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another 240 brake thread...

adamdrives

Member
Joined
Aug 9, 2010
Location
San Jose
Hey Guys and Girls, looking for some help with an 85 wagon that I cannot get a firm pedal in. Long story short, I've replaced the front pads and rotors, master cylinder and front calipers, and the car still has air in the system. Bled in proper procedure (left rear, front uppers, right rear, front lowers) in varying methods (power, pumping pedal engine off and on, stoking pedal to glass jar/hose) I get bubbles from all 8 bleeders with a hose from the caliper submerged in a jar of brake fluid. No fluid leaks visible. After a power bleed, the pedal feels nice and firm. Once running, after a few strokes the pedal becomes low. Am I crazy or is it possible there's an air leak through the back of the master? My thought process is if there was a caliper sucking air it would show in only one circuit, so it has to be something that both circuits share. I don't think there is still air trapped in the system. I've done a few major brake overhauls on 240s, and never had a pedal this stubborn. Any ideas?
 
Did you bleed the fronts immediately after swapping components, or wait and inadvertently send air out back to be trapped in the proportioning valves by cutting to the 'recommended' order?
 
Just a few musings:

A distinction exists between "low pedal" and "spongy pedal" after caliper replacement. One of the benefits of fresh calipers and new flex lines is the amount of piston return after applying pedal pressure. Before replacement, sticky pistons and occluded flex lines can create a very high pedal you quickly get used to. So, low and spongy, or low and firm?

Bubbles can be deceiving if the air is being drawn in around the bleeder threads. A gob of grease removes the deception.

But if you've let either end of the reservoir empty during the process, the air pushed into the rear proportioning valves will be the hell Ken describes above.

brake1121.jpg


brake5648.jpg


brake5707.jpg
 
I definitely trapped air in the proportioning valves. The current set of calipers is the third set. The second set had leaky bleeders and went dry overnight. Honestly I have bled it so many times I can't be sure. Usually after hose or caliper replacement I let the caliper gravity bleed. Any tips for dealing with this situation?
 
To answer your question, its a low pedal. It will firm up on hard braking, but sinks too low.

The res only went dry on the right rear/front lowers circuit, but I'm getting bubbles in both. That's confusing to me. I tried bleeding with the rear jacked up, I still get air in all 8 bleeders. By the time I finish, I can start again and get the same amount of bubbles from all calipers. I tried tapping each of the calipers, junction block and rear valves with a mallet to free up any air. I'm going to try cracking the lines at the junction block next to see if I get the same air there. I've bled each caliper at least 10 times by now.
 
All those bubbles you speak of would give you a spongy, not firm pedal. You haven't mentioned whether you've bench-bled the master, sealed the bleeder threads, or what you're doing to move the fluid while bleeding. How will you observe air at the octopus?
 
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