coldfire

iTrader: (1)

I have an 89 FC non-turbo, and last year i replaced pretty much the entire braking system with TII parts. new OEM rotors, rebuilt calipers, SS lines, all around. i am using EBC green pads up front, and OEM pads in the rear, which i find great for street/autocross driving.
now, i still have the 89 base model booster, master cylinder, and proportioning valve. the car stops great. i have some decently sticky tires on, and in fact i can't believe how fast i can actually get it to stop (stopping distance).

the problem though, is with feel. it is severly lacking. i drove an 2006 Pontiac the other day than had a much more enjoyable feel to the brake pedal.

now, i've pondered over this quite a bit. there are the usual explanations...it's a 20 year old brake system design, new cars have many electronics assisting braking, etc.

anyways, aside from upgrading the MC to affect pedal travel, etc., is my proportioning valve an issue?
how has changing to the Turbo/GXL brakes affected the brake balance?
i feel that i might be getting too much brake bias in the front...does that make sense?

maxcooper

Is the TII prop valve different than the base model? (the 93 Workshop Manual has a chart for it's valve; perhaps a similar chart is available for the prop valves on the 89 base and turbo brakes)

Is the TII master cylinder larger than the base model MC? This seems somewhat likely to me, and could have a substantial affect on brake feel.

EBC Greens are fairly high friction for street pads, IIRC. 0.47 mu or something like that. Maybe try some Greens in the rear to balance things out. Or try some lower friction pads in front (like spare ones you or a friend might have already) to see if it is indeed the pad that is affecting the bias.

-Max

coldfire

iTrader: (1)

i checked the parts fische, and apparently all FCs come with the same proportioning valve. so, i am mistaken, and i'm not quite sure why people post they are different.

the master cylinder and also the brake boosters are different.

the TII master cylinder is indeed larger, however it is not much of a difference:
Non-Turbo 22.22 mm (0.875in)
Turbo 23.81 mm (0.937in)

but yes, that would shorten the pedal stroke slightly. if i were to go that route though, i might be inclined to just swap in a 929 MC, which is a 1 inch bore.

I understand what you are saying about the EBC pads. they do have pretty high friction, however initially when the pads are cold they don't have as good of bite as the OEM pads i have found. maybe that is just me, but it seems it takes a few hard stops to get the pads up to optimal performance. this occurs about half way through an autocross course i find. i figure with EBC pads in the back also, it might take longer than desired to get them biting full-on.
now, i am not sure if EBC has taken this into account with their rear pad material. is the friction number you mention for any EBC Green pad?
but, i will maybe try changing out the pads. the pads back there are decently old anyways...

maxcooper

I think the friction is the same for all pads of the same compound.

One of the reasons that people use the same pads all around is so they have a more uniform behavior over a range of temps (i.e. as they warm up).

This page has more info about the EBC compounds, but no friction vs. temp graphs:
http://www.ebcbrakes.com/Automotive.html

It says Green pads actually have a mu of 0.55 (when warm), which is very high for a street pad. This might be the main problem with your balance.

-Max

coldfire

iTrader: (1)

that's interesting to know.
i think in my effort to balance the temp change, once the brakes are up to temp, my balance is off like you mention.

it's odd that on the EBC website they say the pad has great initial cold bite. i still think the stock OEM pad provides better intial cold bite than the EBC pad, but maybe that's just my experience.

so maybe some EBC pads in the back, and a larger master cylinder, might improve my feel enough...

maxcooper

I don't think you are crazy. I haven't used them personally, but I have read reports by others that said the Greens have more bite after they warm up a bit.

-Max