RX - Drivetrain "Slack"

Kevin8tor

Active Member
Hello all! I have an RX with 800 miles on it. I am enjoying it immensely and don't want anyone to take this as a negative. I knew that sooner or later some adjustment and tuning would be required and I've already managed to tune the derailleur once myself to eliminate some less-than-smooth indexing. I have noticed on my last couple of rides there seems to be some slack in the pedal when riding. As I crank on the pedal (particularly the right one) I sense (and hear) a small amount of play before the drivetrain engages to the point where I feel a direct connection to my pedaling and forward motion. I almost exclusively ride on road, and in Eco level 1, but I ride at a good pace and my area is hilly. I weigh about 225 before gear and accessories on the bike, just so we understand the loading on the bike. Additionally, when I turn the assist to 0 I feel and hear a great deal of drivetrain drag; it's not smoothly rolling like it was new when I'd ride with the power at 0. Any suggestions as to where I should focus my attention? Is this an adjustment to pedals or cranks, or am I looking at something in the motor itself? Feel free to ask questions if I am not giving an adequate description of what I'm feeling and hearing.
 

theemartymac

Well-Known Member
Make sure your crank arms are tight. Mine worked loose a couple of times, but were apparent as a clicking and tiny bit of slack on just one pedal stroke. Should be very obvious before they get loose enough to be noticeable in the pedal stroke, but your symptom might suggest this if it's truly one-sided slack.

The motor generally shouldn't cause any drag unless it faults out due to heat, etc, (the display will flash the little engine icon) at that point it will be very heavy, but also very obvious as there will be no power at all. All cadence sensors have a slight delay from the crank turning to the motor kicking in, but generally shouldn't be more than 1/2 a turn of the crank.

Assuming the chain and derailleur are all shiny, clean and lubed (Don't over lube, it creates a mucky draggy mess), and there are no stiff links in the chain; First thing I would check is to drop the kickstand and with the power off, tilt the bike towards you to get the back wheel off the ground, and spin the wheel slowly forward by hand to see if there is any drag - don't use the pedals, you need the chain to stay still. There should be none, and just the clicking of the cassette freehub. That tells you the clutch is properly disengaging and the hub isn't causing any drag. Do the same thing in PAS 1 (Fingers free of the spokes!!), and the results should be identical. Add some very brief manual throttle and it should spin cleanly, and the hub should disengage immediately upon release of the throttle, and it should freewheel cleanly again. The chain and pedals should not move during any of this.

Then if all good, try the same but use the pedals as the throttle input, and make sure the power comes on and off just as cleanly. It will take a partial rotation to kick in, but should stop power almost immediately when the pedals stop. If you now hear and feel some drag, there is definitely a chain-side issue. Check the 'B-tension' (distance the first jockey pulley in the derailleur is from the cassette cog), and it should be ~1/2 inch or so away. If it's too close it will create drag, noise, and sticky shifts. If it's too far away, it might create slow or sluggish shifts. Make sure the derailleur is just about straight up and down when viewed front to back, and when in a high gear (small cog), the chain isn't dragging on the derailleur frame.

If you can't find anything, take a couple of pictures of your rear cassette and derailleur (side and back view), so we can see if there is anything obvious.
 
Last edited:

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
You COULD be feeling a tiny bit of slack as one of the clutches takes up some slack in the drive train? Maybe after coasting for instance?
 

Kevin8tor

Active Member
Make sure your crank arms are tight. Mine worked loose a couple of times, but were apparent as a clicking and tiny bit of slack on just one pedal stroke. Should be very obvious before they get loose enough to be noticeable in the pedal stroke, but your symptom might suggest this if it's truly one-sided slack.

The motor generally shouldn't cause any drag unless it faults out due to heat, etc, (the display will flash the little engine icon) at that point it will be very heavy, but also very obvious as there will be no power at all. All cadence sensors have a slight delay from the crank turning to the motor kicking in, but generally shouldn't be more than 1/2 a turn of the crank.

