Sometimes it's the craziest problems., Brake bleeding drama Options

[McMark]

I'm working on this 914s brake system, which is already a PITA, as we all know. This system just wouldn't bleed out. We capped all the outlets in the master and pumped the pedal until it was solid. Cool, added in the fronts and bled those until it was solid, added in the rears and it wouldn't bleed.

I pulled the limiting valve (aka proportioning) and swapped in another one, thinking maybe something was bad inside. Same problem.

At this point nothing is making sense. So in a 'hail Mary' move we pull the limiting valve again and use a spare brake hose to connect just the left rear. Bleed that, rock solid. Switch to the right.... same problem. Can't bleed it. (IMG:style_emoticons/default/blink.gif) WTF?

So we pulled the caliper intending to take it apart and check everything inside. as I was pulling it off, I thought maybe there was a dry patch inside the caliper. If it's not coated/wetted with fluid, the surface tension can create a bubble the won't move. I shook the caliper, dropped it in my ultrasonic bath (in a bag) and set it in my vibratory polisher (in the bag). It's back on the car now and it's finally getting close.

I've never had a single caliper be this stubborn, but from now on I'll be adding a little fluid and shaking the calipers before they go on the car. Tim here had a great idea as well, when we're done bench bleeding the master cylinder we'll hook up the calipers and bench bleed those as well, all before it goes on the car.

And people wonder why I hesitate when they ask, "How much is this going to cost?" Who could have known this was gonna happen. And it's a 914--seems like every project has some of this kinda thing. (IMG:style_emoticons/default/wacko.gif)

[Jeff Hail]

Mark,

914s have a unique braking system issue affecting all years, early/ late calipers are all included.

Due to being prone to rust the 914 braking components are "hygroscopically magnetized" to air for some reason resulting in air bubble capture.

I guy named Alfred Teves referred to it as the "BTE" problem in the OEM manuals which stood for Bermuda Triangle Effect. In fact Teves was going to stamp "BTE" on all 914 calipers but his neighbor Ferry wouldn't have any of it being it was a German automobile.

Years later they realized if the 914 bodies had zinc applied prior to coatings the BTE problem was non existent. By that time it was already 1976 and the 914 was phased out.

There was a band aid fix that involved 8 gallons of brake fluid and a constant feed delivery pump capable of 90 psi to enemize the hydraulic system. It was expensive and messy.

Hey this is absolutely true! The Ferrari didn't have this problem while bleeding the brakes. They had zinc.