This is normal and acceptable in all steel gears.

As the gears mesh under load, instead of wearing, the sacrificial coating of additives is either peeled off or worn off. In normal operation, this sulfur/phosphorous additive forms a black sacrificial coating on the surfaces of the gears, as well as anything it touches, with a little pressure and temperature.

This additive system is used in most gear oils today. Somewhere around 25 years ago a deactivated or buffered sulfur was developed that reacted with the phosphorous, creating the protective/sacrificial layer under the temperature and pressure conditions created inside of the transmissions without being corrosive to brass, copper, etc. Eventually it was discovered that the active sulfur caused corrosion of the brass and other soft metals used in differentials and transmissions.

A long time ago they began to be replaced by gear oils with a phosphorous additive (in itself a decent anti-wear additive) that used active sulfur to adhere to the gears and create a very solid sacrificial layer of material that could be worn off, thereby protecting the surface of the gear. The gear oils of a few decades ago had lead additives that were effective at wear reduction, but not very good for the environment. In order to understand the problems inherent to the use of GL-5 gear oil, one needs to understand a bit of history. These bronze components include all three (3) gear selector forks (saddles) of both the three-synchro and four-synchro transmissions, possibly the second speed baulk (synchro) ring of the three-synchro transmission, Second gear and Third gear bushings, and the Second gear to Third gear interlocking ring, as well as the bushings of the D-type overdrive unit. As though this is not bad enough, EP90 GL-5 oils are unsuitable, as their high sulphur content will attack the bronze metals within the transmission and the Overdrive unit. Other problems common to Overdrive units that are filled with EP 90W hypoid gear oil are excessive wear on the roller of the oil pump plunger and the eccentric cam lobe upon which it rides, a result of the higher pressures developed in pumping the heavier oil through the lubrication system of the Overdrive unit. The engagement of the Overdrive unit will tend to be more abrupt. There are certain problems inherent to the use of EP 90W hypoid gear oil in an Overdrive unit.

Jan 07 Updated Power Windows For Our ZBĮP 90 GL4 hypoid gear oil is used in the differential, not in the transmission.

Jan 11 Finally, Off The Rotisserie An.

Laycock overdrive rear seal squeak