GMAC 10T replacing wheel bearings (How many, what type, what size?) Please help. Thanks.

[Pandro]

I've been the happy owner of a GMAC 10T motor for the past 19.231 km of electric cycling, but now, all of a sudden, since my last ride there's a clearly audible grinding noise and a relatively loud tick once for every revolution of the wheel.
Feels like there's resistance at some point in each full cycle of the wheel. Can't be good. Definitely not riding this thing any more.

I'm not sure, but, I think that the bearings in the motor have given out.
Does anyone know how many bearings are inside the GMAC 10T, and, exactly what kind and size?

Any help, specs, model numbers, size specifications, links to any place or shop I could source them... or other insights would be greatly appreciated!
Thank you!

[RunForTheHills]

Have you contacted Grin? They sell bearings for many of their motors.

[Pandro]

I will send Grin an e-mail.

I had hoped not to have to bother them with something as small as this -- I expected someone to have this exact knowledge already.

Thanks for your reply though.

(Should anyone come along who has this information, please do still post. Thanks. - I'll update this thread should I get a definitive answer from Grin)

[Pandro]

Turns out it wasn't any of the bearings, it's the planetary gears that are ruined.

One is missing three teeth (could only find two teeth stuck in the motor windings), and another gear is completely ruined including it's bearing.


Quite disappointing to see this happen after only 19231km (11949mi). Original question remains; Please point me at replacement parts

[RunForTheHills]

EM3EV used to sell replacement gears for the MAC motor, but they are showing out of stock on their website right now. I am not sure why you are reluctant to contact Grin since they are the designer/seller of the GMAC motor, they are the obvious source of parts for it. I am pretty sure the gears are the same as a standard MAC motor, but some parts are different. When I bought mine, I inquired about installing a clutch from a standard MAC motor and Justin replied that it was possible, but the key size was larger and would need to be filed. Or maybe it was the key slot that needed to be filed. I can't remember.

[markz]

http://lyen.com/

[Pandro]

EM3EV used to sell replacement gears for the MAC motor, but they are showing out of stock on their website right now. I am not sure why you are reluctant to contact Grin since they are the designer/seller of the GMAC motor, they are the obvious source of parts for it. I am pretty sure the gears are the same as a standard MAC motor, but some parts are different. When I bought mine, I inquired about installing a clutch from a standard MAC motor and Justin replied that it was possible, but the key size was larger and would need to be filed. Or maybe it was the key slot that needed to be filed. I can't remember.

Thanks for your response. I most certainly will contact them about this - it's just that while I thought the bearings had failed, I would rather get some replacements from within the european union to save on shipping and import fees. Now that it's about the planetary gears, my reasoning is that they simply do not list any gears for mac motors in their webshop.

I certainly will contact them.
It's just that I wanted to broaden my scope, perhaps someone would have had something to add. For instance, stubborn kind of person I am, I have been spending the past couple of hours thinking of possibly replacing the gears with metal gears to prevent this in the future. Mostly because I use this motor to haul my fat behind up mile-high mountains in Switzerland and Liechtenstein.




Aparently I just got the kind of advice I was looking for;
@markz; Thank you! I see some hardened steel gears on that list. *Exactly* what I was thinking about. Great help.

[Pandro]

When I bought mine, I inquired about installing a clutch from a standard MAC motor and Justin replied that it was possible, but the key size was larger and would need to be filed. Or maybe it was the key slot that needed to be filed. I can't remember.

May I ask, why you would want to do such a thing? Wouldn't that have removed the regenerative braking functionality from your motor? Or, am I completely mistaken here? Am I right thinking you chose not to do that?

[RunForTheHills]

May I ask, why you would want to do such a thing? Wouldn't that have removed the regenerative braking functionality from your motor? Or, am I completely mistaken here? Am I right thinking you chose not to do that?

I don't need the regenerative braking. However, I really liked the idea of an integrated torque arm and the 10mm axle so I wouldn't have to file my dropouts. I ride for fun and exercise and wanted less drag when pedaling without the motor. When I asked about installing a clutch, Justin offered to sell me one of the prototype motors that already had a clutch. So I didn't have to do the modification.

[bombadero]

I'm not sure if I'm missing something in this thread, but had a similar issue recently with hard braking where the rear wheel locked up into a skid. It seems to have sheared some teeth because the wheel was locked up but the motor was still applying torque. I have not opened up and verified yet, but Grin says this is the likely explanation for the loud noise now emanating from the motor, and is shipping me some new planetary gears. However, one of my first thoughts was finding a way to replace them with hardened steel gears, although I'm not sure if that would damage the ring gear on the outside in a similar situation. I see that mentioned here, but don't see any links to where they might be obtained. Does anyone here know how I might obtain such a thing? Would it be relatively affordable to have a machine shop fabricate something like that? Is there a third party option available? Googling is not yielding anything. I could theoretically fabricate them myself, but the mills, lathes or CNC machines required are too big and expensive for my small garage and our household income.

