ZCP Caliper Rebuild Pistons and Seals, Questions

[PSUEng]

Looking for input from those who have done caliper rebuilds on a few things regarding a little caliper rebuild project i"m going to get into. While replacing pads/rotors on my 2003 M3 (non-ZCP) with 80,000 miles, I noticed the piston dust boot on one front caliper was unseated (I tried to reseat but couldn't) and the other side caliper dust boot was cracked. So, I thought I'd get a set of used calipers and rebuild them (seals, pistons, dust boots, bleeders, deep clean) and then swap my existing calipers out.

Looking into this, I've a few questions:

1) For seal kits, is the ATE branded stuff fine in lieu of the BMW OE stuff at 6x the price?
2) I only see front pistons available at Bimmerworld--can I get ATE or another reputable brand pistons somewhere? None of the places I usually check have any, especially the rears. Prefer some OE/OEM parts here, not some random stuff.
3) Looks like only the BMW OE seal kit is available for the rear ZCP calipers--anyone know of a source for ATE branded kit?
4) What is an acceptable assembly lube in this situation? I've seen some use brake fluid to re-seat the piston--is there a good DIY anywhere?
5) Is it an issue if I run the ZCP rear caliper on a non-ZCP car? I think I read years ago there was a difference in master cylinder/booster unit between the standard and ZCP cars, or maybe it was a programming setting (?)

Thanks in advance!

[cobra]

Looking for input from those who have done caliper rebuilds on a few things regarding a little caliper rebuild project i"m going to get into. While replacing pads/rotors on my 2003 M3 (non-ZCP) with 80,000 miles, I noticed the piston dust boot on one front caliper was unseated (I tried to reseat but couldn't) and the other side caliper dust boot was cracked. So, I thought I'd get a set of used calipers and rebuild them (seals, pistons, dust boots, bleeders, deep clean) and then swap my existing calipers out.

Looking into this, I've a few questions:

1) For seal kits, is the ATE branded stuff fine in lieu of the BMW OE stuff at 6x the price?
2) I only see front pistons available at Bimmerworld--can I get ATE or another reputable brand pistons somewhere? None of the places I usually check have any, especially the rears. Prefer some OE/OEM parts here, not some random stuff.
3) Looks like only the BMW OE seal kit is available for the rear ZCP calipers--anyone know of a source for ATE branded kit?
4) What is an acceptable assembly lube in this situation? I've seen some use brake fluid to re-seat the piston--is there a good DIY anywhere?
5) Is it an issue if I run the ZCP rear caliper on a non-ZCP car? I think I read years ago there was a difference in master cylinder/booster unit between the standard and ZCP cars, or maybe it was a programming setting (?)

Thanks in advance!

1. I don't know, it's probably fine. BMW doesn't make seals so ATE might very well be the OE supplier.
2. Again, most likely.
3. Not sure.
4. I have used a small amount of silicone grease (3M brand). It lubricates far better than brake fluid and won't interact with DOT4. Just use it sparingly.
5. Dunno.

Hope that helps on #4 at least lol

[akamin68]

I recently rebuilt all my stock e46 m3 calipers and used Castrol Red Rubber grease. https://www.amazon.com/GENUINE-Corro...s%2C155&sr=8-3

Sent from my BTV-W09 using Tapatalk

[PSUEng]

I recently rebuilt all my stock e46 m3 calipers and used Castrol Red Rubber grease. https://www.amazon.com/GENUINE-Corro...s%2C155&sr=8-3

Sent from my BTV-W09 using Tapatalk

Thanks for this info! Looks maybe similar in spec to some Toyota "Rubber Grease" which is a lithium soap-based glycol grease that they specify for rubber brake parts (slide pins, etc. but not metal to metal). I may be able to get away with using that, as I have a tube I use on my Toyotas. Seems the temp ratings are similar and being glycol based, won't interact with the fluid. Interestingly, the ATE Plastilube explicitly says do not use on rubber; so I've used that only on pad to carrier, piston surfaces.

[Estoril]

I use this:



I don't anything on rubber not needed for assembly. I'm not looking to attract (and hold) abrasive grit there. Rubber boots are changed when they get funky.

