How To Build An Ebike From Scratch: Final Assembly Day

Introduction
Step 1: Planning
Step 2: Hunting
Step 3: Tinkering
Step 4: Buying
Step 5: Build Day 1
Build Day 2
Build Day 3 (you are here)
Brakes
Working Handlebar Setup
Test Rides
Custom Motor Settings
Finalize Battery Wiring
Grips On – Finalize Handlebars
Step 6: Perfecting
Tools List

Wrapping It Up!

We accomplished a lot yesterday. What do we have left? Only one major component is left to install – the brakes – and then some final mopping up. We’re almost done.

Put On The Brakes (Literally)

We have already completed a part of this job: We put the brake rotors on with the wheels during Day 1. Now, we add the brake calipers that grab those rotors. We’ll mount calipers to the fork in front, and the frame in back, with the brake hose coming up from each caliper to the handlebars, where the levers are attached. This will be a lot simpler than it could be as hydraulic brake kits ordinarily come as a set with everything attached together already.

For this project, we chose a small 160mm rotor on the front wheel and a 180mm for the rear. A given bike could be built with various combinations of rotors. A brake caliper adapter lets a generic brake kit match up to any rotor size. How to pick the proper adapter is a common question, so let’s take a short detour and explain.

How To Pick A Brake Caliper Adapter

For almost all bikes, there are two different types of adapters: IS (International Standard) and Post. I’m going to ignore some of the fringe products like flush-fit, which you’ll probably never see on an ebike conversion/build.

International Standard mounts have two unthreaded M6 bolt holes, (spaced apart 51mm, center to center) facing horizontally, that pass a bolt through into a threaded adapter. The brake caliper then bolts to two top-down, vertically facing holes. Our project bike has a typical rear IS mount. Here it is, both before and after the brake caliper adapter has been installed.

Figure 1: Rear frame IS brake mounts, bare and with adapter installed.

In the right picture above, that is a Magura brand adapter. They handily have the adapter type printed right on them. You can see the model is QM-10, which is not particularly useful here (its an old part number… I dug it out of my parts pile for this build). What IS useful is the size/type designation under it: ISR-180. That stands for an IS mount type, R = Rear and 180 means it fits a 180mm rotor.

The most important takeaway from this tidbit of knowledge is there is a difference between a front and a rear 180mm rotor adapter for IS mounts. The two are not compatible, and if you try to swap a front adapter to the rear, at the very best you are going to get a bad fit to the rotor. At worst the caliper won’t fit over the rotor at all.

Our project’s front fork is a model-year 2000 Marzocchi Bomber Z2 X-Fly. That old fork has (for 2022) a very unusual disk brake adapter for a suspension fork: an IS mount. Almost all modern suspension forks use Post type mounts.

Here’s a pic from my Smash’s front fork, which is an MRP Ribbon. You can see where the name ‘Post’ comes from as the two mounts look like posts sticking straight out of the fork at a 90-degree angle.

A Post mount adapter bolts straight down onto the threaded posts, which are spaced 74mm apart (center to center). Typically, a fork has “160mm posts” which means you can use a 160mm rotor with no adapter. I have seen some forks with 180mm posts, which means you don’t need an adapter with a 180mm rotor, but those are rare. Regardless, you want to KNOW what size your posts are if you have them, both front and rear.

Bolt the caliper directly to the posts on the fork. Just like the IS mounts, M6 bolts are used on Post mounts.

What Have We Learned?

• Brake caliper adapters with IS mounts are specific to the front or rear.
• If the frame or fork has two unthreaded M6 holes that you put a bolt through horizontally inward across the bike’s wheel, with a 51mm distance (center to center) between the two holes, that is an International Standard (IS) mount.
• If the frame or fork has two threaded holes facing outward (usually that look like two parallel posts) with a 74mm distance (center to center) between them, then that is a Post type mount.
• Post adapters are unthreaded. IS adapters are threaded.
• Pick the adapter that is meant for the rotor size, mount type and front/rear axle that matches your wheel.

One More Thing!

As if the above is not enough, there’s one lesson I have learned that has served me well: Buy an adapter made by the same manufacturer who made your brake calipers. A homebrew brake caliper job often involves using washers here and there as spacers/shims to make up for a slightly wrong/bad fit of the caliper to the rotor face.

I have never had to shim a brake setup since I started matching caliper and adapter manufacturers. Here’s the thing: An adapter is often made with the manufacturer’s calipers in mind. So for example, Avid brakes are mounted with semi-hemispherical washers above and below the caliper (this is used to aid caliper alignment to the rotor). The lower washers take up vertical space. That space is accounted for with a slightly lower rise in an Avid adapter.

