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11-08-2010 11:54 AM #1
Tips from rear brake, p-brake, caliper rebuild
Over the weekend I put the car up on stands and did a bunch of things I had been putting off. One area of this was rear pads, rotors, parking brake rebuild and caliper rebuild. I wanted to share a couple of things "learned" during this process.
1/ Balo has been my go-to brand for rotors for some time. Balo now makes a coated series, similar to the Zimmerman CoatZ I suspect. I ordered these for the rear since I have read these coatings are more durable than painting the hats myself and it goes all or most of the way through the vent channels. It was indeed a stout, durable coating which appeared to be everywhere - even down the vents. I suspect this will dramatically reduce my salty-winter visible corrosion to the rotor edges and vents, as well as inside where the parking brake operates. They come at a bit of a premium but it looks good at this point.
2/ Various online writeups claim that after disconnecting the caliper, fluid will eventually stop running out. It will not. It will gravity bleed the reservoir dry if you're a slow worker on the caliper rebuild. Be careful, or clamp the lines. I elected not to clamp the lines to be sure not to damage them, but monitored throughout.
3/ Various write ups also say that installing the new dust boots on the calipers is a matter of popping it into the groove on the piston, pressing it into the caliper and poof, you're done. Wrong. When you tear into the fine print that comes with the dust boots you're supposed to use a special ATE seating tool to seat the boot onto the caliper. The boot is a smaller diameter than the area of the caliper it snaps onto in order to provide good lock in place. I did not have said ATE special tool nor any other socket or tin can of the right diameter. (As an afterthought, a properly sized hose clamp probably would have worked well - dial to the right size and tap away). I put the boot onto the closed side of the caliper first leaving the open side unseated. I then tapped lightly on the seal edge with a small dead-blow rubber mallet and that seemed to seat it. I could never get it quite as well seated as the one I pried off (before I knew it wasn't going to be easy to get back on). I don't know if the fronts are different/easier, but you have been warned.
4/ The parking brake - yow what a mess. The area behind the rotor needed lots of wire brushing and the interface between the steel and aluminum suspension had white corrosion. I cleaned it up as best I could, treated with rust converter, and painted with black paint. I don't know why all of this stuff isn't coated from the factory.
5/ All of the tips I saw on reassembling the parking brake were not fun or effective at all. I came up with something I thought worked quite well. I may not be the first to do it this way, but I hadn't read what I did anywhere else. For the rest of the parking brake I referenced a lot of material, but in particular I looked a fair bit at (change x to m) http://forums.bixxerforums.com/forum/showthread.php?t=1381731. I'll link a picture from there (if it works - if not: http://www.bixxerfest.com/forums/attachment.php?attachmentid=215151
I now disagree with that assembly order. What I ended up doing was assembling the adjuster (5), the lower spring (6) an the shoes off of the car. Then you can easily open the top and slide it into position from the bottom. I then set the spring loaded fasteners (2 and 7). Ensure that the tops of the shoes are resting on either side of the fixed metal at the top for support. Reinsert the cable lever mechanism and then install the top spring (4). Nothing but a pair of vise grips could provide the force and grab needed to pull this spring into place. You MUST use at least eye protection. I used a full face shield. When this stuff wants to fly around it will hurt - a lot.
6/ As I mentioned in another thread (http://bimmer.roadfly.com/bmw/forums/e39/9588778-1.html) I had some trouble bleeding. I possibly made a mistake near the MC but it's worth pointing out that rebuilding the calipers introduces a ton of air and stubborn bubbles. You will need to use extra pedal pressure while bleeding and tap the piston with a small mallet A LOT to keep encouraging bubbles. Eurodavid has also said he's had good luck with pre-filling the caliper while it's off the car.
7/ If you're replacing the p-brake shoes, also buy one of the full hardware kits with the springs and spring-loaded fasteners. It's much easier and nicer with all-new stuff and doesn't cost a lot more.
8/ If you're removing the caliper, break the torque set on the brake hose (14mm) before unbolting any part of the caliper. Don't forget to re-torque it after mounting everything back up.
9/ I have always been replacing the rubber slide bushings every time I do a brake job (every 5-7 years). It's cheap and refreshes a part which is integral to good pedal feel and even pad wear
10/ It's been 7 years since my rears were done and they were still wearing slowly and within spec. I found, however, that the backing plates on the piston side were starting to come apart and were flexing and cracking. The inner pad material was worn in a slight concave curve and the rear brakes were probably underperforming even though they weren't technically worn out. I should have done the rears with the fronts two years ago. If you have had your rears for a long time (regardless of miles) or are in a high corrosion environment (salt country, ocean side) keep an eye on this.
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