First let me say that I have used the search function because I thought I had seen this here before...I didn't really see much info on the subject though. I have a 2006 Super Glide. Here in the last few months I have noticed that as soon as I shift into fifth gear it sounds distinctly different...sort of a whining sound. It's not super loud, but I can hear it, especially when riding with the windshield. It doesn't seem to have any effect on the bike, just a noise. None of the other gears make that noise as far as I can tell. Could this be the start of a tranny problem or is this normal? I don't believe it's always done it. I have had this bike since 2007 and I am just now noticing it. I have seen references to fifith gear whine but haven't found a lot of info on it.

 

1st and fith gears on the new 6 speeds ar straight cut gears, meaning the teeth are cut straight across the gear . all the other gears are cut on an angle with a slight curve they are called helicle cut the gears it is known that straight cut gears are stronger and do whine the helicle arent as strong but quieter,,,,, i went out and got a quart of,,, golden spectro 75-140 6 speed gear oil,,,, its red in color and it quieted it down some not completely

 

Okay, so I may not have an issue...Ya know how it is...any new sound and you think the world is coming to an end. I'll just keep riding and hopefully all is fine.

 

The MoCo addressed this problem in 2010. 5th gear is now a helical cut gear. No more whine. Prolly cost them all of $5 per unit to do what should have been done from the get.

Point is, it's not you or your bike. I've heard of others addressing this with the use of heavier and/or higher tech synthetic gear lube. Not sure but I think it was Redline Shockproof 75W-140. Don't take my word on it, make sure.

 

Use the Spectro 75/140 trans Lube for 6speeds takes the whine right out.

 

+ 2

 

I use gear oil in my trans and the whine is barely noticeable. Either way it's not really an issue it is just a normal gear noise that straight cut gears make. By the way Helical cut gears are stronger than straight cut not weaker as posted. They have more contact area because the teeth are at an angle. They do place lateral loads on the shafts because of that angle which can be a problem for some transmissions but they are definitely not weaker than straight cut.

 

+3 on the spectra 6 speed oil.

It gets more noticeable when its really hot.

 

I have always heard the opposite, that straight cut are stronger which is why they are used in transmissions for high horse power applications. A good example is the Muncie M22 "rock crusher". It has straight cut gears as apposed to the M20 & M21 with helical cut gears.

 

Helical cut gears are stronger. It's not even close.

Not only can you make the individual teeth bigger because of the angle but more than one tooth at a time is engaged. On straight cut gears, only one tooth on the drive gear and one tooth on the driven gear can make contact at any one time.

This is why your differential uses helical cut gears and not straight cut -- They're just so much stronger. And quieter.

In WWII, when the Germans made the Panther tank, they cut corners and put a straight-tooth differential in it. It broke down all the time giving the tank about a 20% combat readiness. In fact, their drivers couldn't exceed certain low speeds and if they were backing up and tried to turn the tank, the differential would break -- Every time.

As to GM? Well, they're just... GM.