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MG Midget and Sprite Technical - Smooth case gearbox

I have a 1959 frogeye, standard 948cc with a smooth case gearbox.

Occasionally it jumps out of gear which I would like to sort out. I have never done that sort of work before, so excuse my ignorance.

According to Moss, parts aren't available and I understand parts from the Morris Minor are not interchangeable.

I am not bothered about originality, I just want to enjoy the car. To be honest, it isn't the best of its class, and I dont do much mileage, so I dont want to throw too much money at it.

Are there any known sources where I could purchase parts, or a replacement smooth case box, or even an old smooth case box for spares?

Thanks, Graham
Graham V

Graham,

From the information I have, the gearbox for the Frogeye is virtually identical to the 948 engined Morris Minor, Austin A35 and A40.

The only difference between the Frogeye and all of them is the gear lever, and with the Minor the clutch release arm (the Minor has a mechanical linkage, whereas the rest are hydraulic). Swap the existing release arm into the Minor box, and that is it!

The basic gearbox, ratios, gears etc. are all the same.

The 948 MkII Sprite and MkI midget have different ratios (closer), and, I believe, needle roller mainshaft gear bearings, instead of bushes?

The attached chart shows all the key part numbers for the various A-Series gearboxes.

Richard




Richard Wale

"(the Minor has a mechanical linkage, whereas the rest are hydraulic)"

A35 is also mechanical.
Dave O'Neill 2

Graham, as you must be fairly close to them I would speak to Heathrow Transmissions.

Trev
T Mason

what Trevor said. Pop into Hounslow and talk to Gary & his son. Really good guys and very helpful. If they say you require any parts that are NLA then I have a couple of s/hand Frog boxes kicking around.
David Smith

Thanks for the recommendation of Heathrow Transmissions.

Richard that chart looks very helpful but I cant seem to tie the part numbers up to the BMC parts list at http://www.spridgetguru.com/AKD829III/AKD829III.pdf

Are they different part numbers but interchangeable parts maybe?

Thanks
Graham V

BMC says 2A3359, Richard says 2A8358. Looks like a typo somewhere?

Also the late Morris Minor has an input shaft marked G40. I've seen a couple of examples.

Rob


MG Moneypit

Graham,

'Are they different part numbers but interchangeable parts maybe?'

Yes, they are. I have updated the chart to show the early part numbers from the Minor and Frogeye BMC Parts Lists, and they are all the same.

Checking a bit more, have also corrected a couple of errors on the bearing numbers.

The later part numbers are in the Minor parts list, as it used the same box after the Sprite/Midget went 'close ratio', with the later 948 engine and 9CG gearbox.

Richard


Richard Wale

Rob,

Yes, typo corrected as well! My 2A8359 should be 2A3359 - thanks.

By 'late Morris Minor', do you mean the 1098?

Richard

Richard Wale

Hi
I have an opportunity to acquire what the owner thinks may be a Morris Minor box with 2A3368 - VAR7 stamped on the outside. But he's not 100% certain
I cant find any reference to that gearbox - any idea?

Probably useful for parts regardless?


Thanks

Gaham
Graham V

Sorry its VAF7 not VAR7
Graham V

Hi
Sorry to hijack this - has anybody got experience of the uprated front gear box cover with an oil seal - is it a worthwhile addition
Thanks
Stuart
S G Macfarlane

Heathrow transmissions or Hardy engineering in leatherhead can recondition your smoothcase. A worthwhile modification if you want to retain the smooth case its to use later morris minor internals from a rib case gearbox. This has the advantage of baulk ring syncromesh which is better than the cone synchro fitted to the smooth case. The parts for the ribcase are more plentiful.Its usually the 2nd gear that goes on the smoothcase and replacements even 2nd hand in good shape are hard to find.
Bob Beaumont

Stuart, maybe start a new thread (?) as I would be interested too. I've rebuilt a ribcase but left the front cover as original for now, but may still change it.
Bill Bretherton

Bob, since the usual engineering advice is not to mix and match components, it would be interesting to know which parts from the Moggie ribcase can be used. And if any machining is required to fit them in a smoothcase box. Especially as l have both, just waiting for a rebuild project to go in my Frog.

