25 replies to this topic

[Jammy]

Been looking at my straight cut set, trying to work out whether it was close ratio, and if I could find any clues as to who it was made by.

Counted the teeth on the layshaft as being 19, 22, 25 and 31. Also has 22A1737 stamped on it, suggesting its probably this - linky, also suggesting that I have an ST Abingdon gearset?

The ratios of that set being 2.54 1.73 1.22 and 1.

Now, counting the teeth on the gears, 1st was 15 teeth, 2nd was 19, 3rd - 23 and 4th 19.

Is it just me or do those teeth ratios not make those gear ratios? Is there something in my calculation I'm missing??

[Bungle]

come on jammy you know who to ask

tmf's gear box wizard

[Ethel]

Only 1st to 3rd run off the layshaft (+reverse)

The end nearest the clutch is driven by the 1st motion shaft then drives the syncro hubs on the main shaft.

[Jammy]

Ah ok. That explains the anomalous 4th gear ratio. But what about first, I calculated it to be just over 2!

[Sprocket]

Fourth gear is the first motion shaft locked to the third motion shaft, no torque is transmitted through the lay gear. No gearing is actualy used other than the drop gears or final drive

22A1737 number looks like an austin part number?? Maybe as you say the Special Tuning department

[Jammy]

Ok, so there isn't anything wrong with my calculation, I haven't done some glaringly obviously wrong? If the 1st gear on the 3rd motion shaft has 31 teeth, and the corresponding gear on the layshaft has 19 teeth that does produce a 2.06 gear ratio?

[Ethel]

As sprocket said 4th is 1:1 x the diff.

the others will be the ratio of the 1st motion to layshaft gears multiplied by the corresponding synchro hub and its cog on the layshaft.


The ratios I have for 4 sync straight cuts are

2.543:1 for 1st

1.73 - 2nd
1.257 - 3rd

Edited by Ethel, 22 October 2007 - 10:03 PM.

[Sprocket]

Ok, so there isn't anything wrong with my calculation, I haven't done some glaringly obviously wrong? If the 1st gear on the 3rd motion shaft has 31 teeth, and the corresponding gear on the layshaft has 19 teeth that does produce a 2.06 gear ratio?

First gear ratio is

( 'fourth' gear on laygear/ first motion shaft number of teeth) x (first gear on third motion shaft/ firest gear on laygear)

I think i got that the right way round

[Guess-Works.com]

*cough* http://www.theminifo...x...ic=3851&hl=

[Bungle]

pesky kids cant use the search button

[Jammy]

Dammit! Thank you peps!

[Jammy]

Still not doing too well with this. Still trying to work out 1st gear ratio, using following formula, taken from the topic Guessworks linked too above:

1st motion teeth	  Leygear teeth for gear
ratio  =   -------------------  *  --------------------------
				Laygear teeth				Gear teeth

So, (1st motion teeth - 19 / laygear teeth - 31) multiply by (laygear teeth for gear - 19 / gear teeth - 15) = (19/31)*(19/15) = 0.62129*1.26666 = 0.786967.

The topic then goes on to say, divide 1 by the gear ratio = 1.2707

Doesn't seem much like a first gear ration to me?!

[Jake Blues]

What's happened to the link to the conversion page that JW had?
Used to be here?

[Guess-Works.com]

Long since gone...

Now on here... http://www.guess-wor...ox/index_R.html

[Guess-Works.com]

Still not doing too well with this. Still trying to work out 1st gear ratio, using following formula, taken from the topic Guessworks linked too above:

1st motion teeth	  Leygear teeth for gear
ratio  =   -------------------  *  --------------------------
				Laygear teeth				Gear teeth

So, (1st motion teeth - 19 / laygear teeth - 31) multiply by (laygear teeth for gear - 19 / gear teeth - 15) = (19/31)*(19/15) = 0.62129*1.26666 = 0.786967.

The topic then goes on to say, divide 1 by the gear ratio = 1.2707

Doesn't seem much like a first gear ration to me?!

You have more teeth on the laygear than on the 1st gear ???? that's VERY odd....

In fact I've just checked and you have the numbers for the laygear teeth and gear teeth the wrong way round, there's 15 on the end of the laygear and there should be 29 teeth on the matching 1st gear.

For reference you should have 25 teeth on 2nd and 22 teeth on 3rd, and as you say 19 on the 1st motion shaft.

Laygear has 15-19-23-25

which is std ST ratios

2.544, 1.731, 1.258 & 1.000

Edited by GuessWorks, 23 October 2007 - 10:34 AM.