Save The Minis

Corner of the rear load floor cut out, rear closing panel cut off. The rear corners look OK on the outside, but will need to be replaced.

Rear subframe mount, with seized subframe bolt (top right)

Here is an example of hammerforming – reproducing a feature in a body panel using a mold. This method can be used to replicate features on body panels that are expensive or no longer available. The Covell Hammerforming DVD shows the possibilities in more detail.

1. The feature we want to copy – a vent on a Mini sill panel. The panels are cheap, but can cost several times their value to ship…

2. A mold of the feature, made from body filler. Hammerforms that will be used many times can be set into a container. Polyvinyl alcohol (not acetate) is used as a release agent – available from conversation supply stores.

The mold is clamped to the new piece of metal around the edge of the feature. For a small feature like this, a vise and some g-clamps will do. A piece of soft wood was used to buffer the metal against the hammer, to prevent marks.

3. The mold, the hammerformed vent, and the original vent.

Test-fitting new bracket to the floorpan

Goal – no body filler…

Components of a pre-1964 Mini coil spring clutch. Note the use of coil springs instead of a diaphragm. Coil spring flywheels can be converted to diaphragm type by machining a groove around the edge of the inner part of the flywheel for the diaphragm to sit in.

Here are some PDFs of technical articles about the Mini (code name ADO15) that were published in the Automobile Engineer journal. Plenty of esoteric info about the technology and manufacturing process of the time.

BMC ADO15 – Introduction

BMC ADO15 – Part 1
BMC ADO15 – Part 2
BMC ADO15 – Part 3

BMC Gearbox Synchros
Moulton Rubber Springs

How to visually identify an ‘A type’ vs ‘B type’ 3-synchro Mini gearbox

‘A type’ gears from a June 1963 Mini 850 gearbox.

• Steeper pitch on the teeth than ‘B type gears’
• Interlocking ring between second and third gears on the mainshaft (3rd geard is the gear just to the left of the oil pickup pipe)
• First motion shaft has a bush rather than a needle roller bearing

‘B type’ gears from a later Mini Cooper 998 gearbox (22G68 gearbox casting)

• Shallower pitch on the gear teeth than the ‘A type’ gears
• No interlocking ring inbetween second and third gears (you can see a ridge on the side of the second gear instead)
• First motion shaft has a needle roller bearing rather than a bush.

You can also tell ‘A type’ vs ‘B type’ gears by dismantling and checking to see whether second and third gears run on bushes (’A type’) or bearings (’B type’), except for early Cooper gearboxes which had A-type gears running on bearings.

Telling a cone synchro Mini gearbox from a baulk ring mini gearbox

• You can see the outside of the baulk rings (in the above picture, to the left of third gear, you can see the outside of one of these (at right are the bushes that second and third gear run on):

Mini 3-Synchro gearbox info-dump

Here is an assortment of info I have assembled from the Somerford Mini catalogue (PDF), the official BMC parts and workshop manuals (highly recommended apart from the buggy but workaround-able copy protection), the Mini Spares Parts Catalogue (no longer published?) by asking on the Mark 1 Forum.

Corrections and additional information are welcome.

• ‘Cone type’ synchromesh was used until October 1962 (according to the Mini Spares Parts Catalogue). Lack of baulk rings caused the synchromesh to wear, leading to:
• ‘A type’ gears with baulk rings. These were noisy, leading to:
• ‘B type’ gears, used from engine number 8AM/U/H803601 on (plus intermittently from H801243) – September 1964 according to MSPC. These gears were used until the 4-synchro gearbox was introduced in 1968.
• Some Minis were converted from cone to baulk-ring gears using BMC conversion kits, using parts unique to those kits.
• Mini Coopers: Early 997cc Mini Coopers and early Cooper S used ‘A type’ gears running on bearings rather than bushes.
• Cooper vs Standard gearbox: Cooper gearbox has 26 teeth on the first gear on the laygear, regular mini has 28 teeth. Plus, the Cooper gearbox should have a remote-type shift mechanism on the back rather than magic-wand. Other ratios were sold via Special Tuning.

Other info

• Any complete set of 3-synchro gearbox internals will fit into any 3-synchro gearbox casing.
• Almost no parts are interchangeable between the different types of gearboxes (some bearings are the same).
• Almost no new parts are available for any of these gearboxes, getting worse as they get older.
• A 1/8 Whitworth spanner is needed to remove the gear selectors (11/32 inch is close enough). Clearance is too limited to use a socket.
• ‘B type’ gears were shared with the MG Midget.
• You cannot tell if a gearbox is a Cooper gearbox from the part number on the casing, you need to count the gear teeth.
• You can convert a 4 synchro remote-change gearbox to magic wand using adaptor parts from late-60’s commercial minis (vans, pickups).
• Converting a rod-change 4 synchro gearbox to remote change or magic wand is complicated by the diff cover – it usually can’t be swapped over, because it is align-bored and doweled at the factory.
• If you try and fit up a different diff cover than the one the gearbox came with, odds are the two halves of the diff output bearing hole will not line up, meaning the diff will either not fit, or fit, but leak. Possible ideas for workaround (?) – drill the diff case mounting holes oversize, align the diff with the case perfectly, then have new locating dowels fitted (time to consult a machine shop). Or – fit the diff and gearbox casings together, align-bore oversize, and have a sleeve made to fit betwee the output shaft bearings and the case (?) Path of least resistance – modify the floorpan to accept a rod change.

Chipped tooth on second gear

Problems found so far:

• Layshaft case-hardening worn through where the laygear bearings run on it. (Fortunately, new ones are available)
• Double roller bearing on mainshaft disintegrated (bearing cage for one of the roller bearing collapsed)
• Final drive nut backed off, possibly related to mainshaft bearing failure and large amount of end-float in the gears
• Chipped tooth on second gear
• Second gear baulk ring is a little worn (fortunately also available new)
• Input shaft and main shaft have visible wear (unknown how serious it is)

Wanted to buy:

• Any ‘A type’ bushes or thrust washers.
• An ‘A type’ second gear in good condition.
• (Possibly) ‘A type’ mainshaft, input shaft.
• NOS baulk rings (old ones rumoured to be better quality) and layshaft (for any 3-synchro gearbox)