Try mounting a different manufacturer’s caliper on one – where that caliper was not intended to be spaced with those washers in mind – and it’ll be too short. You’ll need two or three M6 washers (or dedicated brake spacers, which are a precise thickness) between the adapter and the caliper to make up for that difference.

Or use a matching Magura adapter with your Magura caliper and everything bolts directly together with no messing around.

Speaking of which, rotors are by no means manufacturer-specific, but you may see a slight misalignment when mixing rotor and caliper manufacturers. So there is a case to be made for matching the manufacturer throughout the entire system unless you are willing to do some experimentation off on your own You may suffer through a little trial and error, but you may also find a perfect combination, as I think I have (I normally use Tektro TR-17 rotors but not on this particular project).

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So, with all that said, for this project bike I need a front (Magura QM-43) 160mm IS mount, and a rear (Magura QM-41) 180mm IS mount.

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Bolt the two adapters on, front and rear. Magura specifies 6Nm for the M6 bolts you will use to do this (they should be included with the adapter you buy). Magura adapters include bolts with a Torx T25 head. 6Nm for an M6 is a good number regardless of what brand(s) you buy.

Attach The Calipers And Levers

Once thats done, you are ready to bolt on the brake calipers. Once again, you use M6 bolts, but the standard 6Nm may not be where you want to be on the torque spec. More on that when we tackle caliper alignment below.

Before you do this, you need to spread the pistons inside the caliper so they are fully retracted. Depending on your brakes, you can do this with a screwdriver, or a brake block that came with your brakeset, or both. The actual procedure for this is illustrated in the Filling / Bleeding Video 2 below. You want those pistons spread wide for that first installation. After you have spread the pistons, if you removed the pads (not really necessary if you just used a screwdriver) put them back in.

Now you can mount the caliper. Do NOT torque it down. Thread down the bolts until there is only a very little play in the caliper. It should be able to slide sideways left to right with fingertip pressure. You need to be able to fudge it around a bit in our next step.

The brakes I am using come pre-assembled – the caliper is connected to the brake hose, and the brake hose is connected to the brake lever that goes on your handlebars, so it is a ready-to-run assembly. The brakeset has hydraulic fluid in the lines already and does not need to be bled unless you cut the hoses to fit your bike. This makes initial installation a lot easier.

After mounting the calipers, your next step is to provisionally bolt the brake lever onto the handlebars (don’t worry about routing the hydraulic hose just now. Thats for later). Since brake levers are manufacturer-specific with their own torque settings and bolt sizes (some are M5, most are M6 and the SRAM brakes that came on my Big Fat Dummy were actually an SAE size) I am not going to get into the bolt or torque spec for the lever. Refer to your manual for yours. Just get the lever on in more or less the right place, and only tighten so its barely held in place. You should be able to rotate it on the bars without effort, which you will need to do later on in the day.

Align The Calipers

With the brakes on the bike but not safe for riding just yet, we need to align the caliper so it doesn’t rub on the rotor, which it will when you do an initial install.

Take up the ‘slack’ in the brake pistons

In the auto racing world, brake pads can wind up getting spaced away from the rotor thanks to the torsion that comes with sharp curves and high speed flexing of the suspension. This gives you something called ‘knock back‘. The cure for knock back is to do some gentle brake pedal depression in advance of that corner you are rushing up to. This tee’s up the pads so they are right up there with the rotor again. Otherwise, your pedal goes to the floor and you need a change of underwear.

We artificially induced a form of brake pad knock back when we spread the pads during the caliper installation. Now that the caliper is on, we need to undo that. The procedure is the same as with a race car: Squeeze the brake lever a few times, and don’t worry that it goes all the way down to the handlebars on the first couple of pulls. Keep squeezing and proper lever travel will eventually come back.

NOTE:
What follows is the ‘brake whisperer’ version of aligning a bicycle brake caliper. This is a lot more effort than most people go to, but it will yield perfect alignment on even marginal brakes, barring some sort of mechanical defect (like a warped rotor). It is almost a you-have-to-feel-it-to-get-it technique. I will try my best to write it down coherently so you can replicate it yourself. Here goes!

Rear Caliper

Lets align the back wheel first. Toolwise, you need to keep within arm’s reach whatever wrench you need to tighten down the brake caliper. Usually that is an M6 hex key wrench, or a Torx T25.

Either spin the rear wheel by hand or use the crankarms. Get an earful as to how much misalignment there is (your ears will tell you how much real quick). Now grab and depress the brake lever to clamp and stop the wheel. Keep holding the lever down so the brake continues to hold the wheel. Since we left the caliper so it had only light play and could move freely, that caliper is now sitting very close to its natural, proper alignment, and is holding itself there thanks to your hand clamping the brake lever.

