Rear Brake De-Linking

[JZH]

So, planning ahead a little bit for when I'm able to treat my 5th-gen to a set of RC51 SP1 forks and brakes, I got to thinking about the rear brake caliper and master cylinder.

Based on the WOTL (er, make that the wisdom of VFRD) I had previously acquired a 14mm rear master, so I wanted to check how close that would allow me to be to OEM, or to some sort of comparable OEM ratio.

Basically, with the RC51 SP1 forks, the linked brakes are necessarily history, so all that remains is to put together something workable for the rear brake. I have chosen the RC36 VFR750F as my OEM "target", as that bike has similar weight and performance (at least in OEM form!) as my RC46-I. I put together the chart below, which shows all of the popular master cylinder and caliper combinations I could think of that are used on Honda sport bikes:

Rear Brake Ratios

RC36 rear brakes have a 9.04:1 ratio (2x 27mm pistons and 12.7mm master), so that is the goal to achieve with my RC46-I rear caliper, because I really don't want to have to engineer a bracket to mount a different caliper (e.g., the ultra-common 38.1mm single-piston NISSIN found on everything from F3 to 1000RR). The RC46-I (i.e., pre-VTEC) rear caliper has 2x 22.65mm pistons tied together and one 27mm piston in the center and a 17.46mm (11/16") master cylinder. It is clear from the chart that using either the two 22.65mm pistons or the 27mm piston alone cannot get anywhere near the OEM-ish ratio of 9.04:1 found on the VFR750FL-V, but using all three caliper pistons together can achieve very close to that (8.97:1), provided I use a 14mm master cylinder. Cool, that's what I've got!

(FYI, the VTEC's rear caliper is different--it has three identical 25mm pistons.)

Now, the only question is, what's the best way to achieve it? I see two options:

Mello Dude's $30 braided stainless steel loop and double banjo solution, as detailed elsewhere, or

Something more solid, like what I think is done in the CBR1100XX de-linking kit sold by J.A.W.S. in the UK (or maybe I'm thinking of the kit that was once sold by 123ignition, also in the UK)? Can't seem to find any pics on the 'Web, but in any case, the approach I'm thinking of consists of a short ~12mm square bar of alloy with three holes: the bar is bolted to the rear caliper by the two OEM banjo bolts (maybe need double banjo bolts), and the third hole is another M10x1.25 on the end--with the hole continuing at smaller diameter (e.g., 5mm) down through the bar and intersecting both of the other holes. It's essentially a manifold.

Oh, and there would be at least one other way I had forgotten about: Remove the caliper from the bike, as well as the pistons and seals, pop it onto the drill press and drill straight through the back of the center piston bore into the connecting passage for the other two pistons. Then, clean everything out and rebuild the caliper--plugging one of the banjo bolt holes with a M10x1.25 plug of some sort. I like it... It does depend on the connecting passage being where I think it is, though!

Requires a caliper rebuild and is permanent, but I'm not too bothered about that. Any thoughts?

Cheers,

[Veefer800Canuck]

Run two lines from the rear master cylinder using a double banjo bolt and connect them to the rear caliper as normal. Eliminate the rear proportioning valve.

That's what I did.

Pics, etc:

[KevCarver]

Run two lines from the rear master cylinder using a double banjo bolt and connect them to the rear caliper as normal. Eliminate the rear proportioning valve.

That's what I did.

Pics, etc:

RC51 or F4i rear master (probably others, but I didn't read through the chart...) and single line to rear and crossover loop to join the two. Works fine, probably better than my RC51. But I dont use it much.

[mello dude]

RC36 rear brakes have a 9.04:1 ratio (2x 27mm pistons and 12.7mm master), so that is the goal to achieve with my RC46-I rear caliper, because I really don't want to have to engineer a bracket to mount a different caliper (e.g., the ultra-common 38.1mm single-piston NISSIN found on everything from F3 to 1000RR). The RC46-I (i.e., pre-VTEC) rear caliper has 2x 22.65mm pistons tied together and one 27mm piston in the center and a 17.46mm (11/16") master cylinder. It is clear from the chart that using either the two 22.65mm pistons or the 27mm piston alone cannot get anywhere near the OEM-ish ratio of 9.04:1 found on the VFR750FL-V, but using all three caliper pistons together can achieve very close to that (8.97:1), provided I use a 14mm master cylinder. Cool, that's what I've got!

Wow, you really are doing your homework - I find it interesting that I used a completely different methodology of calculation to figure out what master cylinders I should use, but still ended up with the same conclusion as your caliper/master cylinder ratio analysis above. Very cool. - Just to refresh, with a 14mm m/c you are close to a 4th gen rear brake, and if you would find a 5/8" m/c that would be just a tick more brake than a stocker RC51.

I find after multi seasons with the bridge over the stocker rear caliper, that it works just fine with no issues. I had thought about some kind of machined part for the bridge, but then you are fooling with custom matching the manufacturing tolerances of the brake outlets on the caliper. The flexible bridge eliminates that kind of concern and ensures a solid seal with bolt up. It was relatively easy and painless to put together.

-That the first time I have seen the HEL delink thingy - looks like that they are selling a connector block. No experience with it, but if its a solid piece, you have the manufacturing tolerance thing to be concerned with.

Good luck - cant wait for future photos of your build!