[MarcZCP]

5) Is it an issue if I run the ZCP rear caliper on a non-ZCP car? I think I read years ago there was a difference in master cylinder/booster unit between the standard and ZCP cars, or maybe it was a programming setting (?)

I don't recall if there is a specific hardware/setting for ZCP/non-ZCP brake system, but I do know that there were changes on both the front and rear brakes for ZCP cars. On the rears, it was just a larger caliper piston. The car came with cross-drilled floating rotor but it is the same size as the regular M3. On the front though, it is a larger rotor. The caliper itself is the same piston diameter, but it sits on a different bracket to push it outwards. In engineering terms, comparing ZCP brakes to regular M3: Rear brakes have larger force, same moment arm. Front brakes have same force, larger moment arm. The net effect is an increase in brake torque in both cases. Whether these scaled up by the same percentage or not I'm not sure - if they don't scale the same, there would indeed be some hardware/setting to correct for this. What I can say though is that the combination of rear ZCP calipers with regular front brakes was never offered. So, if you want to run ZCP calipers, you will at least need the rotor and caliper bracket from a ZCP, and before committing to this you should check to make sure your 2003 has the hardware to accept the ZCP setting (if any).

IMO, it's not worth going to this trouble to "upgrade" to ZCP brakes. On the street, there's no real benefit. On the track, the ZCP is still marginal at best, and there are far better upgrades for that purpose. And then, when it comes to maintenance you're stuck with ZCP brake parts which are more expensive and more limited in terms of options

[PSUEng]

I don't recall if there is a specific hardware/setting for ZCP/non-ZCP brake system, but I do know that there were changes on both the front and rear brakes for ZCP cars. On the rears, it was just a larger caliper piston. The car came with cross-drilled floating rotor but it is the same size as the regular M3. On the front though, it is a larger rotor. The caliper itself is the same piston diameter, but it sits on a different bracket to push it outwards. In engineering terms, comparing ZCP brakes to regular M3: Rear brakes have larger force, same moment arm. Front brakes have same force, larger moment arm. The net effect is an increase in brake torque in both cases. Whether these scaled up by the same percentage or not I'm not sure - if they don't scale the same, there would indeed be some hardware/setting to correct for this. What I can say though is that the combination of rear ZCP calipers with regular front brakes was never offered. So, if you want to run ZCP calipers, you will at least need the rotor and caliper bracket from a ZCP, and before committing to this you should check to make sure your 2003 has the hardware to accept the ZCP setting (if any).

IMO, it's not worth going to this trouble to "upgrade" to ZCP brakes. On the street, there's no real benefit. On the track, the ZCP is still marginal at best, and there are far better upgrades for that purpose. And then, when it comes to maintenance you're stuck with ZCP brake parts which are more expensive and more limited in terms of options

I'm not really looking for an upgrade, so to speak. Just bought a set to rebuild, and fit to my car out of convenience and as a matter of maintenance; the stock setup is quite adequate for my use. I just put the ZCP/CSL pads on and notice an improvement over what was on the car, I''m content with it.

[PSUEng]

So I've managed to get these disassembled, and the pistons appear to have cleaned up very nicely; popped out with just a little bit of air applied to the hose inlet. I plan to touch up the calipers with some black paint, and...note the photos, a bit of oxidation in the cylinder near the brake hose inlet--is this OK or does it need to be 100% removed? Also at this point, debating the OE BMW rear seal kit--big $$, and few places have the Centric kit. But this is big work to disassembly, and pure filth to work in.

[Estoril]

They should be fine until the next rebuild. The Centric seals are fine.

[PSUEng]

Thanks for the input. I did notice that on all four of these calipers, once I popped the pistons out, this solid material was inside the caliper bore--is this a solidified / congealed brake fluid? See attached picture, with white clumps inside the cylinder.

[Estoril]

Thanks for the input. I did notice that on all four of these calipers, once I popped the pistons out, this solid material was inside the caliper bore--is this a solidified / congealed brake fluid? See attached picture, with white clumps inside the cylinder.

I can't get a good sense of it as I've never seen it before. Possibly moisture contamination in the fluid. Watch your bleed-off to ensure it comes out clear. Else keep bleeding.

Check the Master Cylinder for junk.

