Air in brake line

[Kaiser2boy]

OK sorry, I know this question has popped up before but I am getting real frustrated with air.
New master cylinder, new wheel cylinders OK.
Washed all joints with brake cleaner, let it dry then jigged up a way to keep a good deal of pressure on the brake pedal all night long. In the AM checked all joints for seepage,,nothing showing. No drips from any wheels , nothing.
Yet just about every few weeks I need to bleed the brake cylinders. No matter how much I slowly pump the brake I always get some tiny bubbles coming up the fill plug.
Any ideas...

[Doc Dave]

Did you bench bleed the master first?
This is important to purge all air from it to begin with. Not hard to do and you can do it while on the truck, just a little more trouble. Disconnect the output tube at the master. Attach a temporary short stub here of tube so as to allow you to attach a piece of vinyl hose to it, and run hose back into the master's fluid reservoir. Pump this many times to make sure all air is "out" of the MC.
Then, the air in the lines can be hard to eliminate without a pressure bleeder in my experience. I made one from a garden sprayer (details on internet), or you can buy one. The only "extra" thing is you have to buy another MC plug-nut, drill it for a barbed hose fitting, where you can then connect this to your pressure bleeder. Also you have to weld close the vent hole on this plug. The pressure bleeder generates enough pressure to get all the air out. I could not seem to get my system purged of all air until I did this. I also have a vacuum booster on my truck, which added another place for air to "hide".

[Desoto61]

What are you using to bleed the brakes? By fill plug you mean the vent port at the wheel? It's not uncommon to get some air sneaking into the line through the threads of the plug while bleeding it. It's normal and not a problem, it's more common if you are vacuum bleeding as the vacuum will pull the air through the plug threads.

What exactly is happening? You put pressure on the system, had it bled down by the time you came back in the morning? What is making you sure there is air in or getting in? Need to understand what is going on to verify there is actually air in the system.

Don't forget you can also be sucking air in without getting a leak out, or that new cylinders doesn't mean they can't leak in or out. Give us the story and we can better help determine what the problem is.

[Kaiser2boy]

The - fill plug - I am talking about is the threaded plug on top of the MC. I pluged the vent line on the MC also while attempting to pressure bleed the system. I made up a steel section of pipe that threaded into the MC fill plug and by useing adapters from a plumbing supply and a 3 inch section of steel pipe as a resivoir with a cap on it and adapted an air line to it. I applied about 15 pounds of air to the fuid in the resivoir and bled the brakes that way and replacing fluid as needed.
It seemd ok ,,for a while and then air again after a few weeks.
I am now wondering if it is some how sucking in air from one or more of the made in china wheel cylinders or the MC.


I did bench bleed the MC and did my best to not leak any out while instaling it. After the MC instal I had my wife press the brake a tiny bit and I cracked the exit line on the MC to make sure as much air was out as possible.


My test with pressure on the pedal all night showed no leaks and the pedal had not bled down .

[Desoto61]

Based on the over-night test alone I'd have to say that it does sound like an in-only type of leak if it gets worse over time.

Simplest solution is to go around and loosen and re-tighten all the fittings, the lines all seal by the metal seats deforming against each other, sometimes allowing them to re-seat helps. If not, then I'd start looking at the brake cylinders, a bad seal would easily show what you're seeing, with pressure on the rubber seal is pushed against the cylinder and seals, when released the brake return allows air to get in. There could be minor weapage from that cylinder but you wouldn't see it unless you pull the drums, and even then only if it's bad.

[Paul Cook]

A path I have followed many times...

I suggest that you follow the book procedures for a MAJOR BRAKE ADJUSTMENT as required following replacement of the master cylinder. This includes the pedal adjustment.

This is the only way you can be sure of having the relief port and the supply port properly aligned so they will function properly.

It also insures that the brake system fluid volume issue is properly addressed.

A pressure bleeder lets one person do a full brake bleed and adjustment on a WC63 6x6 in under an hour.

Old guy hint: A work shop without a pressure brake bleeder is a work shop that probably uses old dinosaur bones instead of real hand tools.

A printable portion of the Service Manual covering brakes is on the Frequently Asked Questions at my Museum web site. www.texaspowerwagon.com

Good luck. I hope this helps.

[Kaiser2boy]

Ok, after a lot of tinkeing I seem to have located the problem. The front right wheel cylinder is sucking in a bit of air after sitting a few days. It was rebuilt but I guess its past rebuilding. Now for the fun of trying to get it off. looks like everything is in the way of the bolts.
I am hoping I can undo the bolts and keep pulling the cylinder away from the back plate until it comes off and just leave the bolts in the back plate.

[Kaiser2boy]

Finally got around to yanking the front wheel cylinder.
It went better than I figured.
Not having the tool to deal with the killer spring I took off the nut from the front shoes lower pivot point, removed the stud. That allows the bottom of the shoe to move to the left and release the tension on the spring and you can just lift it off with your fingers. The next problem looked like it was going to be trying to get the cylinder bolts off. No problem, undid the brake line, moved it out of the way and washed everything off. Then un-did the bolts from the top a few turns at a time , first the front then the back until the cylinder fell off in my hand.
I pre-filled the new cylinder put the plastic shipping cap back on and held it in place and with a pair of longnose pliers worked the bolts a few turns in then used a wrench, popped the plastic cap, quickly instaled the line , bled it a few times and Ta Da good brakes.
Oh yes putting the shoe back on was just the reverse of removing it, Put the tip in the cylinder, make sure its in the grove, hook up the spring by hand, swing the shoe to the side and over the guide clip, swing it back to the and jiggle the pivot bolt in and install the nut and I was home free. Its been a week now and NO AIR YIPPY !!