Can't prime master cylinder

[johnmr12]

I replaced brake lines on my trailer and when I fill the reservoir with fluid I am unable to push it through the lines. My master cylinder has a slot underneath for a screwdriver so you can manually push the master cylinder piston. No matter how fast or slow I pump that piston, the fluid level stays the same. I have gone so far as to pull out the master cylinder with just the small 2 foot hose that comes out of the master cylinder and screws into the reverse solenoid, and I pumped fluid until it ran out of that line, and then I reinstalled it and before I attached it back on the solenoid I pumped the piston to be sure the fluid was still in the line and it stopped coming out. Its almost like it's sucking the fluid back in rather than pushing it out. I was told to buy a vacuum tool but I really don't want to have to spend anymore money if I can avoid it. Does anyone have any suggestions?

[johnmr12]

Am I the only one who has this problem? I went so far as to pull the master cylinder out and remove the hose that screws into it. I filled it with fluid, expecting it to run out of the hole and nothing happened. I drained it and forced air in and the air came out of the hole so I assume its not plugged. I can only prime it if its installed in the tongue so I put it back in the tongue with no hoses attached and primed it and still no fluid comes out of the hole. This is a fairly new master cylinder. Can anyone think of anything? I am hesitating to buy a vacuum pump because I don't think thats will fix the problem.,

[CatFan]

Can you actually see the piston moving? Verified the breakaway is released? See any bubbles or fluid movement in the master cylinder while moving the piston?

[DABS]

Lower the nose of the trailer and pump it uphill. the air will naturally run away from the master cylinder.

[riverrat29]

It sounds like you may need the vacuum pump to prime. I seem to have the best luck with those. Do each brake individually in sequence. Make sure you keep the master cylinder full and don't let the reservoir to burp air in the process.

[rockytop]

With new lines there is only three places the trouble could be . The master cylinder the reverse solenoid or wheel cylinder. Most reverse solenoids thread right into the master cylinder. Sounds like yours has a section of line between . If you take everything off right at the master and and no fluid,then it has to be the master.

[johnmr12]

In case someone comes to this thread to see the end result, my master cylinder was bad. If you ever replace your master cylinder and don't have a vacuum pump, you can prime it by using the gas siphoning technique. Suck on the end of the hose coming out of the master cylinder and the fluid will flow but make sure not to accidently swallow any.

[Bob G.]

Don't think I would suck on a brake hose to get a master cylinder primed, much easier method using a screwdriver.

[billnorman1]

Suck brake fluid? GACK! Gasoline is bad enough. I haven't seen a good master cylinder yet that you can't manually push and cap with your finger on the back stroke to prime on the bench.

[HaulinBass]

This may be a redundant statement for you.
Unless you’re really creative, bleeding by traditional methods without the use of a vacuum tool, is a two person job. One applies pressure at the tongue with a tire iron or long screwdriver and the other bleeds the calipers. Never let the tongue pressure back off until the bleed screw is tightened otherwise it will suck air back in.

[billnorman1]

This may be a redundant statement for you.
Unless you’re really creative, bleeding by traditional methods without the use of a vacuum tool, is a two person job. One applies pressure at the tongue with a tire iron or long screwdriver and the other bleeds the calipers. Never let the tongue pressure back off until the bleed screw is tightened otherwise it will suck air back in.

Brakes can be bled with one man, just put a clear vinyl hose over the bleeder, run it into a can of brake fluid which covers the end, cycle brakes until you see no more bubbles.

[HaulinBass]

I’m too cheap to waste a can of fluid on discard.

[Snoopy Rod]

Brakes can be bled with one man, just put a clear vinyl hose over the bleeder, run it into a can of brake fluid which covers the end, cycle brakes until you see no more bubbles.

this

[MikeF]

Unless you’re really creative, bleeding by traditional methods without the use of a vacuum tool, is a two person job. One applies pressure at the tongue with a tire iron or long screwdriver and the other bleeds the calipers. Never let the tongue pressure back off until the bleed screw is tightened otherwise it will suck air back in.

Meet creative.


http://www.speedbleeder.com/

[bassin365]

Meet creative.


http://www.speedbleeder.com/

I believe that is the most ingenious thing I've seen in a long time.

[HaulinBass]

Most importantly, they appear to come with caps.