interchangerbility between a series and a plus drops
Turbo Mini Forums

hi, im building a new engine for my mpi cooper


the block is obviously the a plus injection block

the gearbox i have built is a close ratio late a series gearbox.

the plan was to use the a series gearbox and drop gears, along with the a series drop gear housing.

however, the mpi housing is different, as it has a sensor attacthced for the flywheel.

therefore it looks as though i need to use the mpi a plus drop gear housing. obviously this wont work whilst using a series drop gears

can a plus drop gears be used with an a series gearbox ? i would then be able to use the mpi sensor equipt transfer gear housing.
if not, i recall somehwere someone mentioning that minispares make different bearings for the transfer gear housing - does anyone know if there are bearlings to fit the a plus transfer case allowing the a series drops to be fitted?

i have posted along these lines a few months ago, but the post doesnt seem to be on the site anymore.

can someone help?

Edited by Rod S on 23rd Oct, 2009.

Schrödinger's cat - so which one am I ???

ok looks like i need one of these then.

http://www.minispares.com/Product.aspx?ty=...ER%20GEAR%20CO..

how difficult is it to change these bearings? guess you have to heat the case. anyone got any tips?

supposedly if you heat the case up with a big blow torch then slap it face down a couple of times on a bit of wood it should pop out.

tbh i cant remember how i got mine out last time, i think i may have dremeled a slit through the outer bit then puller oit out with pliers.

isnt what?much metal?

right, just been down to the garage to have a look. the a series drop gears fit perfectly into the mpi transfer housing (with its standard bearing. the bearing fits the gear perfectly. i dont know how this has happened. the drop gear is definately a series. the gearbox in question is from a 1979 1275 gt, so would have been right at the end of a series production. maybe the later a series was slightly different, with the coming of A+ just around the corner.

anyhow, the a drop fits the a+ bearing as it should :/

What's the casting number on the gearbox casing ???

That should answer (explain) what you actually have.

A lot of A parts carried over to what was supossedly A plus....

Schrödinger's cat - so which one am I ???

will have a look at the casting no. next weekend. im sure its s deries (has four bolts in centre web). also the diff is a series.

will also measure the width of the shafts. the drops are definatly 'a', the gears are cut different from some late mpi ones i compared them with.

The first A plus boxes had the four bolts (hence asking for the casting number to see if it is one of those).
The first ones also used up the supplies of A gears (inc. diff gears) although they obviously needed the A plus drop gears because of the bigger bearing.

They were a real muddle at the changeover time.

Schrödinger's cat - so which one am I ???

cheers for the reply. will check out the numbers at the weekend. ta

hi rod, just had a look at the casting numbers, layout as follows

A/BZ1 DAM
C&M 2886


date stamp on the diff states '79

there are 4 bolt holes on the centre main web

the drops are definately a+ diameter on the shafts (measured and compared with verniers)

the diff is an A series as oppoed to a+ (compared them)

got a feeling the 'DAM' suggests a+?

Yep,

If you put them in a slightly different order, DAM 2886 was the earlier A plus gearbox casing.

It had the larger drop gear bearing for A plus but still had the four bolts and weaker casting around the 3rd motion shaft bearing. It also still used studs/nuts/gaskets for the diff housing instead of the later bolts and RTV.

The internals fitted however, could have been A or A plus, gear train or diff could have been either, there is even an alternate 1st to 3rd motion shaft nose diameter and needle bearing size at this point in time....

But the drop gear bearing size will be the later, bigger A plus.

Edited by Rod S on 30th Oct, 2009.

Schrödinger's cat - so which one am I ???

cheers rod. just a mixture of what was to hand at the time by the looks.

the gearset itself is 'A', with close ratio laygear. final drive was 3.44, but have changed this for a 3.2

was told it came from a late 1275gt, so this makes sense.

its worked out perfect to be honnest, got the close ratio gearset in there, and can use late drops (will be in mpi so need to use a late mpi drop gear housing with the sensor in it).

did consider going for s/c drops, if i decide to in the future it will be easier as a+ seem easier to obtain, worry about them decreasing the value of the car in the future when i come to sell, plus i do a fair amount of mway mileage!