Geared motor making noise when slowing down

[Nirmala]

The geared hub motor on my Magnum Ui5 makes some noise whenever I am slowing down but still pedaling, like when I am starting up a very gradual hill and my speed is dropping as the motor is working. My wife's bike is the same model but does not make this noise.

Most of the time the motor is fairly quiet, but then it will occasionally make this whining noise. Sometimes I can tap the brakes and it stops the motor for a second and then the noise will be gone even after I let the brakes go. Other times the noise starts right back up when I release the brakes.

It has been doing this for quite a while and I have 2,200 miles on the bike already. Any ideas why this is happening? Is it a sign that the motor might fail sooner, or do some motors just make more noise than others?

 

[JohnT]

Diagnosing a sound is very hard on a forum. There could be a number of causes. Here are a few thoughts.

Some motors do just make more noise than others. Then again, a noisy geared motor could mean worn gears. Sometimes, a noise sounds like the motor, but it's actually something else vibrating or rubbing.

If you think it's the motor, I assume the sound changes pitch with the speed of the bike. If not, it's probably not the motor.

If it's worn gears, I would guess it'd make more noise when strained, like going up a hill, as you said, or when starting from a stop. It'd probably be more of a rattle or grind than a whine though.

Non-motor things I'd check... Is the tire rubbing on the fender or frame? Since braking effects the sound, is the brake cable end rubbing or buzzing against something, or is the caliper or disk loose? Make sure various other things are tight, the axle nuts for example.

If your bikes are identical, you could try riding each other's bike to see if the sound stops when your wife rides your bike, or you could try swapping the rear wheel assemblies to see if the sound stays with the bike or with the motor.

Good luck!

 

[Nirmala]

Thanks....that is the kind of info I was looking for. The motor does not make noise when it is working hard, say climbing a steep hill. And upon closer observation, it is not just when I am starting up a slight hill, but also when I am starting down a slight hill. So I am still pedaling, but the bike is accelerating because of the downhill. The motor is actually working less but it is still engaged. I wonder if it is like the engine braking in a car when you start down a hill while still in gear. The electric motor is still engaged because I have not yet reached the top speed where the motor cuts out, but the wheel is going faster than the electric motor because of the gradual downhill (or if I am providing more of the forward momentum by pedaling, which is why it sometimes happens on a slight uphill because I start pedaling hard and am working harder than the motor).

So it seems like it is a noise that appears during a kind of engine braking where the bike's wheel is turning the electric motor instead of vice-versa. This happens when I am not touching the brakes and does not happen all of the time, so I doubt it is anything to do with the brakes or tires rubbing, etc. And if I do very lightly squeeze the brakes just enough to disengage the motor, the sound disappears instantly...which again makes me think it is the motor. If I disengage the motor with the brake lever, then the wheel can spin at a higher speed without over-revving the motor.

I just hope it is not wearing out the motor more quickly.

 

[Kyle Nolte]

My first thought is that it could be pretty dry in there. Most of the geared hub motors have a good bit of grease inside of them. It's possible that it may just not be lubricated well enough. That can create a bit of an intermittent growling noise. I'm not sure if you're up to the challenge of opening it up and repacking it. If it were my bike and it were under warranty I'd take it to a trusted local dealer. If it were out of warranty I'd consider opening it up and lubricating it. This is all based on the idea that the noise is coming from the motor. The fact that you have two of the same bikes puts you at an advantage with the ability to swap parts for the trial and error diagnostic approach.

As John said some motors just make more noise than others. Anything with moving parts is going to make some noise.

I hope this is helpful. Good luck!

 

[Nirmala]

I ordered it online and it is out of warranty. There is a Pedego shop that just opened up here. Maybe they could service the motor.

 

[Ann M.]

@Nirmala, what happened when you swapped bikes with your wife? If you are considerably larger than her, you're putting more of a load on the motor so it might have to work harder. Definitely make sure that any external mechanical drag isn't happening. There will be some sound with a geared motor and different brands have their own hum but if yours is considerably louder then having a shop check the motor. It may not be the gears but alignment of other pieces inside or a slightly stuck clutch.

Geared hub motors were not designed to do engine braking on an ebike.

 

[Nirmala]

Thanks Ann. That is helpful. It does seem like the motor is trying to do regenerative braking!

I rode my wife's bike today and it was remarkably quiet.....so I think it is something inside the motor. The Pedego store only works on Pedego bikes, but I found someone nearby who works on ebikes and I am taking the bike over there tomorrow. It will be nice to have a quiet ebike for a change.

 

[Nirmala]

So I took my bike over to a local guy who converts KMX tricycles into e-trikes ( and who also created the 80 mph ebike shown in this post: https://electricbikereview.com/foru...for-speed-how-about-80-mph-on-an-ebike.10572/ ). He opened up my motor and found that the grease inside was all dried up into a cake like substance. I am not sure which came first, but this motor also has had a tendency to overheat on hot summer days here in Arizona when climbing a long hill. The controller shuts the motor down and then after a while it comes back on, and so far this does not happen to my wife, although she is about 40 pounds lighter than me so she puts less strain on her motor. So I don't know if the grease has always been bad and that is why the motor overheated very occasionally, or if the motor overheating is what dried up the grease. Fortunately the gears were all still intact with no missing teeth or anything.

In any case, he is going to repack the motor with some high quality synthetic grease (Mobil 28) used in aviation applications. Hopefully, I will have my bike back in a week or so with a blissfully quiet motor. Thanks to everyone who chipped in with some advice....it motivated me to get this fixed sooner rather than later.

 

[Nirmala]

So I got my bike back yesterday. It is much quieter overall, but it still makes a high whining noise when riding downhill and when the motor is still engaged. Because the gears were all intact, the guy who repacked the motor did not think it would be a problem. His best guess is that it is a slightly loose set of bearings that is kind of wobbling when not under load. I will try living with it for now, and he will replace the entire gear assembly if it gets worse. It gives me more confidence to know someone locally who can repair the motor if it comes to that.

 

[Nirmala]

I just went for a longer ride, and the noise was annoying, maybe especially so since I may now have a way to fix it. So I am going to have the ebike guy try the replacement gears and see if that does the trick.

 

[Trail Cruiser]

That is the nature of a geared hub motor. Some are louder than the other but the whirring noise is their trademark. That is actually a noise from the reduction gears, not motor noise. As long as the ebike rides OK and there is no undue drag or resistance then your ebike should be fine. You should try riding other geared hub drives for comparison. Newer ones tends to be more silent since it is still packed with grease and dampens the noise. Once the grease clears the gear meshing points, the whirring noise tends to be more pronounced.

 

[Nirmala]

We own two of the same ebike, and my wife's bike does not make the same noise and never has, although her bike has about 700 miles on it and my bike has over 2200. Also, I just had my motor repacked with grease and the noise did not go away. So I am still thinking that a new gear set might make a difference.

To be sure, her motor makes noise, but mine is ten times louder.