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MG Midget Differential 3.9 ratio to Morris Minor 1000

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tjt77 timothy Trevithick
Grass Valley, CA, USA   USA
its not compatible with the pre '62 M Minor axle.. ( mainly due to lack of oil filler/level hole) you have two routes to use 3.9 diff :- (1)fit the innards into the stock minor pumpkin .. or (2) change the axle case for a later, post 62 axle case with later oil filler/level plug in axle housing.

BTW..you need minimally 65hp / 80 ft lbs torque to pull a 3.9 diff in the minor.. to have acceptable 'off the line' and hill pulling capacity 75-80hp is about right .. you'd then need to upgrade brakes to cope with the added power..although post 62 (8" front drums) with a servo added is generally sufficient..

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66jalopy Silver Member Phillip Jolliffe
Lake City, FL, USA   USA
I put my 3.9 pumpkin in my 1956 housing, just drill and tap a hole for filler plug.

tjt77 timothy Trevithick
Grass Valley, CA, USA   USA
"I put my 3.9 pumpkin in my 1956 housing, just drill and tap a hole for filler plug."
Its one possible route, but the metal on the diff housing is approx 14 guage.. hence BMC added a welded in fitting for the filler/level plug..(one can utilize a standard plumbing fitting and weld it in place) without which there is risk of oil leaks and the possibility of stripping any thread that is tapped for a plug due to insufficient metal thickness for the thread.. OK if conscious of the possible issue.. but risky if another less careful individual changes the diff oil.

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66jalopy Silver Member Phillip Jolliffe
Lake City, FL, USA   USA
Easy fix, don't tap it , drill a hole the same size as Chrysler uses and use the push in rubber plug.

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nudenut Silver Member Reg K
Perth, Perth Western Australia, Australia   AUS
I drilled , tapped and fitted a oil plug into top of casing before I assembled pumpkin . Then made up a copper hook ,hose and funnel to fill with oil from outside..

Merry Christmas from The Colonies

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66jalopy Silver Member Phillip Jolliffe
Lake City, FL, USA   USA
It's pretty easy to just jack up one side, remove axle and fill with measured amount from there.

nbarter Dominic Barile
San Francisco, CA, USA   USA
Have placed a 4:22 and now a 3:90 "pumpkin" where I originally had a 4:55 in my van that was assembled in Perth,AU. These lower ratios after Datsun A-15 & 5 speed install. Bolted right in & being a late model('71) had a fill hole.
Nic

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