6 replies to this topic

[mineeeeee]

I have the remains of a MG gearbox which is unusable at the moment so
got a replacment from a forum member.

The question i have is having looked on minispares site for gaskets and the like
before i fit the replacment it stated that some early MG box,s were close ratio so
how can i tell with the gear box in bits and never having driven a car with this box in.

OR can't i

[Ethel]

I have the remains of a MG gearbox which is unusable at the moment so
got a replacment from a forum member.

The question i have is having looked on minispares site for gaskets and the like
before i fit the replacment it stated that some early MG box,s were close ratio so
how can i tell with the gear box in bits and never having driven a car with this box in.

OR can't i

Mg metro?

Post 84 all 1275 Metros were:

1st 3.647:1
2nd 2.185:1
3rd 1.425:1


There's just been a thread where Guessworks listed all the gearbox ratios have a search.

[mineeeeee]

Did many seaches,found it

Basically i should count the teeth on the first motion gear/shaft.
May not tell me much on its own but i can compare with my standard box

should have thought of that fist

[Guess-Works.com]

No MG metro box was close ratio.. GT and Cooper S yes, but not MG (or infact any A+ box)

[mineeeeee]

No MG metro box was close ratio.. GT and Cooper S yes, but not MG (or infact any A+ box)

Just going on what it says on minispares web site but to be honest
i would rather believe you than them

[Guess-Works.com]

Taken from article 308 on Minispares site

20 August 2005

Engine transplants - gearbox information

By keith calver

Begin date 20-Aug-2005 End date 20-Aug-2010

A subject worthy of an entire book to explain the whys and wherefores, and also causes much consternation on the part of the transplanter.

Terminology -
BBU - Big Bore Unit
SBU - Small Bore Unit
FD - Final Drive (diff ratio)

A subject worthy of an entire book to explain the whys and wherefores, and also causes much consternation on the part of the transplanter. Much confusion’s spread over which gearbox has the best ratios, is best to use, and with which FD. For a detailed account on this and covering all gearboxes fitted as standard to the Mini, see the relevant separate articles 'Gearbox - Standard production gearbox types'.

Fortunately, when selecting a complete engine and gearbox unit from a Metro, the gearbox will pretty much suit the engine and be easily transplantable whole into the Mini. It shares exactly the same rod-change linkage as the Mini. Difficulties only arise when fitting a rod-change gearbox into a pre-1973 Mini that has the old remote-type gear-change mechanism, but not insurmountable. It's dealt with in the 'Ancillaries' appendage to this series.

Practically all Metros had a 3.44 FD including the MG, the only oddballs were the Turbo that had a 3.2, and rare ‘economy’ models that had a 3.1. The 3.44 FD gives the best all- round performance - that’s why John Cooper fitted it as part of his performance package on the late 998 Coopers. The 3.2 is a bit neither here nor there. The 3.1 being good for long distance work and on BBUs tuned for better mid-range, and the same as that fitted in all A+ engined Minis from 1980 onwards. In fact the whole gearbox from the Metro is exactly the same as that fitted to the A+ powered Mini - only crown-wheel and pinions were changed to achieve the different FDs.

Rod-change Minis were fitted with a 3.44 FD up until 1980, when they went to a 3.1. The only exception here was the City E and Mini 25, endowed with a 2.95 - absolutely killed the poor 998 engine’s meager performance stone dead!! Mind you, the French Minis were fitted with a 2.76 FD (as fitted to the very latest Mini)!!

The only way to be 100% certain of the FD ratio if the exact origin isn’t known is to count the teeth on the crown-wheel (big one in diff housing) then divide this by the number of teeth on the pinion (small gear on end of mainshaft by the big retaining nut where the speedo drive spindle is connected).

Ratio-wise, the A+ gearbox used in the Metro isn’t quite as good as the old pre-A+ rod-change set-up. First gear is lowered to cope with the taller FD, and there’s a bigger gap (rpm drop) between second and third. Much of this was due to the utilitarian application to the whole A-series front-wheel-drive range. Identification is easy, the A+ gears have a markedly pointed profile whereas the earlier ones are square topped (blunt). In fact the early type is the same as those first used at the inception of the four-syncro gearbox!! It's also the exact same set-up used in all the A+ Minis and the A+-powered Allegro. See what I mean?

Austin 1300s/AAs and 1300GTs used a remote-type gearbox. The main difference is the horrendous rubber/metal sandwich plate between the remote housing and the back of the diff housing. Made for quite a gooey gear-change once a few miles old. These will fit in place of the Mini remote type, although the rear mount is different. My advice here is to change it to the Mini mounting by drilling/tapping the two holes necessary to carry the Mini remote mounting. Trying to alter the bracket to take the Austin 1300 one is more of a job! Getting a remote-housing type gearbox into a rod-change shell a worse one, taking a fair bit of fabricating and fettling. Internally they use the same gears as the old Mini - square-tipped teeth with the same ratios - except the 1300GT. This used the S/1275GT close-ratio set-up employing the 18-tooth first motion shaft and 22G1040 laygear. FDs-wise, you could get anything from a 3.76 to a 4.1. Best to double-check by the tooth-counting method!

