I have 911 front/914 rear, 19mm master cyilender no proportioning valve. I just replaced the master cylinder and rear pads. The venting clearence is set to spec. When I bleed the brakes I do not see any air in the fluid. Do not see any leaks anywhere. I have run about 3 qts fluid through trying to get firm pedal with no luck. I am using a power bleeder.

any ideas what is wrong?

Jerry

"Set to spec"? What spec? The REAL spec is .004". Try that. After that, check the pushrod clearance. The Cap'n

All four corners bled? If so sounds like a strange problem. I don't use power bleeders as I like to have someone in actually pumping the pedal so I can crack the valve and see the fluid on each pump. Maybe try that way instead.

and are the bleeder nipples on the top??????????

I have given up on most power bleeders that suck the fluid through the system.

I prefer bleeders that push fluid through the master cylinder and lines. I made my own pressure bleeder and it does a good job. I use air pressure to pressurize the reservoir.

The good old pump and bleed, however, works really well and is hard to beat.

I think sometimes a bubble can be trapped in the master cylinder and only will exit when the piston in the master cylinder is pumped.

I had a master cylinder that would internally leak and caused a spongy pedal with no external leaks visible.

Did you recently change any components?

The bleeder I have pushes the fluid .

are the caliper bleeder nipples on the top of the calipers??????

the rear calipers have them on top and bottom. i have blead both

if the fronts have the bleeders on the bottom they will never bleed

fronts are on the top. 911 SC

Just grab someone and do the pump and bleed method. If still mushy after that then we can count that out. I do think that will help though.

I'm a fan of this method. Long clear tubes that run from the bleeders to the reservoir. Open them all up and pump for 30 minutes or so. This get's most of the air out without wasting a ton of brake fluid. And to state the obvious, I only use this technique after the brake fluid has been flushed completely with new fluid.

Dats the way to do it. I've done it this way and it works.... With speedbleeders right?

I've never used speedbleeders. Works fine with normal bleeders. Because the lines are filled with fluid there is no danger of 'sucking in air'. So just pump away. It's work plenty of times for me.

I've been doing the air over method for about 15 years now. Works good. I just put a spare tire valve on a reservoir cap and use about 10psi or so to push the fluid through the system.

I like the long tube thing too.

I suspect there's some very basic and fundamental reason you're having a problem. Check ALL the basics; I suspect you may have missed something.

Hands down best method when all else fails, is to reverse bleed. With a pressurized remote reservoir of fluid, push the fluid from the caliper to the master one system/side at a time. Do it a second time after sitting over night. If it's a race car, do it again after the first practice session.

Andys

Make sure you pump gentle. The more you aerate what air is in there, the longer it will take to get out..

I always bleed the system with a pressure bleeder and come back the next day and put my wife to work pumping manually. Build pressure and release. This gets some velocity in the lines and moves the pesky bubbles stuck in the high spots.

Also, make sure the vent in the side of the MC reservoir is not plugged or you will have a real soft pedal.

Assumption is that the new part must be good. Recently installed new master
cylinder in neighbors car and had the same problem. New master cylinder
was no good. Dimitri

Man can I empathize. I have the EXACT same problem. My power bleeder isn't doing the trick and I couldn't figure out what else to do. So I did a search and came across this thread. I have done the following:

All four calipers professionally rebuilt
Stainless steel brake lines
New rotors & pads
New master cylinder (19mm)
Flushed about four bottles of fluid through the system.

And still, I can push the pedal to the floor. Feels like stepping on a rotten mango. Initially I thought it was a bad master cylinder, so I bought a new 19mm one. But that didn't fix the problem. $$ouch!

I'll be doing the method with the tubes in a circuit. That sounds like a solid plan. I can't ask my wife for help. I did that once already and it was an agonizing experience for both of us. I don't like asking friends to help either and I figure there's enough good mechs out there running a shop by themselves who aren't crippled when a brake job comes their way. So I should be able to do this myself.

Best of luck to you.

Wait.....is that the little black nubbin right on the brake light connector? If so, I left that on. If not, please enlighten me to where this vent may be.

(I'm keeping my fingers crossed this is the solution)

I was asking myself the same question when I read that post...
What exactly are you talking about in regard to the nub ?
Pics ?

Thanks -

No pics (I'm at work) but here's a MS paint drawing. Not to scale obviously, and missing the hyd lines, but I think you get the picture.

The little black nub is a small rubber cap that covers a small hole. Maybe that's it?

and that is the reset button for the failure warning light.

Roger. So where is the MC resevoir vent?

Needs to be removed when completed......see yellow circle
Click to view attachment

Very good. Thanks for the clarification and pictures.

Sorry to highjack, but the "many-long-tubes" approach worked great. I thought I had my brake system free from air but there were many bubbles that came out during the process.

One thing I did was shut it down one tube at a time from shortest to longest. That way I was able to get a lot of fluid through the longest at the end. Much more air than I thought.

Now the pedal is nice and firm like it should be. Thanks guys.

One thing that people under-estimate, is the amount of bleeding it takes to fill a new master cylinder. Glad the system worked for you Rav!

I am going to try the long tube method.

I am trying to bleed a system with all new hard lines, rubber lines, MC, and calipers. It is amazing how much air keeps coming out.

Someone should sell a kit with instructions for this approach. Maybe with a
resevoir cap with 4 holes and the right size tubes, etc.

It would save a lot of marriages...

John

Brake bleeding makes my skin crawl.

Thanks, that is very encouraging!!!