Help ! master cylinder ?
 

Hi,

I'm in the process of doing a front end swap,

I have a 2012 cbr1000rr forks, front wheel, brake disc's and calipers fitted,

I had a new in box 2005 vtr1000 sp2 front brake master cylinder and new Venhill braided lines,

I've bleed the master at the master banjo bolt and bleed down at the caliper bleed screw's with fluid coming out with no visible signs of any air bubbles, (also using new from a sealed container Penrite brake fluid)

problem is, the brake lever feels very soft with lots of travel !? Is the problem with the SP2 master not working with the CBR radial calipers ? or is there some other issue possibly going on ?

Any advice or help will be greatly appreciated.

Without insulting you what is your bleeding technique? For what it's worth if you're not using a Mityvac or something comparable it can get really frustrating. It'll pay for itself in time and aggravation saved the first time you use it. I'm assuming you know how to bleed brakes properly if you've done all that other work yourself but thought I'd ask the obvious first. I know some guys on here have forgotten more about much of this stuff than I know, but I've done lots of brake and clutch bleeding on motorcycles and bicycles (which can be whole other level of frustration) and it can be a real PITA sometimes and often takes a bit of patience.

All that aside I'm sure someone else can chime in on the best match regarding a master cylinder. I'd have to look up the specs of a CBR1k MC vs an SP2 I don't know off the top of my head. If I had to venture a guess I'd say that's not your problem though. A more ideal match (if there is one) might "feel" better but if your lever is super soft and going all the way back I'd say there's still air in the system or you have a small leak somewhere. I recently had a very slight piston leaking on a bicycle caliper and it took me two days to figure it out.

Thanks for the reply,
My bleeding technique is vinyl tube on the bleed screws & pump the lever then crack open bleed screws, close bleed screws, release lever, repeat until I have no visible air bubble & a firm lever, I've used this technique many times with good results, I used the same technique on the clutch & had the clutch bleed in around 10 minutes.
I also installed new bleed screws in the calipers, fairly sure the piston size in the SP2 is 17.5, not sure about the length of stroke tho !?
I thought I would ask on the forum about the SP2 master & radial calipers compatibility because I thought I remembered reading it could be an issue with a soft lever !?

17.5?

Close enough.

https://cimg2.ibsrv.net/gimg/www.sup...da4219b841.jpg

Keep bleeding.

Thanks for the comment,

My concern is if the SP2 master cylinder is compatible with the 2012 CBR1000RR radial calipers ?

I'm happy with more brake bleeding if it will fix the issue, but I dont want to be bleeding in vain !

Do you know for sure the the SP2 master is compatible with the 2012 radial calipers ? if so, I'll keep bleeding ... if not, any one else out there that can confirm my question ?

Thought I would try the ziptie the lever over night method .... :popcorn:

some pic's of my front end swap progress,



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In MY personal experience I can just say I've bled lots of stuff over the years. I'm no expert by any means. Pumping a lever or a pedal and opening a bleed screw has OFTEN worked fine but there are times it hasn't. With all the different bends/plumbing/angles sometimes air gets trapped and sometimes it simply doesn't work right. EVERY time I've used a vacuum bleeder like a Mityvac I've gotten the correct results, and they've always been obtained faster. They're really easy to use (even I can use one) and as soon as the original one I had finally broke I immediately bought another. I had an almost nonexistant clutch lever on one of my superhawks and flushed out the DISGUSTING mess that came out with fresh and in 10 minutes worked like brand new again. The fluid cup makes it neat and easy to catch the old stuff coming out. Just makes jobs like that so much easier and more efficent.

I know someone else will chime in on compatibility and it's not the scientific answer you're looking for but back in the day I had a Brembo radial master cylinder for an SP2 along with SP2 forks and CBR1000RR radial calipers (RC51parts.com brackets) and braided lines and everything worked fine.

Thanks for the advice ,
I will give the vacuum bleeder a try, and see if I get any better results.
I have a feeling the Brembo are 19mm vs the stock SP2 17.5, so unfortunately I don't think that confirms the compatibility issue question !? (Could be wrong) But I do appreciate the help.

The MCs dimensions are not the problem. IIRC, the caliper pistons sizes (ie. 32/30mm) are the same between the SP-2 (RC51) and CBR.

+1 on the mityvac. Not absolutely necessary, but if you do use one, cut a narrow strip of Teflon tape and wrap the bleed screws threads. This helps stop air being pulled in around the threads. Otherwise you can mistake it for the system still having air in it.
While I think the others are right about air still trapped in the system, the long pull and soft feel could be because the master slave ratio is a long way from what is considered ideal. Knowing what size the CBR calipers are and what size master was use with them would be helpful. If you look at the chart that was posted You’ll see with the 14mm SH master and the larger calipers the ratio goes way up.

Do you know which CBR?

Hey guys,

Thanks for the help and comments, very much appreciated !

I think I found my issue.

I went out into the garage for another session of brake bleeding, I have placed paper towel around the master cylinder area just in case I have any spills and can hopefully minimise any brake fluid making a mess, I put a fresh piece of paper towel down this morning and when I came out after having breakfast to start some brake bleeding, I noticed a damp spot on the paper towel just under the banjo bolt coming from the master cylinder, on closer inspection it looks like the Venhill line is leaking from the swivel nut at banjo.

I gave the nut a loosen and tighten, then proceeded to do my old school bleeding technique of pumping the lever, crack open the caliper bleed screw, close bleed screw, release lever and repeat. In a few minutes I had a nice firm lever with less travel !
Cool, I now have a good feeling brake lever and am happy with the bleeding process and now have confirmation that the SP2 brake master cylinder will work and is compatible with the 2012 CBR1000RR radial calipers.

But unfortunately the Venhill line is still leaking from the swivel nut at the master banjo, I took a look at the Venhill website and they say to hand snug up the swivel nut and if leaking, loosen and snug up again. I guess for now at least I sorted the main issue and have a firm brake lever, but I now need to keep an eye on the leak and possibly order a new replacement line !?

Couple more pics of my progress,

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Hey all,

quick update,

Got my replacement brake line the other day and fitted it up on the weekend,

bled the brakes, no leaks, so all good ! :D

thanks for any help and comments every one, have a good one.

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