Installed a complete new to me set of rebuilt calipers on a customer's 914. Master cylinder was recently replaced. Power bled the system with my Motiv bleeder set at 15 psi and couldn't get a good pedal. Did the traditional push/hold/release 2 person method and still couldn't get a good pedal.

If I wait about 10 seconds and then push the pedal hard, there is a hissing sound coming from the front. I thought it was the master cylinder at first but isolated it to the driver's front caliper. I've put close to 2 quarts through the system with absolutely no air.

At my wits end, I put on the old caliper, bled it quick and the pedal is right where it needs to be.



I bled from the top bleeder, the bottom bleeder, as well as tried every trick I could think of. There are no leaks in the rebuilt caliper and yes it is a quality rebuild from PMB.

I'll take apart the caliper and see what I find inside. Again, these are secondhand rebuilds so who knows what could be in there.

If anyone has run across a similar to issue, let me know what you found!

Did you try cracking each line connection and bleed it as if it was a bleed screw?

Yeh...I know it makes a hell of a mess...but in a pinch it often works.

I'm pretty sure it's in the caliper. I put the old caliper back on and the pedal is right where it should be with no hissing from the front.

Found it. Blocked passage inside the caliper leading up to the top bleeder wouldn't allow the air out.

Happens sometimes, we call them caliper worms. When people mix DOT4 and 5.

Sometimes we see them when people tried to use grease to remove the pistons and didn't clean out the passages.

Very hard to diagnose.