Sprag Clutch failure (Updated title) and how common is it?

[Murch]

I have now had two motors fail due to the torque sensor, first failed at 690 miles and the second at 517 miles. Talking with others in the area this is our number one failure. My local shop and Specialized are replacing the motor again but I am worried it's just going to fail once again when get to 500 miles or so.

Bought my Expert Levo 2019 in August of 2019, first motor failed on Dec 27th and the second one on May 1st. I don't ride in wet conditions and never clean it with high pressure.

 

[Tim22]

What are the symptoms of a failing torque sensor?

 

[Murch]

Here is what my second one looks and sounds like

 

[salko]

What are the symptoms of a failing torque sensor?

Usually when you stop pedaling, the motor will keep pulling for several seconds or more ...

 

[Troutwrestler]

 

[Murch]

My first failure the symptom was if I put a good amount of torque/force into the pedals the motor would spin but not provide any power, if I put light pressure on the pedals it would work as normal. The second motor was the opposite as seen in the video, it would work find if I put a lot of torque/force into the pedals but if I pedaled lightly it would just spin or provide no assistance at all.

 

[Ted]

I have had two motors replaced for the torque sensor. The first at 1700 miles and the second last week at 2700. Both sounded much like the chain rubbing on the chain guide. I moved the guide so the chain did not go through it and the sound was still there.

I have heard that Spec has now improved the belts so they are no longer failing. I hope they are doing the same for the torque sensors.

 

[Murch]

I would love to get @Specialized Rider Care thoughts on this, I know they can't state failure numbers but I would really like to know they have root caused it and a fix has is in the works or is being applied on new or repaired motors.

 

[Bearing Man]

This is not the torque sensor. it is the motor struggling to align the crank speed, with the motor speed, with the bike speed. This is the beginning of the end for one of the sprag clutch bearings. This is also what causes the motors to take off on their own when the electric motor speed does not match the signals that are coming from the speed sensor on the crankshaft, it then hunts up and down trying to match the values.
I have only seen torque sensor failure when the sprag bearing on the crank is slipping and people just keep pedalling and pedalling until the torque sensor overheats and eventually fails.

 

[brizi2003]

I have a Kenevo with a motor that failed but not for this reason. It was warranty exchanged due to excessive radial play in the crank shaft.

 

[Murch]

This is not the torque sensor. it is the motor struggling to align the crank speed, with the motor speed, with the bike speed. This is the beginning of the end for one of the sprag clutch bearings. This is also what causes the motors to take off on their own when the electric motor speed does not match the signals that are coming from the speed sensor on the crankshaft, it then hunts up and down trying to match the values.
I have only seen torque sensor failure when the sprag bearing on the crank is slipping and people just keep pedaling and pedaling until the torque sensor overheats and eventually fails.

Thanks for the feedback, makes much more sense. I had been noticing a pop noise coming from the motor at times when I would start pedaling after coasting. It felt like something would bind and the let go. Specialized said it was a worn drive train or bad free hub. I tried three different wheels and replaced my whole drivetrain and it still did it. I ended up giving up on trying to get the motor replaced because of it and told them I would ride it until it failed which was a month later.

In this video you can hear the noise it would make.

 

[brizi2003]

Is it reasonable to expect sprag clutch bearings to last longer than 500-700 miles? What is the main cause of their demise?

 

[Bearing Man]

Thanks for the feedback, makes much more sense. I had been noticing a pop noise coming from the motor at times when I would start pedaling after coasting. It felt like something would bind and the let go. Specialized said it was a worn drive train or bad free hub. I tried three different wheels and replaced my whole drivetrain and it still did it. I ended up giving up on trying to get the motor replaced because of it and told them I would ride it until it failed which was a month later.

In this video you can hear the noise it would make.

When these sprag bearing start to go they can slip and grip. This slipping and gripping action is actually very violent for the bearing itself. It causes the small spacers in between the sprags to break off and eventually flip over and become useless, this eventually leads to slipping or complete failure.

 

[Murch]

When these sprag bearing start to go they can slip and grip. This slipping and gripping action is actually very violent for the bearing itself. It causes the small spacers in between the sprags to break off and eventually flip over and become useless, this eventually leads to slipping or complete failure.

