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MGB MGB tranny oil?

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Scott_Hower said:
Somewhere there exists a factory B/L TSB that discusses the merits of engine oil vs gear oil in an MGB gearbox. In fact, I think (I know) it's in a set of TSB literature that I sold to Tony last year.

:laugh:
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I've not gone through all of it yet - but I will!
 
Even though I use what the factory recommended, 20/50 in the 72 transmission/OD and I realize it's not the same 20/50 oil used 30 years ago, I was curious in the past as why the factory never mentioned anything about using any anti foaming oil of the proper viscosity. If it's in print, I didn't catch it.
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They didn't mention about anti foaming because there's nothing in the transmission to cause the oil to foam up. It's not going to get air whipped into it like it could in the engine.

The reason engine oil will work in the B's transmission is because it operates under mild conditions and is not a high shear environment compared to modern transmissions.
 
Ron, your comment mentioning ZDDP is interesting. Since the problems regarding the lack of ZDDP in newer engine oils have been well documented and those seem to be in regard to lubrication in shear then wouldn't the same be true of helical cut transmission gears as for cams and lifters? Perhaps with a new transmission after a rebuild we should use the same caution as for a newly rebuilt engine? I'm not disagreeing with Tony, motor oil was specified, but would the modern formulas still offer the same lubrication properties in the transmission as originally intended?
 
Good point, Bill...but does even that warrant 90wt?
 
Similar, but very different. The zddp was the least expensive additive the oil companies could find for mass production that would address the anti-scuffing features needed. Gotta remember that cam lobe, and valve train are sliding against each other. Imagine dragging your hand across a dry desktop until it falls off. Add oil to the desktop and you've simulated the adding of ZDDP. Now take your fingers and intermesh them, one hand to the other, now turn either up or down(ideally would need to turn full 360, but I am not double, or triple jointed) that is more like gear shear. THe gears are rubbing together slightly, but with minimal sliding. That is what the industry calls shearing... Also, unless a bearing or something fails, the heat generated in a trans will be alot less than in the engine. The cam is basically producing a heat spot through movement, while the gears are in continual motion and just transferring the energy along their respective shafts...long and winded, but hth.
 
From what I've been told, the gearbox does not require the same "cushion" as lifters because there is a far greater area of contact.

As for foaming, a standard gearbox shouldn't have any issue but a Laycock OD unit is a completely different matter. Oil is pumped through at 400PSI.
 
Can you really be certain that certain oils don't foam when sprayed at 400 PSI? I can't, which is why I would use the manufacturer's specified type or a close facsimile.
 
The oil is used as a hydraulic fluid to engage and disengage the the cone clutch, there's no sparying.

Motor oil or gear oil will both work fine in a gear box.
 
Mark Jones said:
But you don't get foaming from pumping, foaming comes about from agitation.
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Foaming comes from air in the system during the process of pumping! Not just from agitation.
I am very familiar with this subject as I have been over it with Caterpillar, but won't elaborate on it any further than this post.
Just for informational purposes;
My backhoe hydraulics must have the manufacture recommended anti foaming oil to prevent foaming and lose of pressure. My farm tractors use the same oils in there hydraulic systems. Any oil, pumped under pressure, can foam under the right circumstances. This can be caused by heat, possible leak in the suction side of the pump. Also, air insertion during the filling process, which can cause cavitation or use of improper oils. Now I'm talking 3,000 to 4,000 lbs pressure. I really don't think foaming would take place in a low pressure MG overdrive. But, anything is possible I guess.
 
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