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Technical Topics Suspension / Chassis / Brakes Implications of the new brake-by-wire system

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      05-16-2019, 10:14 AM   #1
Ilyam5
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Implications of the new brake-by-wire system

Looking into the Brake design for the new G series I'm finding some disturbing info.

It looks like we have a brake by wire application at least for the M340i. So, there is an electronic connection between brake pedal and master cylinder, and there is no brake booster under the hood. And from the master cylinder, there is a hydraulic connection to the calipers but it is controlled by computer. The implication is that you cannot change your own brake pads easily anymore.

Like the guys on the X5 board found out, the pistons cannot be retracted manually into the calipers. This means that changing pads has to be done with the aid of a computer, and only the dealer has a computer that can talk to the new generation BMW vehicles. However, the dealer will not put on aftermarket pads due to warranty issues. So one has to find ways around it. If attempted manually instead, the dash lights up with warnings, and I'm not sure what the implications are on brake performance if the lights are left on.

For the cooling package with 374mm brakes, we need the same pads as the M550i, 750i, or X5 50i with M brakes.

The pad numbers are:

16-1868 (front)
16-1469 (rear)

I'm not sure if Hawk makes DTC 70 pads in that size. Stoptech seems to have street pads but not track.
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      05-16-2019, 02:30 PM   #2
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Interesting. I haven't seen anything advertised about brake by wire. We all know Alfa is doing it and has mixed reviews when it comes to braking. This would better explain how the M8 adjustable brakes work (also assumed to be on G80 M3).
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      05-16-2019, 02:47 PM   #3
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This is the first time I'm hearing this. The aftermarket will come up with a solution but it won't be cheap. Say goodbye to brake feel.
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      05-16-2019, 02:59 PM   #4
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I can't imagine it would be very difficult for something like the Foxwell or other cheap scan tools to build in this type of functionality. As a home mechanic, I don't mind buying a scan tool to work on my car. Our cars are more advanced and it brings a lot of tangible benefits (though some glaring drawbacks as well). As long as BMW aren't dicks and make it hard for 3rd party companies to access their systems.

That said, why wouldn't a simple brake pad spreader (i.e.g a pry bar) work to spread the retract the pads? The system is still hydraulic. So the brake fluid would just flow back to the master cylinder. I'm more wondering because I'm curious, not because I think they're wrong. But I'd be interested to see the X5 thread where they discuss this and why a prybar or spreader tool won't work.
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      05-16-2019, 03:07 PM   #5
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Quote:
Originally Posted by upsidedownfunnel View Post
I can't imagine it would be very difficult for something like the Foxwell or other cheap scan tools to build in this type of functionality. As a home mechanic, I don't mind buying a scan tool to work on my car. Our cars are more advanced and it brings a lot of tangible benefits (though some glaring drawbacks as well). As long as BMW aren't dicks and make it hard for 3rd party companies to access their systems.

That said, why wouldn't a simple brake pad spreader (i.e.g a pry bar) work to spread the retract the pads? The system is still hydraulic. So the brake fluid would just flow back to the master cylinder. I'm more wondering because I'm curious, not because I think they're wrong. But I'd be interested to see the X5 thread where they discuss this and why a prybar or spreader tool won't work.

I thought so too. Did simple pad swap for the past 20 years on the track between sessions changing pads. Can't imagine needing a laptop to do it now.

My only thought why BMW implemented it is - if master cylinder monitors the level of fluid and position of pistons for drying the rotors when wet and for automated driving.

I Was going to put DTC70 pads into M340 and found this out. I'm asking my BMW dealer to confirm the procedure.
In the meantime here is the thread

https://g05.bimmerpost.com/forums/sh....php?t=1614088
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      05-16-2019, 03:21 PM   #6
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Quote:
Originally Posted by Ilyam5 View Post
I thought so too. Did simple pad swap for the past 20 years on the track between sessions changing pads. Can't imagine needing a laptop to do it now.

My only thought why BMW implemented it is - if master cylinder monitors the level of fluid and position of pistons for drying the rotors when wet and for automated driving.

I Was going to put DTC70 pads into M340 and found this out. I'm asking my BMW dealer to confirm the procedure.
In the meantime here is the thread

https://g05.bimmerpost.com/forums/sh....php?t=1614088
Ooh, this is for the rear calipers. It's because BMW is putting the electronic parking brake in the floating rear caliper now. Which is a reason why even M Sport brake cars use floating calipers instead of the extra weight and cost of a drum brake in the rotor hub.

Yeah, many cars with electronic parking brakes require this procedure although some allow you to retract it by twisting the rotor in and out of the caliper.

But in that thread, it sounds like that person's friend had the software to do it. So I'm fairly confident a "cheap" $150 scan tool like the Foxwell will allow you to retract the rear caliper. You kinda need one to do other stuff on the car anyway, so it's worth it, IMO.

