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Discussion Starter · #1 ·
Background: Front passenger-side caliper on e39 540i 6M is alternating b/w a full freeze and a sticking where I can just barely rotate the wheel with a substantial amount of effort. This will be the third time in exactly one year my brakes have froze on the passenger side (once of these times the D-side froze simultaneously). The first time was a full freeze on both P-side and D-side, second time was nearly frozen on P-side (VERY difficult to spin wheel; D-side did not freeze at all), and this time it alternates b/w fully frozen and being able to barely spin the wheel (again D-side fine & not sticking at all). I replaced w/rebuilt calipers (OE ATE calipers believe it or not) from AutoZone and ATE guide pins purchased online for the first incident, AZ caliper (with new pins) on the P-side only for the second incident (D-side rebuilt caliper has not given me problems since the first incident). I replaced the rubber brake hose running to the caliper (both sides) the first incident only. System was flushed each time w/ATE LV Brake Fluid and the new pins were NOT lubed during reassembly.

Yet here I am, once again. Today, I started to dissemble the brakes for troubleshooting and found something peculiar: the wear pattern my guide pins. I snapped pics of the top pin on the P-side caliper and both pins on the D-side caliper. As the pictures demonstrate, all 3 pins are heavily worn/galled, supplemented by equally spaced wear-circles of some sort. The bottom pin on the P-side is barely worn at all! They were never this worn relative to my first two caliper replacements. The inside of the rubber bushing the pin is housed in is the same pattern, so that's what's causing the circles, but I have no idea why it would do that considering they are housed in rubber and considering the other P-side guide pin is barely worn at all and shows no wear-circles. I have dust caps for all four caliper pin rubber bushings, so they are not exposed at all. Are they designed to wear like this without lube (per BMW recommendation) while retaining functionality?

BTW, I have eliminated the pins as a possible explanation for the frozen caliper on account of the driver's side caliper pins showing comparable wear but without a sticking caliper. I cracked the bleeder and tried to spin the wheel, but to no avail, which eliminates the new hose as the problem and points to the Autozone refurb'd caliper being in need of replacement. I will check out Nu-Geon and pick up a rebuilt caliper from Eeuroparts. I'm just curious as to if you all think the extremely worn pins are symptomatic of something more serious such as a bent caliper carrier-bracket or wheel misalignment, etc. that's maybe somehow causing these frequent caliper failures. I'm lost as to why the P-side caliper keeps failing!
 

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I have always greased caliper pins with copper based anti-seize or synthetic caliper grease designed to grease pins. Have driven tens of thousands of miles without problems regardless of BMW's instructions not to grease pins.

Rebuilt calipers are always questionable because you don't know who rebuilt them. Was it a contientious individual or just someone slapping parts together? Rebuilding calipers is not hard and you can apply grease under the piston sealing boots to retard corrosion. Do some research and you should find rebuild instructions. Rebuild kits are inexpensive.

BTW-changing brake fluid at least once every two years will help to minimized internal brake caliper corrosion. Changing it every year is even better.

Edit-I can't really tell how badly your pins are worn from your pics but I'd probably clean them with a wire wheel, grease them and reinstall them.
 

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Discussion Starter · #6 ·
I ordered a rebuilt caliper from Eeuroparts.com, which from what I understand is a reputable vendor of refurbs. I will be greasing the new pins when I install the refurb'd caliper to control for that variable this time around.

I just find it odd that the one pin was almost unblemished while the other three looked like hell even though all four were un-lubed. Who knows. :dunno:
 

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Discussion Starter · #11 ·
and your pins are shot.. cause your boots are shot..

but why replace them with rubber that will do the same thing again later down the road?
The odd part is that with every caliper i've installed, the rubber bushings came pre-packed with grease/lube which I removed from the caliper before putting it on the car. I doubt the grease precipitated any problems like BMW cautions about, but I can't completely ignore the possibility it did b/c of the petroleum-based grease degraded the rubber bushings while the rebuilds were sitting on a shelf somewhere for quite a while before making their way to me. Then again they go out as fast as they receive the cores so IDK.

Regardless, I will be experimenting with lubing everything with a synthetic lubricant like others have recommended and monitoring pin wear and the condition of the rubber bushings.
 

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Discussion Starter · #12 ·
Plating on OP's pins has failed causing carbon steel to corrode. I've never seen this on factory pins. I suspect factory pins are not plated but made of a corrosion resistant alloy. I wouldn't reuse those pins.
I was not using Genuine BMW pins, but the ATE brand instead, as the ATE pins were $9 each as opposed to Genuine BMW pins being $20 each.

That is excellent knowledge to take into account before purchasing any pins, good call man. I don't suppose you know anything applicable to the type of rubber in the bushings that people should look for or stay away from?

I ask all these anal-retentive questions b/c after the hassle of dealing with these, I would like to isolate what exactly to look for and what to stay away from in order to identify the best rebuilder for fellow forum members to purchase from, thus avoiding the problems i've had to deal with. :beerchug:
 

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permatex green lube,

This pin issue is a known issue on all bmw's Ive only seen this a billion times..

thats why i dont mess with them anymore, the sport pin's are the way to go.. better more even stopping and much much much longer life Idk why your replacing your calibers though, as long as the piston push's back in.. They are still good
(and they dont leak)
 

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Discussion Starter · #14 ·
permatex green lube,

This pin issue is a known issue on all bmw's Ive only seen this a billion times..

thats why i dont mess with them anymore, the sport pin's are the way to go.. better more even stopping and much much much longer life Idk why your replacing your calibers though, as long as the piston push's back in.. They are still good
(and they dont leak)
Burning2nd, i'm a afraid I don't follow; what exactly are sport pins, i.e. how are they different than the OE pins or even the normal oem aftermarket pins? I've seen different aftermarket caliper bushings, made of brass, but never different pins. Do you have a link to these?

Also, i'm replacing the calipers because in trying to isolate the exact source of the sticking, I cracked the bleeder on the caliper and tried to spin the rotor, with no luck of course. This tells me the piston would not retract into the bore at all after pressure is let off through the bleeder. I'm sure if I put a C-clamp on the caliper and forced it in, it would retract against the corrosion that has built up or whatever is preventing its retraction, but letting off of the brake can't replicate that amount of force and so the caliper needs replacement.

I ruled out the pins as being the culprit as a result of the pins on the D-side caliper being in the same heavily-worn condition, yet experiencing no performance issues with that caliper. The hose is less than a year old, so I highly doubt that is the problem. I purchased a new one to throw on if the sticking remains after I install the new caliper. If things STILL don't work, it's going to the shop to be looked over professionally.
 

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In my 30 years of wrenching the 11 BMW's I've owned, I've never had a factory caliper pin fail or corrode, and I assemble w/o lube. In my experience, guide pins are life of the car parts. Likewise the factory rubber caliper bushings work well. I would not waste money on so called "sport pins" or brass/bronze bushings. They have zero affect on stopping power and the metal-to-metal contact will likely make noise at some point.
 

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I pulled those pins out twice since the car was "born" in 2003 (last time was last summer). They were always shiny, with minimal smudge on them, easily cleaned with a rag. And we have very nasty roads in the winter with salty slush etc. ATE is usually a good brand, but maybe the ATE you have were made in CPR? I know the OEM BMW brake calipers are ATE - mine have the ATE stamp on them. Maybe the ATE parts made in Germany are totally different in quality.

P.S.: And I never used grease on them.
 
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