The Powerlite four piston radial mount caliper starts at 2.26 pounds with a sleek profile,
superior strength, lightweight and durable in higher temperature situations. Easily adapted to a wide range
of sports, rally, and off road driving applications.
Strength comes from a combination of process and design. The process of stress-flow forging re-aligns
the metal's grain structure within the contour of the caliper body. This eliminates the stresses and
interruptions to the internal grain structure that occur when machining a straight block billet. The FEA
generated radial transition design eliminates steps and shoulders in the area between the piston housing
body and the caliper bridges. Incorporating a radius in this critical area substantially increases resistance
to deflection and caliper separation under load.
The Powerlite uses a new 7912 type brake pad that is supported from the top by Quick-clip pad retainers.
This eliminates the need for a pad support step in the bottom of the caliper and adds additional clearance
for mounting closer to the hub on small wheel and rotor applications. The pad radius matches to rotor
diameters between 9.45" (240,0 mm) and 11.75" (298,5 mm), and the caliper fits easily inside many
13.00" (330,2) wheel applications. The Quick-Clips also accommodate easy pad access without caliper
removal. Brake pad compounds are available for the full range of sport and competition applications.
Every caliper is equipped with Wilwood's SRS stainless steel bridge plates. The SRS plates eliminate
the bridge wear caused by pad gouging. The spring-loading action of the SRS plates also eliminates
pad rattle and dampens the vibration harmonics that contribute to squeal under braking. Internal fluid
passages eliminate the need for external tubes. Four corner bleed screws assure simple and effective air
evacuation and allow one caliper to be mounted in of four positions.
Bracket kits are used to install the calipers in place of most lug mount calipers. Radial mounting simplifies
service and the bracket kits provide two planes of adjustment for precise alignment over the disc. Bracket
kits include the radial mount bracket, studs, locknuts, and caliper alignment shims.
The stock 320i rotor diameter (vented and unvented) is 255mm. The volvo caliper (a cast iron girling 4 piston) would fit perfect on the e21 with no modification using a 276mm rotor. There is a larger off the shelf rotor that will work. The mini cooper uses a larger 276mm vented rotor (compared to 255mm 323i rotor) that fits but the rotor hat is shorter. the Volvo 240 4 piston girlings sat on 263mm rotors.
Above: You can run 276mm new mini (2003+) rotors which are 21mm larger than the stock 255mm 323i rotors. The rotor height is 44mm, thickness is 21.9mm, and the hub bore is 64.1mm (compared to 63mm for the e21 hub bore) so you'll have to use hub centric spacer rings to center the rotor on the hub. You may also want to drill the rotor for the hold down bolt. In this picture you can see the gap between hub and disc center bore and a new hole for the hold down bolt:
Above: The caliper has to be mounted on the outside of the mount ears rather than the inside. This will make the caliper difficult to bolt on since the rotor will be in the way. You will have to "walk" the caliper and rotor down into position as you tighten the bolts. Another option would be to drill out the strut threads and use a longer bolt and locking nut behind the rotor. J.K.jr.bad recommends seperating the caliper halves, attach the inside half, install the rotor, then bolt the other caliper half on. I would never do that on my car simply for the brake fluid mess. Before you buy minirotors, bolt your calipers on and verify you have wheel clearance.
The Volvo/Girling front brake upgrade is the biggest bang for the buck in E21 brakes. But as you can see in the photo above, the Vovlo/Girling calipers have 2 hydraulic lines, in the photo above the installer utilized a brake line splitter. The preferred solution to this problem is utilizing an E12 master cylinder. This allows you to run the stock 320i vented rotors without the price tag of upgrading to the 323i vented calipers. For much less than stock 323i calipers you can get 4 piston calipers with about 30% more pad area.
According to parts suppliers, calipers off of ANY volvo 200 series car (240, 240 turbo, 242, 244, 245, 264) from 1975 to 1991 with vented rotors will work. Some of the earlier cars used ATE calipers which are interchangable with the girling calipers. Parts suppliers no longer carry the ate calipers so you'll get girlings (more common) anyway.
Here's the volvo naming convention:
1975-1979: three digits (in the format 2XY, where X represents the number of cylinders and Y represents the doors: 2 for coupés, 4 for sedans, 5 for station wagons)
1980-1985: trim level letters (the three digits were omitted in North American market)
1986-1993: 240 followed by trim level letters (third digit no longer reflected body style)
The cheapest deal on rebuild calipers I've seen is on rockauto.com.
Left Girling Caliper '75-'91 Volvo 240w/Vented Front Rotors - Volvo P/N 5002028
Right Girling Caliper '75-'91 Volvo 240w/Vented Front Rotors - Volvo P/N 5002029