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rear e-brake.


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well the work on my rally hatch continues, or will as soon as i get a little more money. anyway, one of the projects im undergoing is a fabbing up a rear hydrolic e brake basically for rallying alone...and playing :brow: .

 

anyway i took a hydrolic master cylinder from a mazda mx6, it might be clutch, it has one outlet. what i did was hooked up the plunger behind my e-brake handle on a rod type doohicky. so when i apply the e brake, (fronts disconnected) it works the cylinder flawlesly. now i need to go about plumbing it. unfortunately subaru hooked the brakes up FL, RR and FR, RL.

 

what i think is that i should put a Y directly on each of the calipers, and had the regular line hooked up as well as my new one, would that work correctly? as in two lines going straight to the caliper. or would the pressure brake all 4 of my tires?

also would i need a bias at the MC outlet, to keep the pressure equal?

 

any help, or critisisim appriciated. thanks

 

 

Please bare in mind that this would be for off road and rallying alone. when i drive on the street i would hook up my normal cable fronts Just in case.

 

tyler,

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It might work, the hardest part is bypassing the way the lines are run. Like you said, Subaru is setup FL/RR and FR/RL. You'll need to install new plumbing to get both rear tires to lock instead of one rear and one front.

 

I think a hydrolic lock isnt the best way to go. You might be better off trying to find rear calipers that'll work. Maybe look into adapting Legacy calipers or something, and use a cable system with rear disc's.

 

-Brian

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i always wondered why nobody has done that yet, if you wanna go through all the trouble.

get the rear disc backing plate, and take two front calipers, and drill new holes in the backing plate, space as nessecary and hook up the cable, like toyota, or any other rear emergency brake car.

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yes i have rear disks. well i checked out swaping front to rear calipers but the holes dont line up and i never really took it farther than that, trying to ponder over ways in which to make it work. also my hatch is a 1980 and yes it is 4WD. if this mod would make the 4 wheels lock up thats fine, because im going to be doing a drivetrain swap anyway. to an Awd system.

 

ill check again on the swaping calipers but... so far my idea is going smoothly, so unless there is a absoulute "no your plan wont work", or a better solution i think ill run with it.

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Hey Tyler

 

Teeing into the existing brake system will be a BIG problem. You will apply hydraulic pressure to at least one whole “side” of the system (one front and one rear) and depending on the configuration of the proportioning valve/master cylinder maybe the whole system (these components are not designed to be back pressured). You really should re-plumb the system into a front to rear split if you want to use a hydraulic e-brake system (which is NOT legal btw).

 

Locking both back wheels with 4WD will lock all the wheels (and kill the engine if you don’t hit the clutch), so AWD is the way to go with that. You might look into the turn/cutting brakes use in dune buggies and sand rails, the rear brake line passes through them and blocks back pressure when the handle is pulled. If you get the two-handle type you can brake either back wheel separately for sharp power on turns (will work with 4WD), or together like a standard e-brake.

 

Gary

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It occurs to me that if you are dead set on using a hydraulic e-brake and you have already converted to rear disks, then why not fab up a second set of mounts and add a second caliper to each side? You'd lose some cooling on the rotor and therefore would be more likely to warp it under heavy usage, but you'd be guaranteed to lock up the rears and ONLY the rears when you yank that handle.

 

It also occurs that all_talk is exactly right. If you apply pressure to the rear calipers, you'd need a way to prevent that pressure from "walking" back up the main lines. Otherwise, 4wd or not, you'd lock up all 4 tires and probably break something, either the proportioning valve or the MC itself, when you grab the handle. A dual caliper system would be the best way, I think.

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I highly doubt it would lock up all 4 tires. What it would more likely do is apply pressure to all 4 and enguage them but not lock them up. It takes A LOT of pressure to LOCK those things up at speeds over 30 mph.

 

When you see ppl lock up their wheels it is usually just the front or the rear ones. Splitting up what little pressure that small cylinder puts out amoung all 4 brake cylinders would give you a pretty whimpy E brake.

 

Now hitting your brake pedal AND grabbing that e-brake... it would be like slaming the pedal and having an extra brake booster. Then I bet you'd be locking up and roasting some tires.

 

I know you said the holes dont line up in the backing palte for the bigger front calipers. What about Arch's idea of drilling new holes and spacing as necessary ?

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ok i was pondering that problem, with back pressure up through the lines and braking the front/rear brake, i do agree with MorganM in that a quick jab arround a corner while applying the gas(like i intend to), not brake wouldnt lock up all 4's.

 

and btw,to clear it up, if the plumbing wasn't FL-RR and FR-RL would locking up the rears cause the fronts to lock up because of the differential and tranny?

 

ALL talk, thanks you for the warnings and legal issue. and yes if i do complete a rear brake system , i wont use it without my Awd.

 

thanks for all your help, in fact please keep posting any more problems or suggestions, i really appriciate it. ill look into the front caliper ex-change again, and ill see what i can do, or any other options i have and can do.

 

thanks again,

tyler

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