Grinding sound during regenerative breaking

[4wheels]

2019 bmw i3 grinding sound


My 2019 i3 makes a grinding sound when the regenerative breaking is engaged.

Dealer has no idea what this is and what is causing the grinding sound.

 

[mojo]

All the time, or only when the battery is 100% charged?

 

[4wheels]

All the time, or only when the battery is 100% charged?

All the time.

 

[spartacus68]

It’s not good enough that your dealer doesn’t know what’s causing the noise. How have you left things with them?

My understanding is that regenerative braking doesn't engage friction braking at all, so you can rule the brakes out altogether, although a cursory check would be worthwhile as the BMW i3 does seem to eat pads and discs through inactivity, more in terms of deterioration and rust than wear and tear.

Found this on a Kia forum, so worth a read.
https://www.speakev.com/threads/braking-regen-noise.138230/page-3?nested_view=1&sortby=oldest
If was the mechanic I’d be inclined to look at the output shafts on the motor for any leaks. For the relatively cheap cost to drain the transmission fluid on the final drive (if done this way), then I’d be checking for any metal filings just to rule out bearing wear.



Only other thing it could be is CV bearings on drive shafts. For some reason the regenerative braking could be amplifying the sound, but you’d normally hear a constant hum or drone around 30-50mph. Very difficult to diagnose on the car, compared to the fronts which I’ve changed before. Luckily they are bolt in place so doable for DIY mechanic and no need for a press.

Anyway, just a thought.

 

[alohart]

My understanding is that regenerative braking doesn't engage friction braking at all, so you can rule the brakes out altogether, although a cursory check would be worthwhile as the BMW i3 does seem to eat pads and discs through inactivity, more in terms of deterioration and rust than wear and tear.

According to i3 owners living on a hill, the brakes are automatically engaged to simulate regen braking when the battery pack's charge level is very high. This doesn't explain 4wheels' grinding sound during regen braking because it occurs at all charge levels.

 

[Marscar]

According to i3 owners living on a hill, the brakes are automatically engaged to simulate regen braking when the battery pack's charge level is very high. This doesn't explain 4wheels' grinding sound during regen braking because it occurs at all charge levels.

That'll be us!
Eventually the noise, and the pulse that came up through the "throttle" pedal, was dramatically reduced by putting new non-rusty discs on ... We still have what I would call a "drone" most obvious around mid 60mph, which sometimes has the feel of good old road noise, sometimes more of wheel bearings.
We'll test the latter theory at the next service .....
I think (ha! what do I know?!) that if 4wheels has the same noise all the time then the wheel bearings, engine mounts or any of the joints between the motor and the wheels need checking?
We will also be changing to Bridge stone tyres from Ecopias when they need changing as apparently they're a better bet in the wet (UK owner :-/ )

 

[spartacus68]

I swapped out front wheel bearings on my wife’s car at 70k miles. If you’re going down a bearing route only fit FAG given labour involved. Again difficult to diagnose with wheels on. I used air hammer as there will be corrosion holding bearing carrier to hub.

 

[clktex]

My 2016 Rex does this from time to time. I have only 31K miles on it.

 

[4wheels]

BMW dealership said they are going to need the car for a very long time to go back and forth with BMW. The car has made this noise for as long as I can remember. I had to bring the car in for service because I ran over a curb and broke 3 rims. While the dealer was fixing the rims they took it on a test drive to do other service on the car. They asked about the noise. So I guess I will get around to fixing this some day.

While fixing the rims - I had the dealer upgrade the computer software, and do other service stuff they said the car needed. When I got the car back, it would go into turtle mode once I ran out of battery and had to switch to REX. I could not go over 50 mph. I don't remember the car doing that when I had to use REX.

So I coded my i3 to enable hold state of charge. This has made a big difference on this car. When going on 'long' trips I can enable rex to kick on after the battery drops below 75%. This keeps me from entering slow as hell mode as dictated by California. F'em! I like the new option provided by coding this car.

 

[4wheels]

During the winter here in Houston - the car is problematic. I got drive train malfunctions, and even had the car stop on me. I tried to pre-condition the car before driving and that did not put a stop to the issues. But after the car 'warms' up it seems to work fine. I hope to keep the car for several more years because I just paid the darn thing off. Now is the time it's supposed to make me money. Mostly by not costing me money!

 

[alohart]

When I got the car back, it would go into turtle mode once I ran out of battery and had to switch to REX. I could not go over 50 mph.

Some REx owners have reported that the charge level displayed had become higher than the actual charge level such that by the time the REx engine started automatically, the actual charge level was below 1% at which point the maximum power output starts to be limited (e.g., your 50 mph max speed). This can be seen on the power gauge where power bars in the upper right section begin to disappear. BMW dealers have a procedure that they can perform that will correct this problem. Hopefully, a REx owner will provide more details.

 

[Starmanager]

According to i3 owners living on a hill, the brakes are automatically engaged to simulate regen braking when the battery pack's charge level is very high. This doesn't explain 4wheels' grinding sound during regen braking because it occurs at all charge levels.

It also happens when the battery is cold. The battery does not like to get charged with so many power when she is cold. You can hear it more or less, depends on how clean the breaks are. It is normal the real breaks are simulate the gegen effect.