# Rear Differential Fluid?



## Refractor (Jul 24, 2015)

I am going to be changing out my rear diff fluid here in a couple of days and wanted to see what type of rear diff fluid you guys are using. I was looking at using the Royal Purple 75W-90 with friction additive. 

It's a 2006 A4.


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## svede1212 (Nov 1, 2005)

Torco RGO 85w-140 and type "F" friction modifier. Dyno oil is recommended over synthetic. Another reason to use that is to fine-tune the modifier over an all-in-one. The friction modifier makes the oil slipperier. Our posi uses cones that act as clutches. The modifier lets them slip smoothly when needed. Too little and they will grab and let go making a chattering or popping noise. Too much and the cones slip when they shouldn't. 

It's a bit more trouble but the best way is to add about an ounce and a half (2 ounces is "normal") and drive it a bit to mix and then do slow hard turns in both directions. If it's fine you're done. If it pops add a little more and repeat. 

The smallest amount that doesn't pop is the best for always getting two-wheel burnouts.


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## Refractor (Jul 24, 2015)

Seems like you know your stuff, thanks for answering my questions. I'll go ahead and buy the Torco & the friction modifier. So about less then 2qt's of Torco and how much of the modifier?


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## svede1212 (Nov 1, 2005)

Like I said start with 1 1/2 oz and add more if you get noise in the back on slow, hard turns in a parking lot. I'd have no more than 2 oz total


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## doww301 (Oct 30, 2011)

*Toro Oil and additive*

Unless you live near a torco dealer you can order the supplies you need from torcousa.com. You want the RGO 85/140 weight oil- NOT the synthetic stuff. It comes in a 1 liter bottle-you will need two. Also, you want the type "F" friction modifier, not the usual type "G" that GM rear ends typically use. Their stuff is very good- pricing is $12 per liter of RGO oil and $9.65 for a 4 ounce bottle plus a few bucks for shipping. I suggest that you also get a pump from your local parts store as you will not be able to add the oil with any type of funnel I've seen. The very bottom bolt is the drain plug and can be removed with a 13mm socket. The fill plug is at the upper right on the diff cover and requires a 30mm socket or a large adjustable wrench to remove. I would recomemend pumping in about 3/4 of the first bottle then adding 1.5 to 2 oz of friction modifier to that bottle and then finish pumping in all that remains. Switch bottles and finish filling up the diff. Replace the 30mm plug-DO NOT OVERTIGHTEN - just make it snug and you should be good to go.


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## Refractor (Jul 24, 2015)

I just changed out oil 2 days ago, and so far this stuff is working great!


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