Brake Pedal Will Not Get Hard

[daloff]

Here is the background. I had 993 big red calipers on the front and 930 calipers on the rear with a brake bias valve in line. I rebuilt a pair of 930 front calipers. Took of the big reds and replaced them with the front 930 calipers. Put new brake pads on, hooked up all the brake lines and started pumping the brake pedal. I can see that the pistons moved out a bit, but pedal goes all the way to the floor. What I noticed is the bias valve towards the front has not pressure in it. Of course there was no such issue prior to changing calipers. Any ideas ?

Thanks
David

[rs6er]

Viagra

[don911]

Sounds like air in the system. Did you bleed the air out of the lines?

[john70t]

There is probably still air in the calipers(which compresses easily unlike the brake fluid).

Single person air bleeding can be done with [pressure]a Motive power bleeder(clamp off the overflow tube on the resevoir!), or [vaccum]a Mityvac. Pelican sells both.
When having someone "pump" the brake pedal while you're at the caliper, make sure you are shutting the bleed fitting before they raise the pedal. Elsewise, air wil get sucked back in. Simply- the fitting should only be opened when the pedal is going down.

Also, never push the pedal to the floor. This could tear important rubber seals in the master cylinder as they travel over imperfections in the cylinder.

[MattAlpha]

Check this out first.

Have a helper push down on the brake pedal slowly and hold it. While your helper is holding down the pedal check to see if there is a separation between the brake pads and the rotors. If there is, then you need to "exercise" the pistons in your calipers because they are too far depressed into their cylinders.

What I mean is, remove the soft line and hook up compressed air to the hard line leading into the caliper. Use the air to force the brake pads against the rotor, when you take the air pressure away and the piston will recess. Do this several times until the brake pads barely recess at all from the rotors. This is the easy/quick fix method.

Its better to remove the calipers and do this on a bench on an old set of rotors (so the distance the pads travel will be a little bit past the width of the rotors that are currently on your car). Re-install them onto your car (you made need to recess the brakepads a bit, but make sure they only have enough clearance to barely get onto the rotors).

If you need to do this, then bleed the system again (RR-> LR-> RF-> LF).

After that you should be good.

-Matt

[911pcars]

"Also, never push the pedal to the floor. This could tear important rubber seals in the master cylinder as they travel over imperfections in the cylinder."

I'm with John on this. Very common occurrence. After you run a couple of pints through the system trying to bleed it (more with a pressure bleeder), you might come to this same conclusion.

Sherwood

[Hugh R]

Sometimes it can take a looong time to get the air out. On my Aston, I bled and bled and then suddenly a big pile of air bubbles came out. Try bending the rubber lines down as you bleed, they can get bubbles in the tops of the hoses and your not moving enough fluid to drive them out.

[Jeff Alton]

Tap on the calipers with a rubber mallet/hammer to help dislodge any trapped air.

Cheers

[ToddM]

Mine wont get hard anymore either

[daloff]

OK Thanks for all the constructive assistance; and of course the obvious humor.