[guccidude1]

Guys: I have developed this air bubble over the last 18 months in my -9A with dual brakes. I have completed an archive search and read the write ups of the various problems with bubbles in brake lines, both left and right.
My problem is a little different, I am getting air in the left brake system only and it is causing the co-pilot's (CP) left brake to fail completely, due to excessive bubble in crossover line in a couple of weeks time. The air bubble grows over time and it is located at the top of the line that runs from the top fitting of the left CP master cylinder to the top fitting of the pilot's left brake. Additionally, I seem to be pumping brake fluid in the firewall mounted reservoir which is evident by the red streaks running down the firewall and onto the belly. The caliper piston is not extended excessively, I used new brake pads, same story.
I have talked to technicians at Matco and they are at a loss to explain the pumping action of the fluid into the reservoir, except that the caliper piston is extending out due to brake pad wear thus filling the reservoir to over capacity. They cannot explain why the air bubble starts little and grows larger until there is no braking due to air compression.
I bleed the brakes from the bottom with a pressure bleeder and catch the excess from the reservoir into a catch bottle with the overflow line submerged in brake fluid. Both the right and left braking system are serviced the same manner, right system has no bubbles. I have replaced the plastic lines running from the CP side to P side with flexible braided lines, no change. I can not find any evidence of fluid leaks. After servicing, I remove brake fluid from the reservoir down to about half capacity, but after a couple of weeks of use, the reservoir is full and starts overflowing. Anyone have any ideas? Dan from Reno

 

[Mel]

Maybe I'm misreading something, but it sounds as if you have your master cylinders hooked up wrong. There should not be a line running from the top on one master cylinder to the top of another. The master cylinders should be in series. i.e. the line should run from the bottom of one to the top of the other.

Complete circuit should be, reservoir to the top of one master cylinder, from the bottom of that master cylinder to the top of the other master cylinder, from the bottom of that master cylinder to the wheel caliper.
Repeat for other side brake.

 

[Mike S]

After servicing, I remove brake fluid from the reservoir down to about half capacity, but after a couple of weeks of use, the reservoir is full and starts overflowing. Anyone have any ideas? Dan from Reno

OK, so air in the reservoir is being replaced with fluid from the lines, and fluid in the lines is being replaced by air (the bubble).

Just a wild guess here, but I would start looking for a very minor leak in the lines on the suction side of the master cylinder, and possibly a bad check valve in one of the master cylinders.

Another possibility is that there is a piece of something in the bottom of the reservoir that is acting like a check valve-----

A MityVac is a good tool to use for this

http://www.amazon.com/s/?ie=UTF8&ke...vptwo=&hvqmt=b&hvdev=c&ref=pd_sl_1lecnkt7n3_b

 

[guccidude1]

New Old thread: Air bubbles in left brake line

Mel: You are correct. I mistyped what I was trying to explain. The a/c is over 8 yrs old and this started being a problem as I said, about 18 months ago. Re bleed the left system and cp brakes are good to go for about two weeks on the right side until the left pedal gets mushy, the pilot's side is unaffected. Dan from Reno




Maybe I'm misreading something, but it sounds as if you have your master cylinders hooked up wrong. There should not be a line running from the top on one master cylinder to the top of another. The master cylinders should be in series. i.e. the line should run from the bottom of one to the top of the other.

Complete circuit should be, reservoir to the top of one master cylinder, from the bottom of that master cylinder to the top of the other master cylinder, from the bottom of that master cylinder to the wheel caliper.
Repeat for other side brake.[/QUOTE]