master cylinder problem
Road Warrior
Joined: Jul 2016
Posts: 1,370
Likes: 439
From: va
Keep trying , even though you are not getting fluid you should have been getting rid of air , enough to start pulling fluid into the plunger , it might take a dozen times
to do the rest of the system is going to be the same way , many people have the same problem , it's a H-D thing
to do the rest of the system is going to be the same way , many people have the same problem , it's a H-D thing
Thread Starter
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Cruiser
Joined: Oct 2008
Posts: 234
Likes: 15
From: Southern California
The air pressure is just coming from the movement of the plunger. No air or fluid is moving from the reservoir. I drained the whole system and opened up the bleeder valve and tried pushing air up through the system. It's being blocked at the master cylinder somehow. same thing as before I rebuilt the master cylinder.
Basically, this is what's happening: When I assemble the master cylinder, initially I can push air/fluid through the system from the bleeder valve, but after the first lever squeeze, i feel a slight click and the system gets "blocked" and even though the lever moves freely no air/fluid moves through.
Not sure if that makes sense, but I've taken it apart and put it together a few times now and does the same thing.
Basically, this is what's happening: When I assemble the master cylinder, initially I can push air/fluid through the system from the bleeder valve, but after the first lever squeeze, i feel a slight click and the system gets "blocked" and even though the lever moves freely no air/fluid moves through.
Not sure if that makes sense, but I've taken it apart and put it together a few times now and does the same thing.
Road Warrior
Joined: Jul 2016
Posts: 1,370
Likes: 439
From: va
Do you have everything assembled ?? and you pushed fluid in reverse to the master cyl with the lever pulled and fluid came into the reservoir -- correct ?? If so do you have dual calipers ?? are they even warn a little ?? how about your pins and bushings ??
The master cyl has very few cc's of fluid for 2 calipers and if anything is worn it's not enough of fluid to push 2 pistons against the rotors , about the time the pistons touch the rotors they run out of fluid and pressure
to check this -- make a temporary shim ( the metal part of a old pad ) and put between the caliper housing and the back side of the brake pad (piston side) and see what you have , do both calipers , also bleed again
The master cyl has very few cc's of fluid for 2 calipers and if anything is worn it's not enough of fluid to push 2 pistons against the rotors , about the time the pistons touch the rotors they run out of fluid and pressure
to check this -- make a temporary shim ( the metal part of a old pad ) and put between the caliper housing and the back side of the brake pad (piston side) and see what you have , do both calipers , also bleed again
Thread Starter
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Cruiser
Joined: Oct 2008
Posts: 234
Likes: 15
From: Southern California
it's a single caliper. I'm pretty sure it is something that I'm doing wrong, because, everything worked fine before I switched out the brake line. I checked the tiny holes in the master cylinder and that's clear. Upon initial assembly, brake fluid comes up through the hole just fine. It's just that after i pump the lever the first time, I feel a very minor click and then after that, the master cylinder acts as if the hole is blocked...even though I can see that it's not. After that initial click, nothing passes through either way from the reservoir to the master cylinder (fluid or air)
I double checked to make sure everything is assembled correctly. I've got the manual, parts catalog and I've watched some youtube videos. I've been at it for a few days now.
I double checked to make sure everything is assembled correctly. I've got the manual, parts catalog and I've watched some youtube videos. I've been at it for a few days now.
Club Member
Joined: Sep 2010
Posts: 15,445
Likes: 7,136
From: Beyond Fucital
Fluids not getting in front of the plunger. Period. I don't know why, I'm not there. The air coming out and the suction pulling back is the plunger moving, but there's no fluid in front of it to push. The clicking might be the plunger sticking and not returning to allow fluid to enter the brakeline or permit it to return. Example when you try to reverse bleed.
Thread Starter
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Cruiser
Joined: Oct 2008
Posts: 234
Likes: 15
From: Southern California
So I've spent the last couple nights reading every forum I can find about bleeding brakes, bench bleeding master cylinders, reverse bleeding, etc and it turns out that none of those were my issues.
I didn't realize that the failure to pump fluid or air occurred when I bolted the master cylinder to the handlebars. It turns out that the push rod switch plate assembly has a little tab that pushes on a switch to operate the brake light. That little tab got bent very slightly. I didn't notice it until just now. It was enough to prevent the plunger from returning to its original position when the brake lever was released. It was only about 1/8" but it screwed everything up. I straightened out the tab and the master cylinder is operating as it should. Just dumb luck that I noticed it. At first I didn't even realize that it wasn't supposed to look like that.. I checked the parts catalog but it doesn't show the part at a very good angle. So I googled the part and sure enough my part was out of wack.
Thanks for all your suggestions.
I didn't realize that the failure to pump fluid or air occurred when I bolted the master cylinder to the handlebars. It turns out that the push rod switch plate assembly has a little tab that pushes on a switch to operate the brake light. That little tab got bent very slightly. I didn't notice it until just now. It was enough to prevent the plunger from returning to its original position when the brake lever was released. It was only about 1/8" but it screwed everything up. I straightened out the tab and the master cylinder is operating as it should. Just dumb luck that I noticed it. At first I didn't even realize that it wasn't supposed to look like that.. I checked the parts catalog but it doesn't show the part at a very good angle. So I googled the part and sure enough my part was out of wack.
Thanks for all your suggestions.
Last edited by das56170; Jul 23, 2017 at 11:35 PM.
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