Brakes don't Bite Options

[bkrantz]

As part of my rebuild I completely replaced the brake system:
calipers and rear pressure valve rebuilt by PMB
new ATE 19mm master cylinder
new hard and flex lines
new disks and Porterfield R4-S pads

I went through many (many!) episodes of bleeding, with different methods. The pedal feels very firm from the first push, and does not pump up. Rear clearance is set at .004". I went through the PMB bedding process, and have driven around a bit.

But the braking force seems weak. When I get on the brake pedal, I do not feel any "bite". Another 914 friend drove the car and also agrees.

Any suggestions?

[bkrantz]

Thanks for all the replies.

Yes, I can lock up the fronts. It takes a good shove, and maybe the left locks before the right.

I hear you about bleeding and stubborn air. Like I said, I went through several episodes with different techniques. And I will do more, with all the chanting and banging on components I can think of.

I went through the bedding process again today, and maybe the brakes feel a bit better.

And I realize that 1960s engineering, and small, single piston calipers can only do so much. But I still think I should feel more bite and urgency when I get on the brakes hard.

[JamesM]

Thanks for all the replies.

Yes, I can lock up the fronts. It takes a good shove, and maybe the left locks before the right.

I hear you about bleeding and stubborn air. Like I said, I went through several episodes with different techniques. And I will do more, with all the chanting and banging on components I can think of.

I went through the bedding process again today, and maybe the brakes feel a bit better.

And I realize that 1960s engineering, and small, single piston calipers can only do so much. But I still think I should feel more bite and urgency when I get on the brakes hard.

If you can lock them up and the pedal isnt doing unpredictable things then you should be good to go as far as system assembly and bleeding.

As I (and Ian) mentioned, the rebuilt calipers take a while to break in and sometimes it takes a lot more then you think to properly bed the pads.

Go find an empty road and run through the bedding procedure again, maybe even a couple more times and this time REALLY give it to them, do not go easy, this is not how you would normally drive, brake as aggressively as you possibly can without locking them up from freeway speeds down to barely rolling. Multiple times, to the point they start to fade before letting them cool off.

I think people underestimate the aggressiveness needed here. If you are not smelling burning brakes and possibly seeing smoke you are not getting them hot enough.

With the Porterfield R4 being a race pad it takes even more to bed them in (Eric recommends the aggressive (near lockup) stops from 80mph) and per Porterfield they don't achieve optimal friction until they are above 450F.

Ultimately it may be that you just prefer the feel of a street pad, but I suspect you need more time to fully bed the pads and break in the calipers so I would run through that again and give it some time before you make the decision to swap pads.