Subaru Master cylinder Sizing

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FunctionAuto
What would you recommend for a center diff for the 5 speed?

STi 20kg Center Diff

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Chris

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Cosworth
There's something not right then, that setup is not too rear aggressive at all. What pads do you have in the front and rear? What type of center diff is on that car? You sure the pads are full bedded already? That's a very light car with 2480 so there should be even less weight transfer. Put the spare tyre is and everything as if you were about to start a stage when you test. How about the rake, maybe too much?

Don't go buying another master cyl, what you have HAS to work

Stuck the spare in and it didn't really squat the back much. As far as rake, I am not sure but I was looking at the car today and it looks a little "stink bug-ish." Going to even some of that out tonight.

I wanted to revisit this after the someone started a similar thread and I had an event to drive my car in an event.

Through the event I slowly moved my bias forward over the weekend which I felt made the car feel more stable. After looking at the pedal post event, the balance bar was moved to about 75% of being fully toward the front master.

I just came in from the garage and was looking at the stroke of each master cylinder. The rear from rest to full lock up moves almost half an inch and appears to be rock solid when it stops, but from there, the front master moves another 3/8" ish and is pretty spongy. So the pedal is having to travel most of its distance to make up for the front master.

Since I used Tilton cylinders, I asked him where him would start given the data I gave from the front page and he says from a spreadsheet standpoint, I should be running out of rear brake and I should be running 13/16" (what I have on the rear currently) on both front and rear.

I am trying to figure out why the discrepancy between what Cosworth and Tilton recommended. I ran the calculations on my computer but I don't understand what I am looking for in the numbers.

If I had more money to throw around I would buy another 0.75" and try it on front and rear and another 13/16" and try it on the front. But that isn't feasible as the last event nearly gutted me and I would still like to make another in Sept of this year.

So how should I go about this? What am I looking for in the numbers knowing my current setup and that I moved bias from 50/50 f/r to 75/25 f/r? My initial concern is if I go with a larger front cylinder, I will loose brake torque for the front so it will be more rear biased. If I decrease the size of the rear cylinder, I will increase brake torque in the rear and once again move bias rearward. But if I decrease my front master cylinder I will increase front brake torque, moving bias forward, increase pedal travel, but will create a larger discrepancy between the distance each master cylinder will travel before it reaches lock up.

Is my thinking correct?

The 0.75" master for the rear brakes is the ticket! Both master cylinders' push rods now travel the same distance and the pedal travel barely increased (1/4-3/8" The pedal feel is marginally more spongy but its much easier to "feel" the brakes through the pedal now. With the bias bar right in the middle you can feel the front brakes actually grab and the rears aren't locking up early.

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FunctionAuto
The 0.75" master for the rear brakes is the ticket! Both master cylinders' push rods now travel the same distance and the pedal travel barely increased (1/4-3/8" The pedal feel is marginally more spongy but its much easier to "feel" the brakes through the pedal now. With the bias bar right in the middle you can feel the front brakes actually grab and the rears aren't locking up early.

so wha's up front? .7?
My normal starting point, thank you Ford for publishing it, is .7 front, .75 rear
Thats assuming a front caliper with either 4 x 1.5 pistons or 2 x 1.5 and 2 x 1.625 progressive or 4 x 1.625... and either 2 x 2" or 4 x 1.25 rear..

Your Subie is the progressive 2 x 1.5 and 2 x 1.625, rear 2 x 1.5 if I recall correctly..
So whatcher gots for front?

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Fronts are 2 x 1.685 per caliper with 0.7" master
rear are 1 x 1.5" per caliper with .75" master and .625" for the handbrake

I think down the road I will probably grab the 4/2pot but that is an investment because I will have to get new wheels since mine won't fit over them

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FunctionAuto
Fronts are 2 x 1.685 per caliper with 0.7" master
rear are 1 x 1.5" per caliper with .75" master and .625" for the handbrake

I think down the road I will probably grab the 4/2pot but that is an investment because I will have to get new wheels since mine won't fit over them

Well whddya gno.
Rememeber this?

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john vanlandingham [ PM ]
Re: Subaru Master cylinder Sizing
-------->October 04, 2012 <----------06:05AM Registered: 12/19/2005
Posts: 9,918
Or one could go by precedence aka praxis
F .7
R.75
Handbrake .625


John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Praxis works PFG when we have numbers.
Whaddya say?

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.