Rear Differential Fluid
 

Anybody use additives? I run a 1.5 way Cusco RS. great diff and i've been running royal purple 75W90 in it and with fresh fluid its great, very little or not clunking, really smooth engagement and the transition from the lock on throttle to the release when you dump the throttle isnt nearly as aggressive and doesnt upset the car. my question is, it seems that the diff. goes back to mediocre after about 3-5,000 miles. still works its just a rougher engagement and that transition from on throttle to OFF throttle is almost nerve racking in quicker corners, really rotates suddenly. I was wondering if anyone uses additives that may improve the longevity? or am I just being a crazy person?

it does see some aggressive driving. mostly autox on 285 V710's (or at least it has been, not anymore) and lots of hard running on mountain roads with little use in between, just seems like every 3-5k for diff fluid is a bit much.

Try better oil, like Redline's. Royal Purple isn't bad, but there's better.

You can easily adjust the slip by combining their regular 75W90 (with too much slip additive) and 75W90NS (without any) in different proportions. Or, use straight 75W90NS and add slip bit by bit until it's where you want it. I've not found a gear oil that lasts longer than Redline.

Amsoil's products come highly recommended as well, but I can't personally vouch for them. If their gear oils come with the LSD slip additive already added, I would bet there's too much.

Asterix

I would recommend Motul, I have the Nismo diff and thats the only thing that will control it. I have used Amsoil for ever, but it just couldn't keep the nismo quiet. Spend a few bucks on Motul and won't have to add any slip additive. My car gets beat on alot, track days, dragon, and autox, so mileage will be cut down. I might try a diff cooler this year. This is my first time with Motul, so I will see how many miles I can get. Amsoil I was going through fairly quickly

Motul from FP or stfu!

+1 :thumbup: been running it in my car since 15k and no issues to report!

I change my carbon diff every 3-4k miles and its perfect!!!

I've run Motul and Motorcraft fluids in my Cusco RS with great success. IIRC I'm still on the Motorcraft stuff