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Discussion Starter #1
As part of my BMW 2002 (175) conversion I an transplanting from a Nissan Leaf (2014). The BMW has vacuum-assisted brake (master cylinder) which I need to replicate.

From the research I understand that:
  • I should be able to reuse the master electric brake cylinder
  • I need the brake computer (hooked back into the car)
  • The ABS can be disabled (hydraulically and/ or via removing specific fuses)

My question is can I re-use the brake master cylinder & what is required ie are my assumptions listed above correct? Does anyone have experience with this?

If I can take this approach rather than an electric vacuum the I will save space & hopefully it will also be simple to implement.
 

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There is also a big storage capacitor that is used with the electric brake actuator. i have studied that motor-driven master cylinder and while it is a cute display of technology, it seems overly complex in my opinion. Need a brake pedal position sensor and a regen strength signal from the inverter.

So you could try to use it, but it will take time to figure out what other stuff you need to carry over to get it working. It won't be plug and play. How much time do you have to spare for re-inventing vacuum brakes versus all the other stuff needed to convert ICE to EV?
 

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i have studied that motor-driven master cylinder and while it is a cute display of technology, it seems overly complex in my opinion. Need a brake pedal position sensor and a regen strength signal from the inverter.
Too complicated? It's an ordinary master cylinder plus a motor driving a screw to push on it; I think it's brilliantly simple, with fewer parts in total than a vacuum-assisted master cylinder plus a vacuum pump.

Yes, controlling it - or any brake booster - would logically include considering how much regenerative braking is occuring, so that the effect of the total system (regenerative plus friction braking) matches the driver's command.
 

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Sounds more complicated than just adding a 12V vacuum pump that you could put almost anywhere. Have you matched up the master cylinder piston size to the caliper pistons? Pedal leverage of the BMW vs the Leaf?

It's likely that your brakes will still be able to lock up the tires unassisted...you just have to push on the pedal harder. My car (Leaf motor and Thunderstruck controller) has strong regen...I rarely touch the brakes at all. I was gonna add a vacuum pump or use an older master cylinder, but...it just doesn't need any more brakes. In an emergency, if I stomp the pedal, the limiter is the tires.

Cool project.
 

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Discussion Starter #5
There is also a big storage capacitor that is used with the electric brake actuator. i have studied that motor-driven master cylinder and while it is a cute display of technology, it seems overly complex in my opinion. Need a brake pedal position sensor and a regen strength signal from the inverter.

So you could try to use it, but it will take time to figure out what other stuff you need to carry over to get it working. It won't be plug and play. How much time do you have to spare for re-inventing vacuum brakes versus all the other stuff needed to convert ICE to EV?
I have the wiring looms / original systems and hence the wiring is probably the easier part. I think it will be a mechanical challenge if I go down this path.
 

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Sounds more complicated than just adding a 12V vacuum pump that you could put almost anywhere. Have you matched up the master cylinder piston size to the caliper pistons? Pedal leverage of the BMW vs the Leaf?

It's likely that your brakes will still be able to lock up the tires unassisted...you just have to push on the pedal harder. My car (Leaf motor and Thunderstruck controller) has strong regen...I rarely touch the brakes at all. I was gonna add a vacuum pump or use an older master cylinder, but...it just doesn't need any more brakes. In an emergency, if I stomp the pedal, the limiter is the tires.

Cool project.
Thanks - I must admit I have been following your conversion and take much inspiration from your documentation and journey.

Good point re the matching of the piston size. I had not thought about that. I will do some research on that.

I believe local road laws mean that I need the vacuum to be maintained. A transport engineer will need to sign-off the vehicle hence I understand that I need to maintain original functionality.
120524

The old vacuum boosters take up a lot of room hence my contemplating the more compact leaf system.

I have plenty of time hence I might pause the brake transplant question till later in the build.
 

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Discussion Starter #7
Too complicated? It's an ordinary master cylinder plus a motor driving a screw to push on it; I think it's brilliantly simple, with fewer parts in total than a vacuum-assisted master cylinder plus a vacuum pump.

Yes, controlling it - or any brake booster - would logically include considering how much regenerative braking is occuring, so that the effect of the total system (regenerative plus friction braking) matches the driver's command.
The current plan is to keep the original leaf controls hence the electronics "should" be Ok. I have some assistance with the controls if needed. I think my conclusion is that I delay this decision but keep the Leaf brakes / wiring / controls in case I go down this path later.
 

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If you read the laef forum you will find there are folks who complain of "grabby" brakes. i drove one for awhile and experienced it also--the brakes will lock up with the least little bit of pressure on the pedal. There is no easing onto the brakes with any sort of linear response that corresponds to foot pressure. When it gets in that mode it is like a switch that goes hard ON.

On an ICE and a normal EV, the brake pedal will have a certain stroke that is very subtle, in that the pedal can be slowly eased down to gently slow down if desired. On an EV with good regen, the brakes are seldom used--the last thing you need is a jerky brake system. My guess is that the electric motor is not backing off from the piston in the m/c, in which case it could be dragging the brakes all the time..? In my experience it is on the list of undesirable "features". There is supposedly some sort of reset procedure in the FSM for the mechanic to fix this, but it's just crap. Have you ever heard of any other car that will grab and lock up the brakes like that?

rant/
i wouldn't have a nissan ice car due to the stupid fuel injector design vs the bosch pintle design. They use tiny 0.010" (.25mm) diameter orifice holes in the end of the injectors, which is asking for pain in this day and age of watered down fuel. Do you think they use 200 proof alcohol to add to gasoline--good luck with all the dissolved crap in the water getting thru those tiny injectors. And let one set for awhile and the water-gas turns to jelly. And they mount them such that it is not at all easy to access for pulling out to clean or replace. Lots of cursing. /rank
 

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Another electric brake booster alternative is the Bosch iBooster, that is used in a myriad of electric and hybrid VW/Audi vehicles, and a number of Tesla's. This guy has written up how he's using a Tesla one.
- Installing the iBooster - EVcreate

I'm currently working on documenting the options on the Open Inverter Wiki. Do you have the part numbers handy for the Nissan Leaf unit you're looking at?

Thanks
 

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Discussion Starter #10
Another electric brake booster alternative is the Bosch iBooster, that is used in a myriad of electric and hybrid VW/Audi vehicles, and a number of Tesla's. This guy has written up how he's using a Tesla one.
- Installing the iBooster - EVcreate

I'm currently working on documenting the options on the Open Inverter Wiki. Do you have the part numbers handy for the Nissan Leaf unit you're looking at?

Thanks
Hi Jalovick, very happy to share information. The system is still in the car. Please let me know the information you want and I will share it. Matt
 

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Hi Jalovick, very happy to share information. The system is still in the car. Please let me know the information you want and I will share it. Matt
Thanks! Probably part numbers to start with, and if there is any info around the pinouts and how to control it, that would be useful. Anything that allows someone to get one and make it work really.

I'll also query the folks on the Open Inverter forum, to see if anyone else has used one.

Jamie
 

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Discussion Starter #12
120595
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Photos of the brakes removed. Unfortunately, I don't know the part number / pinouts. I also have the ABS unit which I understand also communicates with this booster unit.
 

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Thanks for uploading the photos. I can see some stickers and engravings on there and I will look those up online. It will be interesting to see how it's controlled, and what it expects.

A quick search suggests that the booster you have is from an AZE0 model Leaf. Apparently, Nissan have released firmware updates for the unit to increase brake sensitivity and performance:

- Brake Control Module Firmware Update – AZE0-0xxxxx and AZE0-1xxxxx Leaf - EVs Enhanced
 
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