[WillGood Hunting]

Hi,
I have some confusion I need cleared up. This is my first time having to work on this. I was replacing my rear rotors and pads on my F30. Through my overwhelmed distractions on my next steps, I accidentally pumped the brakes without the calipers hooked up with pads inside and one of the pistons popped out of it's spot but not out of the rubber sealed area. The other seems to have stayed pressed down in the caliper.
Noticing this and trying to refit the piston back in, I managed, in it's extended position yet a bit of Brake fluid out spewed out.
I need to press the piston back down into the caliper so I can finish my work but it won't budge. I'll probably open the bleed screw which could let me press the piston down. Will this process also expel any air that possibly got inside? Will I only need to turn on the car and check of the brake fluid reservoir to see if it's within range of Max-Min?
Some tips and help would be awesome. Thanks.

[Billfitz]

When doing a pad change I retract the pistons with a C clamp. You can buy a tool made for the job, but it's still basically a C clamp. You usually don't need to bleed brakes after doing pads, but in your case you should.

[johnung]

Originally Posted by Trill Clinton

Hi,
I have some confusion I need cleared up. This is my first time having to work on this. I was replacing my rear rotors and pads on my F30. Through my overwhelmed distractions on my next steps, I accidentally pumped the brakes without the calipers hooked up with pads inside and one of the pistons popped out of it's spot but not out of the rubber sealed area. The other seems to have stayed pressed down in the caliper.
Noticing this and trying to refit the piston back in, I managed, in it's extended position yet a bit of Brake fluid out spewed out.
I need to press the piston back down into the caliper so I can finish my work but it won't budge. I'll probably open the bleed screw which could let me press the piston down. Will this process also expel any air that possibly got inside? Will I only need to turn on the car and check of the brake fluid reservoir to see if it's within range of Max-Min?
Some tips and help would be awesome. Thanks.

When you say that brake fluid came out, came out of where? If brake fluid came out of the piston area then that is not good.

When you remove brake pads and see the pistons, what you are actually seeing are the rubber dust caps that cover the pistons. Underneath the dust cap is a caliper cylinder that the piston rides up and down in. Around the piston is a rubber seal that prevents brake fluid from escaping.

If brake fluid came out of the extended piston area, then the piston seal had to be out of place. Shoving the piston back in may put the seal back into the correct position or maybe not. The piston may still be in perfect shape or maybe it has been torn or damaged.

IMO don't mess with safety. Take the caliper off and rebuild it with an inexpensive kit that has new piston seals and dust caps. The pistons themselves are probably fine.

Zeckhausen racing has the correct rebuild kits.

https://www.zeckhausen.com/

[WillGood Hunting]

Originally Posted by Billfitz

When doing a pad change I retract the pistons with a C clamp. You can buy a tool made for the job, but it's still basically a C clamp. You usually don't need to bleed brakes after doing pads, but in your case you should.

I read of someone else who had a similar case as mine and they recovered by using a C-clamp to compress the piston back down while the bleed screw was open. So that's what I did. Brake fluid would come out the bleeder through a clear tube that I connected as I pressed the piston back down with the C-clamp. I did have to fix the seal to seat properly, once, as I was compressing down the C-clamp on the piston. The piston looked fine. Didn't see any tears or damage on the seal. I'll do a brake bleed then have a buddy w/ me pump the brakes to see what happens before I go any further. I won't put the wheels back on yet. I'd rather not have to spend money for a new caliper kit like the other guy mentioned... things look favorable. I'll do this tomorrow and give an update then. I have college things to do.

[Billfitz]

There's no need to open the bleeder screw. Every time you press the brake pedal fluid flows into the caliper, forcing the piston outward. When you release the pedal the fluid flows back into the reservoir, and the piston retracts. The only difference here, or any time you replace the pads and use a clamp to fully retract the piston, is how far the piston travels. In normal braking it's only a millimeter or so.

[jh_f30]

Originally Posted by Billfitz

There's no need to open the bleeder screw. Every time you press the brake pedal fluid flows into the caliper, forcing the piston outward. When you release the pedal the fluid flows back into the reservoir, and the piston retracts. The only difference here, or any time you replace the pads and use a clamp to fully retract the piston, is how far the piston travels. In normal braking it's only a millimeter or so.

If I'm not mistaken, opening the brake fluid reservoir cap would also ease piston compression, no? Also, it wouldn't risk introducing air into the system, although that might've happened anyways if the piston seal was compromised.

