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MG Midget and Sprite Technical - Smoothcase Gearbox Numbers

I've reached the gearbox now, and I'd like to enlist your help to identify what I've got. The previous owner notes:-

April 1966 New gearbox
July 1966 New gearbox faulty; MkII close ratio gearbox fitted
August 1980 Gearbox sent out for rebuild - new bearings fitted.

It's a smoothcase, so it seems he might have had a ribcase for three months in 1966, then fitted a second-hand early MkII box - unless the early MkII smoothcases were still available new in 1966. I've searched "gearbox" through all his copious notes, and I'm fairly sure that he didn't change it again after 1966 - just had it rebuilt before he laid the car up in 1982.

So here it is. Is anyone good at numbers?
The stamping on the box says A 6 V 1352
The circular plate on the bellhousing says TYPE 287574
The turret is stamped 2 A 3411, with V A F 4 below.

Nick and Cherry Scoop

There's normally a date code stamped in the side lug on the same side as the filler plug
David Smith

The circular plate would suggest it is a re-con 'box of some description.

Dave O'Neill 2

There is some stamping on the side lug nearest the filler, see below. Are you a certified interpreter, David?

Not sure about that, Dave. The picture on p35 of Horler, showing a supposedly exemplary gearbox, includes the circular plate at the top of the bellhousing.


Nick and Cherry Scoop

Wiped it with thinners.


Nick and Cherry Scoop

Nick

That photo does indeed show the circular plate - well spotted!

AFAIK gearboxes were originally in bare aluminium, not painted as per the photo. I don't see anything to suggest that this was a new, factory supplied gearbox.
Dave O'Neill 2

I guess one way to confirm if its a close ration box is to count the teeth on one of the gears. I have an original frogeye box and its painted green the same colour as the engine
Bob Beaumont

I wouldn't be surprised if there were different finishes depending on where the car went. Off the production line finish (luckly to get paint underneath), showroom finish (make it look really tempting to the punter) and motor show at Earls Court finish (this is what it could be like if we could get the staff to do it).

Rob

MG Moneypit

What I didn't include in my original post was the full text of the PO's August 1980 note:-

"Gearbox sent out for rebuild – new bearings fitted – checked and painted – new rubber mounting asembly fitted for mounting on chassis."

He was a bit of a fanatic, and I've little doubt that it was he who painted it. Though it may already have been gold: were there such things as Gold Seal gearboxes in 1966?

From a driver's point of view, the ratios seem good. On a test, I found that 5000rpm gave me roughly 20, 40, 60, 80.

Here's the whole thing, for further species-spotting.



Nick and Cherry Scoop

Nick,

The table below shows the primary shafts fitted to the various gearboxes - the part number is stamped on the front part of the shaft and is visible through the top inspection hole.

The original Frogeye box ratios were the same as the Minor and A35/A40, and the later MkII were the first 'close ratio' version - please see the table in the attached picture.

Richard




Richard Wale

Just what I need; thank you, Richard.

Now, 'scuse my ignorance, but where is the top inspection hole?
Nick and Cherry Scoop



"... where is the top inspection hole?"

There isn't one on a smooth case 'box.


If there was one, it would be here


Dave O'Neill 2

Oh - thanks Dave. So I should be able to see the stamping on the shaft in the bellhousing?
Nick and Cherry Scoop

If the thrust bearing is removed, you should be able to see it. Somewhere around here -


Dave O'Neill 2

Yes - there's a "20" stamped there. Not a longer number.
Nick and Cherry Scoop

The '20' possibly denotes the no of teeth on the input shaft gear. The stamping on the lug on ribcase boxes is normally a date like 1 4 68 and two initials, possibly the builder?
The circular plates as Dave said are factory rebuild plates, either gold seal or silver seal. They also are seen with a date code but just month and year e.g. 3 74.
David Smith

I think I've got it now. The gearbox front cover is 22 A 224, which appears to identify the gearbox as a 948 MkII close ratio unit from between 9CG-DA-2140 (Jun 61) and 9CG-DA-36711, the last 948 engine (Oct 62).

