Hello there and welcome to the BMW Car Club of America.

If you are a BMW CCA member, please log in and introduce yourself in our Member Introductions section.

caliper piston rebuild procedure

Discussion in 'E36 M3 (1995-1999)' started by tjrinaldi, Mar 21, 2011.

    • Member

    tjrinaldi

    Post Count: 33
    Likes Received:0
    After searching, I can't believe no one has asked about this before...

    I am currently in process of rebuilding my ///M calipers for E36, and am doing so because of a stuck/rusted piston. I am under the impression that the rebuild is cleaning everything up and re-installing new seals (from the kit). IS THERE ANY NEED FOR LUBRICANT/SEALING COMPOUND/ETC AND WHAT IS IT? It is entirely possible I am missing something huge here, but I don't know.

    If there's anyone out there who knows about this please let me know if a special compound is needed in there and what kind, perhaps, they recommend. Thanks in advance.....hopefully someone knows about this before I re-install the new seals...
    • Member

    MGarrison

    Post Count: 3,039
    Likes Received:163
    No lubricant needed, as far as I know. Once filled, I suppose the brake fluid _may_ act as any lubricant. If the piston or the piston bore in the caliper is particularly rusty, you may be better off to replace the caliper than attempt to use it. Last thing you'd want is rust damage compromising the tight clearance/tolerances which normally doesn't allow for any brake fluid leakage past the piston. I don't know the exact spec, but I think the pressures involved when the brakes are applied is hundreds of psi, or between 1 & 2 thousand psi. A pitted piston or caliper bore might leak under brake system pressure, or damage the piston seal and allow for leakage.

    If the piston and caliper's piston bore are clean, I think you should be able to press the piston back in without too much resistance.

    cwbiii guest

    Post Count: 160
    Likes Received:0
    Typically you may need to hone the cylinder... one is on the tool wall or tool carousel in many auto parts stores.(NAPA) Its relatively simple to use and comes with directions.
    Similar to a hone for engine cylinders, only smaller.

    Chuck
    • Member

    granthr

    Post Count: 1,583
    Likes Received:2
    Before reassembly coat everything lightly with brake fluid, it will make it go back together easier, but not easy.

    Be careful when removing the piston. The easiest and most dangerous way is with compressed air. Shove lots of towels between the piston and the arm that holds the brake pad. You don't want that thing to go flying. Goggles and a face mask are also a good idea, as you will be spraying brake fluid out as well.

    Clean all the exterior surfaces with a wire brush, being careful not to score or damage the machined surfaces. Clean up the machined surfaces with a lint free cloth and brake fluid. If there is any damage to the machined surfaces the caliper might not be salavable.

    Once apart and cleaned up look for pitting on the piston and cylinder bore. If there is pitting along the sides you probably should get a whole new caliper. If there is pitting on the bottom (where there is no lateral movement between the two pieces) it might be okay to reuse.

    Rebuild the caliper with all new seals, boots, and lock rings if it has them. This is not a super difficult job, just be sure you take your time and not to damage anything.
    • Member

    MGarrison

    Post Count: 3,039
    Likes Received:163
    Just wanted to reiterate - wire brush on EXTERIOR parts only!

    It takes very little air pressure to pop out the piston (easily done with a rubber-tipped blower-gun: http://www.harborfreight.com/rubber-tip-air-blow-gun-3962.html).

    If you push the air gun into the bleeder screw hole hard and give it a full blast, you'll shoot the piston out like firing a gun (overkill, potentially messy & unsafe). A couple light spurts of air should be adequate.
    • Member

    CRKrieger

    Post Count: 1,616
    Likes Received:21
    Ummm ... guys, if you put a piece of wood into the caliper where the rotor and pads would normally be, the piston won't go flying anywhere.

    I don't sweat a little pitting on the piston or walls if it will clean up with a light sanding (like 1000 grit or higher cloth). I've used hones before, but not always. The piston-to-seal surface doesn't see significant movement and the piston seal will conform to minor imperfections quite easily. The biggest enemy in your caliper is a damaged boot that allows dirt and moisture past it. Otherwise, things pretty much stay the same inside there for tens of thousands of miles.
    Ken.S.330 likes this.
    • Member

    MGarrison

    Post Count: 3,039
    Likes Received:163
    Yes, but that requires advance planning and having wood on hand... all of which has gone looonng by-the-wayside by 3:45 am when you realize you _still_ have to rebuild the brake calipers before being able to drive to work in the morning! :p
    Ken.S.330 likes this.
    • Member

    CRKrieger

    Post Count: 1,616
    Likes Received:21
    OK; yeah. Been there; done that. Actually took apart a seized front caliper, hand-sanded the corrosion out of it and slapped it back together without a boot (the old one was torn all to hell and I didn't have a rebuild kit on hand), put it back on and bled it. It ran that way for about a week until I got a rebuilt one to replace it. One of those times that understanding the simple technology tells you how much you can get away with. ;)
    • Member

    Mike Bergin MikeB

    Post Count: 7
    Likes Received:1
    Just curious as to how you were able to bleed the system. My 97 M3 requires a computer to tell the pressure sensors on the ABS and AST systems to stay open so that the system can be bled. Is there a way to bypass this? I have a master cylinder starting to go bad and would really like to do this myself, but I'm hedging because if I can't bleed the system myself then I'll end up taking it to the dealer and I don't like the Vaseline they use!
    • Member

