Wilwood BBK Piston sizes?

[Fidhle007]

Hey Guys,

So I'm finally back in the world of E30s and I'm trying to sort out my brakes. I have a 25mm 540 MC and my own Wilwood setup with 12.75" fr rotors and 12.2" rears. Front calipers are 4-piston Superlites with 1.75" pistons and the rears are Powerlites with 1.25" pistons. I still have a vacuum booster and ABS.

I've bled the crap out of the brakes but under vacuum the pedal goes nearly half way down before it stops. it's firm and not squishy with the engine off. I have no plates on the car yet so I can't road test but I've run it around the parking lot a few times and it stops like crazy and the ABS functions well but still, I have the spongy pedal. The car sat for a year with minimal fluid in the rear circuit so I'm suspect of the MC but I've also been told I have way too much caliper for a 25mm MC to handle.

I'd love some input on what you guys thing before I rip out the ABS and dual MC and boosterless, which is also a possibility.

Thanks!
Brendan

[Fidhle007]

I think I already know what the answer to this will be, but boosterless with ABS is a really bad idea, right?

[SkinnyVT]

Your master is too small compared to your caliper pistons, resulting in the added pedal travel. Compare your piston areas to the stock calipers and you'll quickly see the issue. The car will brake fine but will have a weird pedal feel.

[Fidhle007]

That's what EVERYBODY else has said too, but I need some concrete numbers. The rear kit is from IE and is designed to work with a stock MC, the front is the usual Massive numbrs... How much smaller do I have to go in the front to make the 25mm MC usable? 1.62" or 1.38"?

I can't seem to find the piston diameters for the 540i, do you have them anywhere?

[Fidhle007]

Ok, I drove the car around today and I agree I need to change some sizing around. Is there a bigger master somewhere out there or do I need to change the front calipers? Lee sells all his kits with 1.62" or 1.38" I believe and seeing as my rotors are bigger then his setup I figure I should go with the smaller option there. That said, I'm worried about too much rear bias as I'm stuck with my 1.25" rears until I find another radial mount caliper that fits the IE setup...

Or do I go boosterless? And then there's a whole new set of sizing shenanigans I'm confused about...

[Fidhle007]

New front calipers are on the way! I found a smaller rear option too but I'll hold off on those until I see how it is with the new fronts.

I have a really dump question though: on the Tilton prop valve, does "MORE PRESSURE" mean more pressure REDUCTION or that it allows more pressure to the caliper?