Technical Hydromatic hard shifts cold, shifts like butter when hot

It appears that the Castrol ATF should be available in the U.S. as well. Though Castrol products don't seem to be found around here as commonly as some other brands.

https://www.castrol.com/en_us/unite...smission Fluid Core#tab_transmax-high-mileage


Around these parts, this mineral-based Valvoline ATF might be easier to get your hands on.

https://www.firstcallonline.com/FirstCallOnline/product/details.html?

 

Ok, got to do a final report. I bought the Chalet Type A ATF off amazon:

https://www.amazon.com/Wholesale-Chalet-ATF-Type-1qt/dp/B076DN7BST/ref=sr_1_1?keywords=chalet+type+a+ATF&qid=1636570520&qsid=146-0977916-0710046&sr=8-1&sres=B076DN7BST,B01EKMGG92,B008QDV2JG,B000C9QX50,B001DKTG0G,B0089LSMSE,B086R9GDV1,B077XNQSMG,B01EGOR40Y,B07T7L31DZ,B08CS1P8NJ,B00DILUBL6,B07Q3H159N,B07NVZQ99P,B07MN2XS8J,B00DWFSJLC,B07QQM7XFF,B071YBH8P1,B000NU6GCS,B004L4YL92

It comes in a 12 quart case for $95. I drained at both the fluid coupling and main drain on the pan. I took out 9 quarts (measured) and put in exactly 9 quarts. After a 5 min warm up and fill procedure per the manual I took it for a drive. And the results were nearly instantaneously better. First shift was a bit rough still and once the new fluid flowed everywhere all the rest were like a different transmission. At easy and hard throttle no more banging. On a full throttle launch it will chirp the tires when going into second but no odd transmission noises to go along with it. Very happy.

 

The newer fluids like Dexron VI seem to lubricate things well enough, but the newer transmissions are also using some drastically different clutch materials on their bands and clutches. By doing so they can be built with fewer and smaller clutch disks and narrower bands. But the newer fluids have a different friction modifier additive to accommodate these newer clutch materials. And as a result the newer fluids react differently with the older organic clutch materials.

The same kind of issues can also occur with using newer synthetic lubes in older manual transmissions with brass synchronizer rings.