I am getting ready to change the trans and diff oil in my 77 124 and bought some Royal Purple MaxGear for the transmission....and then I realized I still had two unopened bottles of Redline MT-90 that I bought years ago for a 89 BMW 325i. It's expensive oil so if I can use it...I need to use it up! So I emailed them again to see what they recommended for the diff....

According to Royal Purple, their MaxGear will work nicely on both the diff and the the transmission. No harmful additives to hurt the soft metals etc in teh trans and perfect for the diff.

Just wanted to share this as I have read a TON of different info on the web about what oils to use. I am not affiliated with RP at all....just wanting to share some info.

So it will be RL MT90 for the transmission and RP Maxgear for the diff!

For your 1977 Fiat 124 Spider manual transmission we recommend Royal Purple Max Gear 75W-90 (part #01300, quart bottle).
Max Gear is completely non corrosive and totally safe for use with soft yellow metals like copper, brass and bronze. Max Gear is completely synchronizer safe. Max Gear is an API GL-4 and an API-5 rated oil, so it is also appropriate and recommended for your differential as well.

Thank you for choosing Royal Purple!

Best Regards,

James Morrissey
Sr. Automotive Technical Support
Royal Purple

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