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Discussion Starter #1
Per ameridan's excellant site, the manual transmission specs a 75W/90 GL4 gear lube. https://21stcenturyfiat124spider.wordpress.com/specs/#MT

I'm curious, is the factory fill a synthetic gear oil spec, or a mineral oil spec? I wouldn't mind a gear oil that would provide a bit smoother cold start shifting, especially in the low gears. Shifting seems smoother once the transmission is up to operating temperature.

Can a synthetic gear oil be run in this transmission? Can I drain and refill without disassembing the entire car (more than the big shields under the car)?

Any other questions I'm not considering?

Thanks,
Steve.
 

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Since the factory indicates it is a long life gear oil, I would assume it is a synthetic one with the correct friction modifiers for synchro engagement.

I have three quarts of AMSOIL's 75W-90 GL-4 MTF ready to go in this car, but haven't had a time to change it out yet. It made an enormous difference in my Cruze. It's 90 degrees out right now so I'm not getting under the car till next week when it cools down a bit.

There's no reason why a synthetic gear oil couldn't be run in a transmission that originally used a conventional based gear oil. If you don't mind waiting, I can provide some impressions of how well this fluid performs in this transmission in cold and hot temps. It's on the thin end of the SAE-90 gear oil scale and is actually recommended for applications requiring either an 85 or a 90 weight gear oil. That should help with the cold shifting.
 

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Awaiting patiently, thank you!

Steve.
 

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Awaiting patiently, thank you!

Steve.
You are a patient man, looking at your previous requests.
I get it. I waited a long time for this car. Suggest you put the same lube as you use on the rear drive for your Moto Guzzi. Last thing you want seizing up is those hypoid gears.
OOOPS! misread your post, Steve. Thought you were discussing the LSD.
 

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Discussion Starter #5
Heck, on the Guzzi, that IS the transmission! Or is it the...?

(Moto Guzzi nomenclature has messed with more owner's heads that just about any other moto manufacturer.)

Steve.
 

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Heck, on the Guzzi, that IS the transmission! Or is it the...?

(Moto Guzzi nomenclature has messed with more owner's heads that just about any other moto manufacturer.)

Steve.
Hee, hee. No Steve, I was talking about the drive on the rear wheel, at the end of the drive shaft. Guzzi probably calls it the "shaft uppa the rear gear"
 

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I haven't had any issues that would prompt me to abandon the OEM oil. My 2K SE Miata MT6 had a "crunchie" on the 1-2 shift even after switching to Redline. The cure was the synthetic Ford oil used in the GT500 MT. That stuff did the trick.
This transmission is common to the NC, so checking with that forum seems worthwhile.
best regards
Pete
 

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Per ameridan's excellant site, the manual transmission specs a 75W/90 GL4 gear lube. https://21stcenturyfiat124spider.wordpress.com/specs/#MT

I'm curious, is the factory fill a synthetic gear oil spec, or a mineral oil spec? I wouldn't mind a gear oil that would provide a bit smoother cold start shifting, especially in the low gears. Shifting seems smoother once the transmission is up to operating temperature.

Can a synthetic gear oil be run in this transmission? Can I drain and refill without disassembing the entire car (more than the big shields under the car)?

Any other questions I'm not considering?

Thanks,
Steve.
Sorry it took so long. We had heat, then rain, then I couldn't find my bottle pump and had to order another. The thread is up.

http://www.124spider.org/forum/361-2017-124-spider-how-diy/17489-how-change-manual-transmission-fluid.html

The AMSOIL 75W-90 GL-4 MTF performed just as I had expected. I was not disappointed. The notchy shifting was eliminated and shifting is smoother and more consistent. This is the way it should have been from the factory.
 

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Discussion Starter #9
Sweet, well done, XR! Thanks for posting that. I'll ask a question in that thread.

Steve.
 
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