Master cylinder size

[speeding_ant]

After identifying an issue with my front master cylinder, I need it replaced. Currently it is 12mm, and I've been told a 14mm will give me more power with the 4 piston caliper.

Will I still have decent modulation if the bore is bigger?

(trying to use technical terms. If I'm wrong, don't blame me, I'm a noob!)

[bogan]

A bigger master diameter piston will give you more flow, but less fluid pressure. You'll have to put more force on the lever to stop as fast, but the lever won't move in as much.

I can see no reason why you would want to do that.

[unstuck]

Me neither.:oi-grr:

[Kickaha]

Will I still have decent modulation if the bore is bigger?
No, with a 14mm a firmer lever and less travel is what you will have

why cant you rekit the exisiting m/c?

[speeding_ant]

No, with a 14mm a firmer lever and less travel is what you will have

why cant you rekit the exisiting m/c?

Yeah, that'll be the first option.

I'd rather have more modulation.

[bogan]

Yeah, that'll be the first option.

I'd rather have more modulation.

What is this modulation and how does it relate to M/C size?

[speeding_ant]

What is this modulation and how does it relate to M/C size?

The ability to control the brakes linearly within the lever action. Eg, not touchy. I figure a larger M/C means less modulation as it's moving more brake fluid to the calliper. I'm just not sure how much change 2mm will have.

[bogan]

The ability to control the brakes linearly within the lever action. Eg, not touchy. I figure a larger M/C means less modulation as it's moving more brake fluid to the calliper. I'm just not sure how much change 2mm will have.

Sounds more like spongy lines tbh, I much prefer 'force-only' braking where the movement of the lever between light and heavy braking is virtually non-existant, so the feedback on force applied is greater.

A 12-14mm jump will be 36% more force required, and 36% less lever movement.

[speeding_ant]

Sounds more like spongy lines tbh, I much prefer 'force-only' braking where the movement of the lever between light and heavy braking is virtually non-existant, so the feedback on force applied is greater.

A 12-14mm jump will be 36% more force required, and 36% less lever movement.

Cheers for the info. Master cylinder is getting looked at for much more serious problems - but for the price of a seal kit I could get a new larger M/S. If it's not just a blockage, then I'll need to decide what to do.

If it means I can brake with less fingers on the lever then I'm happy with that. Less lever action isn't a big problem - there's a fair bit of that at the moment.

As long as it won't adversely affect control, I'm happy.

[bogan]

Cheers for the info. Master cylinder is getting looked at for much more serious problems - but for the price of a seal kit I could get a new larger M/S. If it's not just a blockage, then I'll need to decide what to do.

If it means I can brake with less fingers on the lever then I'm happy with that. Less lever action isn't a big problem - there's a fair bit of that at the moment.

As long as it won't adversely affect control, I'm happy.

Bigger m/c diamter means exactly the opposite of that! Haven't you been reading what has been posted?

[speeding_ant]

Bigger m/c diamter means exactly the opposite of that! Haven't you been reading what has been posted?

Ah, right. Misread/understood.

Cheers

[Grumph]

Cheers for the info. Master cylinder is getting looked at for much more serious problems - but for the price of a seal kit I could get a new larger M/S. If it's not just a blockage, then I'll need to decide what to do.
.

Not true in my experience. "New" M/c cost much more than a seal kit and anything you can find cheaper will probably need kitting anyway.

Try Don at pitlane in Darfield. He's got a very big kit range on the shelf and is open weekends.

Edit - just saw Wgtn....give Don a ring anyway, he'll do mail order.

[Hugo Nougo]

What is so majorly wrong with your m/s that a complete redesign of Mr Honda's brake system is called for?. You're sure it's not just glazed pads?. I have some good second hand m/s in both 12 and 14mm if you want to try before you commit hard cash. my 320mm single disc 6pot with a shorty lever use's a 12mm m/s and it bites quickly and progressively.

[Owl]

I can see no reason why you would want to do that.

Was a recommended fix for my Speed Triple (5/8 from 14mm). Reason for not going back is more consistent lever travel. Feel is compromised somewhat (wooden), but I no longer have to remove/clean my calipers so often.

I can still brake with one finger, but then I do have big fat sausage fingers.;)

[speeding_ant]

What is so majorly wrong with your m/s that a complete redesign of Mr Honda's brake system is called for?. You're sure it's not just glazed pads?. I have some good second hand m/s in both 12 and 14mm if you want to try before you commit hard cash. my 320mm single disc 6pot with a shorty lever use's a 12mm m/s and it bites quickly and progressively.