Do you know what causes it them to fail? Is this something I could be doing wrong? Bike never gets cleaned with water and I don't ride wet trails.

That motor was a replacement for my first motor that failed in the same way and the shop told me they were told it was a failed torque sensor just like the others they have sent in.

 

[Bearing Man]

Is it reasonable to expect sprag clutch bearings to last longer than 500-700 miles? What is the main cause of their demise?

A sprag clutch bearing is designed to be put into a machine where you would like the shaft to spin one way but not the other. They are not particularly strong bearings with a torque limit of around 250Nm. This may sound a lot but how much force goes through the crank when you have a hard pedal strike or fall off the bike for example?
Even just repeatedly stamping on the pedals every time you take off or start pedalling again will take it's toll.
Imagine as you freewheel down a hill over rough terrain. The pedals stay relatively level with your feet on them, but the bike is bucking up and down like a bronco, this is turning the crank around the pedals back and forth and again, hammering the sprag bearings.
We thought these were failing because Brose used plastic bearing cages on the sprag bearings, so we fitted steel cage sprag bearings. It made no difference! They are not the bearings for the job! I would love to get some roller clutch bearings and try them but time is not on my side at the moment.

 

[Murch]

So, the big questions are for Brose and Specialized.

Can Brose solve the issue with the current motor?

If Brose can't solve the issue what is Specialized going to do for those of us that only get around 500 miles between failures?

 

[Bearing Man]

So, the big questions are for Brose and Specialized.

Can Brose solve the issue with the current motor?

If Brose can't solve the issue what is Specialized going to do for those of us that only get around 500 miles between failures?

Why would Brose even try? As far as they are concerned this part is fully fit for purpose. It was in the 1.2, 1.3 and now the latest 2.1 motors.
Brose are happy that in 99% of the bikes this motor is fitted into, it works fine! They would not listen to Specialized any more than they would listen to you or me. If it's a 1% or less failure rate out in the world then that's acceptable.
Remember, there is a big world outside of EMTB's. There are commuter bikes, shopping bikes, cargo bikes etc. And in Europe they outnumber mountain bikes 100/1. So when you factor all this in, Brose failure rate is probably closer to 0.01% with many, many happy customers.
Frustrating though isn't it.

 

[Murch]

Great point, I deal with failure rates in what I do with my job and any failure rate that is below 4% is not worth the cost to drive down.

So, what is the failure rate Specialized is seeing and is it worth the cost to them? I fear it is below what is needed to get a proper fix and the bean counters will be happy replacing my/our motors until the warranty is up and the cost is then put back on me/us. Word will get out and will it be worth the hit to the brand?

 

[LandSurfer]

I seem to have the same problem with my Specialized Turbo Levo 2017. First symptom was scraping sound (thought is was rear hub), which stopped. Soon followed (next day) by motor still engaging a few seconds more after I stopped pedaling. Is there a DIY fix anyone knows? I expect I'm well out of warranty by now... Good thread!

 

[Bearing Man]

I seem to have the same problem with my Specialized Turbo Levo 2017. First symptom was scraping sound (thought is was rear hub), which stopped. Soon followed (next day) by motor still engaging a few seconds more after I stopped pedaling. Is there a DIY fix anyone knows? I expect I'm well out of warranty by now... Good thread!

It's a bit of a major operation to change one of these bearings, the crank one is easier than the pulley one, but both require a few special tools etc. Take a look at my video, you will see the bearings in question.

 

[LandSurfer]

Sweet skills, Bearing Man. I can see it's a job that's well beyond my toolkit. The video is lucid, cheers for that. I wonder if anyone may have suggestions for where (I'm in San Diego) I might go to seek this bearing confirmation diagnosis and/or fix, or shall I simply start with the Specialized dealer nearby. The bike is still rideable but I anticipate the degradation arc will continue; I hear rust never sleeps (seems I didn't clear that creek's low spot as well as I'd imagined, last month)

 

[High Rock Ruti]

This is not the torque sensor. it is the motor struggling to align the crank speed, with the motor speed, with the bike speed. This is the beginning of the end for one of the sprag clutch bearings. This is also what causes the motors to take off on their own when the electric motor speed does not match the signals that are coming from the speed sensor on the crankshaft, it then hunts up and down trying to match the values.
I have only seen torque sensor failure when the sprag bearing on the crank is slipping and people just keep pedalling and pedalling until the torque sensor overheats and eventually fails.

