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Transmission oil


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I recently swapped a five speed transmission from a 1980 720 into my 521, and put new yellow metal safe GL-4 in the transmission.  It shifts slowly, with a bit of a clunk, when cold.  

Is there something like a friction modifier I can add to the transmission, or add some ATF to make the transmission shift easier when cold?

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I use the GM Delco Friction Modified Synchromesh Transmission Oil for the new Camaro and Corvettes. I imagine the Royal Purpla and any other colored semi-synthetic oil is the same base stock and will perform the same. Then just go by which is cheaper. 



I think this is it. The part number is different when sold in Canada but the same stuff.


I was extremely pleased with how well it works, the most notable thing was the cold shifts when first starting out in the morning. It used to be stiff into 2nd until warmed up slightly and this went away entirely. Another was down shifting even when warmed. In fact I rarely did it until at the slowest sped possible. It almost always was the cause of a small grinding into 2nd and forget first above jogging speeds. That also went away. I still don't down shift much but it's there now if I want it. Last is the shifts are faster with the same effort used before. Not that I shift fast but it better matches the engine revs now than before. The mechanics of the shift seem more 'clicky' .... hard to describe. Not as muffled as before, more of a positive, reassuring click into every gear.


The fluid is slightly orange of yellow and thin like engine oil. It isn't cheap at just under $20 CDN about $12 US? Lordco had it and it cost me $36 total but I got twice this in results. I love it.

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