soft pedal

[Vulnavia]

Building a new car [F5] Went to bleed the brakes, by myself using my trusty mighty vac, bleed the mc's started with the farthest caliper and so on. Got bubbles out [fronts and mc bled with a bottle/hose I can reach them when pumping the pedal.Cannot get a hard pedal. My other cars brakes, same set up, pedal is hard, moves 1/4" or so. Rebled a couple of times, brakes appear to work, but pedal moves goes to "the floor". Can't find any leaks, pedal is moving the pads, even tried leaving the bleeders open and slowly pushing the pedal. No bubbles.
Any thoughts ?

Will

[racerdad2]

Just a guess... perhaps the master cylinder needs a rebuild ? Leaking past a seal ?

[BGG]

Did you replace any of the brake parts?
If you replaced the master cyl. they may need to be bench bleed. Or if that is too tough due to being currently installed just pump them 3 times and hold down pedal to bleed.
If the brake parts are original then I agree with above, Bad Master cyl.

[DanW]

The check valve in the master may be leaking back. Known to happen on Wilwoods and Tiltons, but possible on any.

[Vulnavia]

They are Wilwoods. Everything MCs, calipers, lines are brand new. Even changed to raising the reservoirs above the calipers.

Will

[problemchild]

If you are using a pressure technique only (cracking bleeders while holding pressure) then you may have some air trapped and not moving enough volume to flush out. If you are using a flushing technique (pumping pedal with bleeders open) then I would conclude you have a component problem, and would start with the master cylinders.

[t walgamuth]

I'd try bleeding the old fashioned way with a helper.

[Tom Fraelich]

Assuming you have a brake bias bar, it's always a good idea to bleed a front and rear caliper at the same time. If the bias adjustment bar locks up the fronts (or the rears) it can prevent the pedal from moving thru it's entire stroke range and prevent the "other end" from getting bled. Consult Tilton's description of brake bleeding in Smith's tome.

[marshall9]

Make sure pedal at zero pressure is below 90° towards the front of car

[jrh3]

I had a similar problem with a brand new master cylinder. Replaced with a known good cyl and problem solved.
The company denied a problem but as a goodwill gesture they sent me another.

[Roland V. Johnson]

Also check if one of the master cyl is sticking in the bore and not returning fully. That will show up as a lot of play in the pushrod of the offending cyl.

[mark elder]

In an ideal world, we would all have the right size of bleed nipple that fits the outlet of the master cylinder. This way we can both bleed the master cylinder and also trouble shoot. The pedal should be rock hard once bleed. This then means you can cross the MC off the list of problems.

To swap out the bleed nipple to the banjo, you need to get the brake pedal down far enough to close off the master cylinder chamber from its reservoir (ie not much); you need to let a little fluid out to get the pedal down a bit, then 'hold the pedal in this place' while you swap nipple for banjo; this keeps fluid in the master cylinder.

[pacratt]

Sorry if this has already been said...
Roll back the rubber boot on the push rod of the master cylinder.
If there's oil in it, the piston seal is bad & needs rebuilding.
Just a thought.
Glenn

[Vulnavia]

Pulled the boots and no leaking, going through all the suggestions [Thank you all] Going to try to bleed them again. Got the rebuild kits just in case. Watching the balance bar I noticed that when I pulled on the pedal [standing at the front of the car] the MC plungers would move to a certain point and then the rear one would move 1/8 " farther. Everything threaded is the equal, balance bar, plungers. I would think they should be the same. Could this point to the problem?

Thanks,
Will

[Lotus7]

If you pressure the system using multiple pulls on the pedal, so that brake pads are touching discs and pistons are fully extended, then on the next pull of the pedal the rear plunger continues to move after the front stops moving, then perhaps you have a rear brake hose ‘ballooning’ under pressure?

[DaveW]

Another thing that can cause a springy pedal is fresh and/or dry caliper seals that are sticking to the pistons and springing back each time you release the pedal. That will usually disappear or get much less noticeable after a small amount of use.

[Vulnavia]

This morning tried bleeding them again, tapping on everything with a soft hammer. Same pedal. Pulled the mc's and rebuilt them. The original parts differed from the kit, spring wire was thicker, stiffer, ends did not have thin cups[?]. Looked up the kit on Wilwoods website and the parts where the same as the ones in the Mc. The kit part numbers are the same. Put in the new parts. Bled the system and the pedal is much better, still not that 1/4", but close. I'll look at the calipers next.

Thanks again for the advice and the education.

Will

[Lotus7]

Another thought.
I saw you said "no leaks", but can you actually see 100% of the brake line lengths as routed?
Maybe try pulling on the pedal with a stiff bungee cord, and leave the tension on it overnight and see if there's a minor weep that isn't obvious over a short period of pedal pressure.