BG Syncro Shift II; safe/good for Diff?

[munizfire]

Hey all, I just bought 4qts of BG Syncro Shift II for my tranny oil change. I also bought one 6oz bottle of BG Universal MGC.

IF everything goes according to plan, I'd have 1.3qts of Syncro left over (assuming I don't use the modifier, and the fluids chart from LMR is accurate). Seeing as the diff takes 1.6qts of gear oil, I was wondering:
- Could I use the leftover 1.3qts + 6oz of modifier on my diff? (would this even a good idea?)

I understand I might be running a little bit low on 'gear' oil for the diff, and a fellow track enthusiast co-worker suggested I just add a couple of ounces of any 75-90 gear oil to make up any potential missing oil (to avoid running dry).

The reason I'm looking into cutting it with another oil is I'm planning on doing the work this weekend, and I wouldn't be able to get more Syncro until next week.

Alternatively, if it a terrible idea, I can just buy a different (locally acquired) oil for the diff.
If so, what would be the best option?

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[ice445]

I wouldn't, you want a GL-5 spec oil for a hypoid gear interface, not GL-4 which is suitable for transmissions with brass synchros. I'm sure it would work, but for the effort involved you're better off just doing it properly.

Any 75W90 can be used for the rear diff, but the clutch type can be sensitive to friction modifier choice. I use redline 75w85 with 2oz of Motorcraft XL-3. This is as close to the OEM spec as you can get without using the OEM oil, but 75w85 is not easy to find locally while 75W90 is. The easiest thing to do is probably go to any auto parts store and pick up the Mobil 1 or Valvoline 75W90 with limited slip additive, and then see if you get chatter on low speed sharp turns. If you do, add 1-2oz of the BG additive you already have.

 

[Optimum Performance]

No, do not use SSII in your differential. Differentials require a differential lubricant.

 

[NGOT8R]

I have BG Ultra Guard with LS in my diff. I put it in about 1000 miles ago. No issues thus far. They also offer it with without LS.

I also have the non LS variant on hand too. I’ll try that too at some point to see if there is a difference between the two.

 

[munizfire]

Thank you all, will not use the Syncro on the diff.

What would y'all recommend for a daily driven S550 with occasional track days (maybe 4-6 a year) living in AZ. (preferably something I can get at a local shop, since I'll be doing this today)


Also, should I use the BG modifier (Universal MGC) in the diff or in the tranny?

 

[Optimum Performance]

75W-140LS

 

[munizfire]

75W-140LS

Thank you.

I assume something like THIS, would be adequate? Since it has additive, I guess using the BG Universal MGC on the tranny would be the way to go?

 

[Optimum Performance]

Thank you.

I assume something like THIS, would be adequate? Since it has additive, I guess using the BG Universal MGC on the tranny would be the way to go?

Yes, 2 of those would work fine.

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