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As a side note, I started out using 85W-140W in my 4-spd. Shifted fine when cold, but on a hot day after 4-5 hours of driving I would get minimal gear clash if I shifted a little to fast.

I believe the multi-grade was thinning out to much at the higher temps, and not slowing down the gears between shifts.

For summer driving, I tried a single weight 190 synthetic, which eliminated the problem.

http://www.amsoil.com/shop/by-product/gear-lube/severe-gear-sae-190/

I have had the same problem with my 34. It turns out, for my car, that the replacement synchos that were installed many years ago were a different thickness. Tom Rasmussen (Odyssey Restorations) figured this out. I suggest giving them a call (https://packardinfo.com/xoops/html/modules/mxdirectory/singlelink.php?cid=6&lid=144).

Cheers,

Tom