MG Midget Gearbox Oil

Last night. I checked the Midget's gearbox oil for the first time. I couldn't see any!

1.) What oil? Seemingly credible sources give the opposite advice, from "20w-50 or sae 30" to Redline 75w-90. Who is right, AND WHY?

2.) Change or top-up? I've had mechanics tell stories of people changing oil in old car gearboxes, have them fail soon after because of it.

Thank you.

Clarty wrote: Last night. I checked the Midget's gearbox oil for the first time. I couldn't see any! 1.) What oil? Seemingly credible sources give the opposite advice, from "20w-50 or sae 30" to Redline 75w-90. Who is right, AND WHY? 2.) Change or top-up? I've had mechanics tell stories of people changing oil in old car gearboxes, have them fail soon after because of it. Thank you.

The owner's manual calls for various motor oils for the 1275 Midgets but regular gear oil works fine. May need to lower the viscosity for very cold weather.

Not an expert on Midgets. I know B 4-speeds are fine with 20-50 but the o/d units do better with 30w Non-detergent (foaming issues)

MGBE is your friend-

Gearbox Servicing.

This is MGB centric, but the Midget info is also there.

Seeing how you dont know what oil is present, If it were me I'd change the trans oil completely.

Also, don't overfill it. I usually shoot for half a pinky underfilled (stick your pinky in the hole - ahem, the fill hole :) the front gearbox seal is just a spiral cut into the front cover. The rear seal is felt.

This only applies to the ribcase trans tho.

Kendall

Two different oils for MG Midgets.

All "A"-series powered Midgets (ie-"948cc", "1098cc" and "1275cc" engines) use motor oil in their gearboxes.
30W non-detergent motor oil is probably best, but you can use 10W-30 or 20W-50 with no real problems (the latter is more acceptable in warm climates).
Note: very early Midgets use the "smooth-case" gearbox (same as the Bugeye Sprite) and this was followed by the improved "rib-case" trans......but all of them used motor oil. And yes, don't overfill them.
The picture of your car shows a white RWA (round wheel arch) car which would have a 1275 engine, so motor oil is what you'd use.

And just for informational purposes: For newer 1500cc Midgets (ie-"rubber bumper" cars), the gearbox is a much different unit called the "Marina gearbox" (also used in Triumph Spitfires). These newer cars require proper gear oil in their trans, such as 75W-90 gear oil.

Not MG-specific, but remember that gear oils and engine oils are rated for viscosity at different temperatures (40C and 100C, IIRC). The actual viscosity of a 75w90 gear oil is quite similar to that of a 30w engine oil at comparable temperatures.

Clarty's rumor #2 refers to automatic transmissions and is just that , a rumor.

iceracer wrote: Clarty's rumor #2 refers to automatic transmissions and is just that , a rumor. The transmission was most likely ready to fail anyway. Changing the oil on a manual would not cause a problem.