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MG Midget and Sprite Technical - Unusual gearbox identification

Need some help identifying this ? unusual gearbox and then thinking how can fix it..

1960 Mk1 sprite
modified in period by BMC dealer in

948 +60'' flat tops
thick engine back plate
9 spring borg and beck pressure plate
mated to:

rib case gearbox that I cannot identify....
layshaft: HS14 T
1st Motion Shaft OWOG G-4n
3rd Motion shaft cy4u

Case: C865 22g121
Front palte 22g118
Side plate 22a170
Re,pte 22a480/VAF 3
Selector 22a478/VAF10

its a helical set of cogs but the ratios dont match anything I can find anywhere

1st
Lay shaft 13 teeth, 3rd Motion 32, Ratio 2.461
2nd
Lay shaft 19 teeth, 3rd Motion 28, Ratio 1.47
3rd
Lay shaft 24 teeth, 3rd Motion 23, Ratio 0.958 ?!?!

I may well be calculating the ratios wrong but this is what ive read elsewhere seems to suggest to do?!

The first motion shaft has 28 teeth and the layshaft gear 19.

Unfortunately the 1st and reverse and corresponding cogs on the layshaft have had it (Was jumping out of reverse thus why stripped it)

any help on
1) identifying it
2) suggests what to replace with: could I put a new 1st, 1275 layshaft and reverse idler gear in it? or completely incompatible and thus needs a complete new set of cogs....

Pictures at:
http://sebringsprite.blogspot.co.uk/2017/12/gear-box-troubles.html
D Paul

I'm afraid your calculations are incorrect.

To work out a particular ratio, i.e. first, you need the number of teeth on the 1st motion shaft (a), the number of teeth on the laygear input gear (which the 1st motion shaft meshes with) (b), the number of teeth on the laygear first (c), plus the number of teeth on the first speed gear (d).

From memory, I think you need a/b (e); b/c (f) and c/d (g)

Then (e x f)/g should give you the ratio. 'e' is the same for each gear, so you just need to work out 'f' and 'g' for the 2nd and 3rd speed gears.

From the photos, you don't have a 1275 gearset, as there is a bronze spacer between 2nd and 3rd speed gears. Probably Morris Minor or A40.
Dave O'Neill 2

Missed the edit window.

You can't mix gears between sets. Also, if you want to use a 1275 gearset, you also need a 1275 third motion shaft.
Dave O'Neill 2

From your pics I can see the number on your input shaft is G 40. I had one and have seen a few gearboxes with this number though a search on web doesn't give much information.

The gearbox I had with that number on the input shaft had Morris Minor 1000 ratios measured from input shaft to output shaft in all 4 gears. It seems to be a late MM 1098 box.

Rob
MG Moneypit

Thank you, that makes much more sense. Will get the counts and work it out. A 1098 box would make sense in terms of time of build - pre 1275s.

Got a 1275 box on the shelf that needs a rebuild and new layshaft so probably the way to go as less damaged...
D Paul

the input shaft is G-4N - not G40
D Paul

david any where you can clarify that calculation?

1st comes out at 3.595

but im slightly confused on calculating 2nd and 3rd, do you substituate c AND d with the appropriate lay shaft and gear numbers?

if so 2nd is 1.47 and 3rd 0.75 which cannot be correct...
D Paul

Looks like G 40 to me?

Rob

MG Moneypit

found the correct formulas:
http://www.calverst.com/technical-info/gearbox-formulae-for-fd-tyre-size-car-speed-and-gear-ratio-calculation/

gives

1st 3.62
2nd 2.17
3rd 1.1411

which would be a minor 1098 box. which fits
D Paul

thank you all
D Paul

This thread was discussed on 03/12/2017

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