948 engine, 1098 'box

[callyspoy]

Aye up folks,
My car is fitted with a ribbed case box and a 948 engine. It still retains the 948 backplate though.

As far as i am aware, that is a no-no, but i haven't witnessed any obvious problems.

For the record, the conversion was done before I bought the car.

I do have a spare 1098 backplate which i may fit (although i may be going overdrive instead), just wondered what the problem is with fitting the 1098 box with the 948 backplate? Is it a spigot issue?
I'd be gutted to knacker the 1098 box just because i "think" it seems ok. Especially as the box was allegedly reconned last year (it's been painted and probably had a new nut somewhere at least!)

Many thanks
Callum

[MarkyB]

If it ain't broke, don't fix it!

[IslipMinor]

It depends on three things:
Is the 948 clutch still fitted?
Has the front cover on the gearbox been changed/modified?
What carbon thrust is fitted?

Acid test is does the clutch operate 'normally' and look through the opening where the release arm is and see if the carbon thrust rubs on the primary shaft spline when the clutch pedal is fully depressed? If all OK, then probably safe to leave it alone.

The 1098 clutch is much bigger than a 948 and projects further into the bell housing, so the gearbox front cover was modified to move the release arm further away from the flywheel. At the same time the hole positions in the cover were changed, so it is not a straight swap over between ribcase front cover and smoothcase front cover.

Fitting a 1098 box, with original front cover, can result in the release arm 'over-throwing' and rubbing on the primary shaft spline.

I think there are some thicker carbon thrust races that might take up the difference in clutch thickness?

When I fitted a 1098 box to the original 948 engine, using the standard carbon thrust, I had to fill 2 holes in the gearbox case and drill/tap 2 new ones to line up with the 948 front cover. That set-up is still going in a Frogeye Sprite that the engine and gearbox was fitted into 2 years ago.

[bmcecosse]

This from the callyspot who made an 803 gear lever fit on a 1098 box !!!!! As the others - if it's working - enjoy it. Various combos of engine backplate/carbon thrust/gearbox front plate will work just fine.

[callyspoy]

Yes i know Roy, capable of fitting a Fiat engine into a Minor but confused by a ribbed box! All words i have read state that if doing the ribbed box onto the 948 you need to do the backplate.

I haven't had a gander at the set up yet, all i know is that the clutch mechanism is a bit of a hash up, although appears to work well. It has eliminated the complete mechanism, i'll take a picture tomorrow as i can't explain it properly. Basically attaches the threaded adjuster arm to the 2 strips that attach to the pedal. Clutch pedal does feel wonderful, but i have very little trust in the capabilities of the previous owners and also the people that fitted the box. Hence the curiosity about the use of 948 backplate.

Richard, I shall have a gander at the box/clutch tomorrow and let you know what i find, thanks for the detailed info.

[tomtom]

My 1971 saloon has a 1961 948cc engine fitted with a 1098 gear box. I do feel that the car does not perform to its full potential due to the engine and box combination. I am looking for a recon 1098 engine as the 948 is on its way out..

[bmcecosse]

The 'box' will have no effect on the performance - the ratios are not significantly different - it's all just stronger! If the final drive ratio is too low, then that could make a 948 appear to struggle a bit.