Topic: upgrade front brake caliper?

[Industrial Rat400f Killer]

I just put a modern front brake lever and new brake lines on my cb400f but it's not clamping very hard. I bled the thing about 10 times. Should I do more?
Anyway this got me thinking. Has anybody just straight up changed the caliper to a more modern design successfully without changing fork legs? Maybe just modifying the stock caliper arm?

Yes, yes I know. I need a banjo bolt here but I forgot to order one and they take a week to get.


I couldn't figure out which angle to photo this so this pic kind of sucks.

[TwoTired]

Was the front master off a bike with two front disks?
What is it's bore size?

Do you have a hard lever or does it feel spongy?

[Industrial Rat400f Killer]

It came from a Kawasaki with one front disk and I'll have to check the bore size. It feels soft, like it goes to the grip with little resistance.

[Industrial Rat400f Killer]

I should also mention that when I first hooked it up I had a banjo bolt that didn't properly line up with the hole in the banjo so I had to use a thin washer instead of a crush washer.  It leaked but it performed better than the stock set up. I got the right banjo and now it doesn't leak but it doesn't work very well.

[TwoTired]

That's a symptom of air in the system.

Try to imagine air bubbles in the system.  They will rise to the highest point away from the earths core.  Ledges and loops in the lines will trap them at the loop or ledge.
Their only natural escape from the lines is the master itself.  You must give an unimpeded path for the bubbles to that point, or to any bleed fitting.

[Industrial Rat400f Killer]

So should I just bleed it a bunch more times or remove the resevoir cap and let the bubbles rise?

[754]

I just found out that the 750 brake that looks like yours fits on a 500, if you use the swing bracket...

 Dont know how much more area on them, but seems a bit of an upgrade to me..wuthout changing your look..

[TwoTired]

So should I just bleed it a bunch more times or remove the resevoir cap and let the bubbles rise?

When the lever is released, a piston moves back and uncovers a pressure relief hole near the outlet of the master.   This is where air can be released into the reservoir under the cap.  If you can get the bubbles to collect at that point, gentle pressure and very short stokes on the lever will push air out those holes, replacing it with fluid.   You need to position the bike/hoses, components to allow those bubbles to collect at that master cylinder exit hole (it is small).  You don't even have to take off the cap.  Just arrange the the brake system so that the bubbles can collect at an exit point.  I have bled the entire SOHC4 front brake in this manner, without ever opening the bleeder valve at the caliper, and gotten a rock hard lever.  I did have to wait for the bubbles to collect overnight, though.

I can't see the physical changes/arrangement of the hydraulic system of your bike.  You are going to have to figure out where the pockets of air are trapped, possibly at banjos, and either crack them open there to push out the air at that junction, or tilt them to get the air into the main passageways.  Clearly doing more of what you already done isn't getting the job done.  Got to change your technique.  And, if you understand that bubbles rise until they are trapped, you can figure out where the air is and force it out.

It's an adventure...

Cheers,

[tygrant]

hey Rat400,

i have that exact MC on my 550 with one SS line to the caliper with a banjo and it works the balls, the bore is 12.7, smaller than stock by 1.3 but to be honest once bled corectly, i have less lever travel than the stock 14 and i love it, I can really put some meat on the disc. let it sit over night come back and take the ca off and squeeze the lever softly and watch for small bubble to come out of the holes in the mc.  TT is right you dont have to take the cap off but if you do you will atleast know your getting bubbles out and fixing the issue

[Industrial Rat400f Killer]

Just wanted to let you guys know I appreciate all the responses I got and I used the info to dial in some better braking.
I used a lever from an '08 Ninja 250 with a 14mm bore and Russell ss brake lines/connectors.The lever has the brake light switch built in so the two wires from the stock pressure switch just hook right up.
The Russell stuff seems to be of very high quality.

Both levers and all the misc parts were less than $300.

My brake line goes pretty much straight up from the caliper to the lever so there is very little turns or unnecessary connectors. I figure my problem might have come from changing the banjo bolt and not getting all the air out for some reason.

After letting the bike sit overnight I opened the reservoir and slowly squeezed the lever while watching for bubbles. There was only 1-2 very small ones so I added some fluid and bled it a few more times. What ever it was is now corrected.
Thanks.