The calliper seizes up after a run on the motorway -> Paekak hill. M/S needs a rebuild, though have also been offered a new larger Nissin M/S for not much more than the rebuild (cheap).

I've already figured out the solution based off the helpful responses here.

Cheers

[F5 Dave]

oh good grief

A bigger mc will very likely increase your stopping distance. You really don't want to do this.


But your real problem is that the non return valve it being restricted. Happens when there is no freeplay & the heat of a fast run will cause just the issue you describe (think you can also do it by removing the rubber buffer at the cap & blocking the vent).

Usually a cheapo or incorrect replacement lever is the real fault.

Fix this first. New fluid (which has been boiled to shit), cleaned up pistons & deglazed pads (which have been overheated to shit from this fault).

Actually check the pads real careful that they aren't starting to delaminate from excessive prolonged heat. Disc may be glazed or warped if you're unlucky.

[speeding_ant]

oh good grief

A bigger mc will very likely increase your stopping distance. You really don't want to do this.


But your real problem is that the non return valve it being restricted. Happens when there is no freeplay & the heat of a fast run will cause just the issue you describe (think you can also do it by removing the rubber buffer at the cap & blocking the vent).

Usually a cheapo or incorrect replacement lever is the real fault.

Fix this first. New fluid (which has been boiled to shit), cleaned up pistons & deglazed pads (which have been overheated to shit from this fault).

Actually check the pads real careful that they aren't starting to delaminate from excessive prolonged heat. Disc may be glazed or warped if you're unlucky.

Yes, it is apparently the lever. The lever is being modified, and the fluid is being replaced. If it were the M/S at fault, a rebuild would be done - not a replacement with a larger M/C.

I've taken all of that on board, but my mechanic knows best - not me.

[F5 Dave]

Make sure he checks the pads for overheating

[Premature Accelerato]

A question fro F5 dave. I have been following this thread and another regarding spongey brakes etc etc. Your comment about the return valve, do all master cylinders have them (profuse apologies for my ignorance). I have a 96 GSXR 750 with good ol 6 pot calipers and it has been giving me a shit of a time. After half a day around Manfeild, the leaver is almost touching the bars. Have tried a heap of things to fix it but the comment about the return valve has me thinking. I also have quite a lot of travel of the lever before the M/C piston appears to start doing any thing, almost as if the M/C bore has not refilled with fliud. Is that a sign of a blockage in the m/c or perhaps the pads not retractiing properly. I have had the calipers apart a number of times, replaced pads (which appear to wear reasonably evenly), fitted new seals to every thing, fitted braided lines and new rotors etc etc but I kid you not, those brakes work well for 30 laps or so and are then bolldy dangerous.

[F5 Dave]

Yes all mc do have a return. Though the symptoms tend to be that the pressure is not released. You would tend to get the brakes becoming stiff at the lever rather than spongy.

Your problem could be wear or degradation of the mc seal/bore. Or more likely the dumb routing of Suzuki front brakes with that loop over the front mudguard which makes them difficult to bleed properly.


Maybe try all new fluid & syringe to force new fluid over the loop with opposite calliper valve open at same time as close & force fluid in. best option is separate lines from MC to each calliper. Think the AMA banned race use of std Suzi system (from creaky memory).

Outer calliper Dust seals on some callipers can be a pain. They can deform & pull the pistons back more than they should. The inner actual seals are usually surprisingly trouble free.

Failing that find some Nissin callipers off an RF which 'might' bolt on & hope WOF people don't notice.

failing that Imdying may have a better idea being our resident brake guru.

[Premature Accelerato]

Where exactly is the valve. When I put a new kit in the M/C, all it had was a spring and piston with a couple of seals on it. Re the brake lines, I have actually fitted seperate lines on the advice of HEL which as you say, makes bleeding much easier. Comment about the dust seals might have some merit as they do look a little misshapen. Would assembly using brake seal grease assist or just dampen with brake fluid as I have done in the past?

[F5 Dave]

its just a hole that the piston uncovers to return the fluid. as you let go of the lever it squirts back.

When you looked up the bore, was it clean, or some corrosion marks? I give them a light hone with fine oiled sandpaper if minor.

I have an RGV set up on one bike that was a bugger & just didn't want to 'bleed'. The outer dust seals fixed the issue. I used to use hi temp grease but have been warned off that as copper & ally. I must admit I just went to brake flluid despite having bought rubber grease, never used it.


