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I don't know why you guys/girls worry about this. It's not like a cheap DC motor with slotted commutator, it the slip ring type. I don't expect it needs to be changed for the coming ten years. If I have to change already after 8 years... so what? Don't buy a BMW if you can't afford the service. I trust them, after all, they aren't new regarding EVs. Also, as I understand, this design has some advantages also, so I am not worried at all.
 

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Probably a few hours is my guess. You can replace the brushes on an alternator while it's in the car.

My E90 needed new brushes on the alternator after 140K miles. Took about an hour with it in the car.

I suspect the motors, at least that portion will be accessible since they know it's a wear item.

Waiting for my M50......
I think you underestimate the differences. This is not an alternator, but anyway, if I have the car for 140k miles then I gladly pay for the job.
 

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I don't know why you guys/girls worry about this. It's not like a cheap DC motor with slotted commutator, it the slip ring type. I don't expect it needs to be changed for the coming ten years. If I have to change already after 8 years... so what? Don't buy a BMW if you can't afford the service. I trust them, after all, they aren't new regarding EVs. Also, as I understand, this design has some advantages also, so I am not worried at all.
Agree!

We've quickly forgotten about all the things we had to think about with ICE and began to compare it with "zero" maintenance expectations, which is never the case with cars.

Remember these ??
  • Water pump + thermo at about 80k
  • Engine valve cover gasket replacement ... when it starts leaking oil
  • Oil pan gasket replacement ... when it starts leaking oil
  • Oil and filter every 12k, plus topping off a half a quart or so every 6 mos
  • Coolant overflow hose...cracked in 6 yrs
  • Coolant fill...a gallon every two years?
  • Clutch pack...when the car doesn't move, lol :)
If this is the only big ticket replacement/wear item, I guess I'm good with that.
 

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I think you underestimate the differences. This is not an alternator, but anyway, if I have the car for 140k miles then I gladly pay for the job.
No I don't underestimate the difference, I have two degrees in electrical engineering.

I tried to put it into terms everyone would understand. The best analogy of a motor with brushes that I could come up with that people would understand is an alternator.

Although different it's is a brushed motor and those brushes wear. Typically the first failure on an alternator are worn brushes. It's typically an easy procedure to replace them without the alternator leaving the car.

I used that as an analogy for ease of service and replacement. It's not like the whole motor would need replacing. I also can't imagine that the brushes wouldn't be serviceable if those of an alternator are.

Anyway, after 100-200k miles it's not a big deal considering my E90 needed the following out of warranty and more:
HP fuel pump - $1000
Electric Water Pump - $1500
Radiator - $600

So even if it's a couple of grand to replace the brushes, it's still cheaper that the service Items on my E90 were.



Waiting for my M50......
 
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Front drive unit of my i4 had to be dropped to clean "contamination" from the brushes. They say this wasn't wear-related but due to an issue introduced at the factory. They were real cagey about exactly what they were talking about. But it's been like 3 days of labor so far and they're not done yet. My former friend who was a dealership tech got sent to training on the i4 and iX and says brush replacement is one of the procedures they taught them but that no one was really sure how frequent a procedure that would be.

I'm quite used to $4000 repair bills on 10-year-old BMWs, seems to happen more often than not with simple $50 gaskets that require 20 hours of disassembly and reassembly to get to them... I guess we'll see how it turns out.
 

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No I don't underestimate the difference, I have two degrees in electrical engineering.

I tried to put it into terms everyone would understand. The best analogy of a motor with brushes that I could come up with that people would understand is an alternator.

Although different it's is a brushed motor and those brushes wear. Typically the first failure on an alternator are worn brushes. It's typically an easy procedure to replace them without the alternator leaving the car.

I used that as an analogy for ease of service and replacement. It's not like the whole motor would need replacing. I also can't imagine that the brushes wouldn't be serviceable if those of an alternator are.

Anyway, after 100-200k miles it's not a big deal considering my E90 needed the following out of warranty and more:
HP fuel pump - $1000
Electric Water Pump - $1500
Radiator - $600

So even if it's a couple of grand to replace the brushes, it's still cheaper that the service Items on my E90 were.



Waiting for my M50......
OK, but as I said, this is NOT an alternator. The motor has slip rings, not commutator with split contacts, like alternators normally have. There will of course be some wear, as all moving parts wear, but not as in an alternator. In fact, we have no idea of the durability of the brushes at this time, other that it is highly unlikely that wear is anywhere near the brush wear of an alternator. I don't know if it ever needs to be changed but sure, I expect it to be much cheaper than the service costs of any ICE.

BTW, what about timing chain / belt? Those are also common and expensive jobs in an ICE.
 

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Front drive unit of my i4 had to be dropped to clean "contamination" from the brushes. They say this wasn't wear-related but due to an issue introduced at the factory. They were real cagey about exactly what they were talking about. But it's been like 3 days of labor so far and they're not done yet. My former friend who was a dealership tech got sent to training on the i4 and iX and says brush replacement is one of the procedures they taught them but that no one was really sure how frequent a procedure that would be.

I'm quite used to $4000 repair bills on 10-year-old BMWs, seems to happen more often than not with simple $50 gaskets that require 20 hours of disassembly and reassembly to get to them... I guess we'll see how it turns out.
...but surly it can be 3 days of continuous work... I mean, just because they keep the car for several days it doesn't mean they work on it all the time. Also, in your case, maybe there is a whole lot more than just changing the brushes, so maybe to do all that takes a whole lot of time.
 

