Gearbox and backaxle oils

[Eric Worpe]

The original oil specified for both the gearbox and backaxle of the Tabc was called High Pressure 140, as in Castrol's Hi Press 140 which contained a low Sulphur additive to prevent the oil film breaking down at the contact points of the gear teeth. Unfortunately the term EP for extreme pressure started to be used for both High Pressure oils ( GL-4 spec. suit- able for gearboxes and spiral bevel type gears) and Extreme Pressure oils ( GL-5 spec. suitable for hypoid type gears). As an additive type oil was originally recommended for the Tabc gearbox and backaxle, Castrol's EP140 which replaces Hi-Press 140 or the Penrite "mild EP" or any other 140 oil to GL-4 spec. should be used. Use of a non-additive oil would not initially show any detrimental effects, but the long term consequences could be serious as the "gears", which are not available as spares, wear and become "noisy". Possibly the one modification that would prolong the life of the Tabc, is also the simplest. Do consider Aralditing a small magnet into the drain plug of the gearbox. Regards, Eric Worpe.

[Roger Furneaux]

Thanks for that Eric - all you need to tell us now is whether the amount of sulphur added really causes embrittlement of the bronze ball race cages. No problem with the better taper rollers - they have steel cages. good idea about the magnet, RS p/n 297-8703 (6mm diam) would do next time you are ordering from them! BTW the drain plug sold by Moss is hopelessly wrong (not tapered) and I have recently supplied some to Abingdon Spares with a larger than standard square head to take a 1/4" BSF spanner. ocTagonally Eric Worpe wrote:

> The original oil specified for both the gearbox and >backaxle of the Tabc was called High Pressure 140, >as in Castrol's Hi Press 140 which contained a low >Sulphur additive to prevent the oil film breaking down >at the contact points of the gear teeth. > Unfortunately the term EP for extreme pressure started >to be used for both High Pressure oils ( GL-4 spec. suit- >able for gearboxes and spiral bevel type gears) and Extreme >Pressure oils ( GL-5 spec. suitable for hypoid type gears). >As an additive type oil was originally recommended for >the Tabc gearbox and backaxle, Castrol's EP140 which >replaces Hi-Press 140 or the Penrite "mild EP" or any other >140 oil to GL-4 spec. should be used. > Use of a non-additive oil would not initially show any >detrimental effects, but the long term consequences could >be serious as the "gears", which are not available as spares, >wear and become "noisy". > Possibly the one modification that would prolong the life >of the Tabc, is also the simplest. Do consider Aralditing a >small magnet into the drain plug of the gearbox.

[Eric Worpe]

Hi Roger, Thanks for your E-mail. It seems generally accepted that sulphur additives cause problems with "yellow" metals, and I've wondered if even the low levels in the oil specified for the Tabcs could cause the bronze cages in the pinion thrust bearing to break up. Mark Jablonski mentioned that EP additives attack bronze via. a "de- zincifying" process, this would certainly be the case if brass were to be used, but I'm not sure about bronze. Mark did ask for comments from any metallurgists. One clue as to the failure of the bronze cage, might come from the break ups occurring in the half of the double bearing that carries the main thrust of the pinion. You've seen more diffs. than I've had meat pies, did you find this to be the case ? Recently I tried bending a thrust washer from a TC gear- box, which would have been exposed to the same levels of additive. The bronze washer didn't seem to suffer from any brittleness, however I'm not sure if it's a reliable test. Agreed, no problems with taper roller bearings. Regards, Eric.