Higher ratio diff in a standard moggy.

[rayofleamington]

I'm happy to stay with a 4 speed 1098 gearbox (AKA not willing to pay lots to convert to a 5 speed) and I have a good 1098 gearbox.
Replacement diffs come in cheaper than a gearbox conversion.

On the motorway I wish the engine revs were lower - it doesn't sound nice and high revs use more fuel.
The standard 1098 is low geared enough to pull off in second when laden.

What experience do people have when using a higher ratio with a standard 1098?

[Willie]

With a STANDARD 1098 engine you should stick to the 4.22-1.
The engineers know what they are doing when they decide on
these details. The 3.9-1 diffs are fine on the small MG midgets
but that is because they are lighter and are tuned anyway.
Then again,you may be doing a great many motorway miles so
its your choice between the lower diff or a pair of earplugs.
Willie

[olonas]

I agree with Willie. The complete transmission system must have been designed and built with the 1098cc engine, in it's Minor guise, as a complete package. Possibly there was some "over engineering" but maybe not sufficient to start playing around with the rear axle ratio.

[Willie]

I didn't express myself very well above so will be more lucid.
If you accept that a 145X14" tyre revolves 892 times per mile
the resultant sums show that fitting a 3.9-1 diff instead of a
4.22-1 means that you will do 285 less revs per minute @60mph.
This doesn't seem a lot,but,even the lighter and more tuned early
sprites and midgets didn't get the 3.9-1 diffs until they were fitted
with the 1275 engines.
Willie

[lionellength]

Easiest way out of this is to fit a better cylinder head, a 12g295 from a 1098 Midget/mg1100 and a 1 inch and 1/2 SU. A standard 1098 would struggle a bit with a 3.9 but with the above mods, no problem at all. In fact I've run 1098's with the above head and carb with a 3.7 diff.

[rayofleamington]

Fantastic - thanks for the feedback LL. I was hoping to find someone who'd done similar. Did you use a large bore exhaust too?

Anyway I'm off out to the garage to fit a new master cylinder - getting everything ready to add the servo soon,
(then maybe the higher Diff depending on the ££££'s, the other cars, the decorating etc....)

[Willie]

You original question was referring to a STANDARD 1098, I
see you have been bitten buy the tuning bug.
Willie

[rayofleamington]

Hi Willie
I've always had the tuning bug, but have never done that much on a Minor (except for adding a 1275 once whilst rebuilding the 1098 engine).
My First Minor had a big Valve head and bigger carb and that was more nippy, but suffered from the standard gearing on a long drive. I eventually rebuilt a standard engine for it, and then got rid of it when I cut down from 6 cars to 2 (Hmm.. I'm nearly back at 6!)

So in answer I am still reffering to a standard 1098, but one that is also be used for weekends away where I can't avoid the Motorway. I will have to justify the cost of a modified diff (unless I can find a cheap 3.9 somewhere), and if/when I do it will judge the engine power to see if it needs assistance.

(The brake servo will be for Gayle's benefit)

The old brakes had seemed normal, but the new master cylinder is FANTASTIC! The worn/rusty pedal shaft must have also reduced the overall efficiency before I repaired it last night, and the clutch pedal is now much lighter - it was a joy to drive this morning, even in rush hour.

[Willie]

That's good..........it's a fiddley job doing the 'Master' so it's
nice to know you got a good result.
Willie

[rayofleamington]

Actually I found the 'Master' quite easy. A certain someone's off here gave a tip regarding a crowbar on the torsion bar, and saved saved me tons of time getting the captive bolts in and out.

The pedal shaft took a bit more noddle - see tips section.

[Willie]

Blimey Ray! the 'bending the torsion bar to remove the master
cylinder bolts' dodge is inscribed in Minor folk lore! Still, you
proved it works!
Willie

[rayofleamington]

I know a lot of people who'd never heard of it before!!! (Including me)
A few of them were cursing when I mentioned it, as we've all spent ages messing around doing it the hard way.

That's one tip I'm very thankful for.