Oil for your Rear End

[Edbert]

Get your mind outta the gutter...I'm talking about differentials and gear oil here.


I asked Powertrax what oil they recommended for their Lock-Rite diffs and they said to use whatever the original manufacturer recommended. On a restomod/Frankenstein car that ain't always so easy. I have gears from Richmond a diff from PowerTrax, bearings are federal...I think the only FoMoCo parts are the housing, and even it is not OEM (I snagged the 9" from a wrecked 1970 428 Cougar).

So what type and weight of oil should I use?

 

[68conv4sp]

The first time my 8" was replaced with a 3.00 Richmond Gears/Auburn clutch style pack and Richmond gears, I used 80-90 Synthetic w/ friction modifier. After a year it started to chatter during turns despite attempts to use other gear oils and weights. I just installed a pre-built 3rd member w/ 3.55/limited slip and the builder said to use conventional 85-140 w/ fric mod. He said although it is on the heavy side, his experience is that the slight loss in power and increased heat from the heavier oil was more than offset by long life.

 

[68conv4sp]

Oh, and I only have about 300 mi. on the new diff but all is quiet so far.

 

[downpiped]

When I rebuilt my versailles rear end with richmond gears, I used Royal Purple syn Max gear oil. It states on the bottle that no friction modifier is needed...

 

[Edbert]

I should have mentioned that my diff specifically says no friction modifiers or additives (since it is a locker). I am a fan of synthetics for engine oil in all my cars and trucks AFTER initial break-in. is such approach a common thing in diffs too, break in with regular petroleum based products them switch to synthetics later? Or if I want to run synthetic should I just go ahead and put them in now?

 

[garner67]

My rearend builder recommends only RedLine Gear Oil

I only have about 4 months of driving and ~1000 miles on my new setup, so far everything is a-ok.

 

[Edbert]

I'm familiar with Red Line and Royal Purple, don't think you can go wrong with either. Last question...how many quarts will I need?

(I know you use the fill-plug as a sight hole to determine when it is full, I'm just wondering how much to buy)

 

[fasttback]

I should have mentioned that my diff specifically says no friction modifiers or additives (since it is a locker). I am a fan of synthetics for engine oil in all my cars and trucks AFTER initial break-in. is such approach a common thing in diffs too, break in with regular petroleum based products them switch to synthetics later? Or if I want to run synthetic should I just go ahead and put them in now?

From my understanding, the "break-in" period for rear ends is a few heat up and cool down periods (under light load conditions). My Richmond and TrueTrac was done breaking-in within a couple of hours with Royal Purple.

For a 9" rear end you will need approx. 2.5-3 quarts (depending on a stock case or aftermarket).

 

[silverbluebp]

I have Redline Shockproof in my 9". 2 seasons of Autocross and 2 years of Open Track, no problems at all.