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#Disc brake conversion

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 Post subject: Disc brake conversion
PostPosted: Sat May 12, 2018 1:11 am 
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Joined: Thu Mar 03, 2016 11:56 pm
Posts: 12
Hi guys and gals.

I have a restoration going on and I'm going to upgrade the brakes but with budget in mind. What besides WRX/STI brake parts works for a 1990 Legacy which has drum brakes in the rear and small discs at the front?


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 Post subject: Re: Disc brake conversion
PostPosted: Sat May 12, 2018 4:52 am 
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Joined: Tue Aug 25, 2009 7:52 am
Posts: 4693
Location: Des Moines, Wa
Hi Snaer, check out the very first link in each section, which is the "sticky thread" of common questions. In this section, check out the "compiled brake information" first to see what fits.

Then check out the "brake math/torque spreadsheet" link and open up the file in the first post, which will show you the effects of mixing and matching brakes on your braking balance and overall improvement.

To answer your question directly, I have used stock 1991-1994 turbo, 2000-2004 Legacy (all), 2005-2009 Legacy Gt and also 2006-2007 WRX 2 piston rear brakes (these ones required adapator brackets, all others were bolt on, provided I used their specific disc rotors).

They all felt about the same, if I'm honest, since the fronts provide almost all of the brake effort. I could feel the change when I changed the overall brake balance towards the rear. I believe you do in fact want to have a little more rear braking force.

I have never converted a legacy to Disc, but I have converted an Impreza and a Forester. If I'm honest, their braking became extremely sketchy, wanting to lock up the tires way sooner, until I swapped over a brake proportioning valve from the same kind of car that did come with rear discs. The car felt dangerous until I did so.

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1992 Legacy SS 5mt, build in progress


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 Post subject: Re: Disc brake conversion
PostPosted: Sat May 12, 2018 4:54 am 
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On the Impreza and Forester, I used 1st generation Legacy rear parts for the conversion. They were the cheapest and most common in the junkyard at that time.

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1992 Legacy SS 5mt, build in progress


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 Post subject: Re: Disc brake conversion
PostPosted: Sat May 12, 2018 11:23 am 
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Joined: Thu Mar 03, 2016 11:56 pm
Posts: 12
Thanks for the quick reply. I had gone through the sticky compilation thread and to be honest I just thought it displayed so many options that it got confusing. I think I would opt for 3rd gen Legacy brakes since they are very common here in Iceland. But replacing the drums in the back require me to change out the hub assembly right? Should that fit directly or is it more complicated than that you think? Also, where is that brake proportioning valve located usually?


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 Post subject: Re: Disc brake conversion
PostPosted: Mon May 14, 2018 10:41 pm 
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Joined: Thu Dec 11, 2003 11:34 am
Posts: 2479
Location: Missoula
The brake prop valve should be on the strut tower in the engine bay.

3rd gen legacy rear brakes are a good option. Those are the larger "H6" 290mm discs, and go well with wrx front brakes. You would need 16" wheels to go over the wrx front brakes though. I am not sure on the difference between disc and drum prop valves but the wrx/h6 setup is well balanced.

You can keep your wheel uprights. The backing plate, where all the brake stuff attaches, bolts onto it. But finding complete units with the hubs, bearings, brakes etc will make things much cheaper easier. Otherwise you'd have to source all the parking brake parts and such.

Uprights need to be from a 1st or 2nd gen car though, as the later stuff (08+ impreza, 00+ legacy) has a completely different rear suspension design. That does leave you a lot of options and basically everything should be compatible between imprezas, legacys, foresters, etc, but if you have ABS the sensor/tone ring parts from a newer car might not be compatible.

The other thing that means is that almost any upright/brake setup you find is going to have 266mm solid rear rotors. Those will work with your stock front brakes, or the next size up, the 2-pot calipers with 276mm rotors, and also allow you to use 15" wheels.

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