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From DownUnder
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Discussion Starter #1
Replacing rotors and pads and noticed the rear caliper piston dust boot is cracked in one spot. Is this urgent fix that can cause brake failure or can I get to it later in a month or so???

And is this DIYable job?

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Replacing rotors and pads and noticed the rear caliper piston dust boot is cracked in one spot. Is this urgent fix that can cause brake failure or can I get to it later in a month or so???

And is this DIYable job?
You should replace the boot as soon as possible. Water incursion will cause the piston to seize. There will be some difficulty in finding the boot as the parts are not generally sold to the public for liability reasons, so most people just replace the caliper.
 

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This is something you'd like to fix sooner rather than later.

Once did the brakes on my parents 80's Land Rover Discovery. Did the front brakes as I recall. The car did not have dust boots at all on the pistons. Just the piston and the piston seal. I thought that was weird, but that's how it was. The point is, that is kind of what you have now. So, it isn't like don't-drive-the-car, but you want to fix it.

Yes, you can get the rear boot separate. BMW has a repair kit that includes the rear seal and boot. Have a look at Realoem. You can get at the dealer or off the net. You just need the boot and won't use the seal. I haven't replaced the boots on this caliper, but I have replaced boots before on other calipers. The boot is just sitting in a groove cut around the piston housing. You might have to force/roll it into the groove nicely, but it isn't a big deal. You don't need to change the piston seal. You won't have to bleed the brakes. Clean it all nicely with an old toothbrush. Make sure there is no crap wedged in-between the piston and the seal (look at the very small space between the piston and caliper wall). Use some Sil-Glyde on the new boot where it want to mate into the caliper.
 

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As stated above. Piston will seize eventually. How long? No idea

As far as I DIY, after doing this on several calipers if you are comfortable I would try it. They are only a couple dollars on rock auto. Buy extras.

Clamp brake line, remove caliper, and try to figure out how to get out the piston without scratching it. I use compressed air. Then put it all back together. Watch a few YouTube videos. Then watch them again. It’s harder than it looks.

If the boot is already cracked there is a chance the piston may already have some rust on it and can’t be reused. But for the cost of a kit it is worth a try.



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Under the lift arms
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lol sorry i skipped a word...

replace the caliber
 

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This isn't that big of a deal unless the caliper piston is scratched or rusting or leaking around the caliper piston seal. If it is none of those things, clean it up and put on a new boot. Calipers aren't some super finicky sensitive thing. You can do all of this without detaching the caliper from the brake line. Which means you don't even need to bleed the system after the repair.
 

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Discussion Starter #9
Re-visiting this as I can't get the boot locally and from US is back ordered, so might just remove the caliper and give it for repair to a local brake place who can get the dust boot and told me they will sand blast clean the caliper and replace the boot. Not sure if the local rubber boot will be as good as the BMW repair kit, but no choice.

Questtion I have is, if I remove the brake line from caliper, will all the oil just roll out and create air gap in the line? What do I do to the brake line once I undo it from the caliper?

And at the time of putting the caliper back, what torque is the brake line to be tightened?

Last, would I need to bed the rear brakes again after removing the caliper?
 

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Re-visiting this as I can't get the boot locally and from US is back ordered, so might just remove the caliper and give it for repair to a local brake place who can get the dust boot and told me they will sand blast clean the caliper and replace the boot. Not sure if the local rubber boot will be as good as the BMW repair kit, but no choice.

Questtion I have is, if I remove the brake line from caliper, will all the oil just roll out and create air gap in the line? What do I do to the brake line once I undo it from the caliper?

And at the time of putting the caliper back, what torque is the brake line to be tightened?

Last, would I need to bed the rear brakes again after removing the caliper?
When you remove the caliper, the line will drip brake fluid until it empties the reservoir. Ideally, you can plug it with a rubber cap to reduce the flow. Regardless of how well it's capped, air will be in the line, so you will need to bleed the brakes. The hose can be left hanging until you install the new caliper.

While it should be obvious, don't try to drive the car with a caliper missing.

The hose is torqued to about 10 ft-lbs. Just enough to ensure that it doesn't leak.

No re-bed would be necessary, if the pads were previously bedded.
 

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Discussion Starter #11
When you remove the caliper, the line will drip brake fluid until it empties the reservoir. Ideally, you can plug it with a rubber cap to reduce the flow.
Thanks for tips, but if I let it run until the reservoir is empty, then will the big round thing (not sure what it is called brake servo unit) between the reservoir and brake line be empty and cause major dramas?

Silly Q but what rubber cap can I use? :)

I don't mind to bleed the brake, but I do not like the idea of losing all the oil and have the reservoir empty.
 

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Get the caliper unbolted. Take a pair of vise grips or other locking pliers, cut two small pieces of 1/2” inner diameter plastic tubing and place the tubing over the jaws of the vise grips. Use this to clamp the brake line while the caliper is off. Loosen the brake hose where it screws into the caliper and spin the caliper while holding the end of the hose. Otherwise the hose will twist on you.


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