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...but surly it can be 3 days of continuous work... I mean, just because they keep the car for several days it doesn't mean they work on it all the time. Also, in your case, maybe there is a whole lot more than just changing the brushes, so maybe to do all that takes a whole lot of time.
they've had it for a week and a half, I'll get the receipt later that says how many hours of labor but my impression has been that they've actually had it in the bay working on it for several full days. They actually didn't replace the brush assembly but just cleaned it, apparently, but my understanding from talking to the service advisor is that most of the work was in getting the drive unit out so they could access the brushes.
 

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They actually didn't replace the brush assembly but just cleaned it, apparently, but my understanding from talking to the service advisor is that most of the work was in getting the drive unit out so they could access the brushes.
IMHO a very poor design. Woulda been better to have the brush assy easily accessible from below.
 

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OK, but as I said, this is NOT an alternator. The motor has slip rings, not commutator with split contacts, like alternators normally have. There will of course be some wear, as all moving parts wear, but not as in an alternator. In fact, we have no idea of the durability of the brushes at this time, other that it is highly unlikely that wear is anywhere near the brush wear of an alternator. I don't know if it ever needs to be changed but sure, I expect it to be much cheaper than the service costs of any ICE.

BTW, what about timing chain / belt? Those are also common and expensive jobs in an ICE.
Like I said alternator for a point of reference and without split contacts the wear will be less. We are beating the same dead horse here.

Timing chains are typically not wear items, but belts are. My Dodge needs the belts changed every 100k miles at $2000, if you factor in that while you have it open, you change all the wear items like water pump, etc.

I have never changed a timing chain from wear on a BMW. They are typically double roller, so three plates with two rollers. They don't typically stretch or break. I've change tensioners because the seals wear and they stop doing their job so you get chain rattle.

Anyway, I believe that the brushes should last longer than those in an alternator and those can last 200k and more than a decade.

Waiting for my M50......
 

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they've had it for a week and a half, I'll get the receipt later that says how many hours of labor but my impression has been that they've actually had it in the bay working on it for several full days. They actually didn't replace the brush assembly but just cleaned it, apparently, but my understanding from talking to the service advisor is that most of the work was in getting the drive unit out so they could access the brushes.
I am pretty sure that it takes a long time because they have to clean it. Having seen several images of the brush assembly, and it is my understanding that all it takes is removing four screws and three wires, and the actual brush assembly is easily accessible. If however cleaning is necessary than they might need to remove the motor and take it apart, or at least must remove the whole rotor, which is I guess a bit more complex.
 

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I am pretty sure that it takes a long time because they have to clean it. Having seen several images of the brush assembly, and it is my understanding that all it takes is removing four screws and three wires, and the actual brush assembly is easily accessible. If however cleaning is necessary than they might need to remove the motor and take it apart, or at least must remove the whole rotor, which is I guess a bit more complex.
They shouldn't have to remove the whole motor. From the diagram I saw I thought there was a dust reservoir. I could be wrong.

When replacing brushes on motors and alternators, I've never pulled the motor apart. That defeats the whole purpose of making them easily serviceable.

Waiting for my M50......
 
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They shouldn't have to remove the whole motor. From the diagram I saw I thought there was a dust reservoir. I could be wrong.

When replacing brushes on motors and alternators, I've never pulled the motor apart. That defeats the whole purpose of making them easily serviceable.

Waiting for my M50......
But in his case the motor must be cleaned, not because of the brushes but because of crap inside the motor due to manufacturing / QC problems. I have no idea how much it must be pulled apart, but it is certainly not just the brush case which most be removed, my guess is that at least the rotor must be taken out, which is a complicated process due to bearings and gear attachment. If that means that the whole motor needs to be removed or not, I don't know, but I guess that it is a special case, not like normal servicing of brushes.

It the motor must be pulled apart it may in fact be easier to do when the motor is removed. There are many parts to clean, that's for sure. But sure, changing the brushes does not require all that, normally that's a pretty simple operation.
 

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"We asked BMW about the life expectancy of those brushes and commutators, and what happens to the dust as they wear. While they couldn't give us a lifetime estimate for the brushes...", I think that is a wouldn't not a couldn't. You don't go into this scale of design and manufacturing without estimating life expectancy of parts. I don't particularly see anything sinister in this, it is not in BMW's interests to manufacture something that is going to put you off the BMW brand. I suspect it is more to do with wanting to get some real world data before they commit.

I also wouldn't draw too many comparisons with technology used in other fields. If you used the same battery technology in cars that you have in mobile phones, your EV battery would be knackered after a very short time. The principle of using brushes may be old but the implementation can vary a lot.

I would hope that BMW have come up with a design that gives a reasonable (insert your own figure here) longevity but it will be a wear and tear part and being a sealed unit will probably not be particularly cheap.
According to the article, we do not have to worry about the motor life cycle…


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Brushes are made of a carbon composite so they will conduct and wear under low friction. They will dust as they wear. As stated these are within a sealed compartment so dust blowing throughout the motor should not occur. Replacing a set of brushes should be rather simple (maybe not in your home garage) but they have been designed in a way they can be easily reached and replaced. Personally I wouldnt worry about them until you surpass 100k and then maybe inquire with BMW Service. By then we will have lots of miles on the cars and know what the Achilles heels will be.
 
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