Qn on Soft brake pedal feel and Gc8 Master Brake Cylinder
 

Hi all,

Is there a difference between the GC8 MY00 brake master cylinder and those on the 02 onwards STi's ? In terms os size, diameter, brake booster etc?

Had a brembo conversion done to the front but not too happy with the results for now as the pedal feel is slightly softer than before when it was running the standard 4pots/dba4000/race pads. Have bled the brakes in the proccess as well.

Been reading up on brake bias etc and stuff, that i will not fully utilize the brembo 4pots as the 1 pot rear on the GC8 locks up even before the brembo 4pots are utilized efficiently on heavy braking.

Also, will it be ok to run Dot5 or 5.1 brake fluid (silicone base) in it as well? or should i just conform with standards using Dot 3 or 4 brake fluids?

Right now, i have near new RDA slotted rotors, new pads, goodridge braided hoses with brembos at the moment. Will a cusco master cylinder brake stopper kit make the pedal feel firmer? It brakes fine for now, just abit insecure on the slightly softer brake feel as compared to my stock 4pots calipers which was FIRM.

Comments from brake experts... anyone?

DO NOT USE DOT 5 (silicone based)! (Unless it is a dedicated race car, which in that case you wouldn't be asking on a forum)

DOT 4 should be more than adequate for 99% of applications, otherwise use the DOT 5.1.

How were they bled?

Pressure bleeding is the only way to get all the air out.

Soft pedal = air somewhere

You may have a bleeding issue(should not be spongy or soft either way), but also I have found on cars with Brembo fronts and sliding single pot rears the feel is a bit wrong, seems the rear slider doesn`t have the volume to let the front circuit come in properly.

Changing to brembo rears or subaru 2 pot rears solves the issue(good feel)

[QUOTE=GTLeggy;416248]but also I have found on cars with Brembo fronts and sliding single pot rears the feel is a bit wrong, seems the rear slider doesn`t have the volume to let the front circuit come in properly.

Changing to brembo rears or subaru 2 pot rears solves the issue(good feel)[/QUOTE]

i'm swayed into believing this theory...

did flush the whole system twice.. front and back as well. using ferrodo's dot4 and still having the same issue.

remember that the big brembo caliper needs more fluid and that initial take the master cylinder is being over worked and struggles, simple hydraulics.

even switching to a typeRA one will have the same effect but less profound as it has more fluid for the calipers as it doesn't require all the nonesence of the abs robbing pressure away. be careful with running a gd style master cylinder in a gc8, weight and bias is totally different and this could be a serious step in the wrong direction and afaik untried with any success.

Running the incorrect master cylinder may also void any insurance in the event of a accident......

thanks for the advice peeps..

also what's the difference between a dot4 and a dot5.1 brake fluid? different boiling point or such??

ok did the 4th brake fluid flush on all 4 corners and still the pedal is soft... like u can hear the woosh sound when u push the brake pedal full on when the engine is started.

it's running on GD series brembos front and the stock GC8 1 pot rear.. tell me it's not a master cylinder problem. Anyway i need to confirm with those libertys and gc8s out there who have done this conversion and their opinion on brake pedal feel.
Is it really necessary for me to have a 2 pot rear? Or do i have to change my master brake cylinder. Currently my master brake cylinder has 2 letters "GH" on it, with a couple of numbers below ending with '1'.
All those GC8's and Libertys whow have done the conversion pls advice me on what part numbers or letters u've gotten there on your master cylinder.

keep bleeding, have you bled both sides of the front calipers? are you letting in air when you are bleeding? Also have you done a bleed on the abs pump?

If you decide to use a newer master cylinder remember that they dont use a proporioning valve. The abs pump does all the brake biasing so i would swap the pump and rewire in a new g force sensor. you will proberly have to rip apart half the harness to do so though.