960 Brake bleeding problem

Hi all,

The car is a 96 960. So, my brakes weren't working as well as they have in the past, and it was due for a bleed. The front flex hoses were cracked, so I decided to replace all 4 flex lines and then bleed the system.

First I completely drained the system, and maybe this was a mistake in hindsight. But I have done this before (on 940, 240) without problems.

I replaced the flex lines, and now whatever I do, it seems like there is still air in the system. First I bled with an EZ-Bleed, at 20 psi. The pedal was quite soft, but I drove it around at low city speeds for a week, hoping the air would move around and would come out next weekend.

I bought a Motive Power bleeder and bled at 35 psi, but no air came out, and the pedal is exactly the same.

Has anyone else had problems getting the air out of the 960 brake system? And how did you get it out?

Thanks for any help

Did you have the calipers off the car for any reason? Did you accidentally switch caliper sides? The bleeder screws should be at the top of the caliper.

This might sound dumb, but are the bleed screws original? I got some new bleeder screws from FCP and they were the wrong thread, causing a leak.

Also, turn down the bleed pressure. 5 psi or less will keep the fluid from cavitating as it moves through the system. You might try raising the back end of your car just a bit, it seems to help me on all my other vehicles.

You should try bleeding it manually with a partner.

Since you drained the system. That means the master cylinder is empty. A pressure bleeder will fill it but it takes a few minutes. Sometimes still needing a bleed of the master cylinder. If the master cylinder doesn't have it's own bleed screws. You can bleed it by loosening the lines and using the pressure bleeder till fluid comes out. Then tighten the lines and move on to bleeding the brakes. With an empty system start at the wheel closest to the master cylinder and let it go until fluid comes out. Then move around the car. Don't go over about 15psi. Higher pressure has caused the fluid to foam in my experience and you can't get the air out.

Sometimes when you can't seem to get all the air you need to manually bleed out the last bit. Be sure to only move the brake pedal the amount it normally moves. You move it too far in an old master cylinder then you tear the seals and now it needs to be replaced.

I've had to go around quite a few times to get all the air when the system was empty.

Thanks for the responses, it all helps.

-The calipers were not off.
-Bleed screws are original, as far as I can tell. They don't look like the cheap ones that I sometimes get on rebuilds.
-Pressure- I could try lower pressure, but the volume flow at 30 psi is already pretty slow. It seems like it would barely flow at 5 psi. The green book for the 960 specifies 29-44 psi for brake bleeding. One of my theories right now is that the fluid flow is so slow that it isn't forcing the air out of the high spots, and instead the fluid is flowing around the air somewhere.
-This m/c has its own bleed screws, and I start the bleeding process at these.
-Manually bleeding, even if I wanted to, no one is around to help me. My wife knows that I have to work on the car to get it to work, but she's not that thrilled about it. No way is she going to work on it with me! Maaaaaybe I can convince someone.

-Another question - is it possible for the m/c to go bad without doing the classic "sink to the floor at a stoplight, but pumps back up" behavior? That's the way I've always known to change the m/c.