MAC motor hub not engaging

ymd · Jan 21, 2019

My (MAC) hub motor suddenly stopped engaging with the bike gear sprocket. The motor runs with throttle and sometimes the gear sprocket engages with the hub when I can pedal power the bike. Otherwise, when I pedal, the gear sprocket does not engage at all. I used the throttle mostly and used pedal whenever it engaged to get home. After I got home, I removed the rear wheel and checked the gear sprocket. I can spin the sprocket both froward and backward without engaging the motor hub.

Before I open up the motor cover, I wanted to get opinions of someone who might have experienced this and guidance on how to fix this problem.

Could someone please help me? Thank you very much in advance.

amberwolf · Jan 21, 2019

Unless it is a cassette version, then there's no need to open up the motor. The bike-chain sprocket cluster is just a separate thread-on freewheel, which may be available at your local bike shop (along with the removal tool). If not, you can order them online from various places (I know http://ebikes.ca carries an ebike-specific version of the removal tool with larger axle hole for hubmotors).

If it is a cassette version of the hubmotor, you may need a new cover (if it contains the cassette hub parts).

It's also possible the pawls are not actually broken, and that the grease in it has just congealed and stuck the pawls down. In that case cleaning it with a degreaser (citrus solvent works well) and then reoiling it may fix it, without even opening it up.

ymd · Jan 22, 2019

Thank you for your advice. The sprocket is a screw type and not cassette version. I think I have the removal tool. I will remove the sprocket and see if the pawls are broken. If they are, I can order a replacement online.

Thank you for saving me the effort of opening the motor itself. I will let you know how it goes.

amberwolf said:
Unless it is a cassette version, then there's no need to open up the motor. The bike-chain sprocket cluster is just a separate thread-on freewheel, which may be available at your local bike shop (along with the removal tool). If not, you can order them online from various places (I know http://ebikes.ca carries an ebike-specific version of the removal tool with larger axle hole for hubmotors).

If it is a cassette version of the hubmotor, you may need a new cover (if it contains the cassette hub parts).

It's also possible the pawls are not actually broken, and that the grease in it has just congealed and stuck the pawls down. In that case cleaning it with a degreaser (citrus solvent works well) and then reoiling it may fix it, without even opening it up.

markz · Jan 22, 2019

ymd said:
Thank you for your advice. The sprocket is a screw type and not cassette version. I think I have the removal tool. I will remove the sprocket and see if the pawls are broken. If they are, I can order a replacement online.

Thank you for saving me the effort of opening the motor itself. I will let you know how it goes.

Freewheels screw in, removal tool needs to have hole in the middle widened. You can of course purchase one from
https://www.ebikes.ca/shop/electric-bicycle-parts/repair-tools/fwtool.html

Comes in handy!

Freewheels are plentiful and cheap, if the gears look worn and you pedal, some dont pedal, then just buy a new one. I havent pedaled in close to a year, just recently have I installed a chain. Ideally instead of single speed, I'd only need 3 speeds! Just to help out getting going from a standstill and the hills.

ymd · Jan 22, 2019

I tried to remove the sprocket with the removal tool. I tried very hard but it looks like the threads are completely stuck as I could not even budge it try as I may. Is there a way to loosen it up to remove it? Will soaking the inside of the sprocket where I insert the removal tool with degreaser work?

I want to make sure I am not doing anything wrong. I simply inserted the removal tool so that it sits flush inside the sprocket with the hub rod going through it. I used a crescent wrench to turn the tool left to loosen. But it does not budge even when I used as much force as I could apply. Am I doing something wrong?

amberwolf · Jan 22, 2019

If you have any PB Blaster, the catalyst portion, you can try getting some behind the freewheel (inboard side) so it gets down into the threads, and from the front of the freewheel (outboard side), but it may not do anything. May take more than a day to penetrate, depending on fit of threads.

Before you try to take it off, you might just try using the catalyst spray down into the actual freewheel body, let it soak, then spin the freewheel. If the clicking had stopped happening before then pawls were stuck down. When the clicking starts after spraying it it means they re now unstuck. If they don't unstick at first, you can keep spraying while spinning and it may clean out gunk in there, eventually letting it unstick. It's gonna get messy, so you probably wanna wrap a towel or something you don't want to keep around the motor, leaving just the freewheel out of it.

If you do have to replace the freewheel, this is how I get them off:

Tie the wheel down (by it's tire and rim) to the legs of a heavy sturdy table, or a building post, etc., vertically, so it is in the same kind of position it would be on the bike. I use crank-down cargo straps.

Use a box-end wrench (nonadjustable, or you may break it) with as long an arm as you can.

Put a large flat washer on the axle, just outboard of the wrench and tool face.

