Anyone know anything about gearbox oils?

[BirvidikBob]

Being an obedient little soul I followed the instructions in the manual and changed the oil in my velvet drive gearbox. The specs were:

“Transmission fluid. General Motors Dexron II, Ford Merxon, Daimler Benz 236.6 or any SAE 10 hydraulic oil that meets Allison C3, Caterpillar TO-2 or equivalent.”

Having waved these specs round all the suppliers in Malta, the oil that I was advised met them was Shell ATF IIIG automatic transmission fluid. Unfortunately it didn’t have the SAE on the containers and I haven’t been able to find it on the web. The shell site did say that it meets Dexron IV and Allison 4 specs. Borg Warner in the States told me by e-mail that the C4 specs were permissible. They didn't specifically mention the ATF IIIG.

However, when I changed the oil, the new stuff was much less viscous than the old oil, and this worries me somewhat.

Is the ATF IIIG ok for the box?
Would 900 hours of use have increased the viscosity of the old oil?

I don’t fancy the gearbox packing in halfway across the Eastern Med.

 

[Skylark]

We'd all sleep soundly at night knowing that we'd repalced like with like and stuck to the manufacturers recommendations. Sadly, that's not always possible.

Engine and gearbox oil technology has progressed a long way in recent years. Newer oils can generally operate at more extremes of pressure and temperature and their ambient temperature viscosity is often lower. All adds to improving efficiency.

The great debate is "are newer oils a suitable substitute in older applications" If you don't have an alternative, they're certainly better than nothing.

I'd be happier knowing if there were any additives in Shell ATF IIIG that may not be compatible with the seals but if the gearbox previously ran an AFT I think its unlikely.

At the start of a new season or anytime after an oil change I'd use an infrared thermometer to check the stable working temperature of the box. After a reasonable run, check also for leaks.

Hope this is of some help.

 

[pvb]

I reckon the Shell IIIG will be fine. Later-generation ATF fluids were blended to give better low temperature fluidity, so maybe that's why it appears thinner than the old stuff. At operating temperature, it should be fine.

Do you know for sure what was in the box before?

At a pinch, these transmissions can also use straight SAE30 grade engine oil.

 

[AndrewB]

Dexron II ATF has long since gone. It was replaced by Dexron III and then Dexron VI, which would be fine. All the major oil companies make a compatible ATF, this grade is probably the most popular used, you are sure to find it somewhere.

Shell IIIG is compatible with Dexron IIIG which is an ATF designed for automatic transmissions. It should be OK, though Shell Dexron III is the correct substitute. What you must avoid are the the non-friction modified ATFs like Ford Type F. Engine oil is strictly emergency-use only.

 

[Happydaze]

Hi Bob
Just take the gearbox up to the Black Pearl with you next wed. evening and you can all get well oiled !!!!!!

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