    MGarrison

    Post Count: 3,039
    Likes Received:163
    Old post here, reply from original poster, not likely - Charlson may have some insight....
    • Member
    • Technical Service Advisor

    charlson89

    Post Count: 1,382
    Likes Received:69
    Ahh the poor mans ABS bleed is what your looking for. So first I suggest you at least purchase yourself a power bleed of some kind sold and most auto stores or bavauto makes a really nice one. This makes manual bleeding so so so much easier. So you will use this tool and do manual brake bleed starting the normal way the RR to LR to RF to LF making sure all the bubbles come out and pushing on the pedal a couple times will help as well. Ok now make the vehicle drivable so you can go out and make ABS stops. Basically speed the car up and slam the brakes causing the ABS to activate similar to what the dealer tools does. You will need to do these stops a few times. Then back to do another bleed of the system. You may need to do this complete procedure a few times to get all the air out. WORD OF CAUTION while driving the vehicle do this in a wide open area because you brake system still contains air and your brakes may not work well because of this. So keep you hand on the e brake and be cautious. Also make sure you DOT 4 brake fluid.
    • Member

    MGarrison

    Post Count: 3,039
    Likes Received:163
    Also, there's the ludicrous notion of bench-bleeding the master cylinder so as to have most of the air out of it and not push all that air through the system. Every time I tried that, it was an utter failure, no way to get the lines connected to the master cylinder fast enough to not just make a big mess of brake fluid draining out the bottom of the master cyl. everywhere (might google up some suggestions, d-i-y's, or youtube vids for master cyl. bleeding). Pressure bleeder, yes, me likey. Now, one idea to minimize the air-thru-lines-with-a-new-&-mostly-empty-master-brake-cylinder... bleed out the rears & fronts so there's fresh fluid in those lines, install new master cyl., and reverse-bleed via one of the front and rear already-bled lines (then you wouldn't be backflushing old fluid thru the lines into the new master cyl). Haven't done this myself but have considered it. If, say, you could adapt your regular caliper-bleeder hose to the output line, or maybe cap, of a pressure bleeder, and make sure it's well sealed to the bleeder nipple, you could push fluid back thru the system and fill the master cyl. from the bottom up, which might accomplish the bulk of a bench-bleeding process. I suspect you'd still have to do some pedal-pushing bleeding, but seems like that might cut introducing air thru the system substantially. If you don't have someone to help do the pedal pushing while you open/close the caliper bleed nipples for some old-school bleeding, you can do it yourself - make sure the bottom of your bleeder hose stays submerged in fresh fluid; if you have a smartphone or camera w/ recording capability, shine a bright light on the bleeder hose at the nipple (assuming it's clear bleeder hose, or clear-ish), and position your phone, etc. to record a video of the bleeder hose - open the bleeder screw & start your vid. recording - go pump some fluid thru the lines, come back, close the bleeder, and review the vid. to see if you've pushed out air bubbles. If the bleeder line isn't clear, another option would be bleed into a clear plastic bottle (water bottle perhaps) and record that, should be able to see air bubbles if the bottle's clear. Repeat as necessary. For old or original master cyl's, it's a good idea not to push the pedal to the floor, or beyond your typical range of pedal travel, since if the old piston is rusted, you could blow the internal seals; obviously on a new master, that's not an issue. I used a vacuum bleeder for a long time, but have gotten the best results for firm pedal from pressure bleeding for the bulk of it, and finishing off by re-bleeding with a brief foot-pump bleeding of each caliper.

    As for public-road emergency stops, not only someplace open, but secluded - you definitely don't want anyone near you and especially behind you. None of us would ever need caffeine if we were forced to contend with unexpected & inexplicable full-emergency stops in front of us every morning. Oh, wait, never mind, that is rush hour... and caffeine is still needed... :D ;) Do your bleeding and ABS-cycling on a rainy day and you'll be able to cycle the abs more times from lower speeds.

    Street brake fluid: ATE Typ 200 - http://www.bavauto.com/fland.asp?part=ate gold
    • Member

    CSBM5

    Post Count: 344
    Likes Received:3
    The easiest way is to buy one of the available BMW software tools online along with the OBDII cable. Then you can simply use it to run the proper bleed procedure of the ABS. From experience, you will not likely be able to properly, fully, bleed a system with upstream air introduced by just doing multiple ABS applications and rebleeding. Besides, it's much easier and cheaper to just buy the s/w from somewhere like http://www.bcables.com/.
    • Member

    Mike Bergin MikeB

    Post Count: 7
    Likes Received:1
    Thanks for the information on the master cylinder installation and bleeding process, but since I have your interest I have another little dilemma. On occasion the same M3 will not crank. The battery has 12.3 volts at no load and has no indication of significant voltage draw even with the high beams and blower motor on. All fuses are good, and none of the relays appear show any indication of burning or corrosion. I've checked all of the ground connections at the battery, and the connections to the body. I've checked the wires at the starter and solenoid and the connections are clean and tight. The clutch switch appears to function normally (test light connected to the both wires of the switch lights when the clutch is depressed. If you have any ideas or think of something that might resolve the issue, I would appreciate the feed back. Thanks in advance, --- MikeB
    • Member
    • Technical Service Advisor

    charlson89

    Post Count: 1,382
    Likes Received:69
    So this no crank is intermittent? When it happens is there any noise from the starter, like a click?
    • Member

    Mike Bergin MikeB

    Post Count: 7
    Likes Received:1
    No click. Its like there is no power to the solenoid or starter but the battery is strong. My thoughts that it may be a bad EWS module or relay. It seems like power is being prevented from getting to the starting system thats why my thoughts are that the EWS may be at fault. Any way to check the system. I'm not getting any codes being set either,so if you have any ideas please let me know.

Share This Page