Put the axle nut on, but not tightly, just a mm or so away from the washer.

The above will help keep the wrench from coming off in the next steps.

Put the wrench on at about a 10--oclock angle.

Take a hammer, and strike the wrench's far end in a downward motion.

It may take multiple strikes, and you may have to readjust the wrench if it works loose.

Sheldon Brown may have other tips on his site.

aroundqube · Jan 22, 2019

Place the removal tool in a vice , splines up. Lower the wheel with freewheel attached onto the removal tool. Turn the wheel to unscrew the freewheel.

dogman dan · Jan 23, 2019

Interesting trick. Personally I have bent the crap out of removal tools trying to break a well stuck freewheel. I have a crescent wrench big enough to do the job.

Maybe the vice would help prevent the tool deformation. 8)

ymd · Jan 23, 2019

Looks like a great idea! I have a vice and will try it tonight and let you know.

aroundqube said:
Place the removal tool in a vice , splines up. Lower the wheel with freewheel attached onto the removal tool. Turn the wheel to unscrew the freewheel.

ymd · Jan 23, 2019

Can I use WD40 lubricant which I have instead of PB Blaster? Otherwise I will pick one up from the hardware store. If this can unstick the flywheel it would be great. Thank you very much for all your help.

amberwolf said:
If you have any PB Blaster, the catalyst portion, you can try getting some behind the freewheel (inboard side) so it gets down into the threads, and from the front of the freewheel (outboard side), but it may not do anything. May take more than a day to penetrate, depending on fit of threads.

Before you try to take it off, you might just try using the catalyst spray down into the actual freewheel body, let it soak, then spin the freewheel. If the clicking had stopped happening before then pawls were stuck down. When the clicking starts after spraying it it means they re now unstuck. If they don't unstick at first, you can keep spraying while spinning and it may clean out gunk in there, eventually letting it unstick. It's gonna get messy, so you probably wanna wrap a towel or something you don't want to keep around the motor, leaving just the freewheel out of it.

If you do have to replace the freewheel, this is how I get them off:

Tie the wheel down (by it's tire and rim) to the legs of a heavy sturdy table, or a building post, etc., vertically, so it is in the same kind of position it would be on the bike. I use crank-down cargo straps.

Use a box-end wrench (nonadjustable, or you may break it) with as long an arm as you can.

Put a large flat washer on the axle, just outboard of the wrench and tool face.

Put the axle nut on, but not tightly, just a mm or so away from the washer.

The above will help keep the wrench from coming off in the next steps.

Put the wrench on at about a 10--oclock angle.

Take a hammer, and strike the wrench's far end in a downward motion.

It may take multiple strikes, and you may have to readjust the wrench if it works loose.

Sheldon Brown may have other tips on his site.

amberwolf · Jan 23, 2019

WD40 sometimes works, but the PB Blaster stuff that comes as two separate cans works better on stuff that's actually rusted stuck, so it depends on waht's wrong. PB Blaster's lubricant is basically like WD40; thin, evaporative, etc. THe catalyst is just for loosening stuff.

I don't use much of any of these things as actual lubricants, cuz they kinda suck at that, but sometimes they help with really really stuck stuff, and I disassemble a fair bit of "junk" that's old and rusty for pieces and parts I can use for projects, now and then.

Personally, I don't htink you'll need any fo the lubricants/etc, and iether hte axle-flat-in-vise trick or the tied-down-wheel-whack-wrench-with-hammer trick will work.

ymd · Jan 28, 2019

Over the weekend I was able to unscrew the freewheel using the vice. I soaked it overnight in degreaser solution and cleaned it. I found that the clicking came back. But, sometimes it is still gets unstuck, especially when the sprocket is tilted. I have now put it back on my bike. The sprocket worked well for a good part of my 18 mile ride, but got unstuck now and then when I had to use the throttle. Is there anything else I can do to try and fix it?

I have placed an order for a 11-30 DNP freewheel. If I can fix the one I have now, I can have a backup.

Thanks for all the help!

Chalo · Jan 28, 2019

Freewheels are cheap, and one that has misbehaved in the past is more than likely damaged internally and prone to further skipping. When you describe your freewheel as "tilted", I imagine that it is partially unscrewed or otherwise broken. Properly functioning freewheels don't tilt or exhibit more than a tiny bit of side play.

MAC motor hub not engaging

ymd

100 mW

amberwolf

Administrator

ymd

100 mW

markz

100 TW

ymd

100 mW

amberwolf

Administrator

aroundqube

10 kW

dogman dan

1 PW

ymd

100 mW

ymd

100 mW

amberwolf

Administrator

ymd

100 mW

Chalo

100 TW

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