master cylinder bore sizes

[Aa7]

is bore size overly important when replacing master cylinders? the difference between a 1/2inch (12.7mm) bore and a 14mm bore is minimal but is also an almost 10% overall increase. would increasing the master cylinder bore size increase more than just the 'feel' of the lever? i.e would it put extra pressure on the rest of the system aswell and bust hoses and or seals?

[imdying]

12.7 to 14 is about a 20% increase. It won't bust anything. I test all hoses to 4000psi, but on your average vehicles they're likely to see only 800psi at the most.

Increase the bore size will decrease the feel, but reduce the lever travel.
Decreasing the bore size will increase the feel, but increase the lever travel.

Some people like a rock hard lever, some like the feel that comes with more travel. This is why things like the Brembo radial mcycls come in a variety of sizes listed for one fitment.

[Aa7]

12.7 to 14 is about a 20% increase. It won't bust anything. I test all hoses to 4000psi, but on your average vehicles they're likely to see only 800psi at the most.

Increase the bore size will decrease the feel, but reduce the lever travel.
Decreasing the bore size will increase the feel, but increase the lever travel.

Some people like a rock hard lever, some like the feel that comes with more travel. This is why things like the Brembo radial mcycls come in a variety of sizes listed for one fitment.

um yeah, thats what i meant when i was saying increased 'feel'. i meant a harder lever with less travel and it feels harder to squeeze - Doh stupid noob not knowing better hahaha and thanks for your answer so quick

can someone suggest me who in auckland is best to rebuild my front caliper too please. that is something i dont trust myself doing and i like to be able stop when i need to

[imdying]

Calipers are dead easy, you'll manage them yourself without any trouble. I'd be surprised if your 2005 bike need that doing already though?

[Aa7]

Calipers are dead easy, you'll manage them yourself without any trouble. I'd be surprised if your 2005 bike need that doing already though?

i didnt think they would need it either and looked everywhere else for the problems as they didn't seem to be leaking or have any other visable signs of deterioration. After having not much brakes at all and losing braking power nearly completely over the space of a week to week and a half my lever would be nothing but squishy like a dish sponge and air was somehow back in the system it was during a ride that i saw the master cylinder was slightly leaking from around the top seal and the lid has never sat quiet right so i changed the master cylinder in the weekend to a 14mm bore option and at last i have a break lever with the 'feel' (harder to squeeze feeling) i liked and the brakes seems to work better however this morning i noticed that there was a small pool of fluid directly under the caliper and it had fluid on the caliper base itself which is why i was asking if maybe the master cylinder was roo powerful for the rest of the system. it also sounds as if the seals in the caliper are squelching when i squeeze the lever now so i'm guessing they are shagged. but the lever is rock solid at least

i want new fork oil also as the front of the bike dips heavily under hard braking and certain corners ahahahah so i might get the mecanic who does the forks to do the caliper also but if you say its simple who knows, i might attempt it myself, any tricks or tips to look out for if i decide to do the calipers myself? thanks again for your answers

[imdying]

Righto. Well, rest assured, your new master cylinder is not too powerful for your existing caliper. Someone may have washed or 'lubed' the caliper with CRC, a regular grease, petrol, meths, kero, or something similar. That would cause the seal to fail in fairly short order.

The only thing you need to know is cleanliness is next to godliness, petroleum type products like those mentioned above are to be avoided like the plague, and hot soapy water can't be beat.

Essentially, to rebuild your caliper, it breaks down to this:
- Buy caliper seal kit from dealer. Yes you can sort out other bits for less $$$$, but don't bother going down that track unless you've someone to help you source them
- Remove caliper from fork leg
- Remove pads
- Pump out one piston with your master cylinder
- Remove the dust deal and main seal for that piston
- Put piston back in bike
- Pump out other piston
- Remove the dust deal and main seal for that piston
- Remove the caliper from the hose
- Pull the pistons out with your fingers... as there are no seals dragging on them now, this will be easy (they'll drop out)
- Take the bleeder out
- Remove the slide (if it's a slide type)
- Scrub the thing like mad with hot soapy water
- Scrape out any built up corrosion (looks like white furry stuff on the alloy) with a screwdriver
- Scrub the thing like mad with hot soapy water again
- Put the new seals in
- Lube the faces of the seals with brake fluid
- Clean up the pistons with hot soapy water (if they don't clean up just by elbow grease and a raw, use some 800 wet n dry and polish them up)
- Push the pistons home into the bores, probably the hardest bit (not really that hard eh!), just keep them going in straight and you'll be sweet
- Lube the slides with some suitable grease, someone like Pitstop will have a suitable grease that you can steal a little of
- Install pads
- Reattach caliper to hose and fork leg
- Bleed system
- Drink beer

[The Stranger:Me]

would increasing the master cylinder bore size increase more than just the 'feel' of the lever?

No it wont increase the 'feel' the opposite should be the case.

i.e would it put extra pressure on the rest of the system aswell and bust hoses and or seals?

There should be no increase in pressure directly as a result of a larger bore master cylinder. For the same pressure on the lever, that pressure is being distributed over a larger number of square inches thus the pounds per square inch should be reduced.

