Front calipers upgrade - problem

Hi all,

Little problem. I upgraded to CBR900RR front calipers, have new braided lines and all, but can't seem to get them calipers bled properly.

2 hoses coming out from front master cylinder, one to each caliper. When I bleed calipers independently, meaning only one hose is connected to master on the top, bleeding process works and lever gets hard. However when I connect two banjos on the top, there is no way I can get lever hard.

I made sure there was no air in the system , including master cylinder. No air bubbles, left over night with lever squeezed with a cable tie etc.

I am lack of ideas. Last thing I was thinking... Maybe I need to get a master cylinder from CBR900RR and dump old one out. I just rebuild vfr's master...
Thx

 

I suspect the master is not the right bore size for the piston diameters in the calipers. You dont necessarily need the RR master, just one the same size, so style and color options are opened up.

You can use the rebuild kit number to do a "where used" and find the (likely long) list of donor bikes.

 

Thank you for your reply. I believe stock MC is size 1/2. So would you say 7/8 will do the job? I am not sure what size RR has

 

What year calipers?

 

99, honda cbr 919 rr

 

Wow, that is a odd duck. Only the RC30 and 98-99 CBR900RR use that master. Explains why the rebuild kit from Honda is NLA.

You need to go down on the bore size to increase the firmness.

Your bore size is cast in the body of the master.

 

Right, I will just try 5/8. Hope it is the right size... Calipers are old but fully rebuilt and of a bike with 10k on it. The cast on the VFR mc says it's 1/2. Then I did some research about 919 and I found this:
893/919- 5/8 or 15.875mm
2000-2001 - 929 – ¾ or 19mm
2002- 954 -11/16 or 17.5mm
2008-2011- cbr1000rr – 17mm

Hope that the above is correct.

 

Hmmm... something seems off then, and maybe its my brain, but...

With your 1/2 master, the brakes should feel "wooden" or overly firm.

 

I know what you mean but they feel soft. When I delinked brakes, I had to change rear master for F4i to have any feel at all... Now it is opposite. Mad, only way is to check by installing 5/8 and see.

 

Hard to find matching MC online. Trying to get something decent but...
EDIT:
Found 5/8 from CBR600 2001-2006, looks same as vfr one.
I could not get CBR919 because there is no space for the cbr top reservoir.

 

Installed 5/8, bled brakes in 5 mins, all good and it makes perfect sense. You need more fluid to push so you fill larger calipers. 1/2 maxed out pistons travel range and was out of fluid. 5/8 has more capacity and did not max out mc piston travel.

 

Sounds like you got it sorted. I had CBR954 calipers and CBR600RR master on my VFR and that was a great combo. Smaller masters give squishy brakes that are a bit grabby, bigger masters give a firmer feel with less out right grab.

 

Problem I had it wasn't grabbing enough, I could push the bike with help of a friend when lever fully down