Front brake caliper rebuild - very pitted piston - am I going to die?

[ssyberg]

I recently noticed my front driver side brake dragging a ton (and felt a ton of heat from it after a drive). I removed the caliper and popped out the piston and it had a pretty decent amount of buildup, both on the piston body and the inner lip (not sure what to call this, but the lip above the notch that the inner seal fits in to). It was enough buildup that I couldn't get the piston back in the caliper at all without taking a dremel to it and sanding them both down a bunch (gasp!). According to everything I've read / seen on youtube, I know the whole caliper really should be replaced at this point. I did dremel it down and afterwards the piston was fitting again nicely - it went in smoothly with even pressure. I did replace the boot and the inner seal and the piston is completely retracting now. I put it all back together, bled the fluid, and took it out for a drive. It brakes nicely and the wheel is spinning great, no drag, no excessive heat... So it's definitely no longer seized and it's presumably re-seating itself/retracting fine now.

So I know the standard response here is "it's the brakes, spend the money" - but I'd be very interested to know what exactly could happen here - what's at risk with a pitted/not perfectly smooth piston? Is this something that will fail slowly and that I can monitor (e.g. slow brake fluid leak) or are we talking some sort of catastrophic brake failure that's gonna leave me spinning out of control (seizing on the left rotor at 80mph)?

[All2kool]

Remanufactured OEM Calipers from reputable sellers are $40 each EBay. For about $50, you can get NEW at AutoZone or O'Reilly's.

[ssyberg]

Thanks, I likely will get one soon - but I'm still curious. A lot of people who talk about this just say it leads to failure, but no one describes the mechanism. I'm just interested in what pitting actually does to lead to failure because it's not obvious to me.

[ssyberg]

I found a pretty heated debate on this topic, but still seems unresolved: https://www.bimmerforums.com/forum/s...d-Piston/page2

[All2kool]

Thanks, I likely will get one soon - but I'm still curious. A lot of people who talk about this just say it leads to failure, but no one describes the mechanism. I'm just interested in what pitting actually does to lead to failure because it's not obvious to me.

If pitted pistons were perfectly OK, they'd come that way when new. Seriously, though, a pitted piston is an uneven surface. I'll let you take it from here.

[randy72877]

The rough, pitted uneven piston can leak. Probably not a large leak but leaking brake fluid is not acceptable at all. Get another caliper. Not worth the risk.

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[MarcoZandrini]

The engine issue isn’t so much the piston as it is the cylinder. Why? The piston has a large o-ring. This is the interface between the piston and the cylinder.

OP, if one caliper is damaged the chances are the other caliper is in a similar condition. I’d replace both calipers and the brake hoses.

[ssyberg]

The rough, pitted uneven piston can leak. Probably not a large leak but leaking brake fluid is not acceptable at all. Get another caliper. Not worth the risk.

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So hypothetically could you monitor your brake fluid levels and top off as needed? FWIW I did already order a new caliper, but I'm just wondering if this would have been more catastrophic...

[Muzz258]

A couple of question that may help you work through your conundrum
1) What is the function of the piston?
2) how can the function fail?
3) What is the impact on the operation of the device by the failed function? (criticality)

[ssyberg]

A couple of question that may help you work through your conundrum
1) What is the function of the piston?
2) how can the function fail?
3) What is the impact on the operation of the device by the failed function? (criticality)

I think the missing piece in all of these responses is what about pitting causes failure/fluid leakage. I'm guessing this is because pitting creates a slightly abrasive surface which might tear the inner seal allowing brake fluid to leak or drain completely from the braking system.

[EngelhartRacing]

So hypothetically could you monitor your brake fluid levels and top off as needed? FWIW I did already order a new caliper, but I'm just wondering if this would have been more catastrophic...

The brake system is a sealed system. Brake fluid leaking out = air going in. Air in your brakes could lead to catastrophe.

[Eaglesail]

You did right...for the money. The pitted walls of the piston and or cylinder may have a residual leak-bi situation (hold the brake pedal down hard) if you feel the pedal going to the floor...seals within the brake system are allowing brake fluid to leak by.....within the brake hydraulic system....not generally on the ground...hydraulic leaks are internal usually... but not always.

[dhurley34]

Remanufactured OEM Calipers from reputable sellers are $40 each EBay. For about $50, you can get NEW at AutoZone or O'Reilly's.

I agree. Advance Auto usually has them in stock and they regularly have 30% off coupons if you buy online and pick up in store.

[ssyberg]

I replaced the caliper with an Advance Auto reman and it's working great! Thanks everyone!

Note to anyone reading this, the bracket that came with my "new" caliper did not fit and I had to use my old one.