[amberwolf]

However, one of my first thoughts was finding a way to replace them with hardened steel gears, although I'm not sure if that would damage the ring gear on the outside in a similar situation.

Probably not the ring, but the sun, which has far fewer teeth to engage the planets and spread the load.

The motor will likely be much louder with all-metal gearing, depending on the specific sun/planet/ring gear design / tooth type.

They may all wear faster, as well. The plastic planets are the "sacrificial" wear item normally; if you make them harder then they will cause more wear than the plastic ones, and if they are harder than the sun / ring they will wear those out faster than they themselves wear out. Since the sun and ring are not easy to replace, compared to the planets, it means the motor will be less easily repairable for that type of issue.


Grin may have tested this scenario, so you could ask them, just in case.

[Triketech]

I'm not sure if I'm missing something in this thread, but had a similar issue recently with hard braking where the rear wheel locked up into a skid. It seems to have sheared some teeth because the wheel was locked up but the motor was still applying torque.

I've been playing with MAC's for about 7 years now and just noticed this thread.

The OP pointed out he had 11,000 miles; planetary bearings (think 55,000 miles @ 5:1) had plenty of wobble with teeth sheared at the roots. And its a GMAC. Teeth shearing near the roots comes from fatigue which is bi-directional on the GMAC compared to the MAC.

Bi-directional defeats the cold flow mechanism in the plastic gear and heavy shocks will initiate the inevitable microcracks in both directions. FWIW, I didn't notice any signs of overheating.

Gear shock is amplified every time the tire loses grip allowing it to spin up than slow back down when it hits the pavement. Even a 1/2" bit of air briefly underneath the tire causes a rebound shock to the teeth.

Mine has over 5000 miles and looks like it has another 5000 left. I bought clutch/gear spares when I bought one of my MAC kits and will wait for the day mine needs it.

I've dealt direct with MAC Motor but its been a few years. You should be able to order direct depending on payment methods.

http://www.macmotortech.com/

I also have a 3000 mile MAC 12T motor on a 26" rim with 12 FET Infineon for sale.

[bombadero]

So having torn my motor down, my assumption about sheared gears was incorrect, and my issue has now entered the realm of mystery, which seems to happen to me a lot. I've had issues with torque sensors and CA3's that have never been fully resolved. With my GMAC, I had to perform rapid braking from about 25 MPH at a light. Subsequently, the motor made a periodic kerchunk noise.

I have completely removed and unlaced the wheel and torn the motor down, twice to inspect it. There are no scraping marks inside the housing, no debris, all teeth on ring/sun/planets are inctact, bearings look good. I put it that way in a truing stand, no noise. Put it back in the housing on the truing stand, turning by hand, there is a noise. I put it on the bike without disc rotor/caliper/ cassette with the bike hoisted, applied throttle, and it makes a horrible grinding noise. Grin has not been very helpful so far, instructing me to use eyes and ears; the only problem is, to identify the issue I need X-ray vision to peer through the motor housing while it is running, as the noise only occurs during operation and I have removed and eliminated all possible external causes.

Google Photos link attached to a video of the motor under operation stripped of all other wheel components:

https://photos.app.goo.gl/Ln9CmqXFtnWG1T3K8

I'm relieved the motor appears to be intact internally, but mystified as to the cause. The only things I can think to try are running it bolted into a truing stand while attached to the bike and removing the planet gear carrier to see if I can see anything new; I had to order a new gear puller from Grin, as the tips of the claws on my exisiting gear puller are too fat to get under it. Grin doesn't want to do an RMA atm.

[amberwolf]

From the description, the more load there is on the motor, the worse the problem becomes.

The linked video sound appears to be synced with either the motor casing or the freehub. It doesn't seem to be at the 4-5x faster rate that things would be if it was a motor issue.

What happens if you run it without the side cover on so the internals are still visible (and more audible)? Being a geared hub this should still work in the unloaded situation like this (I did it to get a video of a Fusin geared hub in operation some years back
https://www.youtube.com/watch?v=REsMbCNwbEY ).

If the noise stops, it is likely something wrong in whatever is attached to the sidecover (like the bearing).

If it continues, it's something with whatever is still present.

If it doesn't happen with the main housing off (the part with the ring gear) it could be the bearing in the housing, or it could be something in the planetaries or carrier that doesn't show up without it becuase they're not being used to transfer motion to the ring gear.

