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MG Midget and Sprite Technical - Gearbox differences

For ribcase gearboxes, what are the main differences between a Morris 1000 box and a 1275 midget box?

I believe that one difference is the gear shift turret with a reverse gear selection switch. What else?
GuyW

The turret is different, but not just because of the reverse light switch.

Some 1275s didn't have reverse lights, but the turret wasn't the same as the Minor.

The other main differences are internal:-

The main-shaft is different.

The Minor uses bushes instead of needle rollers for the second and third speed gears.

The gears are obviously different.
Dave O'Neill 2

You mean the ratios are different? Or gears are different because of the bushes?
GuyW

The ratios are different.
Dave O'Neill 2

Thanks.
I have a spare MM 1000 ribcase and was wondering if it was a preferable alternative to a smoothcase.
GuyW

Some years ago I bought what was described as a frogeye gearbox. It wasn't until I had dropped it in to the car and came to attach the clutch slave cylinder that it became apparent that there was nowhere to attach said slave cylinder. The casting around that area was completely different. A disappointing exercise.
Simon Wood

Guy

depends what you are attaching it to! The ribcase MM box is fine for a 948 engine and an early 1098 . The ratios are better than the 948 smoothcase thought not as close as the 1275 ribcase. The MM box is a bit vunerable with a 1275 engine with its greater torque and power.
Bob Beaumont

Probably my early 1098, which is fully rebuilt and ready to run. Though l do have the original 950 but it needs a full strip down and inspection, and possibly rebuilt.
GuyW

Sounds Ideal then. The ribcase has superior syncromesh so easier to use
Bob Beaumont

Thanks. What about the missing fixing point for the slave, that Simon mentioned? I will need to go and have a closer look at the box in the shed!

Bob, did you look out the 3/4" m/c internals? Are they still on offer?
GuyW

Guy

They are not at home but I think they are in my inlaw's garage so was going over at the weekend to check. I moved spare parts over there when my original lock up was broken into.

All the ribcases I have ever seen have the drillings for the slave but of course there are always exception
Bob Beaumont

"What about the missing fixing point for the slave, that Simon mentioned?"

Even if the threads aren't there, the bosses should be, so you should be able to drill and tap them.
Dave O'Neill 2

Thanks both. I am away in Scotland at the moment but will check my bosses for tappings when l get back.

No worries about the m/c pistons , Bob. There's no hurry!
GuyW

There were no bosses in the case that I had
Simon Wood

I've had a few smooth case 'boxes with blank bosses.

The early ones may not have had them, but from '58 onwards, I would imagine that the casings were standardised with bosses in the castings.
Dave O'Neill 2

Are Morris 1000 clutches cable or maybe rod operated then?
GuyW

Morris 1000s were rod operated, as were A35s. A40s were hydraulic.
Dave O'Neill 2

My 4th car was an A35 Countryman (not a converted van either!) But that was a long time ago and I cannot remember the clutch arrangement.
GuyW

To clarify on ratios: the 1098 Minor/A40 ribcase box used the same ratios as the 948 Minor/A40 smoothcase box (which are THE SAME as the frogeye box).

The MkII Sprite/Midget got a 'close ratio' smoothcase box and the later Spridget ribcase boxes inherited these ratios.
Tom Coulthard

Apart from the original Frogeye, which has the same construction, with the same ratios as the 948 Minor/A35/A40, all the other Sprite/Midget gearboxes have 'close ratios', including the Sprite MkII/Midget MkI 948.

The 1098/1275 close ratio boxes also had needle roller bearings for 2nd and 3rd gears. The 1275 had a different helix angle as well, which makes it very different from any other in-line A-Series gearbox, and as a result 'stronger' than any of the others.

With a 1275 engine, I would definitely suggest a 1275 gearbox, and if not at least a Sprite/Midget 1098 version. The Minor 1098 'box is really not up to coping with 1275 power!

The attached table shows the various part numbers and the gear ratios as well.

Richard



Richard Wale

Richard - the irony of the 'B-type' gearset in the 1275 Spridget box is that the helix angle was INCREASED.

This was done for quietness, not strength. Without any other changes, the greater spurious sideways forces caused would make the gearbox effectively 'weaker' than before.
Tom Coulthard

Tom, Hadn't appreciated that the helix angle was increased!

A small correction to your post - the 1098 ribcase box in the Minor/A40 has a higher 2nd gear than the 948. All the other ratios are the same.

Richard
Richard Wale

Tom

According to Richard's helpful note the 1098 MM ribcase box does have slightly better ratio's. Second is higher than in the 948 box. Reduces that horrible gap..........! Bob
Bob Beaumont

Yes, thanks for that correction, Richard. I knew when I was writing my attempt at simplification that there was something slightly wrong with it.

However (Bob) I don't think 0.2 of a revolution goes very far in reducing the traditional Morris gap caused by their adherence to a low 2nd - said to have improved their sales in hilly areas!
Tom Coulthard

If you have to tap or even drill for the slave...

Id modify the slave in a way that it can be slide back and forth on a plate and essoly tightened down into place

Id think trying to find the actuating release points of the slave push rod on a non orginal gear box to get the proper push rod extention depth would be daunting and precise in order to drill in the exact needed postion and tap to hold the slave into place

If the slave can slide back and forth it would be much easier to adjust to avoid over extention or not enough push rod length

Just my 2 cents

Prop

1 Paper

This thread was discussed between 19/10/2017 and 25/10/2017

MG Midget and Sprite Technical index

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