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Discussion Starter #1 (Edited)
I want peoples experience with converting the rear brakes to disk from drum.

I bought WRX stock front brakes to replace the single piston calipers on the front of my 98 Impreza wagon and was planning to change the back to disk. I know there is alot involved in changing the back to disk and was wondering if it was worth the hassle?

I spoke to a mechanic friend and he has warned me against swapping them. His explanation was that the rear drum requires less fluid volume to extend the piston than disk brakes. After converting to disk the brake proportioning valve would not let enough fluid volume extend the piston in the caliper to effectively utilize the rear brakes. He also said that by doing my suspension (Eibach springs, KYB AGX struts), it will eliminate some dive under braking, and the result is that the rear brakes are relied on more, which will amplify the problem.

He explained that since I don't have ABS, converting to disk would take away from the peddle feel, due to the ineffective rear brakes, making it harder to judge when the wheels will lock-up. He also said for emergeny stopping and street driving the drums can be as effective as disk, but would fade quick under repeated hard use.

His advice was to do the front, add stainless lines all around, and try to source a good quality shoe (project mu, endless etc.) for the rear.

This advice goes against everyone that is swapping their TS and L rear brakes to disk, so what do you guys think? Good advice or Bad?

Thanks

Matthew
 

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all depends on your pocket book and your goals in the long run really...

lots of work/$ involved to do a proper rear brake swap....

i ran the drums with PORTERFIELD shoes on the 95 L race car
also with steel braided lines front/rear
and motul hi temp fluid.....

car performed perfectly....

i mean when it comes down to it?

are you changing them because "everyone says you should?"
or are you legitimately having a braking fade/failure issue?

:)
Jamie - www.subiegalracing.com
Home of the Rally Wagon - 2003
 

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disc brakes do definitely allow for better cooling which is going to allow longer abuse of the brake pedal before fade occurs. As for some of the reasons that your friend related, i would be skeptical, especially the one about pedal feel. Not to mention that brake dive will effect the handling of the car, but the proportion of braking force divided front and rear is done via the proportioning valve. the real pain with swapping rear brakes (whether it already has discs or not) is having to redue the handbrake, which is back there as well (except on old Saabs ;) ). basically, it can be done, but its kind of a PITA so, like subie gal said, unless you are having fade issues or plan on doing things to the car where fade could become an issue (like track days or auto-x) then I personally wouldn't bother. As for actually doing the conversion, shoot omahasubaru a PM, or maybe he'll grace us with his presence here. He did a drum to disc swap on his (ex)OBS.
 

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Discussion Starter #4
I am in need of new pads and rotors on the front and shoes in the rear, and since I got WRX front hubs, rotors, calipers and pads for a great price ($350 Canadian or $50 US:D ), I thought I would investigate doing the rear swap.

I was originally leaning towards keeping the drum setup, but after looking, it seemed like swapping to disk was the most talked about option. I approached my friend with the question of swapping them and after he expressed his opinion, I came here looking for some more info.

My plan right now is to do the brakes in anticipation of more power later, and the occasional auto-x. I will probably stick to my original plan of, WRX fronts, ss braided lines F/R, master cylinder support bracket, rear drums and DOT 5.1 fluid, unless someone convinces me otherwise.

Keep the info coming please and thanks for the help.
 

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don't touch DOT 5 fluid. that shit is weird. DOT 4 is the way to go in a high performance street car. trust me, that will be plenty. stay away from that silicon stuff. with ATE DOT 4 fluid and some EBC Red pads on the front, I managed to get my front rotors orange, all without the slightest hint of fade. look closely at the front disc in the picture:

 

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Dude...yoo brake too much! :D
10th Warrior said:
don't touch DOT 5 fluid. that shit is weird. DOT 4 is the way to go in a high performance street car. trust me, that will be plenty. stay away from that silicon stuff. with ATE DOT 4 fluid and some EBC Red pads on the front, I managed to get my front rotors orange, all without the slightest hint of fade. look closely at the front disc in the picture:

Seriously, You should be just fine with upgraded shoes. Cooling shouldn't be an issue on the rear of a street car unless you're doing some serious tracktime. For all but the most track oriented applications, rear drums will be fine.

Rear discs may upset the balance if the proportion valve isn't changed accordingly. I did this swap on my last car and noticed a more tail happy performance until I changed the valve to a disc/disc setup. It was downright dangerous in the wet and snow if I trailbraked into a corner.

I wouldn't say not to do it though. If you upgrade to WRX fronts, use WRX rears too, along with the prop.valve and MC too for best results.
 
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