Crown wheel and pinion ratios data;
Tooth count -
Final Drive Ratio Crown wheel Pinion
4.33 65 15
3.94 63 16
3.65 62 17
3.76 64 17
3.44 62 18
3.21 61 19
3.10 59 19
2.95 59 20
2.76 58 21

Note:
A+ Pinions are flat on both sides - Pre A+ have ridges.
Although some ratios have the same tooth count on either
gear they are different angles and part numbers and therefore
not interchangeable.

Useful part numbers:
Remote housing rear rubber mount 21A956
Remote housing rear bracket 21A745

[mineeeeee]

This is whats on there site,i got my info from the first paragraph.



17 August 2004 (revised: 17 September 2005)

GEARBOX - Close-Ratio Conversion Pre-A+ Gearbox

By keith calver

Begin date 07-Jul-2005 End date 08-Jul-2006

As outlined in the 'Gearbox - standard production gearbox types' article, it is entirely possible to change the common 4-syncro gearboxes to the helical close-ratio set-up as used in the Cooper S, 1275GT, 1300GT, and some early MG Metros providing the right parts can be sourced. And you don't already un-knowingly have the close-ratio kit fitted! Part numbers are detailed at the end.

Part No Applications: 22G1094, 22G1095, 22A1371, 22G1040, 88G396, CHM141, C-22A1738, 22G931, 22G860, 22G856, 22G857, 22G858, 22G859, DAM3167, DAM3168, 13H9513, CHM141, C-22A1739, DAM3187, 22G860, DAM3180, DAM3181, DAM3182, DAM3183, C-AHT54, 22A542B, AJM804B, 18G8085, DAM6140, DAM4000

The other pre-requisite for this conversion is that it can only be applied to the early, pre-A+ type mainshaft gears. That's those that have the square-topped teeth as supposed to the distinctively pointed A+ profile. This is because despite being endowed with A+-type fittings for the mainshaft end and layshaft, the conversion gears have the pre-A+ tooth profile. This is not to say that the conversion cannot be put into an A+ gearbox casing - it can and is detailed in the relevant article. What is essential to understand is that the pre-A+ second and third mainshaft gears are going to be needed. First gear is the same in all 4-syncro gearboxes irrespective of whether they're pre-A+ or A+.

It should also go without saying that doing this to an otherwise clapped out gearbox is a waste of time. Take the opportunity to give the unit a good over-haul and fitment of a centre-oil pick-up pipe. Utilise a good manual for general gearbox disassembly/reassembly method. Haynes is possibly the best as it's quite comprehensively detailed.

The following can be applied to either the remote or rod type gearboxes.

When utilising the pre-A+ first motion shaft and laygear, this is very straightforward. Simply exchanging the existing ones for the close-ratio versions is all that's required. Everything else remains the same.

If only the A+ variants are available/sourced, then you will also need to use an A+ mainshaft, pinion retaining nut, layshaft and layshaft centre-web thrust washer, and relevant bearings. The mainshaft is required to provide the larger 18mm first motion to main shaft support bearing, the pinion nut because the thread is different to the earlier types, the layshaft for the increased carrier bearing sizes used and it's accompanying centre-web thrust washer for correct layshaft clearance/bearing retainer hole. Fitting the mainshaft is a simple swap for the pre-A+ one with no other fitting problems. The layshaft is the bugbear here.

Although the two ends are the same diameters as the pre-A+ item, it has an extra step on the first gear end to accommodate the bigger, single needle roller bearing used. The A+ casings have a recess around the bore in the centre web that carries the first gear end of the layshaft, the pre-A+ ones don't. This prevents the A+ layshaft passing through the web far enough to get the locating plate in its relevant slot on the other side. It is not caused by the smaller layshaft thrust washer as believed by some. There are two solutions to this problem.

Either grind the locating plate slot wider by 0.375" towards the end of the layshaft, or grind the first step on the layshaft back 0.375". I would recommend the latter as it's generally easier to do, and doesn't compromise shaft strength at all. The other way brings the slot perilously close to the end of the shaft! And the shaft will have to be ground - it's pretty hard. If grinding the step back, make sure a slight radius is left in the new 'corner' to avoid a stress riser. I finish polish the rad with aluminium-oxide abrasive tape. Wet and Dry paper will do, something in the order of 400 to 600 grit. Doing either of these fixes will not cause bearing lubrication problems, but I would advise properly de-burring the oil feed holes on the layshaft/bearing surface area.

Re-assembly and shimming is as per the standard method/tolerances.


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