A housing/cover bearing problem should show up whether the motor is running or not, simply by hand turning it: If you hear or feel the problem, at the same rate as the housing rotation it's possibly something in the housing or it's bearings.

A housing problem could be the keyway holding the ring gear to the housing, where the key itself has "ridden up" onto the housing, or "ramped" the housing's keyway (which is softer than the key or ring gear) enough to allow a sufficient load on the system to pull the ring gear vs the housing so the ring gear "bumps up" a tiny bit at that point, and puts pressure on the planetaries, so each time a planetary passes that spot it makes the noise.

It could also still be in the planetaries or carrier, a bearing problem, for instance (cracked race, etc).

If it is 4-5x the rate of the housing rotation, it's probably in the motor itself, or the sun gear (on the axle) to the planetaries, etc.

Since the problem was caused by a sudden reverse loading on the system (assuming it was regen brakng used to do the sudden stopping--if that's not the case then the loading would have been on the housing and rotor bolt area assuming rear brakes were used to do the stopping--if neither then there should be no unusual loading and no damage), the most likely point of failure is in the gearing system, something that has caused a misalignment of the parts.

You've noted there is no tooth failure in any gearing, but could there be a hairline crack in a plastic gear such taht under loading it slightly spreads out and causes such a misalignment?

So having torn my motor down, my assumption about sheared gears was incorrect, and my issue has now entered the realm of mystery, which seems to happen to me a lot. I've had issues with torque sensors and CA3's that have never been fully resolved. With my GMAC, I had to perform rapid braking from about 25 MPH at a light. Subsequently, the motor made a periodic kerchunk noise.

I have completely removed and unlaced the wheel and torn the motor down, twice to inspect it. There are no scraping marks inside the housing, no debris, all teeth on ring/sun/planets are inctact, bearings look good. I put it that way in a truing stand, no noise. Put it back in the housing on the truing stand, turning by hand, there is a noise. I put it on the bike without disc rotor/caliper/ cassette with the bike hoisted, applied throttle, and it makes a horrible grinding noise. Grin has not been very helpful so far, instructing me to use eyes and ears; the only problem is, to identify the issue I need X-ray vision to peer through the motor housing while it is running, as the noise only occurs during operation and I have removed and eliminated all possible external causes.

Google Photos link attached to a video of the motor under operation stripped of all other wheel components:

https://photos.app.goo.gl/Ln9CmqXFtnWG1T3K8

I'm relieved the motor appears to be intact internally, but mystified as to the cause. The only things I can think to try are running it bolted into a truing stand while attached to the bike and removing the planet gear carrier to see if I can see anything new; I had to order a new gear puller from Grin, as the tips of the claws on my exisiting gear puller are too fat to get under it. Grin doesn't want to do an RMA atm.

[onitubai]

If the kerchunk noise only happens during regen, that can be electromagnetic crosstalk in the motor harness. It seems to vary from person to person, but if your CA3 returns a garbage max speed sometimes, your signal wires are reporting electrical noise from the unshielded, parallel phase wires in the GMAC motor harness. The signal wires in the harness are shielded, but not by much, and not after the wires enter the motor.

I often get a startlingly loud kerchunk during regen. It's because the phase wires feedback into the thermistor signal, which gets interpreted as the motor temp instantly jumping by hundreds of degrees. The temp shutoff is so violently sudden that the rebound from regen torque hammers the motor, spokes, and frame hard enough to cause that loud kerchunk noise. I've had some luck rearranging and modifying wiring to fix other crosstalk problems that turned out to be going through the frame, but this one appears to be in the harness or motor itself.

[amberwolf]

The clunking noise in the linked video is during motor acceleration, running, and coastdown, with just the bare complete motor (no wheel or cassette) in the bike dropouts.

I don't know if any other noises Bombadero gets in other modes of operation are different.

If the kerchunk noise only happens during regen, that can be electromagnetic crosstalk in the motor harness. It seems to vary from person to person, but if your CA3 returns a garbage max speed sometimes, your signal wires are reporting electrical noise from the unshielded, parallel phase wires in the GMAC motor harness. The signal wires in the harness are shielded, but not by much, and not after the wires enter the motor.

I often get a startlingly loud kerchunk during regen. It's because the phase wires feedback into the thermistor signal, which gets interpreted as the motor temp instantly jumping by hundreds of degrees. The temp shutoff is so violently sudden that the rebound from regen torque hammers the motor, spokes, and frame hard enough to cause that loud kerchunk noise. I've had some luck rearranging and modifying wiring to fix other crosstalk problems that turned out to be going through the frame, but this one appears to be in the harness or motor itself.