I'm not a big fan of Tokico callipers. Perhaps there is a GSXR forum that will cover the issue.

[Premature Accelerato]

Yep, bore was nice and clean. Interesting about the m/C valve. Its almost as if when the lever is released the m/c piston is not retracting far enough and so the cylinder is not filling up properly. So over time the lever gets back further and further with each use. So what you say about the dust seals impedeing caliper piston retraction could be on the nail. Will investigate this further. The tokico 6 pots are apparently notorious for bleeding problems and I would replace them if it wasn going to cost more than the bike is worth. Many thanks of the ideas F4

[F5 Dave]

Yep, bore was nice and clean. Interesting about the m/C valve. Its almost as if when the lever is released the m/c piston is not retracting far enough and so the cylinder is not filling up properly. . . .

um, well, not really how I'd describe it as the pressure doesn't let off, unless the piston seal was leaking & it sounds like it should be fine.

Some calipers are a total pig to bleed as they have a small cavity that never gets the nipple to the top. Usually only on crazy Italian dirtbikes or brake transplants. The Japs don't seem to make that mistake. . . Or maybe.

If you did a section of the top piston, there could be an area that was just retaining some air. Perhaps with the bike bled while elevated at the front or the rear depending while someone held it, would answer that question. I've taken callipers off & bled them on a spare disc, but its a super pain to hold them in place without several hands & clamps.

But I'd put some money on seals.

or http://www.trademe.co.nz/motors/motorbikes/parts-for-sale/mud-guards/auction-617065310.htm

But I can't say if they are a bolt on.

My YZFSP wore R1 blue spots. Much better than the 6 potters it came with. Yes they were std on this model, disprove it mate. Actually no one ever noticed. Lost 1kg unsprung weight too.

[husaberg]

A question fro F5 dave. I have been following this thread and another regarding spongey brakes etc etc. Your comment about the return valve, do all master cylinders have them (profuse apologies for my ignorance). I have a 96 GSXR 750 with good ol 6 pot calipers and it has been giving me a shit of a time. After half a day around Manfeild, the leaver is almost touching the bars. Have tried a heap of things to fix it but the comment about the return valve has me thinking. I also have quite a lot of travel of the lever before the M/C piston appears to start doing any thing, almost as if the M/C bore has not refilled with fliud. Is that a sign of a blockage in the m/c or perhaps the pads not retractiing properly. I have had the calipers apart a number of times, replaced pads (which appear to wear reasonably evenly), fitted new seals to every thing, fitted braided lines and new rotors etc etc but I kid you not, those brakes work well for 30 laps or so and are then bolldy dangerous.

Dave's covered pretty much all the bases All ready, but as an aside re the lever travel before the brakes actuate what does your pivot point (on the lever) look like. is it round and unworn and factory. Some quality levers have a bearing rather than a hole.

Myself I now tend to reverse and sometime suck bleed brakes as per KTM and Husaberg factory recommendations for their brakes and clutches i guess Dave is familar as he may have had a similar set up on the GAS GAS.(i must admit the first time i seen it i thought it was a bodge until i used it :) )
285290

I just use a syringe and plastic pipe on other bikes and bobs ya uncle.

Ballards also sell neat little bleeders with one way valves.(i will find a pic if i can be arsed latter)they work like these but not sure if they are exactly the same
285288285289
http://www.badpennycustoms.com.au/zen/index.php?main_page=product_info&cPath=143_534&products_id=295
On the KTM50 brakes you can just ram in a syringe and work the air out (as they have no nipples at all.)
The factory teams change the brake fluid all the time and bleed them all the time.
Very rarely according to all the brake and pad tests i have seen do any aftermarket sportbike pads out perform standard factory brake pads when used with factory rotors as they were designed to work together and factories spend a huge amounts on R&D.
There is some beautiful variable ratio radial mater-cylinders available.....but they make my wallet sweat.
And i have far too many things i haven't finished yet as it is.

[Premature Accelerato]

Yep, have a good brake lever, its a brand new original so the pivot is not an issue. I will give the reverse bleed technique a go as I have a large syringe that I can use. Might also see about a bleed nipple for the m/c banjo fitting as that would help get air out of that tight bend at the top of the line. As for pads, I have used EBC HH race pads, these have worked well and am now trying SBS which so far have performed as well as the EBCs

[F5 Dave]

I rag cover and crack the top banjo, squeeze, close. When syringing to force fluid in, use cable ties on hose to nipple and another set of hands helps.