BBSO2B clunking noise

[altan]

I'm having a hell of a time diagnosing a clunking noise coming from the rear end. I pretty much eliminated the rear wheel, cassette & other possible culprits, I'm down to a possible broken clutch pawl or other part that may be spinning freely in the hub. The clunking noise is intermittent, independent of whether I'm pedaling or just coasting. I can't duplicate the sound if I have the bike upside down testing the motor or pedaling function. The clunking only occurs when I'm riding even if I'm not pedaling. I know I have some clutch (or chain?) slippage, but I now have a new chain fit to the correct size for the crank and the slippage occurs just on higher gears when climbing not on the lower ones. I thought I'd get to the clutch by following one of your excellent YouTube videos on clutch replacement for the HD model but to my dismay the BBSO2B looks quite different and I am at a loss on the type of tools I'd need to find the culprit, order the right clutch and install the replacement. I'd very much appreciate any help I can get on this subject. Thanks!

[73Eldo]

Does it do it if the chain isn't moving? What kind of rear hub is it? How many miles have you been riding this setup? Is this a new issues or has it always done it?

[altan]

The sound continues with reduced frequency when the chain is not moving (zero motor not pedaling either). This is a mid-drive motor, the rear hub is just a 6 spd cassette (newly re-packed and re-greased). I'm wondering if there is something that keeps spinning in the mid drive while coasting? I'm at about 850 miles with this set-up. Although I have a gear shift sensor, I may have been harsh on the clutch trying to find an optimal gear as I thought I had a chain slip problem on higher gears. I think I eliminated the chain slip problem and the clutch seems to hold fine on lower gears but the periodic clunking noise is now ever present whether pedaling /motoring or not. On higher gears (smaller sprockets 5-6) if going uphill the noise is different, I can hear an awful cranking noise that I assume is coming from the clutch that is skipping.

[73Eldo]

With the chain not moving there isn't going to be anything moving in the drive so you must have something going on in your rear hub. You should be able to prove that by removing the chain and spinning the wheel.

You said 6 speed cassette? So that makes it early 1980's? Which also makes sense if it was something you could repack since sealed bearings didn't get common till into the 90's. Do the bearings have a carrier ring or are they just loose? If they are loose are you sure you have the correct number? With larger bearings like in a wheel you usually can't get too many but not enough they will tend to kinda snap as they go around under load.

Since you say its a cassette are you sure the freehub part is properly torqued? Typically the bearing cup on the drive side has some sort of internal spline down the axle hole that locks it in. If that's loose you can get all sorts of strange things going on under load. Guessing this age its got to be a Uniglide and its been a long time since I worked on one of those. Hyperglide came out in the later 80's and was much more common not to mention still more or less the mid range standard today.

[stts]

There is a freewheel in the cassette. And they got tiny teeth grabbers with tiny little springs making them springy. They certainly can be assaulted by the mid motor makeing the teeth go bang. Not so much noise bang, but still a sudden impact stress that can break the grabber off inside the freewheel. The freewheel is heavily closed up so grease wont easily get inside it when everything else is greased. Your not supposed to get grease inside the freewheel anyway as it interferes with the tiny teeth motion. The oil in the grease leaks into it or you make effert to actually oil the freewheel. But broken tooth grabber can rattle around inside there. I had a bike long ago with a pesky rattle. It took me a year to find that and discovered what a freewheel was.

[73Eldo]

The terminology could be getting confusing too....

Freewheel is a term used for both the actual mechanism ( the tiny teeth grabbers stts mentions above) that lets the coasting action occur as well as a thread on assembly that contains that mechanism and a stack of cogs/sprockets. No matter what vintage you have unless its a single speed 'fixie' you have that mechanism back there. A cassette hub and freewheel hub are quite different designs as to where that mechanism is, where the bearings are, and how the cogs attach.

You said yours was a 6 speed which was only made as a cassette for a few years in the early 80's and I think only on higher end bikes. By the time cassettes started to catch on they were 7 speeds that were fairly quickly replaced with 8's and up. If your bike is a higher end bike from the early 80's then it could have a cassette. If its not from that era then its likely a freewheel. A 6 speed freewheel still dates it or makes it a real oddball. 7-14-21 has kinda been the low end standard for the last 20 or so years. 6-12-18 was kiinda the low end in the 90's when the good stuff was 7-14-21.

I'm not dissin an old bike if that is what you have. A high end bike from the 80's or 90's I think makes a pretty good base for a E conversion. Except for possibly the brakes they are often much better base bikes to start with than any cheap bike you could have bought today or in the last 10 or so years. I also have nothing against a cheap newer bike, you gotta work with what you can get and afford. Knowing what we are working with and why can really help the online troubleshooting process. Troubleshooting a 40 year old Deore Uniglide is quite different than a 1 year old no name.

If you are not sure what you have can you take a picture of it for us? If the wheel is off the bike a shot straight on the sprocket side looking at the end of the axle will do it. If its on the bike try to get an angle in between the frame and the sprockets so we can see where the axle goes into the cogs. A freewheel that's going to be a fairly large area around the axle. A cassette that will be a small area with a locking flange clearly visible holding the smallest cog on. Once we know what you have we can better tell you where to look and how to get to it.

[altan]

Thanks a bunch guys. I did notice one less ball that could fit in both sides of the hub bearing, but when I asked around I was told that it may be common practice and I figured enough grease should keep that movement quieter at least for a while. Meanwhile if I have a broken grabber inside the freewheeling cassette, that would never stay quiet, and this may indeed be what's happening, so I'll try swapping the rear wheel from my early 1990s (a bit newer then my ebike) non-electric bike and report back. Thanfully both bikes are about the same vintage and they can pretty much use all the same parts, though they've been somewhat abused over the years. I'll need to replace two spokes on the other wheel and try to true it before putting it behind the edrive