Topic: CB400F Leaky master cylinder at banjo bolt

[Alaxy Galaxy]

I just swapped my original brake hoses for some reproduction items and I noticed a leak at the banjo bolt on the master cylinder (underneath the rubber boot). Will tightening help or should I replace the copper washers?

[minimo]

A few things about this, one mainly for safety - rebleed your brakes. The leak may have introduced some air into the line so please be sure that once you lock everything down to make sure you’ve bled all of the air out of the front brake.

Do you have the correct sized washers/bushings? Keep in mind that if they are indeed copper, they’ll have changed shape so you may only have the option to wrench down tightly on the banjo bolt.

Have you stripped the thread on the banjo bolt? Hopefully not. If you’re certain that you’ve not stripped the bolt, wrench down on it to see if that seals up that connection and pump out any air that might be left in the line.
Check all other connections and make sure they’re tight.


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[bryanj]

Also have you got a washer either side of the banjo, seen them lost and seen 2 on one side!!!

[Alaxy Galaxy]

A few things about this, one mainly for safety - rebleed your brakes. The leak may have introduced some air into the line so please be sure that once you lock everything down to make sure you’ve bled all of the air out of the front brake.

Do you have the correct sized washers/bushings? Keep in mind that if they are indeed copper, they’ll have changed shape so you may only have the option to wrench down tightly on the banjo bolt.

Have you stripped the thread on the banjo bolt? Hopefully not. If you’re certain that you’ve not stripped the bolt, wrench down on it to see if that seals up that connection and pump out any air that might be left in the line.
Check all other connections and make sure they’re tight.


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I will drain the brakes again, thanks for reminding me.

The washers are probably the correct size, as they are the original Honda ones that came with the bike. I cleaned and installed the brake system when I built up the bike 3 years ago, and they haven't leaked until I swapped hoses. This time, I installed the master cylinder without removing the bars or gauges, so I'm almost certain I just didn't get enough torque on that banjo bolt.

[minimo]

And as bryanj has noted, be sure you have washers installed on either side of the banjo fitting.


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[Bodi]

Tightening a bit will probably seal it, but you should replace the crush washers.

[Alaxy Galaxy]

Also have you got a washer either side of the banjo, seen them lost and seen 2 on one side!!!

Yikes! No, I have one on each side. They seem to become "directional" after prolonged use as well.