Bosch CX Gen5 Motor Clutch clunk/engagement issue AFTER a descent?

[rjceara]

Oreba WIld owner here, 2025, with CX-5, about 700 miles on the bike/motor - I too am getting this clunk in my emtb+ and turbo+ modes - I can feel it through the pedals, it most often happens maybe after techy sections of trail? Or after descending for a while while not really pedaling, and after jumps. Or just riding around on level ground, I can briefly pedal, stop, and I can feel the overrun kick in, but some sort of clutch connection or something happens where I can feel motor or gears go through a revolution, I can feel it in the pedals, and If I try and pedal right after I feel the cycle/kick through the pedals, I will briefly have no assistance, and then it will sort of lurch back on and provide assistance and everything is fine.


I can mostly recreate it by pedaling hard, and then stopping suddenly and coasting, and then I can feel the overrun kick in, the weird clutch/gear thing happens with a clunk, and then if I try and pedal immediately after the clunk, no assistance for a brief second. Turbo+ and EMTB+ modes, have not tried with the others, and have not had it to the shop yet. Seems to be associated with the overrun. Is getting worse and worse over time. Did not have this behavior when new, started about 200 -300 miles in.


Very similar to Han Slomo's issue, I think.

A question for you Bosch CX Gen 5 owners. After a descent at speed when I begin to pedal again there is sometimes a loud clunk that you can hear/feel as the motor engages. It often occurs with what feels like a gap in engagement. I can then feel the hub engage after the clunk and all works fine. This is hindering the bikes performance, a 2026 santa cruz bullit. eg. riding a fast descent, half way down there is a gap after a corner, you come out of the corner and go to pedal... nothing happens for a quarter of a pedal turn (approx) and CLUNK in the motor then another slight pedal turn.. hub engages then pedal to get power. Another scenario where this happens... finish a fast descent with no pedalling, coasting to rest on the raod at the bottom, go to pedal away same thing as explained above. The shop checked it out but they only took it on a flat road... they couldn't reproduce the issue. Has anyone experienced this? Is it normal?

Hi… Owner of a Santa Cruz Vala with the same motor issue… after a descent the motor takes some time to engaged and makes a clutch sound… also it happens going up if I pedal back

Did you find a solution? I normally ride in Emtb+

Appreciate any feedback…

 

[han_slomo]

Oreba WIld owner here, 2025, with CX-5, about 700 miles on the bike/motor - I too am getting this clunk in my emtb+ and turbo+ modes - I can feel it through the pedals, it most often happens maybe after techy sections of trail? Or after descending for a while while not really pedaling, and after jumps. Or just riding around on level ground, I can briefly pedal, stop, and I can feel the overrun kick in, but some sort of clutch connection or something happens where I can feel motor or gears go through a revolution, I can feel it in the pedals, and If I try and pedal right after I feel the cycle/kick through the pedals, I will briefly have no assistance, and then it will sort of lurch back on and provide assistance and everything is fine.


I can mostly recreate it by pedaling hard, and then stopping suddenly and coasting, and then I can feel the overrun kick in, the weird clutch/gear thing happens with a clunk, and then if I try and pedal immediately after the clunk, no assistance for a brief second. Turbo+ and EMTB+ modes, have not tried with the others, and have not had it to the shop yet. Seems to be associated with the overrun. Is getting worse and worse over time. Did not have this behavior when new, started about 200 -300 miles in.


Very similar to Han Slomo's issue, I think.

Sounds like what i was experiencing.... and am now experiencing again. The new motor was perfect then at around 300-400 km made a large metalic crack/ping noise. Now every ride at least once there is a moment after coasting/descending/jumping if I do a quarter pedal crank the over run spins with the motor giving no assistance. Just did a 3 day test with a different wheel and hub and the bike still did it every ride. I can randomly recreate it by coasting and bunny hopping, landing heavily with the back tire down a slight hill then slowing and pedal cranking. This week I am trying to get a video of it for the shop. It is quite dangerous in situations like elevated skinnies when you need a little momentum from a pedal kick and you get nothing.

 

[elesdee]

Sounds like what i was experiencing.... and am now experiencing again. The new motor was perfect then at around 300-400 km made a large metalic crack/ping noise. Now every ride at least once there is a moment after coasting/descending/jumping if I do a quarter pedal crank the over run spins with the motor giving no assistance. Just did a 3 day test with a different wheel and hub and the bike still did it every ride. I can randomly recreate it by coasting and bunny hopping, landing heavily with the back tire down a slight hill then slowing and pedal cranking. This week I am trying to get a video of it for the shop. It is quite dangerous in situations like elevated skinnies when you need a little momentum from a pedal kick and you get nothing.

Been noticing this pattern with the gen 5 CX at the shop I work at. Already replaced two motors under warranty for this same issue. Both at around 1200kms. Both eventually produced torque sensor errors consistently.

Not happy about this pattern, reminds me of Shimano motors and how they fail consistently anywhere between 700 and 1800kms.

