Is my GMAC supposed to sound like this?

davelien

New Member
Region
USA
I've installed a GMAC motor/sub/wheel assembly on my Juiced CCX. It's part of the upgrade kit available from hilleater.ca. https://hilleater.ca/grin-tech-gmac-upgrade-kit-for-the-juiced-crosscurrent-s-x/

The motor has a ton of power, it's quite an upgrade from the stock Juiced motor. The one problem I have is that is makes a noise that I just can't understand. It makes a once-per-revolution sound, whether the power is on or not. The only time it doesn't make the sound is under full power.

I can't imagine this noise what other GMACs sound like. If you have a GMAC I'd love to hear your thoughts. Even if you don't have the same motor, have you heard a similar noise?

Video clips with the noise

Thanks all.
 

JES2020

Well-Known Member
I've installed a GMAC motor/sub/wheel assembly on my Juiced CCX. It's part of the upgrade kit available from hilleater.ca. https://hilleater.ca/grin-tech-gmac-upgrade-kit-for-the-juiced-crosscurrent-s-x/

The motor has a ton of power, it's quite an upgrade from the stock Juiced motor. The one problem I have is that is makes a noise that I just can't understand. It makes a once-per-revolution sound, whether the power is on or not. The only time it doesn't make the sound is under full power.

I can't imagine this noise what other GMACs sound like. If you have a GMAC I'd love to hear your thoughts. Even if you don't have the same motor, have you heard a similar noise?

Video clips with the noise

Thanks all.
That does not sound natural. Pretty sure you have something rubbing. Try locating the sound. Make sure your pads are not rubbing, it sounds external of the motor to me.
 

davelien

New Member
Region
USA
I agree that it does sound like something is rubbing. But, the noise is the same even with the brake caliper removed from the bike. I've also done a careful inspection to verify that there is nothing rubbing against the tire or wheel. The noise appears to be coming from within the hub. For what it is worth, GRIN says that the hub/motor 'sounds normal'.
 

JES2020

Well-Known Member
I agree that it does sound like something is rubbing. But, the noise is the same even with the brake caliper removed from the bike. I've also done a careful inspection to verify that there is nothing rubbing against the tire or wheel. The noise appears to be coming from within the hub. For what it is worth, GRIN says that the hub/motor 'sounds normal'.
I would get a second opinion from Grin. Or ask them to send you a sound bite that confirms that is normal sounding.
Personally I cant imagine why a IGH motor would normally sound like that. But as a last resort you could check the lubrication in the motor gears, however, the frequency just doesn't sound like it's internal.
 

tomjasz

Well-Known Member
I agree that it does sound like something is rubbing. But, the noise is the same even with the brake caliper removed from the bike. I've also done a careful inspection to verify that there is nothing rubbing against the tire or wheel. The noise appears to be coming from within the hub. For what it is worth, GRIN says that the hub/motor 'sounds normal'.
Poke @linklemming he has a GMAC.
 

davelien

New Member
Region
USA
Share the actual quote from Grin?
Who at Grin responded?
What does Hilleater say?
I've been working with Peter F. at Grin, via email. He says:

"Indeed Gmac freehub bearings are known weakness, but this sounds different. A bad freehub bearing begins as a ticking, most often and erratic cadence multiple times per rev, and worsens until the bearing fails entirely and becomes a crunchy bearing noise.

This sounds like a pulsing, once per rev. This could be gear noise, but that shouldn't track wheel rpm. I hate to suggest things I'm sure you've already checked already, but my first thought is a tire rubbing on a fender, or some other tire clearance.

If there's no external cause, my usual approach is to encourage folk to run the hub for a time, to see if the noise lessens or worsens. Opening a gmac to inspect the gears is reasonably easy, reinstalling the motor is the worst of it. They are very lightly greased at the factory, a liberal application of a PAO grease like molykote can cut down on the noise, but will increase rolling resistance."

