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Old 2007.10.10, 02:53 PM   #1
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26T--->28T ball diff gear= longer gear ratio correct?

My rear diff is clicking, so I am replacing my spur gear as well as the gear on the ball diff to this one
http://shop.tinyrc.com/product.php?productid=18085

The stock atomic diff comes with a 26T, and this is the only one the shop here has in stock. Am I correct that this will make my gear ratio longer?(less torque and more top end)

Will I also have to change the front diff to a 28T gear as well? Finally how much of a difference will it make? If it makes it too long and I don't change my pinion and spur setup, I may get get the fets too hot.

Thanks in advance!
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Old 2007.10.10, 03:30 PM   #2
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If you're going from 28 to 26t on the diff, you're right that you'll lose some torque and gain some top end.

If you calculate the whole gear ratio (what, like 21/15 x 26/8?) then the diff ratio doesn't make a huge difference. If I remember right though, you should not have a 26t on the rear diff and a 28t on the front, however, because that would make the rear end faster than the front and possibly cause instability. Better to make the front wheels run faster than the rears (also helps a bit in corners -- you know that a front one-way diff allows the fronts to spin faster than the rears to aid cornering speed).
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Old 2007.10.10, 05:12 PM   #3
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Quote:
Originally Posted by color01
If you're going from 28 to 26t on the diff, you're right that you'll lose some torque and gain some top end.

If you calculate the whole gear ratio (what, like 21/15 x 26/8?) then the diff ratio doesn't make a huge difference. If I remember right though, you should not have a 26t on the rear diff and a 28t on the front, however, because that would make the rear end faster than the front and possibly cause instability. Better to make the front wheels run faster than the rears (also helps a bit in corners -- you know that a front one-way diff allows the fronts to spin faster than the rears to aid cornering speed).
Thanks for the quick reply! hmm, so if i were to have different gears on the front and rear diff, would that be similar to varying the front and rear torque bias?
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Old 2007.10.10, 11:14 PM   #4
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I think the 'torque' will also depends on how you setup your diff(tightness), given the front and rear diff tightness are exactly the same, the 26T end should have less torque and more top end.
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Old 2007.10.11, 05:10 AM   #5
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Quote:
Originally Posted by pinoyboy
.... The stock atomic diff comes with a 26T, and this is the only one the shop here has in stock. Am I correct that this will make my gear ratio longer?(less torque and more top end)

Will I also have to change the front diff to a 28T gear as well? Finally how much of a difference will it make? If it makes it too long and I don't change my pinion and spur setup, I may get get the fets too hot.

Thanks in advance!
Your gear ratio will change as follows:



You have to readjust your total ratio after changing the diff gear and of course you have to change also the front diff gear, or your front wheels will spin slower than your rears

Cheers
Konrad
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File Type: jpg Gear Ratio.jpg (257.3 KB, 101 views)
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Old 2007.10.11, 07:57 AM   #6
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Quote:
Originally Posted by Stoney
Your gear ratio will change as follows:



You have to readjust your total ratio after changing the diff gear and of course you have to change also the front diff gear, or your front wheels will spin slower than your rears

Cheers
Konrad
wow thats awesome, thanks a bunch for that link!


Looks like 17/31 would work great since its just a little bit longer with the 26t diff gear.
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Old 2007.10.12, 04:25 PM   #7
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Quote:
Originally Posted by pinoyboy
My rear diff is clicking, so I am replacing my spur gear as well as the gear on the ball diff to this one

The stock atomic diff comes with a 26T, and this is the only one the shop here has in stock. Am I correct that this will make my gear ratio longer?(less torque and more top end)
pb,

If I'm not mistaken the atomic diff comes with a 28t...?

I have an extra one I never used (swapped to 26t delrins for my drifter) and its yours if you don't mind me shipping it in a cheap envelope lol. Just send me your addy again as I can't find the confirmation from last time.

Also I got rid of most my clicking from shims so unless you don't have them already pick some up.

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Old 2007.11.05, 04:09 AM   #8
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26 -> 28 would make your final drive gear ratio shorter/higher.
28 -> 26 would make your final drive gear ratio longer/lower.

Treat the diff gear like a spur gear. Bigger means shorter/higher gear ratio.

If you have different size diff gears in front or rear, then you are overdriving the end with the smaller gear. This does some very interesting things to handling. Try a 26T in the rear with a 28T one-way in the front. You are biasing/overdriving the rear, so you essentially have a RWD until you start spinning up the tires. You need the front one-way to keep the front tires from fighting the rear tires all the time.

Great chart, btw.
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Last edited by ruf; 2007.11.05 at 04:15 AM.
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Old 2007.11.05, 12:45 PM   #9
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If your diff is clicking, it may not need to be replaced. Inspect it and see if the the gears are worn down. The diff gears are pretty durable and I've yet to see any wear on mine after driving on it for 1+ years. So if all looks good, you should shim your diff to allign the mesh of the spur and diff.
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