Bristol gearbox Oil?

[Exowner]

Hi all, can I ask what oil I should put in a Bristol gearbox? Non detergent straight 30? That's all the info I've managed to find on the forum.
   All advice gratefully received
   Thanks, Glenn

[Klassik Metall]

INracing recommend an 80w 90 such as Millers classic Gear Oil to GL4 spec.
   
   GL5 rated gear oils are generally not recommended for gearboxes and differentials containing brass/bronze components, such as syncro hubs.
   
   However, Penrite produce an 80w 90 GL5 gear oil that is compatible with yellow metals.
   
   Regards Luke.

[Exowner]

Luke, Many thanks for the info, just exactly the detail I need.
   Many thanks, Glenn

[tim isles]

Interesting to learn that a 80/90 W oil will work in a Bristol gearbox. I've always used a straight 30 which works well too. If you have an overdrive fitted then I would worry that the heavier weight oil might not do the O/D unit any favours, given that it needs to spin freely and engage/disengage quickly. Luke?

[Klassik Metall]

Tim, You are quite right if we're talking about an overdrive box then 30 weight oil is a better bet. However I have heard of people using thicker oils in overdrive units but have no personal experience of its effectiveness or otherwise.
   
   Gearboxes with overdrive units require something of a compromise lubrication-wise, as Tim rightly points out they need to work and engage/disengage freely, but the gears and syncros would really benefit from running a proper gear oil.
   
   Perhaps something like Penrite gearbox oil 30 or 40 would be a better solution and it's designed to work with OD units.
   
   Regards Luke.

[Exowner]

Tim, good info, however, I use Castrol Classic 80 in the Aceca which has overdrive. I was recommended this oil by an overdrive specialist.
    The Ace is non O/D. Do you think that if the Bristol box was designed today, they would still recommend straight 30? I somehow think not, but if 30 works......
   Glenn

[bill griffiths]

I recently read a marvelously informative booklet called "Which Oil".
   Unfortunately it did not provide any assistance as to the best oil to use in a pre selector box such as the Roesch designed box
   fitted to my Talbot 110.
   So I sought comment from the Author. He said that an SAE 30 monograde engine oil could be used, preferably one of the 'classic" products rather than a modern diesel engine oil which is the simplest and cheapest way to obtain a monograde.
   He added that it should not be friction modified. He suggested, for manual gearboxes as well, Castrol VMX80.
   It is of GL-4 gear wear protection and has, relevant to our respective climates, ideal viscosities of 180, 59 and 11 at 10C, 40C and 100 cSt respectively.
   I have since used it in the Talbot and in the Ace with overdrive, and plan to use it also in all the other manual gearboxes when oil changes are due.