Do you have any more details ?
GuyW

SG and Bill, I think Heathrow transmissions fit the modified front cover as standard on a recon box nowadays. I have them on both my race gearboxes and they don't leak :-)
David Smith

Guy

I have not done the conversion myself but i gather its straightforward. The bearings are all the same so its a case of getting all the internals from a ribcase MM box and putting them inside the smoothcase. however the fist motion shaft is slightly longer than the original from the smoothcase. It may mean using the thicker backplate on the engine to avoid it bottoming out in the crankshaft. I would not mix and match individual components.
Bob Beaumont

David, thanks,I'm sure the modified seal is much better! I'd considered getting a local engineering company to machine my front cover but haven't costed it yet.
Bill Bretherton

Graham,

You said you were not concerned with originality. If that is the so, I thought that the rib case box was a direct bolt in. Am I wrong about that? If I am right, you would not have to limit your search to a smooth case.

Charley
C R Huff

thanks David - hijack over!
S G Macfarlane

Charley
Yes you are right I am not concerned about originality. But I understood that if I fit the ribcase box , I have to fit a new flywheel, clutch assembly and back plate.
If that's correct, I calculate it adds about £300 plus the cost of the back plate that I am not even sure is readily available.
I do a very low mileage so I cant justify piling the cost up too much.

So I was taking on board Richard's advice and contemplating buying, for parts, what is probably a Morris Minor box (2A3368 - VAF7). Hopefully the parts I will need are interchangeable and are in working order.

Graham
Graham V

No Graham you don't need to change the flywheel etc when fitting the ribcase. I have one mated to my 948, using the thin backplate and standard flywheel. I do however have a 1275 diaphragm clutch which is vastly better than the coil spring type (plus a roller release bearing but that's another story). If you want the 1275 clutch you have to get someone to drill the flywheel for it, so you probably won't want that expense.

I read on the Moss site that you have to machine the smoothcase box in order fit the Minor internals, but maybe that was for the later Minor bits. I have a spare smoothcase in good condition, but I'm inclined to keep it as backup. I also have another one in bits, which might be useful for spares if you are interested. Jumping out of gear is usually caused by worn selector forks.

Overall, if you can get a decent ribcase it's definitely the way to go. The improved ratios and synchros transform the driving experience. It is noisier than the smooth one though.

Les
L B Rose

Les
Thats interesting. So are you thinking I can even leave my existing clutch?
I was working on an archived thread
www.mg-cars.info/mg-midget-sprite-technical-bbs/frogeye-gearbox-replacement-2014091620210326403.htm

and in particular the posting by Alan Anstead that says

The factory recommended way to fit a ribcase to a 948 Sprite as in the ST Manual.

'The 1098 / 1275 gearbox 38G374 is easily adapted to earlier models. Standard ratios are as 948 9CG. Use later engine backplate 12G 453 together with 1098 flywheel 12G 180 and 1098 clutch'.

Leyland letter dated 1977: 'The speedo pinion is common through all models and therefore it should not be necessary to re-calibrate the speedometer. Likewise the crankshaft spigot bush is the same diameter part 1A1559'.


Graham

Graham V

Sorry for late reply Graham - spending too much time in the garage! Yes you can still use the 948 clutch, but you'll have to check the release fork is correct. I would not use the 1098 clutch as it's a huge and heavy lump, despite what the factory says.

It's amazing what you can get away with. Back in the 1970s I put a 1098 Minor engine in a Frogeye. I could not afford a ribcase box but eventually found a 948 Mk II smoothcase. As far as I recall the engine had the thick backplate, and I used a 9-spring clutch from a Spitfire. Somehow it all worked surprisingly well, despite my not knowing what I was doing.

Les
L B Rose

This thread was discussed between 03/03/2018 and 11/03/2018

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.