Now pick up that wrench you set aside with your other hand. While still holding the brake lever, gently tighten first one bolt, then the other so now the brake caliper is just barely held in place. It is imperative you apply only the gentlest amount of torque to that wrench, because even a bit too much will cause the caliper to move and spoil your alignment.

When done with two gentle tugs on that wrench, spin the wheel again. Does the wheel come really close to rotating without any touch to the rotor? Since we only barely tightened it, you can now move first one side and then the other of the caliper side to side, just a hair, with your fingertips to try and eliminate all contact. The slight tension you put on the caliper via the bolt should still allow you to move it, and that movement will now stick. Fiddle with it front and back, gently, side to side until you have the brake caliper in the perfect spot, so it does not rub at any point in the wheel revolution.

If we have the caliper in a final position, since we have barely any tension on the brake caliper bolts, we need to – again, very slowly and gently – apply more torque, alternating from one bolt to the other. It is a good idea to physically hold the caliper and adapter with your thumb and forefinger, clamping it in place with your fingers while you do small wrench turns – maybe 1/16th of a turn or less (!) at a time at each go. After each adjustment, spin the wheel and see whether the caliper shifted a hair in the wrong direction. If so, try and correct with your thumb and forefinger, or back the bolt off just a touch until you can make an adjustment.

You may have to undo and restart the process a few times. It is not at all unusual for the caliper to rotate on its horizontal axis a hair – even on a caliper not using hemispherical washers. Don’t be discouraged by this. Just take it into account as you try (and likely retry) to get the caliper tightened down sufficiently so it is in place, not moving and not rubbing. Do it precisely enough and you will find that sweet spot.

When you do find it, that bolt is almost certainly nowhere near the 6Nm that is typical for a tight M6 bolt. It will be much less. I do not try to tighten the calipers down that tight. Applying torque like that makes it almost impossible to align the caliper with the kind of fine control I want. I have never had a caliper loosen so, anecdotally, you should be fine too.

Its worth mentioning that this procedure is being used with Magura brakes along the lines of what you see in Figure 4 above: No washers, no spacers. Just direct part-to-part contact. And I am often using 2.3mm thick rotors, which are very thick. Even thicker than the 2.0mm rotors Magura recommends for their calipers, which are in turn thicker than the 1.8mm rotors that are the standard for most of the rest of the industry. So this procedure is used to dial in a very tight system that has very little wiggle room in it. Still, it will work great for any system if you are willing to put the time in. And once its done, its done. It will survive wheel removal and reattachment just fine.

Front Caliper

Aligning the front caliper is the same process as aligning the back. Only one additional observation is necessary that applies to both wheels: given the low torque on the caliper used here, you could be forgiven for coating the threads with Vibra Tite gel (NOT Loc-Tite). I use it if a tube of the stuff is within reach. Otherwise not. So its not something you have to do, but it can’t hurt, right? Don’t lose any sleep if you forget to use the stuff.

Route The Brake Hoses

This is effectively the identical process that was described in Day 2 when we routed the shifter cable. Once again the exact process varies greatly by bike, and you’ve already seen how I am going about it on the Day 2 build. So we won’t re-cover the same ground. Below in Figure 5 is a pic showing the anchor points for both brake hoses. Numbers 1 through 3 are identical to the shifter cable that is on the other side. #4 is a simple zip tie wrapped and anchored by crossing the V-brake post. Modern front forks will have some sort of dedicated, manufactured anchor point at roughly the same spot.

Be sure you leave enough slack in the front so there is adequate room to turn the handlebars to their fullest extent without any tugging on the brake hoses. Need an example? Look at another finished bike 😀 . The hoses need to be long but not too long.

The picture below shows the temporary brake routing I used in the first few weeks as initially I did not shorten the brake hoses.

NOTE:
When routing the hoses, they will be longer than necessary. Route them so the excess hose is sticking out in front of the bike. From the caliper forward/upward to the handlebars, the hoses should be tied down as you expect them to stay.

Shorten The Brake Hoses

This is luckily one of those times when a video is the best tutorial, and we have a great one here. Again this is tailored to Magura brakes, but the principles hold across all brake marques. Its only 3 1/2 minutes long so watch it now:

Here’s what I do differently: I use a different hose cutter as shown in the tool list. I also would put on the cable molding cover, nut and olive BEFORE I stuff on the metal hose barb. The reason for this is when you put the barb in, it often spreads the housing of the cable just enough to make it impossible to thread those fittings over the now-finished hose end. So just put them all on before pushing the end barb in.

