The e21 rear drum brake upgrade is a cheap, effective way to improve rear braking, particularly to match a "big brake" upgrade up front. It involves simply pulling the required parts from a donor 320i and exchanging them for the 2002 parts. There are a couple of complications, but its an otherwise fairly straightforward job.
Tools and Parts Needed:
- 36mm socket and big breaker bar for big rear hub nuts. The SAE equivalent is approximately 1 7/16"
- 10, 13, 17, and 19mm sockets and/or box wrenches
- 11mm flare wrench for brake fittings
- 7 and/or 8mm combination wrenches for the bleed nipples
- 5mm allen wrench
- BIG screwdriver or something to pry with
- 3-jaw gear puller for pulling the hubs
- Brake cleaner (get a few cans!)
- New 320i wheel cylinders (optional but recommended)
- Brake Drums from Donor e21 (you could opt for new ones if you feel like spending the extra $$)
- Complete e21 backing plate assemblies with hardware - no need to remove the shoes or any other hardware from the backing plates. Pull them as a unit. (Optional also is a new brake shoes kit instead of the used ones.) The retaining pins are not found on the 2002, so make sure you keep the pins and the fork clips that hold the shoes to the backing plates (one per shoe = two per assembly, or two per backing plate). These pins go in from the backing plate through the shoe and are held on by the fork clip (which also acts as a spring). Again, keep these, or get a new brake harware set for either a 320i or a 318i. The 318i kit uses a small button-like retainer over a spring to hold the shoe to the backing plate.
Your first step will be a trip to the local boneyard for the parts (see list). Don't make the mistake of pulling the shoes and associated hardware from the plates before removing them. Since you are going to be putting a huge amount of removal torque on the main hub nuts, you will need to find a donor that is either sitting on the rear wheels or has working emergency brakes. If that doesn't work, try to wedge some spare wheels/tires under the donor wheel to keep it from turning.
Once the main nut is off or just loose, pull the road wheel and then use the 5mm allen wrench to remove the hold-down bolts on the 320i drum. Remove the drums (mark them left and right first) and then use the 3-jaw puller to remove the 320i hubs. The hubs themselves are useless to you (wrong splines for the '02 application) so don't bother "rescuing" them.
The backing plate bolts are 17mm, and it helps if you undo the e-brake cable at this point to get at them a little easier. Remove the rigid brake lines with the 11mm flare wrench. Use the big screwdriver to pry the backing plates away from the trailing arms. Congrats! Pay for the parts and head on home.
The same procedures apply to removing the same parts from your '02, and the reassembly procedure should be obvious at this point. In order to re-fit the 320i drums, you may need to loosen the e-brake cables under the rubber boot at the base of the parking brake lever between the front seats.
Reassemble and fill the system with new fluid. A pressure bleeder is a VERY handy tool and makes the bleeding process much easier. Bleed starting from the furthest corner from the master and close in from there. I (Rob) have personally found that the exact bleeding order isn't important, but your mileage may vary. If anything seems iffy, just bleed everything again.
That's it! The entire procedure took Marty about six hours, including removal from the '83 320iS and installation on his '73 2002.