Box FD Ratio

[Steam]

I have a newer style box of unknown origin, is there a way of telling what it is or what it came from?
Cheers.

[Halfpint]

Hi Dave,
Usually the box numbers will give the best indication as to which model they may be from.



It’s a start anyway.
HP

[Steam]

Thanks Tony. The numbers on mine are EXACTLY the same as in your picture, so what doea that tell us?

[Halfpint]

That it’s a late model import.
There should be 2 grooves cut into the OD of the gears, hence the “Twin Line” name tag.
Also on the centre web should be only 3 bolts holding the bearing plate as opposed to earlier 4 bolt mount.
The ratios are slightly different as well, but being away at the moment, I don’t have them at hand.

[SaharaDust]

In Tony,s absence My understanding is the ratios for “twin groove” gears are the top row.  The row below are for “standard” gears. Twin groove gears differ in that 1st and 2nd are lower (higher numerically) that what might otherwise be fitted.

ratios:-
1st  /  2nd  /  3rd  / 4th
4.00 / 2.30 / 1.43 / 1.0
3.52 / 2.21 / 1.43 / 1.0

This may be an urban myth but apparently twin groove gears were fitted to very late model minis.  The lower gears were associated with emission reductions.  The cars were fitted with a very high final drive ratio somewhere like 2.95:1 The lower ratio 1st and 2nd gears were fitted so the poor little things could actually get going from a standing start. Once underway the engines did not rev as hard and so reduced emissions.
 

[Steam]

Thanks guys, no hurry as it is a long term solution to a problem. The box it is to replace is still being driven around.
But I am now wondering if there might be better options for a 1275.

[Terry]

Hi,

the three bolt retainer boxes like yours are considered the strongest as the hole they didn't drill in the cross webbing was where they cracked so good for stronger engines. Depending on the diff used the pinion gears in the 4.1 version tended to be a bit weak but if it is from a Mini then you have less teeth so a bit more meat per tooth. The main shaft should have a 18mm nose instead of earlier 14mm.

As a general rule don't mix the contents as it is A+ and you probably have mostly A series gear. I don't know exactly how accurate this is but anything I see with DAM in the part number I consider late model A+ era and you need to do your homework if you are mixing it up.

Terry

[Steam]

Thanks Terry, I will keep what you have said in mind.
By mixing , do you mean if rebuildng the box or bolting an an A engine to the A+ box?

[Terry]

Hi,

the internals, the gears. For engine to the box you just need to check the primary, idle and input gear are all the same.

Terry

[Halfpint]

Thanks SD 

ratios:-
1st  /  2nd  /  3rd  / 4th
4.00 / 2.30 / 1.43 / 1.0
3.52 / 2.21 / 1.43 / 1.0

And Terry

Hi,
the internals, the gears. For engine to the box you just need to check the primary, idle and input gear are all the same.
Terry

Yep, absolutely.
Remember this during my build?
https://www.mokeforum.com.au/index.php?topic=7886.msg166152#msg166152
It tripped me up for a while, so frustrating. But its a nice box when you get it sorted and running 

[Steam]

Thanks Guys, great info. I might be getting oldtimers disease as I have vague memories of this whole GB saga years ago.
I have an odd gear stored with the box which I seem to remember getting after the box.

Tony, did you change the FD on yours?

[Steam]

OK, so I am now officially confused (so nothing new with me and gearboxes then)
Firstly looking at Tony's thread on his box rebuild trggered a memory and on looking at this box I remebered changing the transfer gears and the needle roller bearing to the coarser thread, the two gears stored with the box are the originals with the larger shaft.
The confusion is that the FD is 3.7 to 1 and I cannot find in my literature any box of this type with that ratio. The gears have the groove line on them though.
Any thoughts?

[Halfpint]

It was ages ago, but pretty sure Spider told me it was 4.1:1.
I should have counted and wrote it all down  .
Are there 2 grooves through the gears or 1?

[Terry]

Hi,

in the Mokes the last of the 1275's did come in 4.1:1 but due to the teeth being a bit thin when they got rebuilt the 3.7:1 was a popular choice. I don't think you will find the double groove in the FD, I believe they were just normal A+ with the more pointed gear. And if the 3.7 is used it will just be a normal A gear.

Terry

[Steam]

Sorry should have been more clear
The pinion & crownwheel do not have any grooves
the rest of the gears in the box have 1 groove.