I decided to overhaul my brake calipers and flexible hoses. This involved new seals, pistons and braided stainless flexible hoses.
When working on the four-pot brembo front calipers I found each caliper had one seized piston. I got an overhaul kit on Ebay which included everything needed, seals, pistons, bleed screws). However, I had previously purchased Stainless bleed screws and braided hoses from Gerry of Phoenix Motorsport a couple of years ago (shows how long I have been meaning to do this job).
Once the calipers were off the car, I plugged the hose hole and sandblasted them before removing anything so as to keep the sand out of the caliper. Then I air blasted them to remove any grit residue, srayed them with brake cleaner before giving them a primer undercoat.
Next, I mounted them in a vice and clamped three of the four pistons so they couldn't move. I connected an airline to one of the bleed screws via flexible hose and opened the screw and used compressed air to lift the un-clamped piston. Removing the dust cover and the piston, then fitting new seals and piston. Repeat the procedure for the next piston.
The seized pistons required soaking with releasing oil and a fair bit of air pressure (make sure you prevent the piston from flying out - they can go with a "POP" - experience!!).
When all pistons had been done, I removed the old bleed screws and fitted blanking plugs before painting with caliper paint. 5 coats and then 24hrs hardening time before refitting to the car.
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When trying to undo one of the connections between the flexible hose and the steel brake pipes I found it had seized completely and WD40, Easing oil and heat application would not shift it. I had to cut the connection off and fabricate a new connection by cutting in a new brake pipe.
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Once everything was fitted back on the car, it was simply a matter of bleeding the calipers (rear and front) according to the BMW procedure.