[TropicalM3]

I don't recall if there is a specific hardware/setting for ZCP/non-ZCP brake system, but I do know that there were changes on both the front and rear brakes for ZCP cars. On the rears, it was just a larger caliper piston. The car came with cross-drilled floating rotor but it is the same size as the regular M3. On the front though, it is a larger rotor. The caliper itself is the same piston diameter, but it sits on a different bracket to push it outwards. In engineering terms, comparing ZCP brakes to regular M3: Rear brakes have larger force, same moment arm. Front brakes have same force, larger moment arm. The net effect is an increase in brake torque in both cases. Whether these scaled up by the same percentage or not I'm not sure - if they don't scale the same, there would indeed be some hardware/setting to correct for this. What I can say though is that the combination of rear ZCP calipers with regular front brakes was never offered. So, if you want to run ZCP calipers, you will at least need the rotor and caliper bracket from a ZCP, and before committing to this you should check to make sure your 2003 has the hardware to accept the ZCP setting (if any).

IMO, it's not worth going to this trouble to "upgrade" to ZCP brakes. On the street, there's no real benefit. On the track, the ZCP is still marginal at best, and there are far better upgrades for that purpose. And then, when it comes to maintenance you're stuck with ZCP brake parts which are more expensive and more limited in terms of options

On Realoem I see that rear caliper repair kit only has 1 part number, would that indicate that they both use the same kit? They quote a different part number for the Caliper Housing so I'm not quite understanding, if they use a larger piston, is it that the seals are the same?

[PSUEng]

On Realoem I see that rear caliper repair kit only has 1 part number, would that indicate that they both use the same kit? They quote a different part number for the Caliper Housing so I'm not quite understanding, if they use a larger piston, is it that the seals are the same?

Caliper housing and seal kit are different part numbers from the non-ZCP M3.

[01M3Fan]

Search the centric website for the pistons for the rear calipers - I've bought them before along with their seals.

[PSUEng]

Thought I'd give a quick update on this project that is taking longer than thought.

Pistons are all cleaned up and look fantastic--maybe will hit the insides of them again, but the outer surfaces are great.

All calipers and brackets have been painted with Duplicolor Black Caliper spray.

I have new bleed screws for all, and ATE front seals/boots.

For the rear seals and boots, turns out the only option is to get OEM BMW for $45 per caliper. Now, the boots on the rears look fantastic; I did not remove them because they apparently attach much differently than the fronts and, from surfing ZPost, require a special tool to reinstall or some swearing.

So my question: I retained the original piston seals and they "look" great--no tears, cuts, cracks, nada. However, these came off a Z4M with 76,000 miles and I have this all torn down so, options are:

1) Re-use boots AND seals on the assumption that the seals quite possibly could last much longer
2) Re-use boots and order new seal kits, and replace the square cut seals.

I contacted a few online parts places as well as my local Centric dealer, searched everywhere--I can't find a non-BMW rear kit. And honestly, I don't know where Centric makes parts but the lessons I've learned on this car include one that is for any rubber sealing part, use OEM BMW or the exact maker of the OEM part (so in the case of the front kits, I'm all good with German made ATE--but they don't offer an ATE rear kit).

Any thoughts on my rear seal options are welcome.

Secondly, it seems that if I run the rears on my standard (non-ZCP) car without running the larger front rotors it will introduce some rear bias which, according to some, might be beneficial. I need to look into this more but, for my street driving it may very well be just fine. Since I JUST put on new ZCP front pads and standard rotors up front a few months ago (before getting this set), I may or may not run the larger front rotors since I now have the proper brackets. Anyone find fault with getting some more rear bias? To MarcZCP's point earlier, there may be more to this, I'll need to research more. But way back in the day, BMW offered this entire retrofit kit for $1500 (I didn't have the money at the time, unfortunately) and I don't remember anyone talking about any issues installing into a non-ZCP car.

From what I find, the biasing with the MK60 booster is:

Non-ZCP: F=60.6% R=39.4%
ZCP: F=58% R=42%

Not sure how to actually re-calculate this for my case though...

As an aside, Below are a few pics of "before" and after, up to final cleaning. Not yet reassembled. I still have some minor oxidation inside the bore where the fluid enters the caliper that I need to hit, but overall I think these are turning out great...