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Home > Help Needed / General Tech Chat > Diff pinion teeth

wolfie29177

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The Black Countraaaaay

Ok I've been a retard and mixed up some 3.2 and 3.1 diff parts. Anyone know how many teeth on the pinion wheels and diff wheel so I can work out which 1 is which?

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Tupers

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South Devon

Both use a 19 tooth pinion but the 3.1 uses a 59 tooth crown gear and a 3.2 uses a 61.


TurboDave16V
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SouthPark, Colorado

Both pinions are DAM2808 per calvers very useful links:

http://www.calverst.com/articles/Gearbox-F...es_standard.htm

On 17th Nov, 2014 Tom Fenton said:
Sorry to say My Herpes are no better


Ready to feel Ancient ??? This is 26 years old as of 2022 https://youtu.be/YQQokcoOzeY



wolfie29177

133 Posts
Member #: 476
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The Black Countraaaaay

Thanks lads

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Turbo This..

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1767 Posts
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Previously josh4444

Australia, brisbane

if you didn't already know diff ratios are just dividing the crown wheel and pinion tooth counts

same for any gear ratio or combo


PhilR

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Post Whore

Birmingham

You need to check the part numbers. Luckily, Wolfie's gears are interchangeable but...

On 23rd Nov, 2014 Keith Calver said:

- Although some gears have the same tooth count for different ratios, they are not interchangeable - hence the need for distinguishing part numbers. Therefore use in known pairs only.

- A+ gears have a different tooth profile to pre A+, so they are not interchangeable.

Edited by PhilR on 25th Nov, 2014.


wolfie29177

133 Posts
Member #: 476
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The Black Countraaaaay

they're both from A+ boxes Phil so shouldn't be a problem. Both are in good nick so I can't see an issue but thanks for everyones help

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Nick king

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Bristol England

Hay guys I've not worked on the final drive yet, but from what's been said I'm a bit confused. How can two different ratios have the same size pinion gear, surly if the crown wheel has more teeth then it's diameter must be bigger therefore the pinion needs to be smaller, as the shaft centres are fixed. If the pitch/tooth profile is altered to accommodate the fixed centre dimension then the pinions must all be different for all different ratios. Maybe the same amount of teeth but a different shape. Or have I missunderstood.


TurboDave16V
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SouthPark, Colorado

You have mis-understood.
The module doesn't have to be a round number in tooth geometry, it can be to several decimal places, to allow for the form to be "cheated" to allow different tooth count gears to work with the same tooth pinions (or vise versa when you have similarly sized pairs of gears).
It is a little more complex to achieve this with helical gears rather than spur gears, but a 59 to a 61 gear is only a 3% difference, so is pretty much in the realm of adjustment within the allowable tooth form which is what makes it work. Conversely however, there is no way that you could ever run the same larger gear, with different (much smaller) pinions in a helical form. Something like a 1.1ratio between a pair of gears, it is likely that the ratio coule be adjusted very easily by several teeth up or down to adjust a ratio for underdrive or overdrive -this is basically what the different drop gear ratio's achieve. Another example is the "overdrive" helical set used in the HLE metro's - they were something like a .91 overdrive... Very cool and something I wish I knew about 15 years ago when HLE metro's were all over the place.

On 17th Nov, 2014 Tom Fenton said:
Sorry to say My Herpes are no better


Ready to feel Ancient ??? This is 26 years old as of 2022 https://youtu.be/YQQokcoOzeY



viz139

108 Posts
Member #: 9182
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I never understood how they changed the ratio of the drop gears in the HLE. If you change the diameter of the idle gear the primary and 1st motion must change by the same amount as they are a fixed distance apart unless the idle gear center was also moved. Am I missing something?


TurboDave16V
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SouthPark, Colorado

Please read the post above.... You are missing something...

The PCD of the gear is "theoretically" the mid-point of the tooth in laymans terms, and all the PCD's of a gear train are aligned (not overlapped or not contacting).
But in reality, the PCD can be outside or inside of this theoretical "mid-point, and the tooth form can be adjusted to allow for a slightly "thinner", "taller", "fatter", "shorter" tooth form to be used, and still function against another (un-changed) gear.
Basically, you can squeeze a few more, or a few less teeth (usualy no more than 8-10% however) into a single gear, and still achieve a satisfactory meshing with an unchanged pair.

On 17th Nov, 2014 Tom Fenton said:
Sorry to say My Herpes are no better


Ready to feel Ancient ??? This is 26 years old as of 2022 https://youtu.be/YQQokcoOzeY



Nick king

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Bristol England



Well that is a brilliant explanation, thanks. So I was sort of close in my thinking.
So many ways of adjusting and fine tuning the drive ratios, is that because of race engines running very narrow power bands?

On 27th Nov, 2014 TurboDave16V said:
Please read the post above.... You are missing something...

The PCD of the gear is "theoretically" the mid-point of the tooth in laymans terms, and all the PCD's of a gear train are aligned (not overlapped or not contacting).
But in reality, the PCD can be outside or inside of this theoretical "mid-point, and the tooth form can be adjusted to allow for a slightly "thinner", "taller", "fatter", "shorter" tooth form to be used, and still function against another (un-changed) gear.
Basically, you can squeeze a few more, or a few less teeth (usualy no more than 8-10% however) into a single gear, and still achieve a satisfactory meshing with an unchanged pair.


wolfie29177

133 Posts
Member #: 476
Advanced Member

The Black Countraaaaay

This is why formula 1 cars use helical rather than straight cut gears. They say changing ratios over quickly is a lot simpler with helical gears (this nugget of useless info came from a family member who worked for an F1 team)

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viz139

108 Posts
Member #: 9182
Advanced Member

Got it now ,thanks.
So which would put less pressure on the gearbox, increasing the drop gear ratio or increasing the final drive?


TurboDave16V
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SouthPark, Colorado

Overdrive drops of a .90 ratio would reduce the input torque by 10%, but the biggest gain is by widening the ratios (making them still a closer-ratio than the A+, but allowing us to make use of the much wider torque-band of our turbo engines). The other benefit is that the taller ratio (numerically lower) of FD that you'd probably then go with, also has lower bearing loads than a shorter (numerically higher) FD ratio...
The only extra "losses" is losing a small amount of efficiency as it takes more "effort" to turn the gears in the transmission becuase you've overdriven them and are driving them faster. That said, I suspect the benefits would be advantageous - if you could just get over the little detail of actually doing it....

On 17th Nov, 2014 Tom Fenton said:
Sorry to say My Herpes are no better


Ready to feel Ancient ??? This is 26 years old as of 2022 https://youtu.be/YQQokcoOzeY



Turbo This..

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1767 Posts
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Previously josh4444

Australia, brisbane

so over drive drop gears should really do done if you dont want straight gears and want to run decant power

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