Another brake bleeding thread, ...but this one is a little bizarre Options

[tomeric914]

First, what I have. Fairly new 19mm master cylinder, fluid changed every 6 months or so, car built mainly for DE's. All calipers in good order. Fronts are aluminum Brembo AM calipers from Eric Shea with stock 911 size pistons.

Now the bizarre part. While bleeding the brakes using the buddy method which has always worked for me (push down, open bleeder, close bleeder, pull up), I get very little fluid out of the fronts. What I noticed is with no pressure on the brake pedal, if I open the bleeder valve, more fluid gets pulled back through the bleeder tube than when pushing on the pedal! This is how I get the best pedal though it isn't as firm as I would like.

So I took the feed line closest to the front of the car off to make sure nothing was blocking the port. I also pulled the grommet and the little spacer washer below the grommet out. Everything was totally clean.

This is too weird. Does the front feed line on the MC feed the front brakes as would seem logical? I'm at a loss why it won't bleed normally. (IMG:style_emoticons/default/WTF.gif)

[pilothyer]

If I am wrong, I am sure someone will let us know, but I think the front most feed line supplies fluid to the rear brake system and the rear most line feeds the front brakes. You can confirm this by looking at the lines that go to the calipers. The front half of the master cylinder should feed the line that goes through the tunnel to the rear brakes, and the rear half should feed the T fitting for the fronts.

[pilothyer]

Here is a link to some helpful master cylinder information. This link takes you directly to part 5, but you will have access to all 7 parts. Master Cylinder Diagrams

[stugray]

do you have a bias valve?

I have had fronts that you could barely get flow through.
The flex lines were old and rotted/swollen on the inside.
I replaced them and solved the problem.
I assume since you have recently replaced the calipers, old flex lines should not be the problem.

Stu

[tomeric914]

If I am wrong, I am sure someone will let us know, but I think the front most feed line supplies fluid to the rear brake system and the rear most line feeds the front brakes. You can confirm this by looking at the lines that go to the calipers. The front half of the master cylinder should feed the line that goes through the tunnel to the rear brakes, and the rear half should feed the T fitting for the fronts.

Thanks for the link. It's a nice diagramatic view in general but not specific to the 914. I'll need to find an old MC and pull it apart.

do you have a bias valve?

I have had fronts that you could barely get flow through.
The flex lines were old and rotted/swollen on the inside.
I replaced them and solved the problem.
I assume since you have recently replaced the calipers, old flex lines should not be the problem.

I replaced mine with SS braided 2 years ago. I have experienced the swoillen line problem on other cars I've worked on.

It seems like a flow restriction of some sort on the feed side from the reservoir.

[sixnotfour]

Do you have pedal free space between the master cylinder and the plunger ? should be 1mm

[tomeric914]

Do you have pedal free space between the master cylinder and the plunger ? should be 1mm

Good point, I experienced that on another vehicle. I'm pretty sure I have that but will double check. Thanks!