Put WRX brakes in original 93L FWD auto. With DCCD off brake bias seems heavily front - and actually front wheel right. I mean heavily front. On the stages I rely on the DCCD to keep the front wheels from binding.

Any experience? Do the JDM cars have different f/r proportioning valves?

you have to remember that the L probably had stock rear drums and single piston front brakes, replace the proportioning valve and maybe go to a larger bore master cylinder(the brakes in those cars are horribly balanced to the front of the car)

hmms. i used to run stock FWD braking system from 93L with sti 4 piston front and vented sliding 10.5" single piston rear. would lock up rears a little bit before the fronts

what does your DCCD have to do with brake bias? do you have a front LSD or somthing?

JDM cars have differnt brake booster/MC, dont know about proportioning valves as they are differnt. could be manipulated to work by bending the lines, but tehy are NOT interchangeable directl¥. outputs are on the oppisite side.

what does your DCCD have to do with brake bias?

i was wondering the same thing
i have the same setup on my car but i have a set of rear calipers from a first gen legacy .. seems that they had a smaller pistion .. my bias is good
IIRC the calipers cost $22 for the pair and pads were $33

with the DCCD locked even if I had no rear brakes the effective braking force is applied to the rear wheels. With a welded diff I can lock all four with just front brakes.

With the diff open there is no influence.

Interesting difference of experience in this thread.

you have to remember that the L probably had stock rear drums and single piston front brakes, replace the proportioning valve and maybe go to a larger bore master cylinder(the brakes in those cars are horribly balanced to the front of the car)

This hasn't slipped my mind.

Replace the proportioning valve and go to a larger bore MC? Oh the arm chair analysis....the trival part. Which proportioning valve? What are the ratios or characteristics of the ones in the range of LHD subies out there? Is mine really inappropriate? Which master cylinder? What's the bore of mine? What difference does the bore make? I do have a WRX MC here.

my guess is that my rear brakes sux.

My guess is you have brake trouble, or air in the system.

ok - I'm gonna bleed the crap out of them tonight.... enough is enough.

if your pedal is firm then you don't have air, air will give up a spongy feel. better yet did you bleed the rear brakes when you replaced the front calipers? I only ask because the fluid could be so old and nasty in there that it boils almost instantly. Also have you checked to make sure the rear caliper pistons move freely as well as the rear caliper guides and pads?

yup, sounds like they need to be bled

I looked over the proportioning valve from MY93 to MY02 and they were all the same rates in the Imprezas. I didn't have access to the JDM cars, though. The only thing I noticed lacking after my WRX brake conversion was the amount of fluid being moved by the pedal. I replaced the master cylinder with a 1 1/16" SVX unit was happy with how it felt. At high speeds, the car felt a bit tail happy under braking, but I feel that was probably more attributed to downforce on the wagon.

-Jon

since the car came with drums, it should be rendered that their would be more pressure going to the rear drums as opposed to the front right? But yet, my 4piston fr 2piston rr conversion from my MY93 1.8 fwd still kills my pads / rotors on the front faster than the rears! And switching to AWD shouldn't make any difference right?

I think it would be the opposite. Drums have a self-servo property to them (the shoes rotate slightly with the drum rotation and this movement is redirected into more pressure against the drum).

This provides drums more braking power than discs for the equivalent amount of applied hydraulic pressure. So changing from drums to rear disc should actually reduce rear braking power and bias braking power to the front.

Martin

I see, thanks for clarification, kinda like action and reaction... :rolleyes:

so if i do not want to go the route of switching out the brake cylinder or proportioning valve, would it be possible to just get a grippier brake pad compound for my rear to balance it out a little bit?

yes. you can up the size of the rear rotor as well, or put the STi 4 piston fronts on to send more hydro power to the rear. theres a good post in the brake forum with math and stuff to back up the logic.

my best friend runs stock fat pig 11.4 2 piston sliding fronts, and the 05 LGT 11" vented sliding rears.

works well.

I looked over the proportioning valve from MY93 to MY02 and they were all the same rates in the Imprezas. I didn't have access to the JDM cars, though. The only thing I noticed lacking after my WRX brake conversion was the amount of fluid being moved by the pedal. I replaced the master cylinder with a 1 1/16" SVX unit was happy with how it felt. At high speeds, the car felt a bit tail happy under braking, but I feel that was probably more attributed to downforce on the wagon.

-Jon
good to know the valves are the same, as for the tail happy part...yeah know that feeling, i used to run about 3/10's of a degree toe out in the rear to get the car to rotate, 100+ braking= very interesting experience

i'll have to try the SVX master change over since my fiance's car the brake pedal is very blah.

Run a legacy prop valve. The split point is higher, not to mention I believe the reducing ratio is also lower (which will give you more pressure longer).

Doesn't Perrin make an adjustable brake proportioning valve?

Won't work. We have a dual circuit brake system. In order to use that valve, you would have to replumb the brake lines.

Won't work. We have a dual circuit brake system. In order to use that valve, you would have to replumb the brake lines.

What a shame :( I really would like adjustable brake bias... Is there any simple way around this?

What a shame :( I really would like adjustable brake bias... Is there any simple way around this?

With the adjustable brake proportioning valves I've seen you would need to use two of them. One for each side of the brake system. You would run one for the right front/left rear and one for the left front/right rear.

Noah

That's not really an acceptable solution in my opinion. Even if you were to get the valves' levers/knobs adjusted to the same spot, who's to say the tolerances in the valves are that close, and will provide exactly the same brake pressure to the rear brakes.

There's only two ways I can see that would be acceptable, both ways however you lose to dual brake circuits.

First would be to replumb the brake lines.

Second way would be to tee the two lines incoming to the prop valve to one line, and then split the output line from the prop valve into two lines and connect back up with the two stock lines.

I agree that it would be difficult to balance the system with 2 proportioning valves but it is the easiest, and maybe only, way to keep the safty features of a diagonally split braking system.
I'm hoping someone will design/build an adjustable proportioning valve for diagonally split systems. Or if there is already one out there some one will point it out to us.

It is the master cylinder that has the "dual" chambers. So you would only loose the dual brake circuit if you figured out some way to connect all your brake lines together through the proportioning valve or if you hooked all the brake lines up to just one of the chambers on the master cylinder. Which would of course mean that if you had a leak anywhere in the system you would loose all of your brakes.

The reason a diagonal split system is safer than a front rear split system is that you will have 50% of your stopping power if you loose one line. Where as a front rear split system will provide you with only 30 to 40 percent of the stopping power if you loose the front half and 60 to 70 percent if you loose the rear half.

I just read this info out of my brake system book from the class I took. So don't go thinking I'm smart cause I'm not. :D

Hope this info is helpful :)

Noah

I forgot to say that you could, as you mentioned, replumb the brake lines and, contrary to what you said, keep a dual circuit system. You would have to hook the rear brakes up to one end of the master cylinder and the front brakes up to the other end. Now you would have a front rear split system and you could hook up your proportioning valve to the rear brake lines. Then you would have an adjustable system still with a level of safety that equals what many OEM cars have.

Noah

http://www.mikesphotos.ca/photos/Oct14-2005/SS10_ActiveMountain_12_35_16_2

bled the crap out of them. lots o dirt. I think there're better now.