Rear brake disc and pad change

Okay, so my wife's i3 REx (2015) is at 60k miles and the rear discs have seen better days. Passed MOT earlier this month, but when I was switching over onto winter tyres had a proper look at them.

I've changed the discs and pads on my A4 Allroad with an electric parking brake, so use VCDS software. I don't have any software for the BMW, but stumbled across this video. Now it's not for an i3, but is it doable? I'm familiar with brakes, grease sliders, etc. Am I likely to throw up errors?

https://m.youtube.com/watch?v=BOubDKjnqak

On question of discs and pads, then I rate Zimmermann discs and pads, or indeed Brembo.

Anyone got a view or opinion? Not sure what BMW use from new?

Haven't had the need to do this on my i3 but the video shows pretty much the same procedure that I use on my wife's 2011 535i rear brakes. I can't imagine that you'd have any issue with any errors or codes.

Actually, I'm surprised that you're having to do rear brakes even at 60k miles. I'm at 55k and mine are still in great shape, which isn't too surprising since I hardly ever actually use the brakes. Just enough to keep rust off the rotors...

If the wear sensors haven't been triggered, you probably don't need to replace those.

I haven't looked at the i3's brake rotors that closely, but on some of their models, they use an aluminum center, and cast iron outer wear surface to save some weight. Not all of the aftermarket ones do the same being all cast iron. May not be a huge thing, but those with aluminum centers will be lighter and may do better with heat management.

You might want to replace the pins the caliper slides on.

Thanks for the replies.

Here's pictures of the discs. The pads still have some miles left on them, but if I'm changing the discs, I'll renew the lot. Like I said, this is 60k miles, road salt and regenerative braking taking its toll.

https://ibb.co/sw2gV35
https://ibb.co/YLkMChd

I'll check the brake sliders. In my experience unless the rubber dust cover is torn they just need cleaned and lubed. I've used ProSlip before for pads, clips and pins. If they're corroded I'll definately replace.

I put Zimmermann discs and pads on the Audi and braking is excellent. Uses a zinc disc coating to cut down on corrosion.

The brake pad sensors I've come across before. This is a poor video, but featured here. Surprised they are not wired with the new pads?
https://m.youtube.com/watch?v=mZmpryUQRk4

Depending on the MY and market, the brake wear sensors could be of two different types. One is a two stage affair that gives an early warning the brakes are wearing, and then after things wear down some more, a more critical warning they're about to be gone. On others, it's simply a loop that gets shorted when the pad cuts through and lights a light. The BMW solution sends a signal to the computer, not directly to a lamp to indicate wear. Those with a wire in the pad generally just light a lamp when the wire comes into contact with the rotor, grounding it.

Yes, those rotors do look a bit sketchy. I'd change them too.

Got prices back from BMW. I'm inclined to replace the sensor. The last one has been on 5 years, and the service desk say it's best practice to replace. It's only a £20 GBP part.

All in for discs, pads and sensor £217.22 GBP or $283.00!

I know - and I've still to fit em!

So it's been blowing a storm and the days are short, but I'd picked up the brake parts from the main dealer the other day, so did the job.

I released the rear parking brake, put in some wooden chocks on the wheels, then disconnected the high voltage cable. Jacked one side up, then threw an axle stand in for safety.

Release the brake fluid cap and leave it off.

First off if you're attempting this, then get a new brake pad sensor cable. The one that was on the car was 5 years old, but although not damaged, the plastic is brittle if you try to lever it off, so you don't need the grief if it breaks, and the chances it will. I found my our welded onto the pad. The sensor is only on one side by the way. This is a UK right hand drive so was located on the offside.

There's an anti rattle pin, so that levers off no problem. Then the brake slider pins. Not sure if it's a 7mm Allen key, but I used Torx bits and worked fine. You need longer Torx bits as the lower suspension arm restricts movement if you're using the standard size. Ideally on a 1/2" drive for leverage.

With the brake sliders out (they need cleaned with a little 3M paper and light oil. Now you can lever off the caliper. The brake pad sensor you can trace back to the plastic junction box. Usual clips to separate.

The brake rotor is held on with one Torx screw. With that off, then chances are the brake rotor is seized on. Decent sized lump hammer, couple of blows and it's off.

Now it's possible to fit new rotors without removing the brake carriers, but if you're doing it properly they need to come off. BMW use Torx bolts, Torx socket 18mm fits. There's not much room, but if tight, hit the ratchet drive with a rubber mallet to start the job.

The brake carrier needs a thorough clean. I use brake cleaner and a drill with wire wheel attachment.

Now the brake caliper, ignore the video I posted earlier regards removing the electric drive. The brake piston can be reset by screwing the piston back in with a brake wind back tool. Draper or Laser tools have interchangeable heads with 2 pins to locate on the piston bore face. Turn it clockwise.

Wire brush and use brake cleaner on the caliper. Inspect the rubber piston boot while you're there.

Reassembly is straight forward. The pads are marked inner (has spring clips) and is the one the sensor connects to. I used ProSlip grease for the pads, slider pins and clips. Use a little marine grease on the threads of the carrier and on the hub before you refit the rotor.

With everything refitted and torqued on both sides, refit high voltage cable, check the brake fluid level and pump the brakes a few times before going for a test drive.

The brake sliders were bone dry, so the whole thing is reassembled and greased it should be good for another 5 years.

https://ibb.co/Q6CfjH1
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My allroad rears were a pain in the ass, using the 12 volt retraction method before I had VCDS. Threw an error code that forced me to buy the hardware. Glad to hear the i3 isn't as picky.

eNate said:

My allroad rears were a pain in the ass, using the 12 volt retraction method before I had VCDS. Threw an error code that forced me to buy the hardware. Glad to hear the i3 isn't as picky.

Click to expand...

I've got a B8 A4 Allroad and agree it's a pain. Also have full VCDS given I use it priming diesel fuel pump, etc. Just upgraded the satellite navigation maps to 2020, not with VCDS but with 3 SD cards as that included MMI software upgrade, 2020 Europe map then confirmation, honestly you need a degree in nuclear fusion to undertake it!

The i3 was surprisingly satisfying to work on. Space is tight as mentioned, and goodness knows why BMW insist on these Torx bolts?

Even if the rear rotors and pads look fine it's worth doing a strip down. The caliper and carrier are rusted and the brake sliders were dry, so it's preventative maintenance in my book.