Yeah this is dumb dumb dumb, but it does have some practical benefits. No adjusting the parking brake anymore which is kind of a pain, extra room on the center armrest, less weight from removing the whole drum brake assembly, no nightmares if the parking brake cable snaps, and some people don't put enough pressure on cable parking brakes which makes for a dangerous situation if parked on an incline/decline.
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      05-16-2019, 03:55 PM   #7
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Quote:
Originally Posted by upsidedownfunnel View Post
Quote:
Originally Posted by Ilyam5 View Post
I thought so too. Did simple pad swap for the past 20 years on the track between sessions changing pads. Can't imagine needing a laptop to do it now.

My only thought why BMW implemented it is - if master cylinder monitors the level of fluid and position of pistons for drying the rotors when wet and for automated driving.

I Was going to put DTC70 pads into M340 and found this out. I'm asking my BMW dealer to confirm the procedure.
In the meantime here is the thread

https://g05.bimmerpost.com/forums/sh....php?t=1614088
Ooh, this is for the rear calipers. It's because BMW is putting the electronic parking brake in the floating rear caliper now. Which is a reason why even M Sport brake cars use floating calipers instead of the extra weight and cost of a drum brake in the rotor hub.

Yeah, many cars with electronic parking brakes require this procedure although some allow you to retract it by twisting the rotor in and out of the caliper.

But in that thread, it sounds like that person's friend had the software to do it. So I'm fairly confident a "cheap" $150 scan tool like the Foxwell will allow you to retract the rear caliper. You kinda need one to do other stuff on the car anyway, so it's worth it, IMO.

Yeah this is dumb dumb dumb, but it does have some practical benefits. No adjusting the parking brake anymore which is kind of a pain, extra room on the center armrest, less weight from removing the whole drum brake assembly, no nightmares if the parking brake cable snaps, and some people don't put enough pressure on cable parking brakes which makes for a dangerous situation if parked on an incline/decline.
The danger of not applying enough parking brake is more of an issue if you have MT. Since AT shifts to park automatically unless you're in N when you shut off the engine. It will still shift into P but probably after the car has rolled down the hill and crashed into something. And MT does not exist for G20 except in Europe.
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      05-16-2019, 04:07 PM   #8
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Quote:
Originally Posted by upsidedownfunnel View Post
Ooh, this is for the rear calipers. It's because BMW is putting the electronic parking brake in the floating rear caliper now. Which is a reason why even M Sport brake cars use floating calipers instead of the extra weight and cost of a drum brake in the rotor hub.

Yeah, many cars with electronic parking brakes require this procedure although some allow you to retract it by twisting the rotor in and out of the caliper.

But in that thread, it sounds like that person's friend had the software to do it. So I'm fairly confident a "cheap" $150 scan tool like the Foxwell will allow you to retract the rear caliper. You kinda need one to do other stuff on the car anyway, so it's worth it, IMO.

Yeah this is dumb dumb dumb, but it does have some practical benefits. No adjusting the parking brake anymore which is kind of a pain, extra room on the center armrest, less weight from removing the whole drum brake assembly, no nightmares if the parking brake cable snaps, and some people don't put enough pressure on cable parking brakes which makes for a dangerous situation if parked on an incline/decline.

So what if i leave the rear brakes alone and just change the front pads> Can i retract the front pistons manually?
will it effect the rear brake sensors - i thought it was the same hydrolic circuit for the brakes (front and rear)
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      05-16-2019, 04:22 PM   #9
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Quote:
Originally Posted by Ilyam5 View Post
So what if i leave the rear brakes alone and just change the front pads> Can i retract the front pistons manually?
will it effect the rear brake sensors - i thought it was the same hydrolic circuit for the brakes (front and rear)
Mind you I'm speaking without ever having worked on any of these brake systems, but I'm 90% sure I'm correct here. You shouldn't have problems with the front pads at all since those are purely hydraulic and don't have the electronic actuator.

This issue is just for the rear caliper with the electronic parking brake actuator. Some cars come with a way to retract the rear caliper without a scan tool however aftermarket scan tools will be able to do this function if not now, in the very near future.

The fact that these are brake by wire is not completely relevant since they are still hydraulic brakes. Also, I think there's a good chance the G20 is still a purely hydraulic system.
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      05-16-2019, 04:27 PM   #10
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Yup, the M340i does have a brake booster so it is not brake by wire.



Unlike the G05 X5 which uses a servo unit



So G20 users have NOTHING to worry about.

EDIT (You still need a scan tool to retract the rear caliper. I'm just saying we don't have to deal with brake by wire)

Last edited by upsidedownfunnel; 05-16-2019 at 04:39 PM..
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      05-17-2019, 12:30 AM   #11
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thank goodness it isn't brake by wire. Had an e-class with brake by wire and it was a disaster. recalls and complaints by forum members of brakes not working.
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      07-28-2020, 02:25 PM   #12
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Thinking to buy a 2019+ x5 which has brake by wire (not just the ebrake). Any updates on how to service the brakes ....and if there's manual overrides to retract the pistons? Thx
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