High Rock Ruti

Bearing man Brilliant!

I've had the Sprague clutch fail and bike run on. Thanks so much for knowing.

Warm Regards

Ruti

 

[Zimmerframe]

So, what is the failure rate Specialized is seeing and is it worth the cost to them? I fear it is below what is needed to get a proper fix and the bean counters will be happy replacing my/our motors until the warranty is up and the cost is then put back on me/us. Word will get out and will it be worth the hit to the brand?

I get the feeling, and it's only a feeling, that Spesh push Brose for more. Spesh are smaller and far far far more customer focused than Brose which is where they have incompatibilities. They're more closely connected to the end user. Brose isn't. Sadly, I think the front guys for Brose don't give a feck as long as their spreadsheets show they'll get a new car and a bonus - however they spin it. Too long in the automotive industry.

I can imagine they have very polite meetings, with lots of frustration on the Spesh side and I kinda feel for them. They replace a lot more motors, and cover the cost, than Brose say are actual warranty failures.

Yes, certainly more fail than Spesh would like. I suspect Spesh would like 0. Every fail is money lost for them and damage to a hard built reputation.

For me, I always though Spesh bikes were just over priced and couldn't really work it out, until I owned one (it was heavily discounted). The build quality and attention to detail is phenomenal.

If Spesh could magically fix the motor issues on their own, I think they would. A large proportion are probably down to assembly tolerances (feck ups) . So someone who has a motor fail and then several failures, probably ends up repeatedly getting a motor assembled by "Franky Friday I don't give a feck". They probably goto the same bike shop from the same distribution centre from the same batch - so you're screwed. Hence the repeated failures.

From all the hell I've given mine, all the bad riding, all the crashes, all the endless wet weather use, (there goes my warranty ) I honestly can't believe it still works.

Ultimately, I think they have their hands tied, but they seem to do everything they can for the customer, including full refunds of bikes with multiple motor failures.

 

[Murch]

Specialized has always taken care of me as a customer and is one of the reasons I seem to always end up with another one when it's time to shop. I hope they figure something out motor wise as I love the bike when it's at it best.

 

[Troutwrestler]

I have read this with interest as I always assumed that it was the torque sensor. To a certain degree it is irrelevant, as this has happened twice to me, and the 2nd time was after 65km. I am almost certain that it will happen again.
I am quite heavy - around 95kg - and probably do put quite a lot of power through the cranks at times - I used to singlespeed a lot and went through a phase of struggling to get the rear axle tight enough to stop it being ripped out of the dropout when powering up hill. Perhaps the sprag bearing is the weakest link here?

 

[Matt Seabrook]

So what happens guarantee wise when a new motor is fitted? Does the guarantee run for date of the sale of the bike or does the two years run from the date the new motor is fitted?

 

[Murch]

So what happens guarantee wise when a new motor is fitted? Does the guarantee run for date of the sale of the bike or does the two years run from the date the new motor is fitted?

My understanding right now is it's two years from date of purchase of the bike. Specialized has some work to do to make this right though as I just can't see them letting this go as is.

 

[Funkeydunk]

Guys, my levo has just developed a similar issue, but when I back pedal the sprag doesn’t disengage and is very stiff, it even winds the motor backwards. When I does brake lose it’s got significant resistance back pedalling. I’m assuming this is a motor fail and replacement is needed?

 

[Murch]

Guys, my levo has just developed a similar issue, but when I back pedal the sprag doesn’t disengage and is very stiff, it even winds the motor backwards. When I does brake lose it’s got significant resistance back pedalling. I’m assuming this is a motor fail and replacement is needed?

Sounds like it

 

[kombos]

My first failure the symptom was if I put a good amount of torque/force into the pedals the motor would spin but not provide any power, if I put light pressure on the pedals it would work as normal.

This was the symptom of my recent 2020 motor failure.