My master cylinder hates to do its thing

First off, If anyone here hasn't done business with Chacal, let me recommend the guy. Top notch shipping, fast informative, totally has saved me a huge head ache when i was replacing the sight window on my master cylinder.

Ok now for the business of my possibly malfunctioning M/C.

I have just rebuilt my front brake master cylinder using an OEM rebuild kit.

I have installed it, filled it with brake fluid and have proceeded to try and bleed the system. Only problem is: nothing comes out when pumping it using the hand brake. It will push air but no fluid.

I removed the banjo bolt and looked in through the hole into the body of the master cylinder and no fluid is in there. I can pump the hand brake with the banjo bolt off and nothing comes out. Its almost as if the hole to the where the piston is blocked and nothing is being fed in. But I have cleaned this small hole in the bottom of the reservoir.

I noticed that there is another small hole next to it that looks completely blocked. Are both holes supposed to be free and clear?

Sorry for the vagary here in my descriptions but its my first rebuild of a motorcycle master cylinder and I am at a loss as to what is wrong.

Much thanks to anyone who has words of wisdom.

Chris

 

These guys are always talking about what a hassle bleeding the brakes are. I havent done it yet, but they said that doing it takes (And I'm quoting the Sandlot here) "FOR-EV-VER!" So unless I'm mistaken, be patient.
-SLKid

 

WORD of wisdom: YES! that much smaller hole needs to be clear, but........that probably isn't why your m/c isn't pumping fluid.

You may have installed the rubber "piston ring" on the plunger piston backwards.....

 

Oh man, I was afraid I may have done that. There were two rubber rings that installed both open end (lip) facing up. They were two different sizes though. The one with a wider lip to it was installed closest to the spring and the other with a smaller lip closer to where the rubber boot goes on.

I tried to follow the old rubber seal configuration on the rebuild but I was sort of guessing as to which one went first and second. The originals were so worn I couldn't tell which was fat lipped and which one wasnt. Argh

Guess I will be heading to the garage now to take it all apart and find out if this is another self induced aneurysm.

 

Umm... what bike is this? Are you dealing with a remote-mounted master cylnder, like on the SECA 750's, or one built-in to the handle, like on most other bikes?

 

im thinkin if its similar to a car the seals should be facing oposite directions as for the different sizes im not sure which way they should go

 

Its an 82 xj550 Maxim. Handle bar mounted. I am pretty sure i installed the seals correctly since I matched them to how they were in on the old plunger assembly I was replacing.

The fact that it was able to push a tiny amount of air out the bleeder valve when i first started is good right? I know that most people recommened that you "prime" the m/c before starting to bleed it. I attempted to prime it by looping a plastic tube into the fluid bowl from the port where the banjo bolt attaches. Sort of a closed circuit I guess. Anyway, no fluid is pushed out when I use the plunger, it does however push a bunch of air. That would indicate a good seal for the plunger assembly right?

Thoughts anyone? Maybe I should check the seals again and see if they "lipped" when I installed them, or check to see if they are in backwards as Chacal suggested.

Update * Ok, so am comparing the two plunger assemblies (the old one originally in bike and the new one i i put together from rebuild kit)and they are identical in how they are currently arranged. My question is: should the "open" portion of the seal face toward the spring or away from it? I just recently bought this bike and the front brakes on it were gone when purchased, maybe the owner had installed them incorrectly to begin with?

 

i also no with my one the fluid took ages before it started coming out the port im talkin like 30 or 40 pumps

 

The open end of the little pill box hat shaped rubber cup goes over the narrow end of the spring. The wide end of the spring goes toward the banjo bolt.

The rubber ring that goes around the plunger has a lip on it. That lip should be angled "in" toward the banjo bolt.

 

Well, as others have experienced, using a pressurized system to pull the fluid out of the reservoir to prime everything worked in about 30 seconds. I guess I did have everything installed correctly. The brakes work now but are still dont fully engage until the end of the brake lever "squeeze arc", as it were. I have hand bled the brakes afterwards and all that comes out is pure fluid, no air bubbles.

So now i just went a purchased new brake pads, since the old ones have been on there forever, and I am thinking that this is the reason for the lack of bite at the begining of the braking squeeze. I don't see any air coming out when I bleed it, so is it safe to assume I got it all out at this point?

I somehow feel that i am in the home stretch, but that could be due to the 6 pack of microbrew that has seen me through this journey today.

oh, and Chacal, you mentioned that second hole needed to clear in the reservoir bowl. Mysteriously i now see a little pin hole there after using the pressurizing vacuum. hmmm

 

If you're working with a Maxim (update your signature please) it's really hard to get that last bit of air at the banjo bolt because it's the high spot in the system. Bike on side stand handle bars hard left gets it closer to level.

On the other hand the brakes on the XJs were never world beaters. Add a 25 year old rubber brake line and they get pretty soft. I can guarantee you my 650 wasn't going to stop if there was any dirt between the end of the lever and the grip. A nice set of braided brake lines from Chacal will firm them up a lot.

 

Thanks for the advice all, I couldn't have done it without you! It's definitely a confidence booster to know I have improved the performance and safety on my bike even if just by a little.

I will be looking into those braided lines from Chacal next. Thanks for the info on that MiCarl.