Will an Alcon wrx kit bolt-on to BRZ/FR-S??
 

Hi guys I'm looking at purchasing a second hand Alcon mono4 street brake kit for my "twin". The kit was sold to suit a wrx 2002-2007 and the seller claims it is compatible with the brz/fr-s.

I know the STi Brembos bolt on so theroreticly all of the bracketry and rotors should be compatible with this kit. I am unsure about the brake lines though and also didn't realise that the wrx shared the same 5x100 stud pattern with the brz.

Can anyone offer any insights?

read up on Sri bremno threads front should work after swapping bleeders to the other side (unless the pistons are equal size then just flip the caliper). But I think the rears are lgt brakes, but I don't remember exactly.

So the bleeder needs to be at the top or the bottom?

Top.

Sorry for the newb question but why is this necessary? For the record these Alcon calipers have different sized pistons.

The Impreza brake calipers are mounted on the rear side of the hub. So if you swap them to a BRZ then the bleeder valve will be on the bottom. If the bleeder valve is on the bottom you will not be able to bleed air out of the brake system, because air rises to the top.

Air goes up. If the bleeder is at the bottom you'll never remove all the air from the system. You can flip them just for bleeding but that's a pain in the butt.

If the alcon stuff is differentially bored then you'd mount the left alcon WRX one on the right side of the BRZ, right WRX on left side of the BRZ and switch the transfer tubes from the top to the bottom and bleeders from the bottom to the top, basically similar to what you do with the STI calipers. This assumes the alcon's are external transfer tubes, if they are internal, and there's no ports on the other end for switching the bleeders, then you either run them with the differential bores backwards (not the end of the world, but I wouldn't do that) or get something designed for the car, or that can be made to work.

Dave thanks for explaining, makes sense. What is the sinificance of the differential bores? Do they need to be in a particular order? I'm pretty sure these calipers have internal transfer tubes but the bleeders are reversible according to the seller.

Uneven pad wear will occur if the bores are in the wrong order. STI Brembo calipers are differentially bored so the right and left side must be swapped to get the pistons in the right order on each side; following this the bleeders must be swapped from bottom of the caliper to top. Sounds like the same process on the Alcon units.

So if the bracketry is to suit an impreza, technically it should match up to the brz if it is also swapped to the opposite side with its corresponding caliper?

Knuckles are the same as the Impreza, or should be. Impreza bolt holes fit the Brembo calipers, with new bolts. Alcon calipers should bolt up on either side, the dynamics of the pistons and bleeders is what requires switching sides. That car had heavy front bias...not sure why you wouldn't want to just sell the Alcons and buy something meant for this car.

Oh for sure, I know the heavy front bias was an issue for the WRX but I wasnt planning on leaving the rear brakes stock. I would probably do the STi rear brembo upgrade to balance things out a little but tbh I havent done any bias calculations to work out what the % would be. The kit is available very near new second hand at about half price. TBH I cannot justify spending 4K + on a brake upgrade for this car at the moment as its not really required. I was having a hard time justifying the alcon kit as it was but wanted to ask the questions here. I will probably just do the STi brembo upgrade when the time comes as at least that is a matched kit front to rear.

Math has already been done; rear STI Brembo calipers will move bias forwards. Ask @jamal.

Math has already been done for the STi front and rear kit you mean?