Hopefully Bosch has a solution in the works. This kind of stuff is usually a silent update. So keep pushing your shops to warranty your motors and hopefully sooner rather than later you’ll get one of the new updated ones!

 

[han_slomo]

Been noticing this pattern with the gen 5 CX at the shop I work at. Already replaced two motors under warranty for this same issue. Both at around 1200kms. Both eventually produced torque sensor errors consistently.

Not happy about this pattern, reminds me of Shimano motors and how they fail consistently anywhere between 700 and 1800kms.

Hopefully Bosch has a solution in the works. This kind of stuff is usually a silent update. So keep pushing your shops to warranty your motors and hopefully sooner rather than later you’ll get one of the new updated ones!

trying to post a video captured today of what I think is an issue, says it uploads 100% but doesnt show up.

 

[sjturner2112]

After reading all the other posts, I am concluding that I am experiencing for sure what these other riders are experiencing. The recent Han Slomo post describing how to recreate it is my issue to a T. I Think mine made a noise as well before starting all of this.

 

[han_slomo]

here is a link to the recording I made showing √ proper function vs X malfunction

- YouTube

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.

youtube.com

 

[TheKaiser]

Are you sure that it is not the rear hub? It would explain all of the symptoms.

On my mtb, I had an E13 hub with three spring-loaded pawls on a multi-tooth hub offering 6 degrees of engagement. It was supposed to give "almost instant engagement!". But the hub seals failed very quickly and first one pawl spring rusted through, then a second, until finally after only 128 miles and three months, the hub failed completely. As each hub spring failed, the pawl failed to engage and the symptoms you described emerged.

When the first hub spring failed, the hub engagement would have become 12 degrees; ie a doubling, but not all the time, just one in three! Then when the second one failed, two times out of three it would be 18 degrees of wheel turn before engagement, which was quite a clunk. Followed soon by total failure. The hub, in fact the entire wheelset came with a five-year warranty, which is one of the reasons that I bought that particular wheelset. Yet it failed in three months! It was not at the top of my list for the culprit.

Was that the Sidekick hub, or a different model from E13?

 

[steve_sordy]

Was that the Sidekick hub, or a different model from E13?

As far as I recall, the whole wheelset was an E13 product. It was a while ago now and I have been solidly put off from buying ANY E13 product ever since. Even their chain device off a different bike was crap and had to be removed.

E13 wheel, new.

Hub 700 miles later, not even three complete pawl springs left!

 

[StMartyr]

I’m having the same issue on my SC Vala. Currently at 2,100 km. The problem occurs after a hard landing or riding through very rough terrain. The first pedal stroke afterwards provides no assistance and is accompanied by a loud noise and a kickback into the pedals. Twice now, I’ve gotten error code 500008 - Drive unit error - motor control. If the issue persists even with a new motor, I think I’ll wait a bit before filing a claim, hoping there's a better chance of getting an improved version later on.

 

[elesdee]

I’m having the same issue on my SC Vala. Currently at 2,100 km. The problem occurs after a hard landing or riding through very rough terrain. The first pedal stroke afterwards provides no assistance and is accompanied by a loud noise and a kickback into the pedals. Twice now, I’ve gotten error code 500008 - Drive unit error - motor control. If the issue persists even with a new motor, I think I’ll wait a bit before filing a claim, hoping there's a better chance of getting an improved version later on.

Make sure you start the warranty claim before the two-year (since purchase date) warranty period is up. Bosch has some flexibility during the third year but it’s up to their discretion.

 

[han_slomo]

Update - In the past week the occurance of the issue has increased, Easily over 10 times per ride. I am at 500km on the new motor received from Bosch to remedy this same issue. Both motors began failing between 200 and 400km. When I chat with people on the trail, no one is having the issue??? The bike shop that I am dealing with sells and services a lot of Bosch bikes here in North Vancouver. They say I am the only person with the issue and they have never seen it before. Bosch is sending a third motor after seeing the youtube video I posted above. Neither Bosch or the Shop will provide any suggestions on what the issue is or what causes it. My concern now is related to keeping a motor prone to issues for any length of time because once it is out of warranty I'll be left stranded.

 

[elesdee]

Update - In the past week the occurance of the issue has increased, Easily over 10 times per ride. I am at 500km on the new motor received from Bosch to remedy this same issue. Both motors began failing between 200 and 400km. When I chat with people on the trail, no one is having the issue??? The bike shop that I am dealing with sells and services a lot of Bosch bikes here in North Vancouver. They say I am the only person with the issue and they have never seen it before. Bosch is sending a third motor after seeing the youtube video I posted above. Neither Bosch or the Shop will provide any suggestions on what the issue is or what causes it. My concern now is related to keeping a motor prone to issues for any length of time because once it is out of warranty I'll be left stranded.

Thanks for the update. Hope third time’s the charm.

In my riding group there are three guys with gen 5 CX, all got them about a year ago when it first came out. All three are extremely hard, advanced riders.

