rear brake master plugged?

[671M900]

So while reassembling my bike, I noticed no matter how much I pumped the rear brake master, fluid would never come out, and fluid would never drop in the reservoir.

I assumed a plugged port somewhere, so I took a blowgun to the reservoir port on the master and some fluid flew out the banjo outlet. A few drops of brake fluid in the banjo outlet and the fluid would get sucked in and squirt out when the lever was depressed. however, still doesn't take any fluid from the reservoir. I assume that there is still one port to be clogged?

How does one unclog the ports? a can or brake cleaner? Don't wanna mess with the rubber too much though. If it's any help, it's goldline rear master, but I believe its an early one if it matters.

[ducpainter]

It could be a bad master, or just air.

If you could come up with a way to pressurize the reservoir and then bleed at the caliper it would most likely solve the issue.

Low pressure...10lbs maybe.

[Slide Panda]

I replaced the brake line on my rear and encountered a similar issue. It's not broken, it's just a pregnant dog. Pumping at the lever just got no place - but slapping a vac on it at the caliper got things moving in short order. If you have or have a buddy with a mighty vac that'll do.

[Howie]

Is your caliper mounted on the top or bottom of the rotor?  If the caliper is mounted on the bottom you have two choices:

   1. Remove the caliper, turn it upside down so the bleeder screw faces up, find a piece of        wood or metal about the thickness of the rotor to place between the pads, bleed.
   2. Turn bike upside down.  Bleed.

I suggest  choice #1.  If the bleeder is on the bottom you will not push out the trapped air.

[deanknight636]

Is your caliper mounted on the top or bottom of the rotor?  If the caliper is mounted on the bottom you have two choices:

   1. Remove the caliper, turn it upside down so the bleeder screw faces up, find a piece of        wood or metal about the thickness of the rotor to place between the pads, bleed.
   2. Turn bike upside down.  Bleed.

I suggest  choice #1.  If the bleeder is on the bottom you will not push out the trapped air.

+1

[671M900]

Is your caliper mounted on the top or bottom of the rotor?  If the caliper is mounted on the bottom you have two choices:

   1. Remove the caliper, turn it upside down so the bleeder screw faces up, find a piece of        wood or metal about the thickness of the rotor to place between the pads, bleed.
   2. Turn bike upside down.  Bleed.

I suggest  choice #1.  If the bleeder is on the bottom you will not push out the trapped air.

Sounds good! why wouldn't it bleed if the caliper was mounted on the bottom? After I bleed it correctly and mount it back to the way it was, will I be able to bleed it later without taking the caliper off?

I just took a blowgun to the reservoir tube to push some fluid through the lines, which worked, but not too much. Enough to get some fluid going out the bleeder.

[ducpainter]

The bottom mounted calipers don't bleed well.

[Howie]

The trapped air is on the top and will stay there and just compress since the bleeder is on the bottom.  Once it is bled you will be able to change you brake fluid with the caliper on but if it needs to be bled you will have to turn it upside down.

[671M900]

The trapped air is on the top and will stay there and just compress since the bleeder is on the bottom.  Once it is bled you will be able to change you brake fluid with the caliper on but if it needs to be bled you will have to turn it upside down.

Good to know! So I got fluid in there by attaching a brass barb to a spare rear brake master reservoir cap and fed a few psi of air into it until fluid came out the other side. Now, I'm a bit confused as I just tried to bleed it manually.

Now, it doesn't seem to be drawing fluid from the reservoir unless I flip the master so that the hose from the reservoir is on top. However, it looks like the master mounts the otherway around, with the hose port on the bottom. Seems counterintuitive to me, or does the master cylinder suck in the fluid, as opposed to being gravity fed? Is there a port still blocked?

[deanknight636]

The trapped air is on the top and will stay there and just compress since the bleeder is on the bottom.  Once it is bled you will be able to change you brake fluid with the caliper on but if it needs to be bled you will have to turn it upside down.

true true i had the same problem on my dual caliper setup on my stunt bike.  basicaly the bracket put the caliper at a position where the bleed nipple was pointed strait back, this allows for an air pocket to form within the brake caliper when trying to bleed it.  therefore when you screeze the brakes the fluid just compress up into the air pocket and you get minimum braking.  so just pop the caliper off, make sure the bleed valve is pointed straight up, stick a vacum pump on it, and bleeder out.

[ducpainter]

Good to know! So I got fluid in there by attaching a brass barb to a spare rear brake master reservoir cap and fed a few psi of air into it until fluid came out the other side. Now, I'm a bit confused as I just tried to bleed it manually.

Now, it doesn't seem to be drawing fluid from the reservoir unless I flip the master so that the hose from the reservoir is on top. However, it looks like the master mounts the otherway around, with the hose port on the bottom. Seems counterintuitive to me, or does the master cylinder suck in the fluid, as opposed to being gravity fed? Is there a port still blocked?

The master is definitely gravity fed.

[671M900]

Fed from below? Just wanna confirm.

[ducpainter]

Fed from below? Just wanna confirm.

The feed nipple is on the bottom. The reservoir is above.

[ducatiz]

when you take that bottom-mounted caliper off to bleed it, put a block of wood between the pads which is about as thick as your rotor.  you'll only screw this up once.  use some twist wire to hold it.  do it as soon as you remove it from the rotor.  squeeze that master once or twice and you may pop out the pucks.

[671M900]

I feel so giddy, kind of. I fabbed a pressure bleeder using a glass salsa jar and some hose, filled it with brake fluid, took the compressor blowgun to it and bled it slowly. Now it's plenty firm!