About the 323i rear brakesThere is one system on the E21 323i that is completely unique among all other BMWs. All E21 models except the 323i used drum rear brakes. Rear disk brakes were only used on the 323i. Besides that, many of the parts used on the 323i rear brakes were not used on any other BMW model. This can make parts availability a bit troubling. This page contains all I've been able to put together about servicing and upgrading the E21 323i rear brakes.
The easy stuff first - the rear rotors (discs) are the same as the ones used on all E30s with rear discs except the M3. So those rotors are easy to find, and not expensive, either, unless you pop for the cross-drilled and/or slotted ones. Like most BMWs, the parking brakes are miniature drum brakes contained inside the hub area of the rear rotors. They seldom wear out, and I haven't researched whether any of those parts are common to other models. I'll add that information to this page at a later time. I do know that the parking brake cables are specific to E21 323i.
The drum brake E21s use four flexible brake hoses, one to each front caliper and one at the pivot of each rear trailing arm. The 323i uses six hoses, four of which are identical to the drum brake car's hoses. The remaining two hoses connect directly to the rear calipers. These hoses attach using banjo bolts, which make them different from any other BMW brake hose. Their rarity - of course - makes them rather expensive, around $50 each. A good alternative is to get a set of stainless braided teflon hoses from Korman (the only supplier I've heard of who has them for E21 323i). At last check, the entire set of six hoses was less than $100, which means you get all six high-performance hoses for the price of the two rear stock ones. When I added those hoses with no other changes (fresh DOT 4 fluid, of course), the brake pedal felt noticeably firmer.
There were two different rear caliper types used on the E21 323i, early (through ~78) and late ('79 and up). Both styles are similar and were only used on this model. Similarly, the rear pads are specific to these cars and are not going to be easily acquired locally. There is a pad wear sensor on the right side, which is the same one as is used on the front of all E21s and many other '70s and '80s BMW models.
Factory pads (generally Texar) are still available from numerous sources, but aftermarket pads can be a bit tougher to find. Korman lists Ferodo in their catalog, but I don't know if they are really available. BMP Design had PBR (formerly Repco) Deluxe and MetalMaster rear pad sets in stock during the Summer of 2000.
Seal kits to rebuild the calipers are still available from BMW in Germany, as are the pad hardware kits. If your local dealer can't help you with them, Maximillin Importing can. But note that (at least for the later style caliper) BMWs part references (both CD-ROM and the old fische) call for only a single kit to rebuild both calipers - not so, you need one kit for each caliper! The calipers themselves are still available new, but are rather expensive (~$250 each).
Another option is to fit E30 rear calipers and pads. This makes parts availablity much simpler, everyone knows what brake parts an E30 325e takes. Plus the E30 pads have more surface area, and in theory should perform better. But there are some modifications needed. You will need the rear flexible hoses from an E30, and the mounting holes are not a direct match. More information on this conversion will be added later.
Original Page at http://home.attbi.com/~e21graymarket/library/r_brakes.html, but has since been discarded.
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