Royal Purple, listen for any chatter in the corners, and add some friction modifier if need be. Thanks all!

biz - I ordered a Mag-Hytec cover. Magnetic drain plug and dipstick, o-ring seal, and +/- 6 quarts fluid capacity (about double of stock) . Should keep the rear gears happy for a long time.