[KevCarver]

Yeah, what he said! Lol!

If you don't want to go the make your own lines route and make a short bridge line, I'd say the double line like Rob's is the way to go. Simple and cheap!

[vfrcapn]

I followed Veefer's lead using the f4i master but would like to do what Seb has documented and run a single stainless line through the swingarm with the short crossover loop.

[V4 Rosso]

Now, the only question is, what's the best way to achieve it? I see two options:

Mello Dude's $30 braided stainless steel loop and double banjo solution, as detailed elsewhere, or

Check with the brake hose manufacturer for the minimum bend radius for the hose diameter. To me it looks like a loop this tight puts a tremendous amount of stress on the hose. I would opt for #3: drilling.

[JZH]

Well, despite almost no one else going for the idea, I'm leaning towards drilling the caliper--it's much more fun to make one-way mods than all this cautious pussy footing around!

(Unless someone can point out any as yet unknown folly, of course.)

More stealth still would be running the brake line through the swing arm...

Cheers,

[V4 Rosso]

(Unless someone can point out any as yet unknown folly, of course.)

Just a reminder when drilling: drill in a location and direction that doen't make bleeding the caliper more difficult.

[SEBSPEED]

More stealth still would be running the brake line through the swing arm...

Cheers,

Cheers for the trip down memory lane, that was a fun project.

(Unless someone can point out any as yet unknown folly, of course.)

Just a reminder when drilling: drill in a location and direction that doen't make bleding the caliper more difficult.

I kind of like the drilling idea, although I'd try my hardest to find a really cheap used caliper to practice with. If that worked out, then I would run the line to the rear-most banjo hole, so that a system flush would push all of the old fluid out.

[JZH]

I set up an eBay-UK search for a non-VTEC rear caliper and once I find one, will drill it here. That way, I will have a spare if anything goes wriong.

Who (in the USA) stocks K&L caliper rebuild kits? It's K&L pn. 32-7479, but nothing's coming up online (same kit fits '96-'02 ST1100A and '01-'04 GL1800).

Cheers,

[2FAST4U]

More stealth still would be running the brake line through the swing arm...

Cheers,

Cheers for the trip down memory lane, that was a fun project.

(Unless someone can point out any as yet unknown folly, of course.)

Just a reminder when drilling: drill in a location and direction that doen't make bleding the caliper more difficult.

I kind of like the drilling idea, although I'd try my hardest to find a really cheap used caliper to practice with. If that worked out, then I would run the line to the rear-most banjo hole, so that a system flush would push all of the old fluid out.

Agree.

People still ask me about it. In the past three weeks alone, two different VFRD members have PM'd me about it.

I was actually up in Cairo a couple months ago.

[SEBSPEED]

I set up an eBay-UK search for a non-VTEC rear caliper and once I find one, will drill it here. That way, I will have a spare if anything goes wriong.

Who (in the USA) stocks K&L caliper rebuild kits? It's K&L pn. 32-7479, but nothing's coming up online (same kit fits '96-'02 ST1100A and '01-'04 GL1800).

Cheers,

K&L is distributed in the US by Parts Unlimited - pretty much the biggest distributor in the country. You'd be hard pressed to find a dealership in the States that ISN'T a P.U. dealer.

People still ask me about it. In the past three weeks alone, two different VFRD members have PM'd me about it.

I was actually up in Cairo a couple months ago.

Still holding up fine? It's been about 3 years now.

[2FAST4U]

I set up an eBay-UK search for a non-VTEC rear caliper and once I find one, will drill it here. That way, I will have a spare if anything goes wriong.

Who (in the USA) stocks K&L caliper rebuild kits? It's K&L pn. 32-7479, but nothing's coming up online (same kit fits '96-'02 ST1100A and '01-'04 GL1800).

Cheers,

K&L is distributed in the US by Parts Unlimited - pretty much the biggest distributor in the country. You'd be hard pressed to find a dealership in the States that ISN'T a P.U. dealer.

People still ask me about it. In the past three weeks alone, two different VFRD members have PM'd me about it.

I was actually up in Cairo a couple months ago.

Still holding up fine? It's been about 3 years now.

Of course. You did it.

Although I didn't stop in Cairo, I took some back roads to get to Cooperstown. I'm not a big baseball fan but since I've been to the Pro Football Hall of Fame in Canton, Ohio and the Pro Basketball Hall of Fame in Springfield, Massachusetts, I thought I'd check out the Pro Baseball Hall of Fame, too.

I snapped this pic before I went in:

[RVFR]

Just a thought here from on oldie but good thread with the rear brake caliber re plump.  I'm wondering if just plugging the other banjo bolt on the caliber that hooks to the system from the front.  I know it eliminates a 3rd piston, so?  if you use only the rear brake as it is now,  you only active two pots in the rear if I understand the system correctly. Any one done this where you just plugged that port in the caliber?  Results? 

[mello dude]

I think calculation wise, you would need to go to a 1/2" piston m/c if you want to use just the outer 2 caliper pistons. 

[mello dude]

On 6/13/2011 at 6:52 AM, V4 Rosso said:

Check with the brake hose manufacturer for the minimum bend radius for the hose diameter. To me it looks like a loop this tight puts a tremendous amount of stress on the hose. I would opt for #3: drilling.

I'm being the smart ass, but 9 or 10 seasons going on the loop -- waht stress?