Two of them had the issues you describe, and both at about 1100km had the motors replaced under warranty because they just got to the point where it cuts out all the time and produces critical errors (torque sensor, among others).

The third guy is the one I was expecting to have killed the motor first but it’s a complete opposite story. This guy is the gnarliest rider I know and has now over 3300km on the motor with absolutely zero issues to report.

I’m thinking there is a bad batch out there, and perhaps you got the bad motor twice. So hopefully the third one will be a good one!

 

[steve_sordy]

....................

I’m thinking there is a bad batch out there, and perhaps you got the bad motor twice. So hopefully the third one will be a good one!

I've had that with a rear hub, tyres, and a charger. Not all on the same bike and thankfully, non my current emtb!
Don't see why it couldn't happen on a motor.
With the way products are produced and quality assured these days, it's a racing certainy that many will be produced and not just one!

 

[Rob209]

- YouTube

Is this the same fault as everyone else is getting?
This is happens quite often on the trail usually after a rough decent & when you least expect it. It’s caused a couple of crashes when I need to lift the front over logs etc.
Have taken it to a Bosch dealer & they couldn’t replicate the fault & said it was ok.
(The bike is now clean)

 

[han_slomo]

- YouTube

Is this the same fault as everyone else is getting?
This is happens quite often on the trail usually after a rough decent & when you least expect it. It’s caused a couple of crashes when I need to lift the front over logs etc.
Have taken it to a Bosch dealer & they couldn’t replicate the fault & said it was ok.
(The bike is now clean)

It seems similar to my issue. But it would help to see the drivetrain side in the video. Here is my issue - YouTube
when Bosch saw the video they sent my shop a new motor.

 

[Rob209]

It seems similar to my issue. But it would help to see the drivetrain side in the video. Here is my issue - YouTube
when Bosch saw the video they sent my shop a new motor.

When it does it there is no motor assistance at all & there is no output to the chainring.
I can still pedal fine until it finally kicks in, it’ll do it when you need a quick crank to hop over something & you’re expecting assistance but get nothing apart from leg power.

 

[han_slomo]

When it does it there is no motor assistance at all & there is no output to the chainring.
I can still pedal fine until it finally kicks in, it’ll do it when you need a quick crank to hop over something & you’re expecting assistance but get nothing apart from leg power.

Your video should be enough for your shop to get you a new motor.

 

[e*thirteen Components]

As far as I recall, the whole wheelset was an E13 product. It was a while ago now and I have been solidly put off from buying ANY E13 product ever since. Even their chain device off a different bike was crap and had to be removed.

E13 wheel, new.
View attachment 178735

Hub 700 miles later, not even three complete pawl springs left!
View attachment 178736

Hi Steve,
Chris from e*thirteen here. Sorry to see the trouble with that hub. The wheel you have there is a VERY old wheel (from production ~10 years ago). Our hubs have improved greatly since that version and Id gladly get you set-up with one of the newest versions. Could you drop us a line at [email protected] so we could get a bit more info from you about the wheel.

Thanks in advance and sorry again about the trouble.

Chris

 

[StMartyr]

As I wrote earlier, I had the exact same motor issues as han_slomo, and my motor was making the same noises as Rob209's. I finally took the bike to the shop, where they diagnosed an oxidation issue on the connector between the battery and the motor. Water must have gotten in there somehow. I’ve just done a short test ride and the problem is gone, but I’ll keep testing and keep you guys updated. If this really is the root cause of the clutch issue, I think everyone can easily do this maintenance at home themselves, and there's no need to take the bike to a dealer for a warranty replacement

 

[StMartyr]

Further testing was conducted today. On the trail sections where the motor issue previously occurred, everything is now functioning properly. According to the service technician, it was a contact issue with the motor cable on the battery side. Make sure to check your connectors!

 

[sjturner2112]

Further testing was conducted today. On the trail sections where the motor issue previously occurred, everything is now functioning properly. According to the service technician, it was a contact issue with the motor cable on the battery side. Make sure to check your connectors!

IS this easy enough to check/repair ourselves? Was there any more specific information given? Thanks.

 

[StMartyr]

It will depend on the technical proficiency of each individual and the specific make and model of the bike. On my SC Vala, the motor must be removed to access the battery.

 

[sjturner2112]

It will depend on the technical proficiency of each individual and the specific make and model of the bike. On my SC Vala, the motor must be removed to access the battery.

Yes, I understand that, the same with my bike, but was there more information about the oxidized, or loose connection? What was the specific fix? Was it a cleaning, and reseating of the connectors? Thank you.

 

[StMartyr]

The connection was oxidized due to water ingress; it wasn't loose. The fix was just cleaning it, spraying the connectors with electronic contact cleaner, and reseating them

 

[sjturner2112]

The connection was oxidized due to water ingress; it wasn't loose. The fix was just cleaning it, spraying the connectors with electronic contact cleaner, and reseating them

Thanks so much.