Diff

[northyorkspaul]

Hello,sorry if this is old ground...but I have a 69 minor is it worth changing the diff to a higher ratio to lower the revs a bit at 50 mph?...and if so is a 3.9 the one to get?....I think the one in is 4.2.Ta.

[don58van]

A 3.9 will certainly help, but it is a small percentage change. As you might know, 3.9 diffs don't come cheaply.

If your rear tyres need replacing, you could look for a new pair with significantly bigger rolling radius. You might need to think about wider wheels to achieve this (like the 4.5" ones from ESM for eg). This is an often overlooked solution.

The combination of theses two approaches will certainly make a worthwhile change.

Roy (bmcecosse) will be along soon to tell you that he has a 3.7 in his mildly warmed up 1098 Traveller and it goes very well. It probably will not be satisfactory with a standard 1098, especially if it is getting tired.

Of course, 3.7 diffs are relatively rare and even more expensive than the 3.9s.

You will have to weigh up whether you do enough fast motoring to warrant the expense.

Don

[MarkyB]

It may be a small change in percentage terms but is still worth doing IMHO.
Your engine does need to be in reasonable condition.

[BLOWNMM]

Hi Paul
It would be a good idea to positively determine the ratio of the diff you have fitted. If it happens to be 4.55:1 then a change to 4.22:1 would be of benefit and a lot cheaper and easier to find than a 3.99 or 3.7. There have been quite a few ways of determining the ratio posted on this forum, by jacking a wheel and counting the turns of the prop shaft and the wheel.
Cheers Bob

[northyorkspaul]

Hello chaps..many thanks for your helpful comments,a bit to ponder on...the engine is pretty good and the car is totally standard.Thanks again.

[bmcecosse]

Just to point out that 3.9 final drive is a LOWER ratio than 4.22.... At current prices it would take many miles to recoup the money. But if you happen one for £ 50 or so. Grab it!