eMTB’s Dirty Little Secret

If you have been riding mountain bikes for a long time, you know that components tend to fail because of normal use and wear and tear, particularly if you ride a lot. It’s even worse if you live somewhere like Scotland, the Pacific Northwest or anywhere wet, mucky and cold.

We all know that grips, tires and brake pads get shredded over time, but bearings wear out as well. In the age of sealed cartridges, you can swap the old bearings in your headset or your hubs and have them spin like new in no time. Bottom brackets are a little different because they are generally sold pressed into the cups. This is a reasonable trade-off because most bottom brackets aren’t very expensive compared to other MTB components, and they seem to last much longer than they used to.

This math changes entirely when the bottom bracket you are talking about is sealed inside the drive unit of your eMTB. If you have a mid-drive motor, which covers virtually every electric mountain bike an enthusiast would ride, that is the way almost all of them work. Your cranks mount directly to the drive unit.*

*The Dyname drive unit, used on Rocky Mountain Bicycles, is the only widely used exception to this rule that I am aware of. The drive unit sits ahead of the bottom bracket, which powers a pulley, allowing a conventional BB to be used. It will be interesting to see if Rocky keeps rolling with the Dyname system now that the company has been sold.

If you have owned an eMTB, you may know what I am getting at here. On virtually every bike sold in the world that doesn’t have a mid-drive eMTB motor, the bottom bracket is a user-replaceable part. You can pick one up for between 30 and 100 bucks, and then grab the tools to replace it for between 20 to 60. If it’s a press fit, and you are good with tools, you may already have everything you need. It’s a bicycle, FFS, you should be able to fix it yourself.

For all but the most determined, schooled and tooled-up DIY riders, the user-serviceable eMTB motor is a fantasy. Not only is that drive unit not user-serviceable, in almost every case, your dealer won’t be able to fix it either if the problem is on the inside. Depending on what’s wrong, they may be able to run some software to diagnose the issue, and maybe even correct it, but they aren’t authorized, trained, or even armed with a manual that tells them how to open the grey grenade that lives between your cranks. It’s worse than that, though. Even if they had authorization, training, literature, and parts to repair them from the manufacturer are virtually impossible to track down.

What is the solution then, when the parts that perform the same function as your bottom bracket live inside the sealed capsule of your eMTB’s drive unit? If you ask the manufacturer of your drive unit or your bike shop, they are likely to tell you that once your bearings fail, your drive unit is toast. If you are within the warranty period, you will likely get a new motor. If your warranty has expired, you will need to purchase a new one, and likely pay a shop to install it.*

*If you are able to change a bottom bracket or bleed brakes, you could likely swap your old motor for a new one, aside from any programming that may be required. I have removed both Shimano and Bosch motors to dig out or replace cables or brake lines, and while the jobs were straightforward, they were a little time-consuming the first time with a particular bike.

I know how I’d feel if the motor attached to my eMTB (that cost as much as a used Tesla), was declared DOA because 140 bucks worth of parts needed replacing. Obviously, issues can be more serious than that. Several knowledgeable people have told me that most drive units fail because of water damage, and guess where that gets in? That’s right: the only way moisture can get in is through the axle that drives your cranks, especially as it begins to get worn. So even if the bottom bracket isn’t worn out, once the seals go, if you live somewhere wet, you may be living on borrowed time

In some locales, there are options. Here in North America, there are a few specialty shops that have taught themselves how to disassemble, diagnose and repair eMTB motors. Sometimes this happens with improvised parts, including bearings and seals that may be better than stock, and other times with parts tracked down in Europe, where the rules seem a little different. Right to Repair legislation is more robust in the EU, and it applies at least partially to e-bike drive units; repair parts can be purchased, and information about repair and diagnostics is more accessible.

Here in North America, there aren’t many shops that specialize in drive unit repair, but there is one not far away, in Bellingham, Washington. Alpine Edge is owned and operated by Grant Gunderson. Despite being trained as an engineer, Grant has spent much of his adult life as an action sports photographer. When he was in college, he moonlighted doing high-end camera repair, which turned out to be solid training for tinkering with electric motors.

At this point, Grant seems pretty dialled at cracking electric eggs, figuring out what’s wrong, and putting them back together. That may sound flippant, but the reality is quite complicated. Every time Grant takes on a new motor model or brand to repair, it requires bespoke tooling and fixtures made in his own machine shop. He uses an electronic microscope to inspect boards, has designed and built a testing fixture for Shimano eMTB motors (below), and has begun working with manufacturers to build custom bearings and seals that he has designed to perform better than stock. This would be a heavy undertaking for your average bike shop without hefty support from players like Bosch, Specialized and Shimano. DJI will be entering that territory soon as more brands spec. the high-powered, Chinese-made powerplant.

I asked Grant a few questions about what he’s learned diagnosing and repairing drive units.

What would you like to see from manufacturers that would benefit consumers and repair shops?

Grant Gunderson – If manufacturers wanted to improve outcomes without turning it into the wild west, the best steps would be:

• Spare parts availability for wear items: bearings, seals, belts (where applicable), common gears, fasteners, sensor subassemblies
• Publication of the specific lubricants / greases they use. I’ve fixed a number of motors where people tried to service them themselves but used the wrong lubricants. In some cases, the wrong lubricant can cause irreversible damage.
• Service documentation for trained independent shops (torque specs, shim stacks, inspection criteria, and error codes that translate to specific components / issues)
• A certification pathway for independent repair (training + audit + access to parts)
• Better ingress protection that acknowledges real‑world riding: pressure equalization, improved sealing interfaces, smarter drain paths
• More transparent diagnostics (clearer error codes, better separation of motor vs. bike‑side faults)
• Reman / refurb programs in North America (so “replacement” doesn’t automatically mean landfill)

Do you get a sense that brands are moving toward a more repair friendly model in the future or does it seem we are stuck here?

