Itinerant Air-Cooled

I have just replaced my master cylinder. I bled the front lines without incident, however, now I am wondering how much air will come out of that rear left line. I have someone pumping the pedal for me and each time it looks like the same amount of air is coming out of the line. I have flushed it and can tell it is new fluid but after 20 or more pumps I wondering if there is an end to the madness or I had a ton of air in that line. It did drip for a while...
Thanks!

Could be a bad wheel cylinder sucking air back in...? The bubbles are right there every time my helper pumps. It would be leaking in but not out.

I had this on my Ghia which turned out to be a rusty brake line which sucked air/bled fluid next to the drivers seat rail.

I'll look through the lines closely again but from what I've seen they look pretty solid.

upnorthman wrote:I'll look through the lines closely again but from what I've seen they look pretty solid.

Try the gravity method. Your reservoir is at a higher elevation than the entire system. Open the left rear bleeder with a little hose leading to a jar. Ensure that the reservoir is kept full. Leave bleeder open until the jar is about half full. Close bleeder.

Please be sure that the brakes are adjusted correctly before any bleeding operation. Remember that each bleed sequence is about a half inch of brake line travel. That means if the left rear brake line is full of air, you can expect twenty cycles of bleeding from the tee to the wheel cylinder.
Colin

Amskeptic wrote:

upnorthman wrote:I'll look through the lines closely again but from what I've seen they look pretty solid.

Try the gravity method.

Silly question follows.... If this pushes all air out how do I know if air might be coming in via a bad cylinder? I mean that is if after the pedal is released it could be pulling air in through a bad cylinder, no? I'm not opposed to replacing them both as they are just a tid bit old after all....

upnorthman wrote:

Amskeptic wrote:

upnorthman wrote:I'll look through the lines closely again but from what I've seen they look pretty solid.

Try the gravity method.

Silly question follows.... If this pushes all air out how do I know if air might be coming in via a bad cylinder? I mean that is if after the pedal is released it could be pulling air in through a bad cylinder, no? I'm not opposed to replacing them both as they are just a tid bit old after all....

Air only comes in when there is negative pressure. There is only negative pressure when you release the brake pedal. If the brake pedal is just sitting there, the reservoir is opened to the lines and gravity will take care of filling the line, albeit slowly.
Colin

So it would be safe to assume that there would not be enough negative pressure during normal (b-r-a-k-i-n-g) to re-introduce air into the line?
David

If you press the pedal, no matter how hard, the return of the pedal upwards creates that negative pressure...so yes...normal use will introduce air if there is a leak. Colin above was referring to the gravity bleeding method. If you open the rear bleeder, and do not touch the pedal, and keep the reservoir full, there is no negative pressure, and no air will enter the lines. Also, if you have a leaky wheel cylinder, you should see some fluid seeping out..I think.

For what it's worth: BellePlaine assisted me in a full bleed last year, after an on the road brake failure. He was the pedal-pump man; the method was: pump up the system with ~5 short fast pumps, then steady pressure on the pedal, while I'd briefly crack the bleeder valve on the caliper and then close while still under positive pressure. It kind of amazed me, on the rear left, as I recall it took at least a dozen (if not more) of the aforementioned cycles and about a cup of brake fluid before I was sufficiently happy that all of the air was out...

-miz

the miz wrote:For what it's worth: BellePlaine assisted me in a full bleed last year, after an on the road brake failure. He was the pedal-pump man; the method was: pump up the system with ~5 short fast pumps, then steady pressure on the pedal, while I'd briefly crack the bleeder valve on the caliper and then close while still under positive pressure. It kind of amazed me, on the rear left, as I recall it took at least a dozen (if not more) of the aforementioned cycles and about a cup of brake fluid before I was sufficiently happy that all of the air was out...

-miz

Important to give the pedal a moment at the top of the stroke, to allow the reservoir time to refill the lines.
A slow powerful pump is more effective than the quicky.

Each bleed is good for barely a half inch of line, so yes, it should take many pump cycles to get air all the way down a 75" run.
Colin

Ok. Almost back to bleeding. I put new cylinders on the rear (no sign of leak), however, my adjustment procedure is 'lacking'. Should I start another topic?

Just in case... With new cylinders it appears that I should back both adjusters down to zero then work my way back up to drum contact, however, it sounds as though I have contact at all times. This is on the rear left and it is only 30-40% through the full spin of the wheel. I am thinking I'll try to go to a change in contact then back off the three clicks and follow this with a test drive. No, I've not bled them yet. Still adjusting.

So goes things in my garage... The parking brake line is rubbing (very loudly) against the rear right wheel hub. When I say line I'm talking about the spot where it attaches to the parking brake cable lever within the brake assembly. I caught myself wanting to put that lever into the vise and give it just a little bend...

Thanks!

upnorthman wrote:With new cylinders it appears that I should back both adjusters down to zero then work my way back up to drum contact, however, it sounds as though I have contact at all times.

Do you know the shoe slots in the adjusting screws are directional? They have an internal slant that should match the slant of the brake shoe. For example, on the rear of a VW bus, the cylinder is at the top, and the adjusting mechanism is at the bottom, so the slants might look like this:

/{star}V{star}\

Regardless of my piddly diagrams, make sure these screw slots are angled flush with your shoes. I had trouble getting a drum mounted on a bug with well-worn shoes when I installed the adjuster screws backwards. See the slant where the shoe resides?

Robbie

Hmmm I will check that out tomorrow eve. I thought I left those alone but they could have spun a bit on the re-install. Thanks! I've thrown the towel in for today and will be tenting it tonight. I need campfire time.

upnorthman wrote:I need campfire time.

Don't we all. Enjoy it for us,
Robbie