Originally Posted by oscar

Hey ya!

Man I hate brakes ;D

I remember your issues and I've been keeping an eye on any ideas people have but I've got no answers yet. I'm 4 days away from putting povo on the track again and I don't reckon I'm going to get the brakes the way they should be. I've been PMing koan who's gone thru the same probs before and together we still haven't come up with an answer.

I'm gonna quote both your PMs here in one.
Funny that, I had a similar feeling in the pedal towards the end of a pump when I put a new MC on. Not sure what it is. Did you see in peterq's thread where Carl Jones mentioned about the MC and suggests pushing the MC all the way in will screw it up? That go tme thinking if I've stuffed the new MC as well as the three others I've tried. I've met Carl and traded a few emails and phonecalls. He's a very knowledgeable guy, got all the right gear and can do everything himself. Attention to detail and procedure is incredible. But I just don't believe that pushing the pedal all the way in will screw up the MC. I'm not game enough to say his wrong on the forum but I've done a number of tests on a couple of my MCs to prove that pushing the pedal to the floor whilst bleeding did not damage the MC.

Eg, I've plugged the MCs' outlets and have hardly been able to move the pedal. No sponge, very solid pedal. I also made four bungs that screw on and cap off the ends of the flexible hoses. Once again, the pedal was hard as rock with or without the engine running. The MCs are not leaking internally (or externally).

Don't do it is what I think. No new MC or booster.
Everything I've done leaves me with one conclusion, that being the front callipers are to blame for the sponge and I'm thinking air is trapped in there.

Thing is, you gotta rule out both the MC and booster out if possible.
For the booster; one night, idle the car and don't touch the brake. Leave it overnight then the next day jump in and with the motor off, press the brake pedal a few times. You'll hear the booster working 2-4 times before it runs out of vacuum and the pedal will firm right up. If there's no vacuum in the booster, suspect the one way valve first then the booster last.
For MC; easiest way would be to block the four flex hoses with clamps of some kind (vice grips, G clamps, proper brake clamps) Your pedal should be harder and shouldn't sink. If it does, double check to make sure the hose clamps aren't letting any fluid thru. If they're ok, and the pedal sinks still, then you can suspect the MC as part of the problem.

Pretty similar to what I have although more pronounced in your case. It makes the MC sound sus but don't replace it unless you can test its operation with lines bunged or capped or clamped first. Check there's no fluid leaks and bleed screws are tight and aren't sucking air in. Did you end up getting new bleed nipples? It's something I haven't done but meant to do.

That's weird. At idle the vacuum is the highest and equals the greatest amount of vac assist. You've mentioned that you've got a vacuum pump on the engine which until PB or someone said it in that thread, I would never have believed it. But this pump may work opposite as it works off engine RPM. The greater the RPM, the greater the vac assist maybe. That may be why it feels crappy in a parking lot. It needs revs to operate properly.

I gotta get some shut eye before tomorrow I finally get back on the tools and working on the car. My brake probs might be different to yours but like I said before, I'm thinking it's all coming down to air in the front callipers. If I have a breakthgouh in the next couple of days you'll be sure to hear about it.