I thought I would try to consolidate info about Subaru rear disc brakes in one location for reference. This post will only cover rear disc brake system parts available as oem equipment on Subarus, either USDM or abroad. There are excellent rear brake systems available from aftermarket manufacturers including Wilwood, Brembo, etc. I will leave info on those systems to other posts. This info applies to Subaru rear disc set-ups from 1990 to current.
REAR CALIPER ATTACHMENT
All Subaru rear calipers ultimately bolt to a heavy-steel rear backing plate, which in turn is bolted to the rear knuckle. This backing plate has a thin steel dust shield, appropriately sized for the rotor, spot–welded around its perimeter.
1. Subaru single pot rear calipers are sliding type calipers, and utilize a caliper bracket to hold the pads and attach the caliper to the backing plate. This caliper bracket could also be viewed as an adapter, which adapts calipers to different sized rotors and vice versa. The single pot caliper attaches to the caliper bracket and the caliper bracket bolts to the backing plate via 5.75” spaced mounting holes. The single pot rear calipers can further be divided into either “older” or newer” style. The actual phasing from “older” to “newer” style caliper varied by model. For Imprezas and Foresters, this seemed to occur during MY98. For Legacys and OBs, the “newer” style calipers appeared on MY00 cars.
2. Subaru 2pot rear calipers(Sti and Brembo) do not use a separate caliper bracket, they bolt directly to the backing plate. The 2pot calipers bolt to the backing plate via 4.5” spaced mounting holes.
INTERNAL REAR HAND/PARKING BRAKE
All USDM Subarus with rear discs since 1990 have utilized an internal drum rear hand/parking brake of 170mm in diameter. The rear drive assembly used on the AWD versions of these cars is designated as R160.
Some recent, JDM and abroad, WRX-Sti and Impreza models have come equipped with a larger rear drive assembly designated as the R180. I am positive these assemblies have been available since 2001, but may have been available back to 1997. Along with this larger rear assembly, these cars came equipped with vented rotors of either 290 or 316 mm utilizing an internal rear drum hand/parking brake 190mm in diameter.
There were/are three rear rotors that have been installed on USDM Subarus since 1990
1. 266x10mm(170mm) solid rear rotor. Most widely used rear rotor. Found on numerous Subaru models from BC Legacys to current WRXs. This rotor is found equipped with a single pot caliper of either the “newer” or “older” style.
2. 266x18mm(170mm) vented rear rotors found on 1990-94 Legacy Turbos. This rotor is found equipped with a wide single pot caliper of the “older” style. The bolt spacing on the caliper seems to be unique to it.
3. 290x10mm(170mm) solid rear rotor. Found on all 2000+ Legacys equipped with rear discs. This rotor is found equipped with a single pot caliper of the “newer” style.
Other rear rotors used on JDM and abroad Subarus since 1990
1. 290x18mm(170mm) vented rear rotor. Found on 2000+ B4s and GT-Bs, et. al. This is also the vented rotor used with the Sti 2pot caliperon on 170mm hand brake equipped vehiicles.
2. 290x18mm(190mm) vented rear rotor. Found on at least 2001+ WRX-Sti(and maybe as far back as 98.) This rotor came equipped with the 2pot Sti rear caliper and the R180 rear assembly.
3. 316x20mm(190mm) vented rear rotor. Found on 2001+ WRX-Sti Limited, some type RAs, Prodrive, S202, etc. This is the F50 Brembo rear rotor and came equipped with the Brembo 2pot rear caliper and the R180 rear assembly.
UPGRADING THE REAR BRAKES
The first thing to do if you want to upgrade is to determine what you have already. Once you have determined that, you can follow the info below to figure what parts you need to get which upgrade. For my purposes I am considering the 266x10mm/single pot rear brake setup (“older” or “newer” style caliper,) the baseline from which to upgrade. If you have rear drums, do a quick search will get you the info needed to prepare for the rear discs options listed here.
1. Legacy Turbo vented rear brake upgrade. Gains: Moving up to a vented rotor of the same diameter yielding more heat dissipation. You will need to replace calipers, caliper brackets, pads and rotors. This upgrade is covered in great detail with pics on the northursalia.com website by our own and beloved North Ursalia.
2. “H6” upgrade (a misnomer, but nice and short.) Gains: Moving to a larger (290mm) solid rotor yielding moderately better heat dissipation and more angular advantage for the caliper. If you have the “older” style caliper you will need to replace calipers, caliper brackets, pads, and rotors. If you have the “newer” style caliper, you need only replace the caliper brackets and rotors (retaining your calipers and pads.) Regardless of the caliper you’ve got, you will also need to bend or remove the dust shield or replace the entire backing plate (probably not worth the effort.)
3. JDM B4/GT-B Upgrade. Gains: Moving to larger diameter and vented rotor (290x18mm) yielding the cumulative of the gains above. You will need to replace the calipers/caliper brackets/pads(from a 2000+ JDM or abroad B4 or GT-B,) and rotors. You will also need to bend or remove the dust shield or replace the entire backing plate (probably not worth the effort.) This may be a good upgrade for people with the “older” style calipers because they need to replace these parts already to get to either of the upgrades above. The part numbers needed for this upgrade may be found here: http://forums.nasioc.com/forums/show...hreadid=234120
4. Subaru Sti Rear 2pot upgrade. Gains larger and vented rotor(290x18mm) and 2pot opposed piston rear calipers yielding all gains above plus excllent brake feel and uptake, and reduced caliper flex. You will need to replace calipers, pads, backing plates, and rotors(if you want to maintain your US R160 rear assembly.) If you want to go to the R180 rear assembly setup see below.
5. Sti Brembo 2pot upgrade. Gains huge vented rotor(316x20mm) and Brembo 2pot rear caliper yielding all gains above plus higher heat dissipation and Brembo quality brake feel. Because this is only available with a 190mm equipped rotor, you will need to replace calipers, pads, rotors, backing plates, hubs, knuckles, rear drive axles, rear diff and other front gears. This, I have to admit is theoretical, as no one I know of has pulled this off. It could be easier than this, but just a heads up of the worst case scenario.
This info has been collected by myself and others over a period of time. It has been gandered by experience, reading, annoying phone calls, interrogating pimps, and sooth-saying.
People that have contributed from these boards, either knowingly or otherwise: North Ursalia, DBASteve, 8Complex, Concillian, cardin555, johnfelstead, CKTAG, GarySheehan, monovich, mav1c, ciper and dsmawd.
I believe all this info to be correct, but I do miss things. There are also some gray areas listed above that could use defining. If you see something that is incorrect please feel free to keep it to yourself - j/k please post away. It was fatiguing searching around for all these bits of info, maybe we can get it all together in one thread.