GG – Not yet. I think most brands are still focused on generational model improvements. I do see small signs of improvement in overall build quality from generation to generation, but the trend toward true repairability is slow. None of them seems to be making a real commitment to supporting rebuilding yet.

What pushes repair friendliness forward:

• parts availability
• regulatory pressure
• sustainability commitments that become real
• warranty cost reduction (repairing can be cheaper than replacing)
• consumer backlash when a “sealed” unit becomes a throwaway item

If I had to summarize, we’re not stuck forever, but it will likely require either regulation or strong market pressure before you see truly open parts, manuals, and independent certification pathways.

Tearing One Down

To get a sense of what it’s like to work on a toasted drive unit, I managed to get a scrap one from Obsession: Bikes here in North Vancouver. It was a gen. 4 Bosch, but that doesn’t suggest a higher failure rate than others. All the big brands have a failure rate and different vulnerabilities. I don’t know how old this one was, how many miles were on it, or what caused its demise. We chose it because someone (likely in the shop) got as far as removing the T25 security Torx bolts that hold the two sides of the shell together. That’s where they stopped, though. With Deniz’s help and some high-quality circlip/snap ring pliers, she was cracked open. I took it home from the shop in that form and set about getting it the rest of the way apart.

Luckily, there were conventional Torx bolts on the inside, and I got to work. A few were hidden and at difficult angles, but eventually I found them all. Things were still pretty tightly packed and secure, so I got a little aggressive, busting circuit boards and a few other plastic pieces. It wasn’t pretty, but it was effective, and soon I had all the main mechanical components apart.

Inside, I was impressed to see ample grease. Some of it was dirty but still doing its job, coating gear teeth and other sliding surfaces. And everything else looked pretty good as well. Once we got beyond the main drive axle, things looked clean and pretty mint, really.

Grant made another point that eMTB manufacturers should pay attention to: “Being able to repair these motors is vital to keeping the used e‑bike market healthy, and that in turn supports new bike sales when people can sell their old bike to help fund the purchase of a new one.”

Obviously, there are riders out there who can shrug it off if their bike becomes worthless, but they will start getting annoyed if it happens more than once. And a healthy used market is how many riders will start riding eMTBs. If they can’t trust what they are buying, that’s a huge barrier to entry.

How Did We Get Here?

If I were a conspiracy theorist, I’d wonder if there was a global cabal of drive unit manufacturers who meet semi-annually. If they do, it’s likely in Switzerland. If there is no such shadowy group, what explains the fact that not a single large manufacturer services their customers’ motors, refurbishes ones that have had problems, makes parts or service literature available, or does anything but toss ailing motors into the dumpster? Did one company go first boldly, deciding the market would bear it, and then others followed, recognizing that higher profits and fewer complications would result? Or perhaps they followed other industries that rely on planned obsolescence and scheduled failure? Someone must know the answer to this question, and so far, they won’t talk to me.

What I Have Learned

I had some questions I wanted answered. I reached out to my usual media contacts at three different eMTB motor manufacturers. I wanted to speak with someone at each company who could explain why a $30 blown bearing was sufficient to warrant replacing an electric motor that costs up to 1300 CAD. Each rep. asked me for a list of questions and passed them on to whoever they determined was the right person, promising to get me answers.

I waited a week and had no replies. I followed up and was assured by each that answers were forthcoming. They were not. I finally gave each a deadline. It came and went without a single response. I extended it yet again, but two weeks into this charade, it became obvious there wasn’t anyone willing to stick their neck out to defend this wasteful and disappointing corporate policy, and I can understand why.

In the age of reduce, re-use, recycle, to have large companies producing expensive bicycle components that they have chosen to deem unrepairable, is shocking. This is the first time in 26 years of doing this job that I have been stonewalled by any representative of a company, and it’s what I got from all three.*

*not the media reps to be clear, and I wouldn’t be surprised to learn the decision not to answer my questions came from higher up the corporate ladder.

It’s not like I don’t understand where they are coming from; these are complicated and finicky mechanisms. To rebuild one properly, you need to use three different types of grease, in the right places, for fuck’s sake, or risk causing irreparable damage. And that’s a minor issue. And of course, in New York, the string of fires (caused by e-bikes that were user-modified) must have sent a chill through the industry. Safety concerns, performance issues, and complicated repair workflows: these are not easy problems to solve. And yet they aren’t impossible either.

Apple, one of the most secretive, careful and locked-down companies in the tech world, will sell you a refurbished model of virtually everything they make. They are very well tested and can be had at a nice discount. Bike companies don’t even bother collecting older motors that have been deemed total losses, although newer motors seem to be getting returned to some companies.

The ability to buy a refurbished motor for less cash would be a huge relief for some riders, not to mention bringing peace of mind to new buyers. If they don’t want bike shops or consumers repairing their drives, companies should staff up and fix them in-house, where they could be thoroughly tested before returning to the wild.

A bare minimum strategy would be to provide training, tools and parts to those who are already refurbishing written-off motors, and add some in-house support. There doesn’t seem to be anything inside these shells that isn’t replaceable. This would also allow for preventive maintenance to be performed, to head off many of these issues before they start.

If you have a motor that isn’t performing as it should, have a look at Alpine Edge in Bellingham or Ebike Motor Repair near Nashville if you are further east. In Europe there seem to be more optioins as well.