So, one of 34,572 possible units, probably reconditioned by the factory after about 4 years of hard use, and bought and fitted by my PO in July 1966. Then sent out for rebuild in August 1980 after 104,290 miles. Probably needed it.

David - maybe the chap who reconditioned it and painted it gold had the initials JB, and did the job on 5 March 1966 while listening to Spanish Flea by Herb Alpert and the Tijuana Brass.

It's only got 20,000 miles on it since then, so I shall stick it right back in.

Thank you, everybody.
Nick and Cherry Scoop

Nick,

I'm afraid the front cover 22A224 was common to all the smoothcase gearboxes - it is only the primary/input shaft that provides the unique identification, without 'counting turns'.

The simplest way is to engage 1st gear and count the number of turns that the input shaft completes in comparison to 1 turn of the output shaft:

3.6 turns of the input shaft = MkI Sprite, i.e. the original Frogeye, Minor, A35/A40 etc.

3.2 turns of the input shaft = MkI midget and MkII Sprite AND has the closer ratios.

The complete part number table is in the attached picture.

Richard
Richard Wale

Here's the picture!


Richard Wale

Ha ha. I was expecting that. Romantic, aren't I? Thanks, Richard - I will apply the final test, and prepare for disappointment.

I must say, though, Moss lists a different front cover for the early smoothcases, and goes into some detail about the numbers.
Nick and Cherry Scoop

Nick,

From the Sprite/Midget BMC Parts Manual, there was an earlier cover 2A 2087, but it was superseded by 22A224 during the life of the Sprite MkII and Midget MkI, and stayed until the change to the 1098 engine and ribcase gearbox.

The same supersession took place on other 948 engine cars as well, e.g. Morris Minor.

In the Moss catalogue I have, they quote 22G118 as the front cover for all 948 and 1098 gearboxes, which is wrong, it is only on the ribcase gearboxes. The 948 and 1098/1275 front covers are different because the stud layout changed and one will not fit the other.

Richard

Richard Wale

Ha! Success! Once I had found the gear lever among my boxes of parts, we carried out the test, and if the Lovely Assistant can be believed (she refused to trek back to the house for her glasses), it was 3.2 turns.

Thanks again. That's a really useful table, Richard, which I've printed and filed away.
Nick and Cherry Scoop

Well done Nick the smooth case CR box is I gather quite rare. Hopefully the synchro on 2nd gear is still ok.
Bob Beaumont

Nick - I don't think there is evidence for supposing the new gearbox fitted in 1966 would be a ribbed case one. I have a smoothcase box which has original black paint and BLMC branding, so post-Jan 68.

Tom
Tom Coulthard

Actually on checking out in the garage, the BL Catherine wheel is on a sticker which bears the legend "factory rebuilt unit". (Though with the cost premium I still think an owner might quite likely refer to one as a "new gearbox" in contrast to a rebuild by a garage or specialist.)

For the record, the alloy disc is reverse-stamped TYPE 514455 and stamped 28G 111 (this number is also painted in yellow on the black paint of the gearbox). I have a BL issue of AKD 3566 which gives 28G 111 as the replacement for 2A 3413, the 9C (frogeye) gearbox.
Tom Coulthard

That is a surprise, to me at least, because I would suppose that by 1968 shafts running in bushes might not be thought worth rebuilding.
Nick and Cherry Scoop

Interesting gearbox on 'the bay'

http://www.ebay.co.uk/itm/132301432383
Dave O'Neill 2

it looks like a Minor one i think i can make out the mechanical clutch cable mechanism.
Bob Beaumont

Though the seller says it's part no. is 22G 111 it's actually 28G 111, just like my 'Sprite' box. It does look like BMC/BL replacements were commonised onto the Minor/A40 gearbox 'W.S.E.' (When Stocks Exhausted, as it says in the parts book) of the Sprite ones.

