Replacing axle on a GMAC

[Bush mechanic]

Whether it is just normal wear and tear or other factors too, the axle threads on my GMAC look pretty awful. I popped the non-drive side cover off while I had it off the bike and had a quick look inside while I was at it, quite impressed actually that there is very little visible wear on the gears, but I could not see any obvious way to remove the axle.

Has anyone replaced a GMAC axle? Just wondering how hard a job it would be. I am guessing Grin would be able to supply one, although I cannot find them listed on the site.

 

[amberwolf]

I didn't get mine quite that far apart, but it looks like there are circlips holding the axle in place at the sungear/stator area. My pics are not very clear unfortunately, but they're over here if they're useful:

The SB Cruiser : Amberwolf's 2WD Heavy Cargo Trike & Dog Carrier

clamping / pinching dropouts both ends, tight and flat to axle both ends both sides, no nuts needed on either side (have one on outside anyway just because there's axle length for it) is hubmotor with solid axles, can't see anything like qr axles or hollow ones? shear was at shoulder of axle...

endless-sphere.com

 

[Bush mechanic]

That's an awesome write up, thank you! I'll wait to hear if i can get an axle and pencil this in as a job to do.

Did you ever find a way to meaningfully reduce the noise of the GMAC? I've got a love-hate relationship with this thing. Fantastic torque for its size but I hate the noise more and more. My overall feeling after 3 years is that the welded clutch /regen mod causes a lot of problems with little meaningful benefit. I'd instantly trade 5-6% regen and replacing my brake pads more often for the ability to freewheel quietly and pedal easily if my battery dies.

 

[amberwolf]

That's an awesome write up, thank you! I'll wait to hear if i can get an axle and pencil this in as a job to do.

Be sure to ask Grin if they have any tips or guides on doing it--I'm sure they've had to at some point for some reason.

Did you ever find a way to meaningfully reduce the noise of the GMAC? I've got a love-hate relationship with this thing. Fantastic torque for its size but I hate the noise more and more.

Packing the whole planetary area full of grease made maybe some tiny amount of difference. Maybe.

Complete grease or oil-fill (no air at all) might make a difference, as it would damp some of the cover / casing vibrations, but it would also cause more direct transfer of all internal vibrations to that case, so while it would change the noise, I don't know if it would quiet it down. Not a test I am likely to do; would be VERY messy either way.

The only way I can see for sure to keep from making so much noise (without major mods to go helical gears or whatever) is to spin it slower. The faster it goes the noisier it gets, and in the small (20"-ish) wheel I've got it in, even under my 20MPH limit it's noisy enough to bother me. So using a larger diameter wheel would help, but that also takes away the torque advantage that smaller wheel has.


Noise is relative...but I like *silence*.


It might be possible to convert to helical gears, but you'd want to add thrust bearings to take up the sideload those create, and that might reduce the width of the gears, depending on how you do that.

My overall feeling after 3 years is that the welded clutch /regen mod causes a lot of problems with little meaningful benefit. I'd instantly trade 5-6% regen and replacing my brake pads more often for the ability to freewheel quietly and pedal easily if my battery dies.

Maybe see if you can get a clutched planetary set from them while you're getting an axle?

I really like the regen not for what it recovers (big enough battery for just about anything I will "ever" do), but for the added braking power on my heavy trike, which still has only front mechanical brake, and only regen for the back wheels (which has to be variable to be useful).

 

[Bush mechanic]

might be possible to convert to helical gears

This would make the ultimate motor! I love the Bafang G310 I have on my daily commuter, it is fairly delicate of course being so small (4th set of gears I think?) but man it is quiet. Sadly I think I am a long way from having the skills to successfully do such a conversion on the GMac though!

I have been wondering whether a replacement set of gears with clutch (Mac or even Ezee perhaps, they look very similar) could simply be dropped in.

 

[RunForTheHills]

Maybe see if you can get a clutched planetary set from them while you're getting an axle?

When the GMAC first came out, I emailed Grin asking if it was possible to install a clutch in the GMAC motor. Justin said it was possible, but the keystock for the planet carrier was larger in the GMAC than the standard MAC so filing or shimming would be required to make it work.