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MG Midget Differential 3.9 ratio to Morris Minor 1000

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nudenut Avatar
nudenut Silver Member Reg K
Perth, Perth Western Australia, Australia   AUS
Has anybody had this problem when fitting 3.9 ratio CW & P to 4.55 ratio Differential ?
Crown Wheel will not mesh with pinion, needs to be moved to A side approx. 2 mm, do I machine bearing mounting of carrier on CW side deeper and compensate with shims on other side, or do I machine mounting plate thinner where Crown Wheels bolts on, bolt heads would have to be thinner to avoid fouling. I have checked both Morris Minor and MG Midget part numbers for carrier and casing, they are the same. Did factory machine match carriers with Crown Wheel ?
Cheers
Reg
Perth
Western Australia

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66jalopy Avatar
66jalopy Silver Member Phillip Jolliffe
Lake City, FL, USA   USA
I attempted to do the same thing and gave up quickly. I used the whole 3.9 assembly from the Midget I realize you have a problem with obtaining the whole thing down there.

nudenut Avatar
nudenut Silver Member Reg K
Perth, Perth Western Australia, Australia   AUS
Hi Phillip

Thank you for information, I have just found out from a reliable source in UK that a 3.7 or 3.9 ratio will not fit into a 4.55 casing.

I now have the casing and carrier from donor diff. being shipped from UK

That will teach me to be " Cheap Charlie " regarding freight

Cheers

Reg

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66jalopy Avatar
66jalopy Silver Member Phillip Jolliffe
Lake City, FL, USA   USA
Remember, your new casing will not have a fill hole. You will have to make one in the back of axle or fill with one half shaft removed like I do..... Next time it comes apart it will have a fill hole!

nudenut Avatar
nudenut Silver Member Reg K
Perth, Perth Western Australia, Australia   AUS
Thank you for that information, I will do that while I am waiting for parts to arrive.

Propshaft Colin C
Kneesall, Nottinghamshire, UK   GBR
Hi I have just ( last week) put a midget 3.9 diff into the original 4.55 casing it seemed to fit perfectly it turns ok no tight spots . Will not be running it for quite some time so cannot comment on that

dodyudynosur1213 Avatar
dodyudynosur1213 Abbas Abboobaker
Durban, kwazulu natal, South Africa   ZAF
1957 Morris 1100 "Miracle"
Hi Sir hope you can help I have Morris minor have fitted a v4 engine am trying to modify diff any tips sure your car is running well would the mg midget work wellp

gjoakes Silver Member Greg Oakes
Cornfield, IL, USA   USA
1958 Morris Minor Traveller "Bridget"
1972 MG MGB "Buttermilk"
In reply to # 15847 by 66jalopy Remember, your new casing will not have a fill hole. You will have to make one in the back of axle or fill with one half shaft removed like I do..... Next time it comes apart it will have a fill hole!

You can also fill through the vent hole (at least that is how I did it) but you're correct, when doing this conversion adding a new fill hole is worth the effort.

nudenut Avatar
nudenut Silver Member Reg K
Perth, Perth Western Australia, Australia   AUS
Hi, you will have to check what diff ratio went with your replacement Engine , gearbox and tyre size , MG crown wheel and pinion I used is 3.9 ratio to match Nissan A12 engine with matching 5 speed gearbox, as mentioned on this site donor diff casing / housing will not have a oil filler hole, I drilled and fitted plug in Top of housing, on the donor MG casing you will find a solid square section in the area fill plug for 4.55 ratio is fitted, you can drill and tap there, be aware of metal filings when drilling.
Cheers

dodyudynosur1213 Avatar
dodyudynosur1213 Abbas Abboobaker
Durban, kwazulu natal, South Africa   ZAF
1957 Morris 1100 "Miracle"
Hi Philip so this crown and pinion is not gonna fit Morris casing what do I have to get am trying to get a 3.7 will appreciate your help

nudenut Avatar
nudenut Silver Member Reg K
Perth, Perth Western Australia, Australia   AUS
HI, you will need a casing to suit 3.7 / 3.9 ratio CW&P ,from a MG Midget , Austin Sprite or similar , 4.55 standard ratio diff housing will not accept 3.7 CW&P., Pinion bearings are different also.

MG casing can be identified by having NO OIL FILL Hole , fill hole is in axle housing , you need to drill and tap oil fill hole before you assemble diff.

Cheers

Reg

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#12
Annywill Avatar
Annywill Anny Will (Disabled)
Disabled Account, Antarctica   ATA
Post has been removed by the administrator due to violation of the Terms of Service.

dodyudynosur1213 Avatar
dodyudynosur1213 Abbas Abboobaker
Durban, kwazulu natal, South Africa   ZAF
1957 Morris 1100 "Miracle"
Hi Colin am trying to do the same mod any idea where I can get one will appreciate your assistance and advice

Deleted
#14
Annywill Avatar
Annywill Anny Will (Disabled)
Disabled Account, Antarctica   ATA
Post has been removed by the administrator due to violation of the Terms of Service.

0123 Mike D
Biddulph, Staffs, UK   GBR
Have you considered a 5 speed box Dody?

You'd get about 50 instead of 45 when your speedo shows 37/39

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