hub slippage?

[confusedcyclist]

I need help diagnosing a problem with my Bosch 2020 CX equipped e-bike.

I noticed lately that if I back peddle, and then apply forward force again, there is a sudden jerk forward in the drive train. This feeling of the drive train slipping, not to be confused with chain 'slippling', this is almost definitely another phenomenon, and also seems to occur when the hub is being disengaged and engaged. It is also noticeable when applying just enough force that the pawls engage in the freehub when applying just enough force to drive to the hub, just a slight jerk. If I'm applying a lot of torque, but perhaps unevenly so that the hub engages and disengages, say when hill climbing, I am fairly sure I can feel this jerking in the drive train. It's a disconcerting feeling, especially in stop-start traffic, but other than the initial loss of motion with the jerkiness, I don't feel like I'm losing forward driving power like I have experienced with worn cassettes and chainrings.

I dissembled the freehub body (Shimano XT FH-M8110), cleaned it out and re-greased it according to the dealer manual and it seems to have made no improvement. Could it be the motor/bottom bracket? Or am I missing something else? The chainring is still in good condition and the cassette and chain are virtually new, only about 400 miles on them. This problem didn't seem to coincide with their installation, so I'm sure this is not a worn chainring issue as there were no issues at the start, though I may just order one just to rule it out.

Could this be a wear and tear issue in the Bosch CX motor?

 

[HMS_Dave]

I need help diagnosing a problem with my Bosch 2020 CX equipped e-bike.

I noticed lately that if I back peddle, and then apply forward force again, there is a sudden jerk forward in the drive train. This feeling of the drive train slipping, not to be confused with chain 'slippling', this is almost definitely another phenomenon, and seems to occur when the hub is being engaged. It is also noticeable when applying just enough force that the pawls engage in the freehub when applying just enough force to drive to the hub, just a slight jerk. If I'm applying a lot of torque, but perhaps unevenly so that the hub engages and disengages, say when hill climbing, I am fairly sure I can feel this jerking in the drive train. It's a disconcerting feeling, especially in stop-start traffic, but other than the initial loss of motion with the jerkiness, I don't feel like I'm losing forward driving power like I have experienced with worn cassettes and chainrings.

I dissembled the freehub body (Shimano XT FH-M8110), cleaned it out and re-greased it according to the dealer manual and it seems to have made no improvement. Could it be the motor/bottom bracket? Or am I missing something else? The chainring is still in good condition and the cassette and chain are virtually new, only about 400 miles on them. This problem didn't seem to coincide with their installation, so I'm sure this is not a worn chainring issue as there were no issues at the start, though I may just order one just to rule it out.

Could this be a wear and tear issue in the Bosch CX motor?

My initial thoughts are maybe something is loose? Especially as it happens when back peddling then there is a sudden jerk when peddling forwards again, almost as if a reverse thread is re-engaging...

 

[confusedcyclist]

I did explore that possibility too, but will give it another once over tonight to be certain. The cassette and hub were put back correctly after servicing as I'm aware of appropriate torque. The chain ring did come loose many moons ago, so I'd know what to look for there also, that's been ruled out. This is why I'm concerned it might be the motor. Possibly the one-way clutch mechanism, but I'm not that familiar with the engineering with them, it's a sealed unit, so don't fancy too much prying.

 

[PaulSB]

I've had what sounds like a similar problem on one of my road bikes, not an e-bike. A spring under one of the pawls had failed which caused a slight lag or jerk when some force was applied.

Out of interest why would you be pedalling backwards? Is it something to do with riding an e-bike?

 

[confusedcyclist]

I am back pedaling only to position the pedals optimally when stopped or coasting. Unlike a regular bike drive train, the Bosch system is a mid-drive motor, and when you back pedal, the one way clutch keeps chainring/chain still, but your pedals/cranks move freely. So, this is why I'm wondering if it may be an issue with that clutch bearing system. I don't know enough about it to determine how it fails and my internet searches have failed to turn up clues.

 

[confusedcyclist]

It's a close one, because I can't tell how much is acceptable with my components, but it seems to me there may be play in the cranks. That might indicate something not quite right in that general area, either something is loose in the crank/motor assembly, or there is an issue in the motor. I called the retailer to discuss my findings, the chap I spoke to was reluctant to offer advice on the phone for home diagnosis and wants me to bring it in, OK, but I was just after a bit of advice incase it's a quick fix. The shop want to see it first (ka-ching!). He also said it sounded like the hub. I'm not convinced. The hub itself has only done 2000 miles, well serviced, and the freehub was replaced at around 1000 miles when I accidently dropped and stood on a tiny plastic spacer during a service. Maybe I buggered something up unintentionally, it wouldn't be the first time, but since this issue has gradually worsened over the course of a couple of months, and well away from the previous service interval, I'm hoping not!

 

[iluvmybike]

So you have a problem which you are unable to diagnose accurately but you are unwilling to take it to the shop so they can take a look? And the 'ka-ching' comment seems very unfair - did you even ask them if there was a cost to them 'having a look'? I don't blame them for wanting to see the bike as it could be several things from simple to compex - if they try to advise over the phone and it doesn't fix it you'll probably then be slagging them off for giving you duff advice. Unroll that tight fist and pay them a visit - you may find it is a cheap fix - and at that point you can always decide to do it yourself - but be careful not to accidentally stand on a vital part!!

 

[keithmac]

What warranty do you get on the Bosch motor?.

I get asked to diagnose motorcycles over the phone regularly, as the bike shop have said you need to let them have a proper look as it could be either hub or motor fault.

 

[iluvmybike]

What warranty do you get on the Bosch motor?.

I get asked to diagnose motorcycles over the phone regularly, as the bike shop have said you need to let them have a proper look as it could be either hub or motor fault.

Bosch motor warranty is 24 months

 

[confusedcyclist]

To be fair, I wasn't bad mouthing them, just acknowledging that they have an interest in generating a revenue stream. Is this not a forum for discussion of DIY repairs after all? I have years of experience in the latter, just none in electronic motors. Taking my bike to the retailer involves a 18 mile bike ride, then 3 separate bus rides home, and then the same in reverse for collection, so I don't lightly drop my bike off with them every time something goes wrong! On this occasion I have admitted defeat, it's now with the pros. I do know my limits and the motor is still technically under warranty so I shouldn't be tinkering.

 

[confusedcyclist]

LBS confirmed it was the motor that has failed and they are fitting a new one as soon as Bosch get it to them. So I was right, it wasn't the hub! *smugface*