Delink - stock rear m/c with two caliper pistons?

I've been reading up on all the delink threads I can find, but one possibility seems not to have been tried:

Has anyone done brake ratio calculations on using the stock VFR rear master cylinder with just the two outer pistons on the stock VFR rear caliper?

Has anyone tried this installation? If so, what are your results?

Thanks for any input.

 

Whoops - I was going the wrong direction in my hopefully optimistic way. The stock gen 5 rear m/c is 11/16 or 17.5mm and is intended to move two rear and two front pistons. So using fewer pistons with the same m/c - even before doing an area calculation - obviously results in a bad ratio. Thus the move to a 14mm rear m/c when using only the three rear caliper pistons. See, I'm getting it. Slowly, yes, but getting it.

Sorry for starting a thread with a question I could have answered myself.

 

Well, you do have a legitimate question... I'm not sure I have a good answer! Why not use just the two OEM rear pistons? I don't recall why, but I've decided to use all three--but possibly just because I can.

Let's see....



Okay, the two OEM rear pistons are either 22.65mm (5th gen) or 25.4mm (6th gen), which add up to a piston area of 807.2mm2 or 1013.4mm2, respectively. With the OEM master cylinder, that results in a ratio of 3.37 or 4.23, respectively (but, as you point out, the OEM rear master also applies the front middle pistons, and the secondary master cylinder also applies pressure to the rear middle piston at the same time, so these ratios are not "real" in the same way non-linked ratios are). A more useful ratio is something like the one used on the 3rd gen, which is 9.04, or the CBR600F3, which is 7.41. Using OEM ratios as a guide, and given the weight of the RC46, it would seem that something around 9.0 would probably be good.

However, if you look at the chart, it is clear that there is no OEM-type master cylinder that would achieve a 9.0 ratio with an OEM-spec RC46 caliper. The closest you could get would be 8.0, using the 6th gen caliper and a 1/2" master. Probably close enough if you have a 6th gen caliper and 1/2" master already, but if not, the temptation would be to go ahead and acquire the parts in order to hit 9.0 (it would be for me!) Tbh, I really don't know if that ratio is better than 8.0 or even 7.41; the only way to know for sure would be to test them. I haven't heard of any problems from people who have used the 14mm master with all three pistons (such as wooden braking feel, or easily locked brakes), so that's probably the right one.

Ciao,

 

Wow - that rear brake ratio chart rocks. Thanks for linking me up to it.

Also thanks for helping me follow through with my thought on the RC46 rear master cylinder. I think we can safely kick that master cylinder to the curb.

Do you know of any Hondas that use 1/2" rear master cylinders?

 

Aww crap - the 1/2" rear master cylinders are right there in the table. I've really got to do my reading and research before posting a question.

 

A Semi related question here. Are the 6th gen FRONT pistons bigger than the 5th gen ones as well?

 

In my experience,that depends on who is getting the FRONT piston.

 

I didn't do the front brake calculations because my front calipers were always destined for the bin... But if you want to do the calculations for yourself, that data comes from the General Information sections in the Honda Workshop Manuals for each of the bikes mentioned in the Notes. Electronic versions of these manuals are available on the Web...

Yes, I believe both the 3rd and 4th gen VFRs use 1/2" rear master cylinders.

Ciao,

 

Thank you gentlemen - you've got me on the right track for brakes. I'm going to purchase a 14mm rear master cylinder and gen 6 rear caliper [If it's a bolt-up to my gen 5 motorcycle?] and drill the center piston to join it with the outer two pistons. I like the idea of avoiding the external bridge line between the center and outer pistons.

 

To be clear here, if i read it right, the 6th gen rear caliber does bolt right up the the 5th gen mounting?

 

Actually, I'm not certain if the gen 5 and gen 6 rear brake calipers and or caliper carriers are interchangeable. Still trying to figure that out - anybody have an answer?

 

Part numbers for the 2001 and 2005 rear sub assembly are the same.

 

Thanks OZ - you're right about the subassembly part numbers! Cool.

Mello - I'm willing to sacrifice a caliper's stock state by drilling through the middle piston into the passage between the outer pistons, and I thought I'd drill a gen 6 because their pistons are a tiny bit larger, thus a tiny bit more brake ratio/leverage/power. Just a tweeky 'what if' choice on my part.

 

The 3-piston ratio works out slightly better with a 6th gen rear caliper.

Ciao,

 

For what its worth, I have delinked my 6th gen and looped the 3 pistons together. I am using the stock caliper and master. The feel isn't great, but I can lock the rear tire fairly easily. I have thought of using the f4i rear master, as I have read that it improves the ratio, but I am kind of on the, "good enough" and "don't fix it if it ain't broke train" right now.

 

Me, I'm always looking for the little bit more = better, maybe? In that, since I'm on board with the drill as well, I'm not going to ruin the one I have, so if the 6th gen bolts up has the possibility to be a tad better, so be it is my thinking

LOL CR, you have a 6th gen.

 

Yes, the stock master with either rear caliper and three pistons is too aggressive.
I have the 5th three pistons with a 14mm master and I think it lacks a bit of power and feel.
My opinion is that you will get a better response with the 6th.

But I do have a 2014 two piston rear on the way to see if I can make it fit.

 

When I drilled mine two years ago, I could not find any definitive information online that the drilling idea was going to work or that I was drilling in the correct spot. So, needless to say, I was a bit apprehensive about drilling into a fully functional (and my only) rear caliper. As a backup, I purchased a spare Gen 5 rear caliper from eBay just in case I screwed up. So...I do have an extra rear Gen 5 caliper as a safety net if anyone needs it...free, just pay me for shipping. My contribution to the delinking efforts!

Merry Christmas,
Mike