OS Giken OS-250R LSD Gear Oil (80W-250)

[Redd]

There's already at least a half dozen threads expounding on the virtues of the clutch-type OS Giken Super Lock LSD (all true!) so I won't get into that. But I did not manage to find much info on the OS-250R Gear Oil. So, I thought I would share my experience so that it is searchable for future reference.

The OSG LSD is a fantastically built bit of kit. Tolerances were so close to stock that my installer just put everything back with the original factory shims and gear lash was well within specs. However, he did not have the OS Giken LSD Gear Oil in stock during my install so we decided to use Redline Lightweight Shockproof 75W-140 gear oil for the break-in period. The Redline oil is one of the few oils tested and approved by OS Giken for their LSD, so everything should work well, right?

WRONG! After about 50kms of driving with the Redline oil, the rear diff started to make some scary noises. Chatter, binding, wheel hop, popping, clacking... you name it, I heard it. It was so severe and loud I thought someone had put a bag of rocks into my rear diff. Slow turns, especially in carparks, was torture. Even my installer, who builds race cars and who initially gave me the #BecauseRaceCar excuse, found the noise to be excessive. I did the recommended break-in process - tight Figure 8s for 30 mins - and that didn't help at all. I decided to tough it out for the 500km break-in period, then change the oil to OS-250R LSD Gear Oil.

500kms couldn't pass quickly enough. I finally did a diff oil change today and I was half expecting to see metal shavings and pieces of clutch being drained with the oil. The good news is that the Redline oil was relatively clean - not even black - so it was doing a decent job of protecting the clutches. Just that it was noisy as hell. After the oil change, OMG, that OS Giken gear oil is some sort of magic juice! Zero noise now. As quiet and smooth as the stock LSD!

TL;DR - You can absolutely daily drive the OS Giken LSD, but you MUST use the OS Giken OS-250R Gear Oil if you want smooth, noiseless operation.

[SAMM3Y]

👍... the osg fluid is thicc..

[Redd]

Yeah closer to the consistency of honey than a regular oil/fluid.

[tigermack]

Liquid gold.

[tdott]

Did you use the Redline 75W-140 without Friction Modifier? There are two types

[Redd]

Originally Posted by tdott

Did you use the Redline 75W-140 without Friction Modifier? There are two types

That's a possibility. And maybe why it was so horrendously noisy.

[tdott]

Originally Posted by Redd

That's a possibility. And maybe why it was so horrendously noisy.

That would absolutely explain it, the one without FM is made for open diffs.

[///M3 Gusta]

I've got a load of Royal Purple 75w140 in mine (breaking in 4.10 gears, used OSG) and it's fine.