Oddly, all the 'signage' on this box is different to that on my gearbox - looks like it was 'factory refurbed' in a different factory.

Nick - the thing that strikes me about the table in Richard's post is how many parts are common to all 6 boxes, including 'Input shaft bearing', 'Rear mainshaft bearing/bushing' and 'Laygear needle bearings'. I thought MMs weren't supposed to have needle rollers, only bushes!

Tom
Tom Coulthard

I need to fish out my BMC Special Tuning parts list for MkII Sprite to see what ratios were offered to private competitors.

NB I am talking about BMC Special Tuning Department, which had connections with the BMC Competitions Department (the factory 'works' competition department based at the MG plant in Abingdon, noting the importance of Morris engines plant and the Longbridge, Birmingham Austin factory as a source of standard cars, parts and input to design and production or application of non-standard to the car but other production parts for competition, as well as external parts suppliers and developers). I am not talking about the Healey 'works' competition dept at The Cape Works in Warwickshire.

Any know what gearbox internals - ratios and whether straight cut - were in the BMC works prepared and entered 948cc MG Midget MkI rally cars, or the more famous Sprite MkII racing cars prepared by the Healey works?

Tom - any info on gearbox ratios for the above MkII Sprites as well as Sprinzel and Sebring Sprites? (and I am nervous of being caught out on my possible incorrect use of 'Sebring Sprite'!)

Cheers
Mike
M Wood

AFAIK all 'boxes had needle rollers for laygears. It was the second and third speed gears which were bushed. Also there was a bush between the first and third motion shafts.
Dave O'Neill 2

Dave is right. The later Spridget ribcase boxes were all needle rollers on the 2nd and 3rd gears and the ist /3rd motion shafts.The MM ribcases remain bushed.
They use the same ratios and cogs as the cooper s
Bob Beaumont

Tx Dave and Bob for reminding me of that: I suppose the problem of 'gearbox strength' with bronze bushes - fine when new - comes about because they wear sacrificially, whereas with roller or ball bearings there is steel/steel contact.

The extra needle rollers of the late 1275 box no doubt accounts for its reputation for (comparative) strength, despite the increased spiral angle of the 'B' gearset - changed for quietness - increasing the sideways loads put into the casing.

Mike - the BMC Special Tuning Dept didn't exist until 1964 (see Bill Price). The earlier Sprite booklets describe Tuning that is Special because, in 1958 and '59 before homologation was implemented, they include optional equipment which could be fitted - the more 'trick' bits requiring a Touring Car to run in the GT category, like Pat Moss's Weber-carbed A40s.
Tom Coulthard

We believe that every Healey race entry used an engine and gearbox unit from Morris Engines in Courthouse Green, Coventry - supplied complete and used more or less 'as is'.

The 1959 Sebring Sprites are reported in Road & Track to have ratios of 3.1, 1.99 and 1.35. I've previously assumed this was journalistic inexactitude (they are close to the Mk II ratios), but they may have been special - the cars used twin-plate clutches (where did they come from?).

I don't know where the gearboxes for front (BMC) engined Formula Juniors were built: the likes of Lolas and Elvas. Morris Engines may well have been involved, as there appears to have been quite a budget for FJ -
for the PR benefit.

Tom Coulthard

There was a 'close-ratio' box available during frogeye production - this had standard Mk II ratios but was straight-cut, and is presumed to have come from Courthouse Green. Most if not all the early race and rally Sprites are thought to have used this box, as the standard one was just not considered strong enough.

The 61/62 Sprites and Midgets had to be homologated, so gearbox ratios needed to be declared: the 'Sprite Sebring Mk II' had 3 alternatives, the frogeye box (oddly), the std Mk II and a close-ratio box with 2.93, 1.754 and 1.242 gearing; the Midget had only the frogbox and the std Midget ratios.

Tom Coulthard

This thread was discussed between 07/08/2017 and 31/08/2017

MG Midget and Sprite Technical index

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