kaighn80 Posted February 4, 2011 Report Share Posted February 4, 2011 ive changed the whole front end on the vfr750 for sp1 stuff, so i have 4pots, didn't come with any lines or a master cylinder, so i used the viffer cylinder and bought a pair of goodridge braided hoses off egay for £10.20 posted and new. fitted it all up and bled through new dot5.1 to make sure i had the best possible start. anyway im used to the brake lever coming almost all the way back to the bar and feeling quite spongy (it did have the OE rubber hoses and they weren't great, i could feel them expanding as i pulled the brake lever) but now i'm getting about 10mm of travel and then the brakes are on, ive had the front up in the air to check that the wheel would actually turn, its fine when the brakes are off turns ok just the noise of the pads skimming over the disks, but when the brake lever is moved 10mm its locked solid. i know that braided hoses make a difference but really? is it supposed to be that good? Link to comment Share on other sites More sharing options...
szrdave Posted February 4, 2011 Report Share Posted February 4, 2011 I guess the viffer calipers are two pot sliding pin? If so the m/c now has to push twice as much fluid, so you'd expect it to feel a bit softer. It could just be that you've gone from old brake fluid, full of air and running through knackered old lines, to a freshly bled setup. How does it feel to ride? Link to comment Share on other sites More sharing options...
drunkn munky Posted February 4, 2011 Report Share Posted February 4, 2011 Get a matching master cylinder, or a brembo one Link to comment Share on other sites More sharing options...
lorenzo Posted February 4, 2011 Report Share Posted February 4, 2011 What size is your master cylinder on there at the moment? Take a look underneath and there should either be a fraction (imperial) or a number (metric, in mm's). For a pair of 4 pot brakes you want to be aiming at about 15-18mm. You've pretty radically changed the hydraulic ratios going from pushing 4 to 8 pots, you'll want to change the master cylinder too, otherwise you'll find that your brakes are like an on/off switch or can simply never get firm enough, depending on which way round the original master cylinder is. I think (and my memory's pretty bad) that the small the master cylinder the firmer it'll be, although the max pressure that you can exert is less. Something like that anyway, but what's certain is that you'll want to get something else on the front. I had a brembo off a ducati on my old sp1 brakes and they were lovely, a nice balance of feel and firmness, but if you want it, I've a master cylinder here off a gsxr1000 (k3 I think, not a radial) you can make me an offer on, comes with the lever but I'm not sure about the reservoir, the ratios on that should be about right as they gsxr comes with very similar size 4 pot calipers. Link to comment Share on other sites More sharing options...
gurninman Posted February 4, 2011 Report Share Posted February 4, 2011 It sounds as if you definitely need to change the master cylinder - Lorenzo has it about right Although you've now got more braking force acting on the disc, you're brakes will actually be less powerful because the master cylinder can't move the pistons out far enough - so although it feels really firm, you're not applying the optimum amount of force to the disc. I had a similar problem when I fitted gold spot R1 calipers to my old EXUP - the lever was too firm, and was like an on-off switch with absolutely no feel at all. Definitely go for a master cylinder from a bike with 4 pot calipers - probably a 16mm (5/8") one or a nice Brembo radial one Would be nice if you could find out the stroke of the master cylinder piston too, then you could make a useful comparison between cylinders for a given surface area provided by different configurations of caliper pistons (providing that the leverage remains the same) Link to comment Share on other sites More sharing options...
szrdave Posted February 4, 2011 Report Share Posted February 4, 2011 Ah but he's gone the opposite way to you gurninman, you had a large volume m/c to push a smaller (down from 12 to 8 pots) volume slave. You would expect him to find an increase in feel at the expense of increased lever travel, however he's reporting a much firmer lever. Ideally you'd replace the m/c to one sized correctly for the calipers, but if the brakes work well, why bother! It may even be that the standard m/c is the right size anyway, depending on the design of the VFR braking system. Link to comment Share on other sites More sharing options...
gurninman Posted February 4, 2011 Report Share Posted February 4, 2011 Ah but he's gone the opposite way to you gurninman, you had a large volume m/c to push a smaller (down from 12 to 8 pots) volume slave. You would expect him to find an increase in feel at the expense of increased lever travel, however he's reporting a much firmer lever. Ideally you'd replace the m/c to one sized correctly for the calipers, but if the brakes work well, why bother! It may even be that the standard m/c is the right size anyway, depending on the design of the VFR braking system. You're thinking of the ZX9 ..... I have changd to 4 pots in the past on that, and get good feel at the lever, but the master cylinder for the ZX9 with 6 pots is the same as an oil-cooled GSXR with 4 pots - same Nissin master cylinder. The trouble with having a brake lever so firm is that there's no feel at all Normally you'd mebbe be looking at a smaller master cylinder for better feel, but if the stroke is too short you're buggered Link to comment Share on other sites More sharing options...
szrdave Posted February 4, 2011 Report Share Posted February 4, 2011 You're thinking of the ZX9 Lol, didn't read it properly. In my head gurninman = ZX9! Link to comment Share on other sites More sharing options...
kaighn80 Posted February 6, 2011 Author Report Share Posted February 6, 2011 checked the master cylinder its a 5/8 one. Link to comment Share on other sites More sharing options...
lorenzo Posted February 7, 2011 Report Share Posted February 7, 2011 Well, that's 16mm more or less which is pretty much in the right ball park at least. I'd say zakalwe's right, you're just discovering what proper modern brakes feel like! Sliding calipers do indeed suck. Link to comment Share on other sites More sharing options...
kaighn80 Posted February 7, 2011 Author Report Share Posted February 7, 2011 happy days! this season i will be mostly doing stoppies everywhere the brakes need to be applied! Link to comment Share on other sites More sharing options...
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