Also:

"It's hard to speak confidently from a video, but what i hear sounds normal for a Gmac. Perhaps this is because I am hearing the motor powered, and you describe the worst of the noise occurs when the motor is rolling unpowered.

I can dispatch a set of replacement gears which you can install and grease. Or if you prefer you can ship the motor here and I will compare the noise to other gmacs."

David at Hilleater has been very good to work with, but I've decided to work directly with Grin on this issue since it is definitely not something that he (Hilleater) can resolve.
 

davelien

New Member
Region
USA
Agreed, there seems to be a lot of wobble even the frame is moving from side to side!
Yep. And this is after I sent the entire assembly (motor, hub, wheel) back to Grin for truing. The original was even further out of true believe it or not. Per Peter F., "Yep i see some runout in the motor case. Above average perhaps, but nothing that would give me concern if i saw it here- provided the sideplate bearings are solid and there is to 'play' in the motor case."

I sent it back to Grin at my expense ($120) and it came back better, but still not as true as I would expect a brand new wheel assembled by the manufacturer (Grin).

I have asked Peter for a second opinion but have not heard back from anyone else at Grin. I guess I will try again.
 

davelien

New Member
Region
USA
Yep. And this is after I sent the entire assembly (motor, hub, wheel) back to Grin for truing. The original was even further out of true believe it or not. Per Peter F., "Yep i see some runout in the motor case. Above average perhaps, but nothing that would give me concern if i saw it here- provided the sideplate bearings are solid and there is to 'play' in the motor case."

I sent it back to Grin at my expense ($120) and it came back better, but still not as true as I would expect a brand new wheel assembled by the manufacturer (Grin).

I have asked Peter for a second opinion but have not heard back from anyone else at Grin. I guess I will try again.
But to be fair, the top video in my original post is after Grin re-trued the wheel. It is much better than the bottom video which was taken before re-truing.
 

davelien

New Member
Region
USA
I recorded another short video just now, I think it more clearly demonstrates the noise. Especially off throttle when the RPM is coming down, the same noise no matter what. I reached out to linklemming, my guess is that he will confirm that his Gmac sounds nothing like this. I'll push back on Grin.

 

PedalUma

Well-Known Member
Region
USA
Just putting it out there. Sometimes you need a spacer between the cassette or freewheel and the hub. Could something be in there rubbing? That does not sound right. I am thinking this because it is not on the brake side.
 

tomjasz

Well-Known Member
Just putting it out there. Sometimes you need a spacer between the cassette or freewheel and the hub. Could something be in there rubbing? That does not sound right. I am thinking this because it is not on the brake side.
Man I remember the first time I had that issue. I tore my hair out! That first group of builds threw a bunch of curve balls. Now they’re routine checks.
 

PedalUma

Well-Known Member
Region
USA
@tomjasz, OMG, me too! Just a little spacer, 1/2 mm thick solves the problem.
Totally off topic, I stayed up until midnight making this bike electric. It is a Black Mountain frame, handmade in Point Reyes, California. That is an amazing place to ride. I am taking the gravel bike out right now.
Take a look for two minutes here:
 

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PedalUma

Well-Known Member
Region
USA
You're lucky you didn't end up in Oregon, riding Point Reyes on the San Andreas !
Seriously, when people talk about California falling into the sea, this is what they are talking about. The pirate/privateer Drake discovered it. The San Andreas is also why we have these beautiful hills to ride. 🤣
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tomjasz

Well-Known Member
the gravel bike
NICE, as usual. You know, you're setting a high bar!
My "gravel" bikes were 1971 Schwinn Sports Tourers. Nervar cranks Weinman rims Campy derailleurs, topped by Brooks. Quite narrow tires are slightly deflatted.
It's where I learned to wear gloves and leave the tweezers at home. Gravel riding is all about reading the road, not unlike learning to read the water sailing. For me at least. Alas too crazy for me these days.