No pressure in master cylinder

bieda137

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This is my first post to the forums but have been gathering great information from you all, thanks!

Recently I purchased a new master cylinder, but after the install it wouldn't build pressure while I was trying to bleed the line. Before the install I didn't notice any caps or plugs of any sort.

Thinking a block may have been somewhere in the line, I back tracked from the caliper but no fluid. Working on this bike is all new to me and if anyone reading this has a suggestion, please let me know.

Thanks everyone
 
Sounds like the master may be air locked - no fluid entering and none coming out. I use a vacuum bleeder on the bleed screw to draw the air and fluid through the system initially.

Then I pump up pressure in the system, and while holding the pressure, with a clear tube attached that runs upwards and then into a container, open the bleeder screw. Once the fluid stops flowing, close the bleeder screw and pump the lever to build pressure again. Repeat this until there are no more air bubbles coming out. Then let the bike sit over night and repeat the pressure bleeding. Don't let the reservoir get empty or you will have to start all over again!

This works for me every time, on cars, trucks, bikes, motorcycles, and airplanes. Heck, it even worked on a helicopter once! :)
 
Ok since I rebuilt my caliper I having this problem that no pressure will build in the system.The brake line coming from the master cylinder is full of fluid but when I try to bleed I cant build up any pressure.I dont beleive the problem is in master cylinder since it was working fine before.
 
What worked best for me after I rebuilt the master cylinder and front caliper was to attach a syringe to the tubing coming out of the front caliper. I then added fluid to the master cylinder and sucked the fluid through the system using the syringe. It was the only thing I could get to work as trying to pump up the system using just the brake lever wasn't working... YMMV...
 
What worked best for me after I rebuilt the master cylinder and front caliper was to attach a syringe to the tubing coming out of the front caliper. I then added fluid to the master cylinder and sucked the fluid through the system using the syringe. It was the only thing I could get to work as trying to pump up the system using just the brake lever wasn't working... YMMV...

I happen to have syringes and was thinking about trying that.My thought is the whole system has to be filled with fluid before it can start building pessure.
 
Yep. As long as there is air in there it is hard to build up any pressure. You'll be amazed how easy it is to bleed the brakes By drawing the fluid down from the M/C to the caliper with the syringe...
 
When I got my new MC, I was surprised how long it took for me to get the system bled. All the lines were empty when I started since the caliper was rebuilt as well.

It took me a very long time, but what worked for me was to first bleed the caliper. After that, I still had no pressure, so I figured the lines and MC had air in it towards the top. I pretty much sat there for about an hour pulling and releasing the brake lever. I kept the fluid level relatively low so that there wasn't too much back splash.

What I found was that when I released the brake lever, I could see an air bubble coming back out from the fluid inlet at the cylinder in the reservoir. I did this for a long time, periodically tapping on the MC and turning the handle bars to allow the air to move around. After much much longer than I anticipated, I noticed that no more bubbles came out and the brake firmed up. It was a very quick transition from squishy to rock hard.

Just my personal experience, hope it helps a little bit.
 
I would think with thebleeder screw open on the caliper gravity would do the rest:shrug:I filled the line and caliper with several syringes full of fluid,Its not doing its thing as of now.
 
I put the fluid into the master cylinder and then pulled it down to the caliper filling the syringe from the tube on the bleeder valve. I've not tried it the other way around...
 
Well I`ll be stuck for a bit cause my brake handle broke off again.It has to be welded and have to wait till I get paid.So for now this topic will be on pause.
 
I just did this a month ago, I ended up attaching a long hose to the bleed screw, just like the vacuum thing, and created a vacuum the old fashion way, (i used a new hose). Once I got fluid filling up the hose. I also noticed the bubbles in the MC. and kept squeezing till all the bubbles got out. As long as the hose was filled with fluid, I had no fear of air returning to the caliper. I flushed it our really good since I was doing that.

Of course I wouldn't have had to do that if I would have looked at the front caliper after replacing my tire on there. I had squeezed it(front caliper) locked up tight with out the second brake pad in place. Oops.
 
Ok so I got a new brake handle and its time to start to bleed them again.I still cant get any presure to build in the master cylinder.I know the line has fluid in it and so does the caliper.Once in a while when pumping the brake handle I get air and some fluid to come out of the bleader screw hole but no continous stream what so ever.I almost wonder if the piston in the caliper isnt moving or possibly the holes in the master cyclinder that feeds fluid to the line and caliper are plugged with dirt.So what steps should I try first to remedy the problem?Is there away to check the caliper off the bike?
Need help and brakes thanks
 
Pull it off the rotor and squeeze the brake lever and see if its moving at all. I had a stubborn rear caliper on my CR500 supermoto, I ended up pulling the cap on the reservoir and leaving pressure on the lever over night to allow the air bubbles to flow naturally. Next morning the rear brake was much more solid.
 
Ive always had to use a c clamp. Its annoying with multiple pistons, one will try to come back out as you compress the other. Sometimes from sitting in the same position for so long they will kind corrode, so a short of WD to free it and then some grease afterwards helps.
 
Mine shouldnt be corroded it should be all clean cause I went through it a couple of months ago.This is why Im guess whats causing my problem.
 
Attach hose to bleeder screw and run it up about 6" before looping down into container. With bleeder screw closed, pump lever quickly a number of times, then hold down.
Crack bleeder screw and allow any air or fluid to escape, then close bleeder screw.
Repeat 3 times and then top up reservoir.
Repeat as required to get a firm lever.

A bit of air may still be trapped in the fluid once you are done. It will either rise to the master and get worked out, or it will be sitting at the bleeder screw. Ride the bike a couple days and then bleed it again once to get any air out of the caliper.

Once the lever is pulled, the system is closed and pressurized, so no air or fluid will be able to escape. If the lever is adjusted incorrectly, with no freeplay, then the system may be closed and no fluid will enter the master nor will air exit. If ridden like this, the brakes will drag and overheat.
 
And I didn't say that you shouldn't use a c-clamp. :) The average person should be able to push the piston back in by hand. If it is too stiff, then it is time to check out the braking system and find out why. There shouldn't be that much resistance.
 
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