5th-gen VFR master cylinder replacement: front brake feels too hard/touchy

I've gone and done something odd with my 5th-gen VFR, and now I'm a little concerned before I go take it on a test ride.

I recently replaced both master cylinder/reservoirs with those from a ZRX1200 (I needed the ability to mount mirrors to them), and after some work I finally got them primed and bled. I only bled them at the banjo bolt at the reservoir though. What's weird is, the front brake feels extremely touchy. I was expecting them to maybe be a little soft because I hadn't yet bled the whole system, but instead they're rock hard. Pull the lever in a bit and it's already braking, and very quickly I can't pull it in any further. I almost feel like I need to put a little air in the system to soften it up a tad.

With the bike on the centerstand and help pushing on the rear, I got the front wheel up and it spins. With the reservoir open, I can see fluid shoot out of the compensating port at the start of the lever's travel (it will very easily break the surface and make a mess), so I don't feel the system is under constant pressure due to a problem with the port or the piston being perpetually depressed.

The ZRX master cylinders do have an extra port right next to the compensating port (I've seen it called an equalization port or intake port), but I think it's function is simply to prevent a vacuum from forming in the line if the lever is released too quickly.

I'm just wondering if there's something wrong with this setup or something I should check before I take it out for a test ride. I haven't been able to test it because I've had the wiring apart until yesterday. I'll also be going on a 650 mile ride on Sunday so I'm hoping to get things sorted quickly.

 

You have to look up the piston diameters and compare them to the VFR. It may be the ZRX's brake piston size is much larger and is going to lock up the VFR's brakes much more easily. I wouldn't introduce air in the system, it will work until you really need it and then you'll have no brakes.

Here's what too much front brake does, 1:20 in..

MT89_MotoGP_2006_Barcelona_Start_Carnage_Extended_English

 

A front lock-up is actually why I'm fightering it... was on the third day of a 2-week moto-camping trip and was paying more attention to my GPS than traffic in the George Washington Bridge tunnel in NYC. As luck would have it, locking up was a better option than staying upright and bending my forks, I was able to finish the trip with the front end held on with rope.

Back to the topic at hand, you're right, the ZRX1200 master cylinder bore diameter is 5/8" (2002 I think), the VFR800 is 1/2". So if I understand this correctly, I'm looking at (5/8) / (1/2) = 1.25 ratio in diameter, squared to get the area ratio = 1.5625, which would mean approximately 56% more force for a given amount of lever travel? Guess I'll see how it feels when I take it out today...

 

Took it on a test run, and the front brakes seem to feel pretty good. It's 40's today, so I didn't get real aggressive with the braking with cold road and tires, but I think I'll be fine. Thanks for the help!

 

Good deal. Sounds like you can modulate it and it will be fine.

I guess the bigger question is why were you mounting mirrors old school style to the reservoir? What was the project, got pics?

edit: Just got done reading your trip report to Alaska, what an epic ride. Congrats, it's on my bucket list. :thumbsup:

http://www.blinkenbyte.org/motorcycles/deadhorse_2010/index.html

 

Last year, my wife and I took a 7000 mile moto-camping trip to Gaspe, Quebec on our bikes (myself on a VFR800, my wife on a CBR600). After crossing the George Washington Bridge, we entered a tunnel and I was trying to figure out from the GPS which exit I needed to take and didn't notice the car in front of me stopping until it was too late.

Tried to stop, locked up the front and immediately went down and slid under the car's bumper. It smashed up the front pretty good, broke off one of the tabs on the headtube that holds on the little frame that the front fairing, headlights, and gauges mount to. Headlights were smashed and pointing down and to the right, luggage rack was bent, handlebar bent, etc. My jacket and gloves saved me, and though my jeans were tore up, I didn't get it too bad.

After the police left I limped it over to a sidestreet and spent a couple hours taking it apart and trying to get it somewhat fixed. Beating bent things straight, dremeling holes in the fairing to do some zip-tie stitching, rope to hold the headlights up (later adding a big lag screw to push them down so the rope had tension). I was determined to get the bike rideable, _really_ did not want to cut short my wife's first big trip. Got it fixed up enough to drive out of NYC and find a hotel that night didn't feel like camping that night. The next day, we stopped by a motorcycle shop to find a mirror I could bolt on, and finished the rest of the trip that way. I'd been up to Nova Scotia before, but this time we continued north and followed the coast to Gaspe, and it was beautiful. Definitely worth the extra time to go up there!

So after I got back home I pretty much let it sit and rode my ZRX instead, but it's not good for distance. I had an upcoming trip to San Antonio, and figured that'd be my motivation to get the VFR going again. I decided to just get rid of the front and side fairings. I ordered some dual headlights with brackets off ebay, and made some brackets to mount turn signals and the gauge cluster. Wiring was stuffed into a 3" PVC pipe above the headlights. I cut the ends off of a tube that was welded to the subframe and replaced the ends with some larger threaded nuts since one of the small diameter bolts used to hold to stabilize the luggage had broke off in the crash. Replaced both master cylinders with ones I bought off ebay for a ZRX so I could mount mirrors.

Made it to San Antonio yesterday with no issues Here's some pics of the bike when I wrecked it, and its current state:

 

Well, when there's a will, there's a way. Explains the move to the new master cylinders. Nice job on the front end. Hiding the wiring is one of the harder parts of making the VFR "naked".