Need help--Brake pedal goes all the way to floor after several new parts replaced Options

[914xr75]

I posted a few weeks ago about leaking reservoir tubes under the gas tank. I replaced those and the leaking stopped. I bled the calipers, but did not bleed the master cylinder. This was the first time I had about 5% stopping power and the pedal went to the floor, not sure if you'd call it spongy, but there was no resistance. That was a couple weeks ago.

Today I replaced the master with a 17mm ATE, rebuilt one of the front calipers, replaced the front soft lines. The rear steel lines still looked good, so I left them. I bled the new master. It took about an hour of pushing out air bubbles, and two quarts of brake fluid into the system to complete the MC bleeding. Once done, the pedal was still pillow soft.

Now on to the caliper bleeding--I purchased the Motive pressure bleeding system. Pumped it up to 5 psi as recommended by Ian Karr. About 30 seconds later the Motive bottle was at 0 psi. There aren't any fluid leaks in the brake system. I replaced the reservoir seal and added Teflon tape to the fitting in the Motive hose. Still loses pressure.

I tried the HF bleeder you hook up to your compressor. For 3 minutes about 5% fluid and 95% air entered the bottle. About 8 ounces of fluid came out. That is where I left off after a full day of brake work. Then I thought, did I cross the reservoir lines? I don't believe I did that, and I don't think that would cause my situation.

Any help you can offer would be greatly appreciated. Sean

[davep]

Your profile does not list a 914, so that does not help.
Normally, when bleeding brake system, you start bleeding at the furthest point which is the right rear, then the left rear, right front and finally the left front.
While I do use a vacuum bleeder tool to do initial bleeding, I always use the foot on the pedal method (two people) to do a final bleed. The foot on pedal method can build the pressure to a much higher level that squashes the bubbles much smaller to get through the pressure regulator and the calipers. Also provides great feedback as to how the system is clearing up.
If fluid is disappearing, then check under the master cylinder, and in the pedal cluster.

BTW, I almost always drain the calipers of all fluid first; just to get rid of all the old fluid. I have rebuilt a lot of calipers since 1975, and the outer pistons are often full of sludge because ordinary bleeding does not force a fluid exchange in the outer caliper halves. Particularly in the rear calipers with the adjusting mechanism in the pistons, no fresh fluid can displace the old fluid with a normal bleeding process.

[fiacra]

Your profile does not list a 914, so that does not help.
Normally, when bleeding brake system, you start bleeding at the furthest point which is the right rear, then the left rear, right front and finally the left front.
While I do use a vacuum bleeder tool to do initial bleeding, I always use the foot on the pedal method (two people) to do a final bleed. The foot on pedal method can build the pressure to a much higher level that squashes the bubbles much smaller to get through the pressure regulator and the calipers. Also provides great feedback as to how the system is clearing up. If fluid is disappearing, then check under the master cylinder, and in the pedal cluster.

BTW, I almost always drain the calipers of all fluid first; just to get rid of all the old fluid. I have rebuilt a lot of calipers since 1975, and the outer pistons are often full of sludge because ordinary bleeding does not force a fluid exchange in the outer caliper halves. Particularly in the rear calipers with the adjusting mechanism in the pistons, no fresh fluid can displace the old fluid with a normal bleeding process.

I think this is spot on advice. Not much to add to it other than to say I am a big fan of the Motiv pressure bleeder, but I've never used a vacuum bleeder so maybe it's better (IMG:style_emoticons/default/confused24.gif)

Here's my take on what's going on: First off, if you've never bled a 914 before it is a very different experience than bleeding the brakes on just about any other car. It takes forever (at least for me) to get all the air out of the system. While on my other cars I might use somewhere around 1 to 1-1/2 pints of fluid to bleed the system, in a 914 I often use up to three quarts after replacing calipers, lines, and MC. I have been told by another member that that is ridiculous, but brakes are the things that stop your car, save your life, and save you from hurting others. If I get a bit carried away making sure the system is free from air I have no shame about that. I'm going to assume that you have confirmed that there is no brake fluid on the floor by the pedal cluster (a common spot to find fluid when the MC fails, and yes a new MC can be defective) and that there are no other areas where you are seeing brake fluid leak. Failing that, and being sure that all your connections are solid (especially at the lines into the MC from the reservoir) you just still have air in the system. Be persistent, keep bleeding, and recognize that it may take several cycles to get all the air out. You can't just work your way around all the calipers and assume you've gotten it all. Keep doing the circuit. And yes, tap the pressure regulator to make sure you are dislodging air from it. Shake the soft lines to dislodge air, etc. If you don't know where the pressure regulator is, then just follow the brake lines and they will take you there. It sits low on the firewall between the engine and the passenger compartment. I keep the Motiv at just between 5-10psi and no higher. It should hold there pretty well, so if you are having rapid loss of pressure after filling the system then there is a leak somewhere. Like Dave I finish with a cycle of pedal bleeding. I'm lucky that my wife is willing to help out in the final step. If she had to be there for the whole process we would end up in counseling. That to me is the real value of the Motiv (IMG:style_emoticons/default/biggrin.gif) .

Bottom line, assuming the system is closed then you just have to be even more persistent to get the air out.

Finally, I don't think it makes any difference which feed line goes into either the front or rear position on the MC. All the MC cares about is that it has a fluid source to each circuit. What does make a difference is how well those lines are seated in the grommet, and that the grommet is properly seated in the MC. Also, be sure you put the washer in place under the grommet.

To help you find it, here's a link to a picture of a pressure regulator on the PMB website. Good luck!!!

https://pmbperformance.com/products/porsche...01840&_ss=r