ausmini :: View topic - Gearbox question

Hi guys. I've been loaned a 1275 motor and gearbox to get my Mini back mobile after a crank meltdown in my old (but really new- long story!) motor.

It's a 12H902UH prefix motor on a gearbox casing number DAM2886.

Allegedly, since it came with the rest of the car, it's from a 1977 Moke Californian, also allegedly with only 53,000 odd km on the clock.

The lender is pretty sure it has a 3.444 diff in it, but I find that a bit hard to swallow given the 12 (or 13) inch wheels on a late Moke. I don't intend changing my Deluxe from the 10" ones.

If it has that diff, then I'll try it as a unit, otherwise I need to swap gearboxes, which I'd rather avoid if possible. Equally, if what I've read on the odd pommy forum is accurate then it may well be an early A+ box which would perhaps mean all sorts of mismatches with drop gears and idler bearings I believe.

Is anyone out there able to enlighten me please as to the likely diff ratio without me resorting to stripping the thing? Needless to say, the sticker showing the ratio, that occasionally survives on diff housings, is long gone.

I await input with a mixture of hope and trepidation!

Cheers, Pottsy

Author:	Pottsy [ Thu Apr 21, 2016 5:27 pm ]
Post subject:	Gearbox question
Hi guys. I've been loaned a 1275 motor and gearbox to get my Mini back mobile after a crank meltdown in my old (but really new- long story!) motor. It's a 12H902UH prefix motor on a gearbox casing number DAM2886. Allegedly, since it came with the rest of the car, it's from a 1977 Moke Californian, also allegedly with only 53,000 odd km on the clock. The lender is pretty sure it has a 3.444 diff in it, but I find that a bit hard to swallow given the 12 (or 13) inch wheels on a late Moke. I don't intend changing my Deluxe from the 10" ones. If it has that diff, then I'll try it as a unit, otherwise I need to swap gearboxes, which I'd rather avoid if possible. Equally, if what I've read on the odd pommy forum is accurate then it may well be an early A+ box which would perhaps mean all sorts of mismatches with drop gears and idler bearings I believe. Is anyone out there able to enlighten me please as to the likely diff ratio without me resorting to stripping the thing? Needless to say, the sticker showing the ratio, that occasionally survives on diff housings, is long gone. I await input with a mixture of hope and trepidation! Cheers, Pottsy

Author:	simon k [ Thu Apr 21, 2016 5:43 pm ]
Post subject:	Re: Gearbox question
Ray Potts in Class C!! I never thought I'd see the day!! best thing to do is put it in 4th gear and turn the flywheel for 1 revolution of the diff output shafts... see how far it goes. You only need to take the flywheel cover off and it'll be pretty accurate

Author:	kiwiinwgtn [ Thu Apr 21, 2016 5:57 pm ]
Post subject:	Re: Gearbox question
Isnt the 3.44 dif perfect for 10 inch wheels.

Author:	Scoop [ Thu Apr 21, 2016 6:12 pm ]
Post subject:	Re: Gearbox question
kiwiinwgtn wrote: Isnt the 3.44 dif perfect for 10 inch wheels. Being out of a Moke its probably not 3.44 though. Likely to be 4.11 or something

Author:	Maelgwn [ Thu Apr 21, 2016 6:45 pm ]
Post subject:	Re: Gearbox question
4.11 you'll be smoking those 10's

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Author:	78Clubbie [ Thu Apr 21, 2016 8:39 pm ]
Post subject:	Re: Gearbox question
Pottsy wrote: Hi guys. I've been loaned a 1275 motor and gearbox to get my Mini back mobile after a crank meltdown in my old (but really new- long story!) motor. It's a 12H902UH prefix motor on a gearbox casing number DAM2886. Allegedly, since it came with the rest of the car, it's from a 1977 Moke Californian, also allegedly with only 53,000 odd km on the clock. The lender is pretty sure it has a 3.444 diff in it, but I find that a bit hard to swallow given the 12 (or 13) inch wheels on a late Moke. I don't intend changing my Deluxe from the 10" ones. If it has that diff, then I'll try it as a unit, otherwise I need to swap gearboxes, which I'd rather avoid if possible. Equally, if what I've read on the odd pommy forum is accurate then it may well be an early A+ box which would perhaps mean all sorts of mismatches with drop gears and idler bearings I believe. Is anyone out there able to enlighten me please as to the likely diff ratio without me resorting to stripping the thing? Needless to say, the sticker showing the ratio, that occasionally survives on diff housings, is long gone. I await input with a mixture of hope and trepidation! Cheers, Pottsy Our 1275LS is also a 12H902UH but it also runs 12 inch wheels. No help on ratio, sorry ! Geoff.

