another brake priming issue

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Twowheeltitan
Posts: 6
Joined: Wed Feb 28, 2018 10:43 pm

another brake priming issue

Postby Twowheeltitan » Thu Mar 01, 2018 9:06 am

Hey guys. Lots of great info on the forum, long time lurker.
I've got an 83 650, rebuilding from basket case. I rebuilt the front brakes and have been unable to get the mc primed. I've tried pulling the banjo bolt at the mc and doing the normal finger over hole, but no go. I have also pulled the guts out and recleaned and inspected all the pieces.
I'll be able to get a vacuum bleeder tonight, but does anyone have any other ideas?

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GeorgeSweety
Posts: 323
Joined: Tue Aug 08, 2017 11:47 am
Location: UK.

Re: another brake priming issue

Postby GeorgeSweety » Fri Mar 02, 2018 12:33 am

Hi, I've never encountered many brake problems myself but you may get some tips from this.
https://www.youtube.com/watch?v=jiWnc4fNGCo

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Folsoml
Posts: 1621
Joined: Sat Apr 07, 2012 9:02 pm
Location: North Florida

Re: another brake priming issue

Postby Folsoml » Fri Mar 02, 2018 6:26 am

Twowheeltitan wrote:Hey guys. Lots of great info on the forum, long time lurker.
I've got an 83 650, rebuilding from basket case. I rebuilt the front brakes and have been unable to get the mc primed. I've tried pulling the banjo bolt at the mc and doing the normal finger over hole, but no go. I have also pulled the guts out and recleaned and inspected all the pieces.
I'll be able to get a vacuum bleeder tonight, but does anyone have any other ideas?



So we know the problem is in the MC itself. When you pulled off the brake line at the MC, and put your finger over the hole, It does not build any pressure at all? I've manage to put one together and put the rubber piston cup on the wrong side of the spring. Are your rubber parts new? If the piston cup is on the correct side, I can only imagine the piston cup is no good, or is the wrong size for that MC.
Have a problem with your CB650? Have a technical question? Click here!


My Current Bikes: 2005 HD FLHTCUI Electra Glide Ultra Classic, 2007 Yamaha Vino,

Twowheeltitan
Posts: 6
Joined: Wed Feb 28, 2018 10:43 pm

Re: another brake priming issue

Postby Twowheeltitan » Fri Mar 02, 2018 10:52 pm

This is a brand new rebuild kit, and I double and triple checked the install order with the parts fiche and instructions online- I can't find anything that shows anything different than what I did. Does anyone have a picture or a link to a pic online that is correct?

When I cover the outlet, I do get pressure, just no fluid.
I'm going to try a vac system in the morning and get some fluid through that way.
I don't have any ability to back bleed brakes.

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Folsoml
Posts: 1621
Joined: Sat Apr 07, 2012 9:02 pm
Location: North Florida

Re: another brake priming issue

Postby Folsoml » Sat Mar 03, 2018 8:11 am

When you put your finger over the hole and pump it, when you feel the pressure, do you hold the lever down, release the pressure from under your finger, re-seal the hole with your finger, then release the lever, and then repeat?

How strong is the pressure you feel?

Edit: There is also the possibility that the kit you have is not the correct size. Even if you've double checked and confirmed it the same size for the bike you have, a lot of things could have happened in the four decades since it was built. A previous owner may have switched out master cylinders.
Have a problem with your CB650? Have a technical question? Click here!


My Current Bikes: 2005 HD FLHTCUI Electra Glide Ultra Classic, 2007 Yamaha Vino,

Twowheeltitan
Posts: 6
Joined: Wed Feb 28, 2018 10:43 pm

Re: another brake priming issue

Postby Twowheeltitan » Sat Mar 03, 2018 11:59 am

It's a fairly strong vacuum. Yeah, i know the drill for doing brakes... im the brake gopher when we do cars lol.
The mc I think is the right size because all the rubbers fit well. Slightly tight...?

Twowheeltitan
Posts: 6
Joined: Wed Feb 28, 2018 10:43 pm

Re: another brake priming issue

Postby Twowheeltitan » Sat Mar 03, 2018 1:14 pm

Actually I know it's the right size, I have some other pistons that are the 14 vs 16.
I think the problem is this new red grease shit that I used for the first time that came with the kit. I used it as grease and I think it sealed the rubber with no oil getting by. We are cleaning it all off right now.

We were able to get the mc primed via vacuum, but we could not get any fluid to fill the lines or the caliper.

Twowheeltitan
Posts: 6
Joined: Wed Feb 28, 2018 10:43 pm

Re: another brake priming issue

Postby Twowheeltitan » Sat Mar 03, 2018 1:40 pm

To clarify, I actually know its the right size, what came out was original and this is the same size.

Sorry for the rapid Twitter posts, we found out after shining a flash light into the mc that the return hole is plugged. Used a guitar string, cleared that. Looks like another case of mistaken cleanliness! Reassembling now.

Twowheeltitan
Posts: 6
Joined: Wed Feb 28, 2018 10:43 pm

Re: another brake priming issue

Postby Twowheeltitan » Sat Mar 03, 2018 2:31 pm

Second major issue we found was that the bleeder screws were plugged up.


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