master cylinder question?

[jon.haas]

hey guys, i have a brake question. do you have to have the vacume assist? my porsche all run 19mm master clyinders with no assist. and so did the 87 tbird. it seems like the opel is light enough?

the reason i ask is that i came across a front clip from a 2000 BMW M coupe. my buddy just rebuilt and front end wrecked M coupe and had the better part of a clip left over. i have taken the dash off of it, absolutely beautifull! and it should fit with some serious mods. i have also taken the steering column and wheel. then i took off the pedal cluster. it has a hyd. clutch setup (perfect for my 2.3 swap), and a very nice brake pedal system, and girling master cylinder.

could i use a larger master cylinder with no assist, or is that going in the wrong direction? i will be using the front and rear discs off of the tbird. my porsches were 150-200 hp 2500 lbs cars running a 19mm master. the opel has a 22mm master. is this overkill? i have to admit that i haven't had my gt road worthy this century, so i have forgotten what the brakes are like.

any ideas?

jon

[RallyBob]

You should either decrease the master cylinder diameter OR increase the pedal ratio to lessen the effort. A larger master with no booster will have a pedal like a ROCK, with little feedback. It will require great effort to engage the brakes, and it will be difficult to modulate.

I went with a longer pedal ratio on my friend's Ascona when I switched his car to manual brakes, and it was STILL a much harder pedal (ask Travis on this list, he drove the car). There's a thread on this somewhere in this forum with photos of the Wilwood master cylinder I used.

Bob

[RallyBob]

Oops, just noticed in your post you are using the T-bird brakes. Measure the diameter of the pistons of the calipers, and calculate the area of them. Compare this to the Opel's calipers (2-piston remember!), and check the ratio of the master cylinder area vs. the caliper area. Another issue...if you're using rear discs, the GT master is ALL wrong anyway. Not enough rear bias, and no way to increase it (you can reduce it however). You'll need another master cyl. with the correct front/rear bias anyway.

Bob

[RallyBob]

Here's the link to my manual brake conversion:
http://www.opelgt.com/forums/showthr...hlight=wilwood

Bob