Re: Quaiffe Helical Gear set for 4 speed
Posted: Fri Apr 12, 2019 10:27 am
rgh0 wrote:Yes modern GL5 oils contain less sulphur based anti wear additives to achieve the GL5 rating for sliding tooth contact so they are less corrosive for brass components.
The real question is why GL5 at all as the gear box is a helical gear set with only rolling tooth contact it should have no sliding tooth contact like a hypoid diff does which is what GL5 oils are intended for.
The other question is why a 140 weight oil compare to the lighter oils orginally used in this gear box. There may be minor differences in gear geometry but the loads and pitch circles and gear tooth contact faces are pretty much fixed by the dimensions of the box and the gear ratios so what is creating the need for such a signficant change. The heavier weight oil will also not help the syncro performance especially when cold
Maybe you can asked the "boffins at Quaiffe" that and see if you can get a sensible engineering based answer.
cheers
Rohan
I find the best trade off is not always easy to define : from what I've read AW (Anti Wear) additive used to be lead based, and has been replaced by phosphorus based additive in the 1990s. A sulphur based EP (for Extreme Pressure) additive has been developped so that a layer is bonded to the metal and prevents metal to metal contact by forming a sacrificial layer. Problem occurs when it bonds very strongly to yellow metal, so that a layer of that yellow metal can be peeled off as well (occurs at high temperature and pression).
To prevent that other additives have been developped, "buffuring" the sulfur so that it would not be corrosive to yellow metal, and I understand this is why manufacturers claim modern GL5 oils are not damaging brass synchros.
I've also read that GL4 would contain about half the amount of sulphur additive with respect to GL5 in average, so it's not a black or white situation.
There are also other additives (anti-foam, anti-rust etc)
(nb: film based EP additives using sulphur are not the only option, there is also the dispersion based approach, when molecules are in suspension and would end caught between the surfaces in contact without bonding e.g. Redline Shockproof series).
Ideally one would like the lower viscosity possible for reaching all areas, and at the same time that the film would stay and endure pression and shear when necessary.
Also, slipperiness has to be just right for proper synchromesh operation (friction modifiers FM can be added to play on that parameter, esp. for tuning clutch based LSD).
Yet in some cases (vintage racing) gearboxes are still exposed to harsh condition : I have in mind the Jaguar gearbox of a friend's E-type, that has a tendency to fail from the needle bearing between the input shaft and the output shaft... I would think that the main load there would be pressure, but obviously some shear has taken place eventually, to the point that the film was broken resulting in a time consuming gearbox out maintenance.
I know some of his fellows E-type racers mix oils (GL4 and GL5) in hope to get a better compromise (or is it superstition?), the price of synchros being a fraction of that of the gearset and synchros are not the weakest link apparently anyway (though most have a Moss gearbox, not the Jaguar 4 synchro gearbox, I'm not sure if the weaknesses are identical)... in any case gearbox lubrication is not a simple question (there are some discussions on lubricant topics, e.g. https://www.bobistheoilguy.com/forums/u ... cant_Rheol but it's still not obvious to solve the problem).