Morris Minor Owners Club

Has anyone used a 3.9:1 diff on a 1098cc. I used to have a 4.55:1 then went to a 4.22:1 it made some difference, but I find on long journeys the car is happiest cruising at 55mph but is somewhat noisey. I wouldn't mind a 5 speed box, this seems to be an expensive option though. Thanks for any opinion. Alex

I asked this a couple of years ago and there were a few ppl who'd used a 3.9 diff and were happy with the lower revs at high speed. The downside is loosing a bit of acceleration and needing to change down on hills but if you do a lot of long journeys it would be a nice option.
The downside is that a 3.9 is very hard to find.

Myminor,

I fitted a 3.9 diff to my 1098 earlier this year - the most noticeable effect is the loss of acceleration and the need to change down a little more often.
Conversation does prove a little easier tho'
The other effect is that of speedo readout -the speedo measures at the gearbox and assumes a 4.22 diff - if you change the diff then you change the final drive ratio, and hence the speedo will underread if going from a 4.22 to a 3.9. I am not a scientist but I believe that most speedos overread by about 10 percent anyway, and the change from a 4.22 to a 3.9 diff represents an approximate change of 10 percent. So what your speedo reads should not be far off (but do not quote me!).

A good source is any MG midget website. the diff is appropriate to the 1275 model, not the later 1500 model.
Expect to pay £60-100.

The part bolts straight into the standard moggie axle and onto the std moggie prop.

Max

most speedos overread by about 10 percent anyway

Are you sure?

If you get the 5-speed gearbox and keep the 4.22 diff then you get the best of both worlds - higher cruising speed and decent acceleration, but of course it's hassle and can be expensive.

Thanks all for the info. The reason on thinking on changing the diff was for cost reasons and it would be easier. Unless someones got a 5 speed complete with fitting kit for £100. . alex[/code]

If the 'cost' relates to fuel saved I should think the initial outlay would take forever to recover in saved fuel.

If the 'cost' relates to fuel saved I should think the initial outlay would take forever to recover in saved fuel.

I think he meant the cost benefit when comparing it to a ~£300 to £600 Ford 5 speed conversion

Yes, looks like it Ray, doh!