Author:	HI-HO JAMES [ Thu Apr 21, 2016 9:05 pm ]
Post subject:	Re: Gearbox question
I was just thinking and I am pretty sure the 12H902UH engine prefix was for the 1275ls only, the moke 1275 engine has its own 12H prefix in the same way the 998 engines do,oh and the moke was not available with 1275 engine again until early 79 i think , but definantly not 77 .

Author:	Pottsy [ Thu Apr 21, 2016 9:28 pm ]
Post subject:	Re: Gearbox question
simon k wrote: Ray Potts in Class C!! I never thought I'd see the day!! best thing to do is put it in 4th gear and turn the flywheel for 1 revolution of the diff output shafts... see how far it goes. You only need to take the flywheel cover off and it'll be pretty accurate Simon, sometimes you just have to lower yourself to the proletarian level to see how the riffraff live! I'll be back in Class A eventually, just probably not this year. After having a bit of a play out with the mossies, I've got a nasty feeling it's a 4.11. A bit over four turns of the crank for 1 of the diff with 4th selected by the trusty vicegrips. Damn! This assumes that top gear is 1:1, which I'm pretty sure it is, and that the primary gear and the first motion shaft gear are the same diameter, which the samples I pulled out of the drawer are. The head is also interesting. It has the numbers "567" above a "1201316" with a "28F" on its side beside the long number. Rockers are cast units and very clean. Also has a cast in symbol: a W inside a diamond all enclosed by a circle. W for weird maybe! Also seems to have a late model "bulgy" timing cover, which I assume means it has a tensioner? I hope this doesn't mean it's an A+ gearbox & drop gears as that will complicate what promised to have been a simple drop-in transplant. The research (well let's call it that) is ongoing. Cheers, Pottsy

Author:	MiniVLT [ Thu Apr 21, 2016 9:34 pm ]
Post subject:	Re: Gearbox question
You could also put it in 4th, roll the car forward 1 wheel revolution and count the revolutions of the dizzy rotor instead of taking of the flywheel cover! Cheers Shane

Author:	Pottsy [ Thu Apr 21, 2016 9:37 pm ]
Post subject:	Re: Gearbox question
Thanks Shane, yes, I could, if the motor were in a vehicle instead of on a table in my workshop. In any case I simply turned it with the fanbelt pulley nut and a large socket. Haven't pulled the wok off yet. Cheers, Pottsy

Author:	Phil 850 [ Thu Apr 21, 2016 10:10 pm ]
Post subject:	Re: Gearbox question
I had a 4.13:1 diff in my 1100S powered 850. Engine was out of a Morris 1100S with big wheels. Screamed on the freeway at 80kph. Now has a 2.95:1 and cruises beautifully at 110.

Author:	minimanic [ Thu Apr 21, 2016 10:24 pm ]
Post subject:	Re: Gearbox question
No need to change the whole gearbox to swap diff ratio. You can change the crownwheel and pinion for your desired ratio by removing the front housing and the diff housing. I have done this a few times swaping the same engine between 13" moke's and 10" wheel minis.

Author:	Pottsy [ Thu Apr 21, 2016 10:35 pm ]
Post subject:	Re: Gearbox question
Thanks MM. I know I can change it relatively easily, but was hoping to avoid having to do it! Ah well, I guess if wishes were fishes we'd all swim in the sea! Thanks, Pottsy.

Author:	simon k [ Fri Apr 22, 2016 11:35 am ]
Post subject:	Re: Gearbox question
Phil 850 wrote: Now has a 2.95:1 and cruises beautifully at 110. jeez that must be lazy - I have a 3.1 in mine and am taking it out on Monday to change back to a 3.44. The 3.1 is nice to cruise with, but just too sluggish without any boost

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Author:	Phil 850 [ Fri Apr 22, 2016 9:41 pm ]
Post subject:	Re: Gearbox question
simon k wrote: Phil 850 wrote: Now has a 2.95:1 and cruises beautifully at 110. jeez that must be lazy - I have a 3.1 in mine and am taking it out on Monday to change back to a 3.44. The 3.1 is nice to cruise with, but just too sluggish without any boost It's no drag car, but I am surprised how well it still accelerates.