I've got a 2006 Street Bob and I noticed what seems to be a bearing noise (or similar) in 5th gear at low and part throttle. Seems fine in every other gear. Is this just a quirk of the 6 speed gearbox? I bought the bike used a month or so ago with 49K miles on it and supposedly fully serviced.

 

I would think at low and part throttle you should be in 3rd gear. Just how fast are you going in 5th that you hear it?

 

If I remember right, the 06s had 5th gear noise...I am pretty sure it is normal...

 

Maybe around 45-50 mph steady cruise.

 

Seems kinda low to be in that gear, even when I'm lightly cruising I don't shift into 5th until about 50-55 and even then, its pretty low cruising rpms. My guess is you are hearing/feeling some lugging... Never hurt to change out your fluids tho and get some fresh lube in there. Never take the sellers word for anything...

 

I had heard of the 6 speed noise, but I thought it was at idle and was a rattle. Interesting how the flow for 5th appears to spin the two needle bearings on the main gear drive of a 6 speed. Seen quite a few post of the bearing going out. And also not all of the gears are helical cut. My 5 speed are all straight cut and all a little noisy, but the same, were the 6 speed has a mix of quite helical and a little noisy straight cut so transmission sound different depending on gear range. If you can hear something at 50, it must be loud. All I hear is wind and exhaust. And I run stock exhaust and wear a full face helmet. Get you a stethoscope and add an extension piece of vacuum hose to it. Attach the probe to the transmission and listen to the transmission at speed. May prove interesting. You may have a problem or may not, but noises migrate all over these engines, transmissions and primaries. You really need to pin it down were it is before you think this.

https://www.hdforums.com/forum/touri...-your-ipb.html

To sum up the gears in a nut shell. Straight are stronger, have less hp loss, require little side load bearing surfaces, but have a slight whine at high speed.. Helical are a tad weaker and require side bearings, there for, thinner gears or a wider transmission case. Note that in both a 5 and a 6 speed Harley transmission, all the gears stay meshed all the time, only the shift dogs move.

 

Normal, it's the way the gear is cut, for some reason they put a straight cut gear in 1st ( which I get ) and 5th....

 

The fifth gear is a straight cut, not helical. The reason it's like that is because MOCO did it to save money.
Cruising at those speeds, you should be in a lower gear anyway.

 

Guitarded, I also have a pronounced whine in 5th gear. I don't notice it much if I am running through the gears, but more in a cruise. 40 to 50 it really whines, and when it gets warm, it can rival the engine in sound. Sound familiar? I called the H-D mech and he said that that much noise is NOT normal. I am changing the oil this weekend to a heavier fluid, and I am interested in what you are doing for this. Will (H-D) said that if that doesn't quiet it down, I may have a problem. I read that one guy took his new bike in, and they changed the 5th gear and bearings and it was cured. I hope the heavier fluid works. Let me know how you are doing, k?

 

As others have mentioned, 5th gear whine is normal. I think they changed the trans design in '10 to eliminate the noise, but my '09 FXDC definitely whines in 5th. Switching to Redline Shockproof fluid helped a little, but its still there.