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320i Rear Drums Upgrade

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.

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As a warning, I had retrofitted Tii trailing arms before performing this rear brake upgrade (in case it matters, but I don't think it does). I found the e-brake cables too short by about 1/4 inch after fully extending both from the handle inside the car. I'm told parking brake cables from a Turbo are the necessary solution (available on eBay).

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An option I found to deal with the slightly short brake cables was to increase the depth of the slot on the parking brake actuator arm on the shoe. This gave me the 1/4" of slack I needed to get the drums on with some room for adjustment.



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Thanks for the write-up!


Two questions:


1. What model years 320i does this work with? 

2. What was the approximate cost of the parts from the yard?

1. All year US spec E21 will work

2. Approx. $50-$90 (some yards may have a 40% off sale going on, and price may vary depending on what cashier you get. Some will charge you for every nut & bolt!)

Update 03-19-16: Just purchased everything for the rear brakes from the junkyard (no 40% off sale today). Told the cashier I had both complete rear brake assemblies, showed it to him, and he only charged me for the rear brake drums. Total cost = $35 + gas + time (rear wheels were already removed).

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A few notes from having done this this weekend with a kit from Ireland Engineering.


First, I am generally willing to pay up for new parts to avoid having to go to the junkyard, so I got the prefabbed kit - http://www.iemotorsport.com/bmw/item/02bbk06.html


While I have had good luck with IE in the past, I was a bit disappointed with the generic pads that were included and really, really disappointed that they didn't get the hardware in the box (They did get them here the next week).  After some searching around (including here on the forum), I ended up ordering some RS4s (and fronts, too) from Porterfield (rear for 250mm - https://www.porterfield-brakes.com/product_info.php?productID=4013) (front for tii - https://www.porterfield-brakes.com/product_info.php?productID=3506)


Motivated by a desire for no rust behind the Panasports, I opted to paint the drums as well, using Rustoleum flat BBQ paint.  While not necessary, I masked off the center circle where it will meet with the wheel (It just seemed correct to do it that way).


A couple quick things I learned the hard way:

  • The pins for the retainer clips, on my car at least, needed to go in before the backing plate was mounted (or, in my case, remounted)
  • Like others (me, being me, I discovered others after I battled this myself), I had to file the inside of the e-brake notch to get the drum over the pads.  With all the power stuff I have, this was done manually, and after 30+ years of driving a desk, my arms were not fully prepared. [pic - filed notch with unaltered one for comparison]. 
  • I was nervous about overdoing it with the file and took them on and off a ton of times.  A tip as a result - a 90 degree pick is a great way to get the various springs off (and the retainer springs back on).   I figured this out after about 1000 times using lesser means. 

A couple things a learned the easy way:

I am going to drive a couple days and readjust the rears after they bed in a bit better, but so far, so good. 


Notch comparison.jpg


Rear brake.jpg

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