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MG MGA - Gear ratios

Does anyone know exactly what ratios were fitted to the MGA with the flanged mainshaft. More to the point I need to know how many teeth are on each gear!!

Reason- I have 2 gearboxes which are in bits, all the bits in one box, and one of them is supposed to be a close ratio type, but I cannot find any info on the actual teeth count.

Can anyone help?

Colin
Colin Parkinson

Colin,
I am pretty sure the tranny that I checked is stock. First gear is straight cut and the rest are bevel cut gears.
First gear - 28 teeth
Second gear - 31 teeth
Third gear - 25 teeth
Fourth gear - 20 teeth
Hope this helps. Have a good day!

John
John Progess

I am fairly certain that there is a difference in the gear on the first motion shaft and the driven gear on the laygear.

An extra tooth on the 1st motion shaft and one less on the laygear as the effect of raising all the ratios without affecting top gear - ie givein 'closer' ratios.

Cheers
ian F
Ian Fraser

Ian,

The close ratio gear set does not raise the first three gears by an equal proportion, they do in fact get closer together.

Standard CR
1st 3.64 2.445
2nd 2.214 1.62
3rd 1.374 1.267

On some old notes I have the following gear counts for the CR box (Caution - these were not counted by me).

Individual gears
1st gear 28
2nd gear 32
3rd gear 29
Input gear 26

Layshaft (cluster)
1st gear 11
2nd gear 19
3rd gear 22
Input gear 25

Top gear is direct drive.

John,
Do you have a gear count for the standard cluster gear?
Also, there is no separate gear for 4th, do you mean the input shaft gear?

Mick

Mick Anderson

Hi Mick/Colin

It was just a possibility that I raised, as the difference between the stump pulling gears on the Morris/Austin light commercials of the era was only the first motion/laygear ratio. (and of course lower geared rear axle)

I have a van laygear
Driven gear = 31 teeth
1st = 11
2nd = 20
3rd = 26

MGA laygear
Driven gear = 30 teeth
1st = 11
2nd = 20
3rd = 26

Mainshaft gears for both van and MGA
1st = 28
2nd = 31
3rd = 25

I also have a 1st motion shaft, dont know if it came from the van or the MGA.
Driver gear = 20 teeth, but going from Johns list, if what John describes as 4th gear, is in fact the driver gear on the first motion shaft (the input shaft from the clutch) it would seem that my 1st motion shaft is MGA, and the van one (which I know had one tooth less) would be 19 teeth.

The first gear set seem consistant through the all options (11/28), so the reverse idler will be the same for all as well.

So Colin - there you go. Start counting teeth!


Cheers
ian F





Ian Fraser

Well guys I have got my counting finger out, and this is what I have:

1st motion shaft 21 teeth or 26 teeth
1st gear 17 teeth
2nd gear 25 or 29 teeth
3rd gear 31 or 32 teeth

Lay gear 11, 20, 26, 30, and another lay gear which my mate has, teeth unspecified, but the same as his twin cam!

And just to confuse the issue even more I also have some bits from a couple of 1500 boxes:

1st motion shaft 21 teeth
and then 2nd and 3rd gears 23, 25, 27, 31 teeth

and
Lay gear 17, 22, 28, 32

So which gears make up the set, and what are the ratios. In fact how can I work that all out?

Many thanks

Colin
Colin Parkinson

Colin and Ian,

This is getting a bit complicated, so I have written it all down in a Microsoft Word file at:

http://www.angelfire.com/amiga/mga/index.html

Colin, you have a mixture of standard and close ratio gears, as can be seen in the file. Also, in your comments you have reversed the gear count for second and third gears.
The one problem is the first gear of 17 teeth. This cannot give the correct ratio. Surely the first gear must have 28 teeth?
What do you both think?

Mick
Mick Anderson

Good one Mick

Now John - could you put your info in the same format as Micks - makes it a lot easier to follow and less room for errors.

I will reformat mine in the same way as Micks. (but later - I've got to have my breakfast now!)

Cheers
ian F

Ian Fraser

Colin,

I have updated that file with the gear teeth numbers on:

http://www.angelfire.com/amiga/mga/index.html

I am not happy yet with the figures for first gear on the close ratio gearbox.
I am waiting for someone to challenge the figures (they are theoretical, not counted).
Can you compare all the gears that you have?

Mick
Mick Anderson

This thread was discussed between 02/09/2005 and 04/09/2005

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This thread is from the archive. The Live MG MGA BBS is active now.