Gearbox Parts Questions - 1098cc Midget and Minor

[woolfman]

Good day,

I think this is my first post on this forum so far. I have been reading here for quite some time though.

Now has the time come for me to rebuild my ribcase gearbox and I wanted to ask you something. Maybe someone with experience knows about this:

Are shims, interlocks, thrustwashers, springs, balls and detents fully compatible between Midget and Minor 1098cc gearboxes?
Are inner and outer dimensions the same for all shims and thrustwashers?
Could I switch remote shafts and selector forks without problems between those two gearboxes (no difference in sizes?)?

I there was someone who could tell - that would make my life so much easier, as I could source parts easier.

Many thanks for your help and support.

Kind regards from snowy Vienna,
Wolf
MG Midget Mk2 1964

[IslipMinor]

Hi Wolf, and welcome.

The main differences between the Minor and Midget ribcase gearboxes are the gears themselves. The ratios are different and the later 1275 gearboxes have a different tooth profile as well.

The mainshaft is also different, as the Midget mainshaft uses needle roller bearings for the gears and the Minor has bronze bushes. The rest of the bearings, seals, shims, selection mechanism, rear extension etc. are all interchangeable.

There is a further difference - the clutch operating mechanism is hydraulic on a Midget, and mechanical on a Minor, but presumably this is about rebuilding a Midget gearbox, not fitting one into a Minor?

[woolfman]

Richard,

I am rebuilding the gearbox for my Midget, and I am not going to fit it to a Minor. I just wanted know, which parts from a Minor would also fit as a replacement. I rather use new parts than worn ones, that is why I am asking. It makes it easier for me to choose sources ;-)

So if you know what parts definitely DON´T fit, I´d be happy to hear

Thank you + regards,
Wolfgang

[IslipMinor]

Wolfgang,

Firstly, do you know that you definitely have a 'real' Midget gearbox in the car? If the gearbox has been changed in its life, it is possible that a 'Minor' version could have been fitted.

The simplest check is the input/primary shaft part number - that will tell you what gearbox is currently fitted. Also the Minor one well? The input shaft part number is visible though the hole in the top of the bellhousing. For the 1098 Midget it should be 22G172, if not then check in the table below.

As a confirmation you could check the ratios by counting the input shaft turns needed for 1 revolution of the output shaft in 1st, 2nd and 3rd gear? 4th is the same at 1:1.

The Midget ratios are:
1st 3.20
2nd 1.92
3rd 1.36

For comparison the 1098 'Ribcase' Minor gearbox ratios are:
1st 3.63
2nd 2.17
3rd 1.41

Assuming that you do have a 'proper' Midget gearbox, then anything related to the gears will NOT fit:

Primary/input shaft
Mainshaft gears
Mainshaft
Mainshaft gear support bearings - needle roller
Laygear cluster (the layshaft itself is dimensionally the same, but may well be a different, and inferior material, so fit new)

The part numbers for the reverse gears are the same for the Minor and Midget 1098 engine, so possible use here.

The table below shows the part numbers used for the major components:
[frame][/frame]

[woolfman]

Richard,

thank you very much for your detailed answer!

I will check my mainshaft and have a look what I got there

Did I understand you right - when I look at the chart - different part numbers also means that those part will never fit?

Thank you.

Best,
Wolfgang

[woolfman]

Hello all,

I finished my mechanical restoration on my Midget last week and had a few good drives.

There were a few things that I would like to add to topics, which were not covered or not in that detail in the rebuild manual:

-thoroughly clean every gear to get rid of the old gunk (which sits in every corner; you might need a flat screwdriver at times, and scotchbrite). My gearbox was full of dirt and it took me a complete day to clean it inside out, every bit of it.

-it is best to replace front and rear bearing with the ones supplied by Moss, as they resemble the original ones. They come with a manual for additional shimming (shims are supplied with it as well).

-better buy more shims than you expect to need for 1st and 3rd motion shaft. You WILL need them.

-replace ALL springs (synchro and all detents/anti-rattle...) , even in the synchro hubs. They do get old with age and are shorter and/or weaker, or even the wrong ones. Don´t spare the extra money needed, you will get a completely new feeling, and I can assure you will be happy with it. It is not that hard to push the outer wheel over the inner hub again. If in doubt, get a friend to help you - shouldn´t be a problem for most of you, as you have club members on call ;-)

-clean all holes religiously. That way you make sure all detent balls and plunger work perfectly. If in doubt, sand the detent plungers a bit, the´ll get a little sideplay which actually is good.

-clean mainshaft and 1st motion shaft on a lathe, those areas which are in contact with the housing and seals. Start with 400 paper and go up to 1000, until you don´t see any scratches and the surface looks absolutely gorgeous. Also the outer end of the prop shaft, which goes onto the layshaft, it touches the oil seal. That way you make sure, that the oil seal will work on the rear. If you put one on on the front as well, this will help in making it last longer.

-you don´t have to warm up the ball bearings, you can hammer them on with a hollow drift. The drift hast to hit on the inner ring (the one which sits on the shaft) ONLY. That way you cannot damage the ball bearing, and you´re way faster in assembling.

-always replace 1st gear and laygear as a unit (for new ones). Don´t save the money, it´s not worth it. You´re already dismantled it...

-don´t shim to 6 thou for laygear - that was always the MAX allowed play. I did 1 thou, and I have an absolutely quiet 1st gear. The other reason for that is simple: the laygear will mesh much better with all gearwheels, hence better and more even transmission of load!

-put a 2mm shim (I used a plain washer for that...) on the 1st/2nd gear fork rod so that you never accidentally shift too far into 1st gear.

So far my experience. I am happy with my "new" gearbox. Feels very very good in shifting now, and it doesn´t happen again, that I erroneously shift into 1st when I want to hit 3rd. Reverse is much harder to shift now, which is also very good - I slid into it accidentally before the rebuild many times ...

My 2 cents.

Hope it helps someone.

Best,
Wolfgang