MM differential

[hvannieuwkoop]

Hello friends

I have a 1950 918cc sidevalve mm. Has anyone put in a differential with a different gear ratio in a similar powered vehicle in the hopes of gaining faster speeds?

Thanks,
Henk

[bmcecosse]

The 918 goes very well for it's engine size - arguably better than the later 803 car. I doubt there IS an alternative final drive ratio to fit that axle. What you need is more power if you want to go faster....they were sometimes lightly supercharged - probably the best way to go.

[hvannieuwkoop]

Ok thanks! I have one laying around that apparently fits my car according to the guy I bought it from. Next time I'm at where I store my Minor I'll try to remember to find the ratio.

[bmcecosse]

Without more power - a lower ratio final drive will just make the car slower - except going downhill........

[hvannieuwkoop]

I see... Not exactly what I want:) I guess they would have figured out the best ratio when they built the car.

[bmcecosse]

Depends - if you are in a very flat area with no hills then a lower ratio may be ok. But remember it will throw the speedo out too. And any 'speed' difference is likely to be marginal anyway.

[liammonty]

Bear in mind too that the final drive ratio is the same for the MM as for the 948-engined 1000 cars, which had over 30% more power! The Series II cars, which had a similar power output to the MMs (but a horrible weak engine) had lower (or is that higher?!) overall gearing at 5.375:1 (vs. 4.55:1) which was awful, but with a similar power output, it still managed around the same top speed. I suspect this means that with the MM set up (which unlike the Series II I've never driven), you aren't losing any top-end with the taller gearing of your car; you have actually got the best balance for 'cruising' and top-end. I'd leave it well alone!

[mike.perry]

The standard ratio for a side valve Series MM is 4.55 :1 which is the same as the 948 Minor although the axle is a different design. The early Series 11s had the same design axle as the Series MM but with a 5.375 ratio. You could fit a Series 11 diff to a Series MM but I think that you will just rev the nuts off the engine

[smithskids]

I have a 5.375:1 spare axle and if you live in a hilly area it is ideal. The acceleration is good but 50mph is max and as mike says thats at 4,500 rpm. You also have to change the gear box speedo drive wheels and the speedo.