[The Stranger:Me]

- Buy caliper seal kit from dealer. Yes you can sort out other bits for less $$$$, but don't bother going down that track unless you've someone to help you source them

You omitted the first step.
- Contact your mortgage broker and arange the loan for step 2.

[Aa7]

well i'm at the ahhh …… stage.

i decided that it wasnt such a hard ask to change a couple of seals on a simple hydraulic system since i was armed with clear instructions, and the need to keep my brakes. So it's off to the garage with my hot water and palmolive to soften hands while cleaning calipers and two shiny new piston and seal kits from a dealership. everything is going fine and she looks cleaner than new and it's dried off and the new seals put in lube them up with fluid ready to push in the new pistons and in goes the first one seeming almost too easy…… the next one just slides straight in even easier. i take it out and try again and it seems to have almost no resistance again. i clean up the old pistons and try them but it's no different. back in with the new pistons, assemble the caliper all back together, connect it up only to see fluid dripping down the caliper as i pump the lever.

So what's next? these where supposedly hyosung caliper seals but they arent sealing?? can someone suggest to me a good brake mechanic in Auckland i can take this to or can i get a range of seals from a bike shop, pitstop/midas or the like which might work?? damn it's back to the cage. hope it starts ahahah

[imdying]

You omitted the first step.
- Contact your mortgage broker and arange the loan for step 2.

Typically a caliper kit is about $80 a side IME, although the seals are generally obtainable for around $2.50 - $4 each. YMMV, but not much point having a $6k motorcycle you can't ride for wanting a few bucks in seals...

[imdying]

the new seals put in lube them up with fluid ready to push in the new pistons and in goes the first one seeming almost too easy…… the next one just slides straight in even easier. i take it out and try again and it seems to have almost no resistance again. i clean up the old pistons and try them but it's no different. back in with the new pistons, assemble the caliper all back together, connect it up only to see fluid dripping down the caliper as i pump the lever.

I'm guessing that you've either got the wrong seals, or you've put them in the wrong places. Some pictures would help. Each piston bore has two grooves, 1 larger than the other? If you put a piston on the bench, and then slide the seal over the top, it should drag on the edges... not a tight fit, but it shouldn't drop down the sides. The new seal, it's about 3mm square? Did you get new dust seals as well? Use macro mode on your camera, bad pics are as useless as no pics.

[jonbuoy]

Advanced Seals 094796285 off constellation drive could probably source equivelant seals if needed - take the old seal and caliper in - they custom made a seal for my rear master which I tore during the rebuild. I thought I would have to buy a whole new re-build kit from Honda, they've helped me source numerous other o rings and seals. Top blokes to deal with.

[Aa7]

I'm guessing that you've either got the wrong seals, or you've put them in the wrong places. Some pictures would help. Each piston bore has two grooves, 1 larger than the other? If you put a piston on the bench, and then slide the seal over the top, it should drag on the edges... not a tight fit, but it shouldn't drop down the sides. The new seal, it's about 3mm square? Did you get new dust seals as well? Use macro mode on your camera, bad pics are as useless as no pics.

i have taken some photos and hopefully they are clear enough. the photos are with the new seals in place, the larger square seal is sitting in the back groove and the smaller one in the front same as the way they came out. the piston sitting beside the caliper is the new one that just falls out when you tip the caliper upside down and has no resistance. the pistons and seals sitting in the parts bags are the old ones with the new ones now in the caliper. they are genuine hyosung seals but for some reason dont seal. they look the same so i dont thin k they have been mispacked at the parts factory but dont have verniers to check only the old eye-cromiter

Advanced Seals 094796285 off constellation drive could probably source equivelant seals if needed - take the old seal and caliper in - they custom made a seal for my rear master which I tore during the rebuild. I thought I would have to buy a whole new re-build kit from Honda, they've helped me source numerous other o rings and seals. Top blokes to deal with.

wicked, i work just off of Constelation Drive so will shoot down there at lunch break if i cant get them sorted before cheers

[Aa7]

Advanced Seals 094796285 off constellation drive could probably source equivelant seals if needed - take the old seal and caliper in Top blokes to deal with.

Thanks for the advise about these guys jonbuoy!!! they ARE awesome guys and are willing do do all they can to help with your hydraulics highly recommend them to anyone looking for anything to do with seals. even if you have a weird-ass one off seal these guys will be able to do a custom made one for you within a few days.

Oh also while I'm here. A quick word of caution to anyone buying genuine Hyosung caliper and seal kits…… the ones i ordered from kwaka have the wrong seals in there for the calipers. everything looked the same as previous ones but once measured they are fractionally too small even for the new pistons they come with, dont find this out the hard way like I did. I took the seals and the caliper into Advanced Seals and they measured everything up and found that the main seals where supplied too small in the genuine seal kits but where able to supply me with slightly larger internal diameter ones that will work.

[imdying]

Yeah mate, very much doubted you'd messed it up... it's as easy as I made out (retarded Korean parts man notwithstanding) isn't it!

How they buggered that up I'll never know... the number of vehicles that run something other than the standard 1/8" square section orings is pretty limited.