tranny noise
5th gear noise
Cruiser
Joined: Apr 2008
Posts: 175
Likes: 1
There are a couple of reasons and fixes for the noise. For some reason the engineers at Harley decided to use a set of gears with straight cut teeth. They are stronger and so will take a lot more 'abuse', however the down side is the whining noise they are well known for.
May our Moderator Rest in Peace
Joined: Sep 2006
Posts: 11,386
Likes: 35
From: Rochester, NY
I would be very careful reading/believing anything you find in Wikipedia. Much of the information in there may not necessarily be wrong, but is often incomplete.
Whether a Straight cut or a Helical cut gear is better is more often a question of the required function rather than outright strength.
You say that they use Helical gears in a steel mill (for example) but they have a more practical need for them than outright strength. Its because they operate smoother and require less power to drive. Straight cut teeth would not turn the rollers as smoothly so the steel sheets would not come out the end in a uniform thickness. The lower power requirement is a bonus that means they save on production costs so the finished product costs the customer less money.
In general terms Helical gear sets are better suited to operate in high speed precision setups but the trade off is that their smaller steel on steel contact patch makes them more susceptible to breakage from shock loading.
Straight cut teeth by contrast have a contact patch that spans the entire width of the gear and because of the geometry the teeth can be cut much thicker for any given gear diameter.
Their handicap, if you will, is that it takes more power to turn them, that big wide contact patch creates more frictional drag and because of the greater clearance requirements their transition from tooth to tooth is more abrupt making them less well suited for precision operations. It’s also the reason for that characteristic whine they are famous for in roots style superchargers and infamous for in Harley transmissions.
Whether a Straight cut or a Helical cut gear is better is more often a question of the required function rather than outright strength.
You say that they use Helical gears in a steel mill (for example) but they have a more practical need for them than outright strength. Its because they operate smoother and require less power to drive. Straight cut teeth would not turn the rollers as smoothly so the steel sheets would not come out the end in a uniform thickness. The lower power requirement is a bonus that means they save on production costs so the finished product costs the customer less money.
In general terms Helical gear sets are better suited to operate in high speed precision setups but the trade off is that their smaller steel on steel contact patch makes them more susceptible to breakage from shock loading.
Straight cut teeth by contrast have a contact patch that spans the entire width of the gear and because of the geometry the teeth can be cut much thicker for any given gear diameter.
Their handicap, if you will, is that it takes more power to turn them, that big wide contact patch creates more frictional drag and because of the greater clearance requirements their transition from tooth to tooth is more abrupt making them less well suited for precision operations. It’s also the reason for that characteristic whine they are famous for in roots style superchargers and infamous for in Harley transmissions.
Road Warrior
Joined: Sep 2009
Posts: 1,257
Likes: 2
From: Gastonia, NC
The 2010s have a helical cut fifth gear now. Not sure if changing just that gear will work or not. Mine wines quite a bit but I'm just getting use to it. I understand HD did that because fifth is hit pretty hard a lot for passing. I rode a friends Road King with 5000 miles and it does seem to get a bit better with time.
Banned
Joined: Sep 2009
Posts: 36
Likes: 0
Man, that's not the a fifth gear whine...that's your scoot crying for running it in 5th gear at 45mph. Twinkies like to be revved, that's 4th and even 3rd gear territory if you're pulling a hill or out of a corner.
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Cruiser
Joined: Apr 2008
Posts: 175
Likes: 1
I just added that, as it was a good reference on gears.
They use helical gears because of strength, loads, stress and shock. They roll coils not sheets. There are various sizes and thickness but a coil can be 5' in diameter and down to 0.010 thick. The thickness control of the process is very complex.
They use helical gears because of strength, loads, stress and shock. They roll coils not sheets. There are various sizes and thickness but a coil can be 5' in diameter and down to 0.010 thick. The thickness control of the process is very complex.
Last edited by Recon Dad; Sep 19, 2009 at 07:30 PM.