Additionally, I use the specialty tool (brake hose needle driver) that carefully drives the end pin into the hose. Its a lot easier than hammering in the pin. Video 2 makes this process look easy as pie and it is seldom that. If you don’t want to spend the $26 for a specialty tool, yes you will get the job done by using the method shown in the video. For me, I never want to fight with a hose barb again and I’m glad I sprang for the needle driver.

Bleed The Lines

Once you have cut down the hoses, you have air in the hydraulic lines, which is very bad. You have to bleed the brake lines to get the air out. Here are two videos that show ‘the long way’. This is how you should do it at least the first time after cutting the hoses down. I am also showing you Video 3, which is much less messy than the ‘official’ instructions in Video 2. It is worth mentioning that the instructor in Video 3 is a Magura tech specialist. So its not like he is breaking any rules.

The only issue with this next method is you have to remove the caliper, which means you have to realign it per the procedure above.

And now for the short way. Use this method for a touch-up bleed down the road. You can probably get 90% of the efficacy received from a full bleed by doing it this way, which is much simpler and does not involve disconnecting brake lines and spilling fluid. Its also faster.

Note also that when I do ‘the long way’ I just use a syringe stuffed into the reservoir hole like is done below and do not bother with the expensive bleed bottle that is used in Videos 2 and 3 above. I use just a syringe with a hose and screw-on tip, a syringe reservoir and a bottle of fluid. No need for any fancy bleed kit.

Handlebars!

Its time to start getting the handlebars set up in their final format. Now that the brakes are on, we’ve pretty much got a working bicycle here and all thats left is some tidying up. The only thing we aren’t going to do is put the grips on, and thats because the grips I put on often have to be cut off. So I want to wait until the last second to take that final step. Everything else should be put in its final position.

Brake Levers

These are what you position first. Nothing is more important than being able to easily reach your brakes without having to work at it. So having them set up right is Priority #1. They go closest to the grips. Always. And everything is fit around them. You don’t move your brakes to a sub-optimal position to make up for anything else. It is done the other way around.

Shifter

The next most important item on the bars is the shifter. Here again, you must have unrestricted accessibility. You also don’t want to have to change your grip to use it, so the shifter should be directly up against the brake lever. On an ebike, typically you have only a right-side shifter (for the rear cluster).

Throttle

If there’s a shifter taking up the space adjacent to the brake lever on the right side, that leaves the left side for the throttle. I am assuming a thumb throttle here and will not get into the nuances of a grip or half-grip throttle as I never use them, so I don’t have much to say for them or about them.

One nuance of a thumb throttle that is often overlooked is ‘clocking’ the lever. You want to position the lever so when it is fully engaged, the tip of your thumb is comfortably holding the handlebars, and preferably the paddle is fully extended straight down. The reason for this? When you hit a pothole or similar road imperfection, if you are putting any sort of weight or grip on that fully depressed throttle paddle, your hand/thumb will bounce down thanks to gravity and inertia… and can snap that paddle clean off as a result.

If you clock the throttle so it is pointing down when fully engaged, then your body’s reaction to a terrain impact will just cause your thumb to slip off. The throttle snaps back to zero input. Maybe a bit annoying to have to re-engage, but nothing is broken. Maybe for you straight down is too much. Experiment with it to find out what works for your preferred grip on the bars, while keeping this fail-safe technique in mind.

Once that is done, this is what the bike looks like now.

Whats with the handlebar bag?

Well, in addition to being a handy way to store wallet, phone and keys, it also hides any excess wiring that I can’t easily get rid of. In this case, even though the wiring harness I am using is a little shorter than normal, it is still probably an extra foot longer than it needs to be. That slack has to get taken up somewhere. Likewise, there are wires connecting to the left brake, the right brake, the display and the throttle. In addition to the usual shifter plus right and left brake hoses. Thats a lotta wires.

I have found a handlebar bag – especially this particular molle deployment bag I am using here – is great at hiding that rats’ nest in addition to being a convenient dump pouch for what is usually in my pockets. The molle loops on the bag are perfect for running excess wire so it is literally integrated into the bag’s surface. In these early build pictures, I am using a leftover brown bag I had in my parts pile. A black bag hides black wires running along its surface much more effectively, and I switched to one later on for that reason.

Test Ride Time

Go on. You’ve earned it. Go for a ride. If you’ve done your job as described here, its ready. Sure, the grips aren’t on yet, but you can hop on and ride around the neighborhood. Start out slow. Engage the pedal assist. Give it some throttle. Figure out how it handles, keep things mellow. Oh, and wear gloves and a helmet. Some of my worst mishaps occurred on test rides that were supposed to be a 5 mph toodle around the neighborhood cul-de-sac and ended up with a faceplant. Right now you are a test pilot. Dress like one. At least a little.