Assuming the chain and derailleur are all shiny, clean and lubed (Don't over lube, it creates a mucky draggy mess), and there are no stiff links in the chain; First thing I would check is to drop the kickstand and with the power off, tilt the bike towards you to get the back wheel off the ground, and spin the wheel slowly forward by hand to see if there is any drag - don't use the pedals, you need the chain to stay still. There should be none, and just the clicking of the cassette freehub. That tells you the clutch is properly disengaging and the hub isn't causing any drag. Do the same thing in PAS 1 (Fingers free of the spokes!!), and the results should be identical. Add some very brief manual throttle and it should spin cleanly, and the hub should disengage immediately upon release of the throttle, and it should freewheel cleanly again. The chain and pedals should not move during any of this.

Then if all good, try the same but use the pedals as the throttle input, and make sure the power comes on and off just as cleanly. It will take a partial rotation to kick in, but should stop power almost immediately when the pedals stop. If you now hear and feel some drag, there is definitely a chain-side issue. Check the 'B-tension' (distance the first jockey pulley in the derailleur is from the cassette cog), and it should be ~1/2 inch or so away. If it's too close it will create drag, noise, and sticky shifts. If it's too far away, it might create slow or sluggish shifts. Make sure the derailleur is just about straight up and down when viewed front to back, and when in a high gear (small cog), the chain isn't dragging on the derailleur frame.

If you can't find anything, take a couple of pictures of your rear cassette and derailleur (side and back view), so we can see if there is anything obvious.
Themartymac,

Thanks for the detailed reply. I'll get the bike on my work stand and check out all of your suggestions. If no results, pics will be forthcoming. I really appreciate your time & input, cheers!
 

Nashville615

New Member
Make sure your crank arms are tight. Mine worked loose a couple of times, but were apparent as a clicking and tiny bit of slack on just one pedal stroke. Should be very obvious before they get loose enough to be noticeable in the pedal stroke, but your symptom might suggest this if it's truly one-sided slack.

The motor generally shouldn't cause any drag unless it faults out due to heat, etc, (the display will flash the little engine icon) at that point it will be very heavy, but also very obvious as there will be no power at all. All cadence sensors have a slight delay from the crank turning to the motor kicking in, but generally shouldn't be more than 1/2 a turn of the crank.

Assuming the chain and derailleur are all shiny, clean and lubed (Don't over lube, it creates a mucky draggy mess), and there are no stiff links in the chain; First thing I would check is to drop the kickstand and with the power off, tilt the bike towards you to get the back wheel off the ground, and spin the wheel slowly forward by hand to see if there is any drag - don't use the pedals, you need the chain to stay still. There should be none, and just the clicking of the cassette freehub. That tells you the clutch is properly disengaging and the hub isn't causing any drag. Do the same thing in PAS 1 (Fingers free of the spokes!!), and the results should be identical. Add some very brief manual throttle and it should spin cleanly, and the hub should disengage immediately upon release of the throttle, and it should freewheel cleanly again. The chain and pedals should not move during any of this.

Then if all good, try the same but use the pedals as the throttle input, and make sure the power comes on and off just as cleanly. It will take a partial rotation to kick in, but should stop power almost immediately when the pedals stop. If you now hear and feel some drag, there is definitely a chain-side issue. Check the 'B-tension' (distance the first jockey pulley in the derailleur is from the cassette cog), and it should be ~1/2 inch or so away. If it's too close it will create drag, noise, and sticky shifts. If it's too far away, it might create slow or sluggish shifts. Make sure the derailleur is just about straight up and down when viewed front to back, and when in a high gear (small cog), the chain isn't dragging on the derailleur frame.

If you can't find anything, take a couple of pictures of your rear cassette and derailleur (side and back view), so we can see if there is anything obvious.

Check for play or looseness in your rear cassette. I had that problem and found the cassette needed to be re-torqued. Re-torqued that and it went away.