low brake pressure - bleeding the brakes wrong?

[pen]

obligatory 1978 cb750k
I got this bike about a year ago and finally got it up and running this spring. I’ve been riding it around town and to work and such, no apparent problems with the brakes. About a week ago I found out the brakes weren’t in tip top shape when I needed to stop very suddenly. Luckily nothing bad happened, but it was scary enough to put it up until some new pads came in. I installed the pads today, bled the brakes to the best of my ability, and ended up with worse front brakes than I started with. I don’t know if I put the pads in wrong, if the piston is seized in some way, or if I bled the brakes incorrectly. I’m hoping it’s the first or the latter as I don’t exactly have a workshop to rebuild the caliper.

I used a method I saw online where you squeeze the lever, open the bleeder, close the bleeder, and let off. I don’t know how correct this is, but I’m hoping a better or correct technique would alleviate this issue.

 

[pen]

Something else i feel might be important is that I hear about people’s brake lever being able to be pulled all the way to the bar, mine stops about a centimeter short and is not able to be pulled further.

 

[jpdevol]

obligatory 1978 cb750k
I got this bike about a year ago and finally got it up and running this spring. I’ve been riding it around town and to work and such, no apparent problems with the brakes. About a week ago I found out the brakes weren’t in tip top shape when I needed to stop very suddenly. Luckily nothing bad happened, but it was scary enough to put it up until some new pads came in. I installed the pads today, bled the brakes to the best of my ability, and ended up with worse front brakes than I started with. I don’t know if I put the pads in wrong, if the piston is seized in some way, or if I bled the brakes incorrectly. I’m hoping it’s the first or the latter as I don’t exactly have a workshop to rebuild the caliper.

I used a method I saw online where you squeeze the lever, open the bleeder, close the bleeder, and let off. I don’t know how correct this is, but I’m hoping a better or correct technique would alleviate this issue.

Replacing pads doesn't necessarily require bleeding of the hydraulics. You may have a a problem with the master cylinder or the caliper piston however. Some pics of the caliper as mounted and of the master cylinder may help determine what is going on.

When bleeding the caliper at the bleeder valve, you're really only bleeding the caliper itself. If there is air in the fluid in the brake line, that air will rise and it's often more effective to bleed the line at the banjo fitting at the master cylinder. Wrap the fitting completely in a rag so fuild doesn't get on anything (eats painted finish).

Have you opened the master cylinder and flushed new fluid through until it comes out the caliper bleeder?

 

[pen]

20 days later, sorry if this seems silly. I did run new fluid through the system until it was clean coming out. I bled from the top as well and no bubbles or foam indicating air up there. Somehow I think the plunger or piston or something in the master cylinder is causing it to not actuate the whole way. There aren’t any obstructions I can see looking in and around it, but I’m afraid that I’ll have to rebuild or replace the cylinder

 

[Biebs]

Using the correct brake fluid?? Dot 3

 

[pen]

yes.

 

[hinksy]

The system will collect water after time and the brake piston will rust and sieze in the caliper . So it doesnt hurt to completely tear them down for peace of mind . It isnt hard , just do what you did before and use the youtubes for the info and check them out . A new seal and boot for the caliper dont cost much and then you will have the knowledge of how its done and peace of mind that they wont fail

 

[Floshenbarnical]

Something else i feel might be important is that I hear about people’s brake lever being able to be pulled all the way to the bar, mine stops about a centimeter short and is not able to be pulled further.

Personally I can't pull my lever anywhere near to the bar, and my front brake is extremely responsive. And it's an extremely shitty, old master cylinder that I hurriedly rebuilt. Have you checked your brake lines for tiny leaks? I made custom brake lines for my clip-ons and I messed up the first time around, didn't get a good seal on one of the banjo cuffs.

Just buy a new master cylinder mate. Save yourself some time and worry. That's what I'm doing as soon as I have the coin.