Tailor The Motor Settings

This procedure will vary depending on your chosen motor. For this project, we are using a BBSHD and I have that platform down pat. I know exactly what settings I want and I have a tool to change those settings that I can plug right in.

Here’s the process I use. Once you’ve read thru this article, follow on to the sequel linked at its page top. I plugged in the Version 2 screens in that second article on this bike in a couple of minutes (shown below). These are the most neutered pedal assist settings I have in my toolbag. The gentlest stuff you can find while still retaining the ability to lay on full motor power with the throttle if its ever needed. Look to the linked articles for sterner stuff.

Clean Up The Wiring

OK so you were having fun riding your new bike around. Unfortunately there’s a bit more drudgery to get through. You need to finalize the battery wiring … at least you do on this bike because everything is out in the open. So we need to do something short, strong, neat and tidy that is also color matched so it doesn’t stick out.

Figure 6: The finalized exterior wiring. Bottom wire is AC Power to the motor. Top wire is battery charger input.

Here’s what we are looking at in Figure 6 above. First: the power lead that sends battery power to the motor. A BBSHD comes with two fairly long (roughly 35cm), separate black and red 12-gauge wires, each terminated in an Anderson Powerpole connector. While Anderson connectors are adequate, they are susceptible to water and far from your best choice, which is generally considered to be a water-resistant, spark-resistant XT90S.

It so happens the wireless Luna Wolf pack I am using also has a female XT90S built into itself, so the decision to use the more capable male XT90 is made for us by the battery.

The job was to measure thrice and cut once. I had to shorten the power cables running out of the motor just right so a similarly shortened 10-gauge XT90 pigtail could wrap around the frame at just the right length to be snug, yet removable without being so tight it would break something.

Remember:
The tutorial on making safe, reliable crimp connections is here and gives you complete details, tools and instructions on doing this exact sort of work.

Since this power cable is in the worst possible place for collecting grit, grime and water, I went overboard on the protection for the connection. I used 3:1 marine adhesive butt-end connectors and surrounded the connection area with thick marine 3:1 adhesive heat shrink. This effectively waterproofed and armor plated the connection. I topped it off with a hand-wrapped spiral of frame-matching red silicone tape to lower the visibility of the thick wire. This also adds more protection and waterproofing. If I could have found a reasonable way to use the same red PEX or PVC tubing to further armor the connection I would have done that too. But as it sits, if something gets through all that its probably going to destroy the bike, too.

The battery cable was made almost the same way. Two short 12 gauge male and female XT60 pigtails were crimped together with marine heat shrink butt end connectors to make a short extension cable. No 3:1 heat shrink this time as I need this cord to be flexible. The loose end that will be attached to the battery charger is tucked into the velcro strap that is helping to lock down the pack onto the frame. What you can’t see in Figure 6 is the open female end of the extension cord is further covered with a waterproof cap made to fit the XT60 like these (also widely available on Ebay). I finished the job with a matching, protective wrap of red silicone tape.

Put The Grips On

My chosen silicone grips are 50/50 in terms of being removable. Half the time they have to be cut off, so they only go on at the last possible moment. That moment is now. We’ve got everything installed, laid out, positioned and generally nitpicked so we can put the grips on without worrying we have to take something back off. Further, we purchased as many parts as possible that use clamshell type attachment (the one exception is the throttle) so those items can be removed without also having to remove the grips.

For silicone grips like those I am using (Wolf Tooth Fat Paw), I have found some drug store denatured alcohol inside and on the grip is the way to go. Here is a video that shows removal and installation of a variety of grip types using various methods, including the use of alcohol.

My chosen end caps are the compression-plug type that screw on and off. Also, if you look at the final pics you will see I am using bar end extensions for some grip variety and a bit of added certainty my hands won’t come off the bars in extreme circumstances. When setting up placement of my shifter, throttle, brakes and grips I took into account the extra 1.5cm or so I would need to fit these extensions onto my 760mm handlebars. In fact, I chose bars a little wider than I like because I knew I would have these ends on, which effectively shorten the bars by placing the grips a bit further in.

Figure 7: The handlebars. Note the little lever hiding in between the throttle and brake lever in the left photo. We’ll get to what that is in the next ‘Perfecting’ post.

And we’re done. Holy crap. We’re done! We did it. We made a bike.

Epilogue

(link coming soon to “Perfecting”)