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Four pot Brembos - centre O-ring - splitting the calipers Fri Sep 05, 2014 4:02 am
Dai
Life time member
I guess this piece of information is available somewhere but I couldn't find it. When you get an overhaul kit for the four-pot calipers you don't get the O-ring because BMW don't expect you to split the calipers. It's the same O-ring as fitted to the P08 caliper and does have its own British Standards number - BS610. I couldn't find the ISO number for our non-UK members - sorry. I bought fifty of the Viton variant from this guy
http://www.ebay.co.uk/usr/bearingshopuk-eb?_trksid=p2059210.m2749.l2754
because they were cheap in that quantity!
When it comes to splitting those calipers, another bit of way-too-hard-earned experience; you can almost guarantee that the bolts are corroded in. I used a lot of heat but more importantly, I took a half-inch drive, quarter-inch allen bit and just touched the sides to a grinding disc so that it needed hammering into the 6mm allen caps on the caliper. No chance of slippage. Inevitably though, one or more bolts won't come free. Don't bother using high speed steel (HSS) bits to drill the caps off because they will slip and case-harden the allen bolts (this applies to P08 calipers with corroded bolts too). Go and buy a set of cobalt drills (6, 7 and 8mm), then drill slow and keep the pressure on to stop them from skidding. You can't do this by hand - you need a pillar drill. Also, tungsten drills are no good because you can't resharpen them but you can resharpen cobalt drills.
(I wish I'd taken a picture of the last bolt I had to drill out from a four-pot. I had it so perfectly centred in the pillar drill that the cobalt drill left a paper-thin wall on the allen bolt and didn't touch the anodising on the caliper casting!).
http://www.ebay.co.uk/usr/bearingshopuk-eb?_trksid=p2059210.m2749.l2754
because they were cheap in that quantity!
When it comes to splitting those calipers, another bit of way-too-hard-earned experience; you can almost guarantee that the bolts are corroded in. I used a lot of heat but more importantly, I took a half-inch drive, quarter-inch allen bit and just touched the sides to a grinding disc so that it needed hammering into the 6mm allen caps on the caliper. No chance of slippage. Inevitably though, one or more bolts won't come free. Don't bother using high speed steel (HSS) bits to drill the caps off because they will slip and case-harden the allen bolts (this applies to P08 calipers with corroded bolts too). Go and buy a set of cobalt drills (6, 7 and 8mm), then drill slow and keep the pressure on to stop them from skidding. You can't do this by hand - you need a pillar drill. Also, tungsten drills are no good because you can't resharpen them but you can resharpen cobalt drills.
(I wish I'd taken a picture of the last bolt I had to drill out from a four-pot. I had it so perfectly centred in the pillar drill that the cobalt drill left a paper-thin wall on the allen bolt and didn't touch the anodising on the caliper casting!).
