Zerkster

iTrader: (22)

This may sound newbish but Im flustered and looking for help.

Just replaced my brake master and booster cylinder because I had lost my brakes but wasnt losing fluid. Repeatedly pumping the pedal would build pressure then bleed off.

So I replaced the master and booster, Both front calipers are relatively new remaned from advance, both rear calipers were replaced at the same time as the master with good S5 calipers.

After doing all the labor I bled the brakes to a good feel on the pedal, not to what it used to be but the brakes were definitely there.

Car sat for about a week and I started it up to move it and the pedal went to the floor, no brakes at all, reservoir was still full.

So now Im clueless, I have not attempted to re-bleed the brakes. All I can think is there was still air in the lines that finally made its way to the calipers, or a proportioning valve would be bad.

Vehicle is an S4 non abs 4 pot calipers

If anyone has any ideas let me know, thanks guys

clokker

iTrader: (2)

Probably air in the system.

After sitting for a week, air in the lines wouldn't magically migrate to the calipers, it would travel to the highest point in the system- the master cylinder.
You may have to bench bleed the MC to solve your problem but possibly not.
Try a normal bleeding procedure and if you get pedal back, let it sit for a while and then repeat.
You may have to do this a few times.

BTW, a proportioning valve- unless it was leaking like a sieve- could not produce a completely dead pedal, so you can ignore that area.

Zerkster

iTrader: (22)

thank you. I was really trying to avoid bench bleed...

fml

farberio

iTrader: (7)

Yeah, I have done an entire bleed and gotten a firm pedal with the car up on stands....only to set it down and still have air in one of the lines.

Sucks but an easy fix.

AGreen

iTrader: (11)

I've had alot of experience bleeding FC brakes. If you removed the master cylinder, you need to bleed the system AT the master cylinder. I.E. apply pressure, crack the lines, shut lines, repeat. Also, sometimes it turns out that you have to reverse bleed them. By that, I mean you have to get a mityvac and fill a little portable reservoir with brake fluid, go to the farthest bleeder screw (RR caliper) then start pumping fluid into the system. It'll force air up through the master cylinder.

Now, make sure that since you've replaced your master cylinder, you absolutely have to check for pedal freeplay. It's crucial. Make sure you have about 1/2" or so of pedal travel before the pedal actually makes contact with the master cylinder pushrod. The reason is because there are small ports inside the master cylinder that will not operate properly if there is no freeplay. Just trust me, it's crucial.

Also, try tapping your calipers w/ a rubber mallet to free any trapped air inside the calipers. By this time, all the air should be collecting at the highest point, so you'll probably be golden if you bleed the lines at the MC.

-AG