Master cylinder bleeding

[jbolty]

I can't remember if I posted about this before but long story short I have been fighting with a brake issue for weeks now. I have not been able to get a good bleed on the fronts and no pressure on the fronts.  Looks like I found the reason but now what?

How to fix it?

In this video the master is in a vise and set up for bench bleeding.  You can see that fluid starts coming out of one of the hoses instantly, the one furthest from the boost and which feeds the rear brake circuit.  At the same time no fluid comes out of the other hose until the piston has traveled pretty far, maybe 1/2 - 3/4 inch.  Anyone ever seen this before? I have pumped this thing about a million times trying to get it working.

I swapped in one master already because I was not getting front pressure and maybe it was for the same reason but it seems unlikely that two in a row were bad.

http://www.youtube.com/watch?v=3pqOT3mXnUE

anyone with a solution?

[Mikegyver1]

That's interesting... hard for me to follow what's going on. does your jeep have a proportioning valve? If not that maybe why it's like that..  .. most common mistake I've seen is people installing the calipers flip flop (right and left sides) bleeder always above the feed line.

[jbolty]

It does have a proportioning valve but I don't think that's the problem.  According to what I have been reading the piston on this particular master should not travel more than about 1/2" under normal conditions so in that case the front brakes would not be getting any pressure at all.  Which is exactly what's happening since no fluid starts to move on that circuit until pretty far into the travel.

I guess my question is am I bench bleeding the wrong way? Or, did I get two bad master cyl in a row?

Cheers

[Metal Twister]

We bled mine today just like you would a wheel with a bleeder. Only we did it at the fittings. Pumped up pressure and cracked the fittings for the brake lines when we hit bottom we tightened the fittings and repeated. It worked for us...   

[Mikegyver1]

 I would guess that under pressure it would work correctly and the working function is in the middle. On the bench it's cycling through the valving to quickly to accurately display the pressure it's exerting on the brake pads while compressed in the lines...
Just a guess.. I'd like to think the mfg build the pos correctly. Could the lines be flipped front to back some how?

[jbolty]

I have had this thing off and on 5 dozen times and bleeding and switching lines around and blocking off one wheel at a time.  Getting another new m/c seems like the best bet but of course no one has one.

Meantime the whole front of the jeep and the driveway are soaked in 2 gallons of brake fluid.   

Tomorrow is power washing day.

[Metal Twister]

LOL... Me too Jeff, its a slip and slide at the shop!

[2wdrckcrwlr]

I had a truck that wouldn't bleed out or get pressure and it tended up being at the calipers. The pads were worn to a point that a small pocket of air in the caliper. Had to compress the caliper in with a big "c" clamp or caliper compressor to get the air out.  After that it worked great.

[jgorm]

I sucked the master dry a few times while bleeding brakes and i never had to bleed the master on the jeep.  I just bled it like normal from the calipers.  On my mustang once i sucked the master dry (yeah, i stopped making that mistake now!!) then i had to bleed the master before i could get a pedal.  Your video was a little short.  I would have liked to see 3-4 pumps with longer lines draped over something so observe bubbles and flow.  It may be possible that you have some back flow going on due to the open setup (guessing).  I have had issues when brake bleeding where the bleeder did not seal well and let air in if it was turned more than a 1/4 turn past when the fluid came out.

[jeepsterrob72]

if you figure it out let me know im having the same issue with the commando. been through at least a gallon of fluid trying to get it bled and still not getting pressure like i should.

[Redneck sami]

What style brakes do you have? Disc/Drum? disc/disc? Is one fluid chamber bigger than the other on the master? I know with disc/drum, the larger chamber, witch is usually the further one from the booster, is for the front brakes. calipers need more volume of fluid than drums. with that, you might have the lines crossed. even with disc/disc the front calipers are usually larger than the rears so the larger chamber would still be used for the front calipers. some times it does take a lot of pumping on the bench to bleed the master out, thus is why they say to bench bleed... so your not pushing fluid through 20 feet of line to get bubbles out from the start of the system.