KAOS_3.0
Hard-core CEG'er
The differential gears on most front wheel drive vehicles are not hypoid gears. Hypoid gears are needed for rear wheel drive. To minimize the driveshaft hump, the pinion gear is moved as close to the bottom of the ring gear as possible and the resulting gearing applies tremendous pressure on the gear faces. This extreme pressure would kill the gears (metal breakdown) very quickly if not for ep (extreme pressure) additives. The ep additives are somewhat related to friction modifiers.
Front wheel drive transaxles usually do not have hypoid gears. As a result, most do not need ep additives. The level of ep additives is part of what determines the difference between GL4 and GL5 specifications. Manual transmissions do not need ep additives, but they may need friction modifiers. Manual transmission fluids can be GL5, but they should be specifically blended for manual transmission use so that the entire additive package is appropriate. Something to be aware of is that older style GL5 additive packages may not be compatible with yellow metals (synchros). Only use GL5 in manual transmissions if the label says it is safe for such use.
ATF is a gear oil. It is made to lubricate the gears in an automatic transmission. It is specified for use in many manual transmissions. There will always be a debate as to if it really should be or not. One of the problems with using gear oil in a manual transmission meant for ATF is that some of the gear oil additives may not be the best for the application. This seems to be the case with Contour MTX75 transmissions, especially those with higher than factory power levels, when Red Line MTL was used. The fluid sludged up and the sludge blocked some lubrication channels on the shafts of the spyder gears. This was the topic of one of the longest threads in the old forums titled "watch out". Subsequent oil analysis of new MTL showed that it did not have a very high TBN (total base number) which is an attribute that fights sludge creation. The gear oil additives are what broke down causing the sludge.
Ford Honey is very near 10W40 engine oil. It has a high TBN. It is made mostly of group III base (considered synthetic in the US). It has little if any friction modifiers or ep additives. Some suppliers (Royal Purple for one) recommend their synthetic 10W40 for use in our transmission.
Probably more than you wanted to know.
I actually want to know more...
so would royal purple synthetic 10w40 engine oil with a bottle of friction modifier be better than royal purple synchromax?
also, do you think the lucas atx additive I have mixed into the synchromax will sludge it up?
where are these channels that block up on the spider shaft? I dont remember seeing anything like that in there.
also, do you have an opinion as to what cocktail is best for the open diff VS. what cocktail would be best for the synchros?
feel free to write a novel in response