@Erica_Moss is absolutely correct (once again)…Best thing I ever learned about shifting a Moss box is a slight pause between gears. Makes all the difference in the world. JS
I just read some old road tests…which discussed the necessary pause shifting thru the gears. I have always done that…it is slight…once you get the feel of it…too long or too short doesn’t work…
Correct specified gearbox oil is essential for the correct speed of the synchros to work…unless there is wear that changes the system. Then experiment for what is best…but most modern oils have too much friction reducers. So I think vintage type oils–low detergents, low in friction modifier compounds, but test viscosity in a monograde vintage oil.
STP is a completely newtonian fluid with a very steep viscosity/temperature line. At engine/transmission operating temps it is as thin as water (ran this test in my college Rheology class). I would never put that stuff in an engine I cared about.
Since I assume I am NOT the only slug who was unfamiliar with Rheology
I have seen a teardown of an engine where too much STP was added to the engine oil…thinking that for sustained competition–hot running it would be just great. Kinda looked like baked bean casserole left to cook on extreme high in a cast iron skillet for a few hours.
Makes one wonder if any of the teams that plastered their cars with STP decals while gladly taking Andy Granatelli’s STP sponsorship money actually used the stuff. I’d guess probably not.
Back when Andy G was pushing the product, I knew I guy that was sold on STP being the best stuff ever. He and his friends put it in everything, including personal cars as well as their dirt track race cars. They believed it helped. I do not know if it helped, but there was no evidence that it did any harm.
I think STP is ok in the recommended “dose”. Over dosing caused problems. Have to look up what it was…I think mostly a viscosity improver., it has a zink based additve…just more of the stuff used to make a high viscosity multi grade. It increased oil film…too much and not good in a modern and new car calling for 0-20, or 5-20. But ok for cars using 10-30 and similar. The film helps rings seal–(as Bardahl No Smoke and similar products advertised to reduce blow by smoking and increase compression)…that also helps the combustion chamber run cleaner…reducing oil into the combustion chamber, STP has some varnish reducing agents…like gumout does…but a lot less. But TOO much STP getting too hot makes a crusty mess…whether in oil ways, or if too much gets into the combustion chamber–as in a big oil burner engine.
I would not use STP in a trans…and only moderately in a worn engine.
Next to look up–Lucas Oil Stablizer–also a film and viscosity improver…designed to be “clingy”.