[johnung]

Originally Posted by Trill Clinton

I read of someone else who had a similar case as mine and they recovered by using a C-clamp to compress the piston back down while the bleed screw was open. So that's what I did. Brake fluid would come out the bleeder through a clear tube that I connected as I pressed the piston back down with the C-clamp. I did have to fix the seal to seat properly, once, as I was compressing down the C-clamp on the piston. The piston looked fine. Didn't see any tears or damage on the seal. I'll do a brake bleed then have a buddy w/ me pump the brakes to see what happens before I go any further. I won't put the wheels back on yet. I'd rather not have to spend money for a new caliper kit like the other guy mentioned... things look favorable. I'll do this tomorrow and give an update then. I have college things to do.

You are not understanding that you are not looking at the piston seal. You are looking at the dust cap that covers the piston. The piston has a round seal around its body that keeps brake fluid out. Please see photo.

Just because you press the dust cover back on doesn't mean that the seal down under it around the piston is okay. The fact that brake fluid leaked out means that it wasn't okay. You are risking safety if you just pop a dust cover back on and hope for the best.

Below is a link that explains what needs to be done. See the photos for the piston, seal and dust cap. It's the seal that is preventing fluid from leaking and the caliper operating properly, not the dust cap.

The rebuild kits are not expensive, <$20. Call or email Dave Zeckhausen and he will get you the correct kit.

Zeckhausen Racing
123 US Highway 46
Fairfield, NJ 07004
P: 800-222-8893
E: info@zeckhausen.com

If you don't feel comfortable doing the work find an experienced local BMW mechanic on BimmerShops website.

https://www.zeckhausen.com/catalog/i...Path=6446_6494

[Billfitz]

Originally Posted by jh_f30

it wouldn't risk introducing air into the system, although that might've happened anyways if the piston seal was compromised.

Once the piston came out of the caliper far enough for fluid to come our air was in the system. That's why he'll have to bleed it when done. Normally when you pull the pads and retract the pistons air won't get into the system.

[WillGood Hunting]

Originally Posted by Billfitz

Once the piston came out of the caliper far enough for fluid to come our air was in the system. That's why he'll have to bleed it when done. Normally when you pull the pads and retract the pistons air won't get into the system.

He's right. Air got into the system once the piston popped out of the bore But it didn't pop out of the dust boot. I'm a mechanical engineer so this stuff interested me because one day I plan to actually throw M-performance brakes on.

So, yes crazy but I did it. I disconnected the brake caliper from the brake line, threw a vacuum cap on brake line to stop the leaking and took the piston right out of the caliper for learning lessons. I have to tell you. I've learned a lot just doing this. So I found the Pressure seal O-ring sits inside the bore of the caliper which has an indent ring made just for that pressure seal o-ring to sit snug into. Located the inlet where brake fluid is introduced to the caliper. I learned a ton.

Take a look at this picture I took. It'll help describe what I'm getting at.
So now I want to put the piston back in the bore of the caliper, but the dust boot (connected on the bore of the caliper) seems to be in the way. Most online DIY videos show the M-performance Brembo calipers of this part with a new dust boot being placed on the piston by the indent then piston placed into bore afterwords, compress the piston down carefully then fit the dust boot in place by pressing the lips on and around the bore of the caliper.
My dust boot is already in place, the piston isn't. The dust boot seems to be snug onto the caliper and I'm afraid to even try pulling off the dust boot at all so I can start placing the piston back into the bore.
What should I do?


Reminder, The seal, dust boot and piston all look in fine with no scratches, dents or any sign of damage.

[Billfitz]

Put it together, put a block of wood into the caliper to prevent the piston from being pushed out, bleed the caliper, clean it up and then pump the brakes a few times to see if there's any fluid leaking past the piston seal. I had this happen to me once, after re-assembly it was fine.

[WillGood Hunting]

Originally Posted by Billfitz

Put it together, put a block of wood into the caliper to prevent the piston from being pushed out, bleed the caliper, clean it up and then pump the brakes a few times to see if there's any fluid leaking past the piston seal. I had this happen to me once, after re-assembly it was fine.

By putting back together, how? The dust boot prevents me from putting the piston back in.

[Billfitz]

Remove the boot, attach it to the piston, insert the piston, put the boot back on the caliper. https://www.newtis.info/tisv2/a/en/f...kes/1VnZ2zqrLv

[WillGood Hunting]

Originally Posted by Billfitz

Remove the boot, attach it to the piston, insert the piston, put the boot back on the caliper. https://www.newtis.info/tisv2/a/en/f...kes/1VnZ2zqrLv

Well.. I've tried to pry off the dust boot by hand over and over but it won't budge... I wonder if I should just get a new caliper in a kit and rebuild. I went ahead and ordered a new dust boot and pressure seal ring just for safer measures and in case I damage this dust boot... but sure seems like it just won't come off.
This is a bummer. I haven't been able to drive my F30 since this.

[Billfitz]

You may have to trash the old boot to get it off, but all you need to get is a new seal/boot kit.