zf gearbox fluid/oil

rodmanMember

Hello Everyone:
I purchased a ZF gearbox from Jerry at PIM Motorsports in around 2010. It had totally been gone thru and rebuilt. Castrol HYPOY C 80w-90 is what I've used in it. Read a thread on the redline lightweight oil and want to switch to that for smoother shifting. Also read that pulling the plug and letting it drain does not totally empty the gearbox. Said there will still be a little less than a quart left inside. I have three questions. Would it be ok to switch to synthetic at this point? Would adding synthetic with the residual non synthetic do any harm? Or, should I just leave well enough alone? Searched other threads to see if I could get this answered before posting this one but couldn't find an answer that satisfied me...
thks.

1/6/171:08 PM

Original Post

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