Lotus Elan

DIFF RATIO

PostPost by: graham » Tue Oct 27, 2009 9:18 am

My 74+2s is still a thousand bits. How do you tell what the diff ratio is without stripping it ?
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PostPost by: bcmc33 » Tue Oct 27, 2009 12:58 pm

Graham,

Fix one of the output shafts to prevent it turning, then rotate the opposite output shaft one full turn and count the rotations of the input shaft/flange. If the input shaft/flange rotates about 3.5 turns then the ratio is 3.54 or 3.55, if it rotates about 3.75 turnes the it is a 3.77 ratio.

To know if it is 3.54 or 3.55 ratio you will need to take the diff apart and count the number of teeth on the CW&P.
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PostPost by: paddy » Tue Oct 27, 2009 1:18 pm

If you hold one of the output shafts steady, won't the input shaft turn twice as many times as the ratio?

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PostPost by: paddy » Tue Oct 27, 2009 1:40 pm

paddy wrote:If you hold one of the output shafts steady, won't the input shaft turn twice as many times as the ratio?


... or half?
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PostPost by: oldelanman » Tue Oct 27, 2009 2:21 pm

To know if it is 3.54 or 3.55 ratio you will need to take the diff apart and count the number of teeth on the CW&P.


Or rotate one output shaft 20 turns (with the other fixed) then the input shaft rotation will be 10 times the ratio and you should be able to distinguish between 3.54 and 3.55.
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PostPost by: paddy » Tue Oct 27, 2009 4:38 pm

[quote="oldelanman"Or rotate one output shaft 20 turns (with the other fixed) then the input shaft rotation will be 10 times the ratio and you should be able to distinguish between 3.54 and 3.55.[/quote]

Specifically, if you mark the pinion's starting position, then it will line up exactly with that mark after either 18 or 22 turns of one of the output shafts.

After 22 turns means the pinion has 11 teeth so ratio is 3.54 (39/11) or 3.9 (43/11)
After 18 turns means the pinion has 9 teeth so ratio is 3.55 (32/9) or 3.77 (34/9)

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PostPost by: oldelanman » Tue Oct 27, 2009 6:07 pm

Specifically, if you mark the pinion's starting position, then it will line up exactly with that mark after either 18 or 22 turns of one of the output shafts.

After 22 turns means the pinion has 11 teeth so ratio is 3.54 (39/11) or 3.9 (43/11)
After 18 turns means the pinion has 9 teeth so ratio is 3.55 (32/9) or 3.77 (34/9)


Don't forget to count the number of turns of the input (pinion) shaft as well or you still won't know which ratio it is !

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PostPost by: graham » Sat Nov 07, 2009 8:16 am

Thanks guys for the help -was still a little confusing but found we have 3.77 diff. Also found info from this link :lol:
http://www.mgparts.co.nz/diff_ratios.html
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