Author Topic: Double disk front master - all suggestions welcome (Read 4757 times)

SKTP · « **on:** May 26, 2013, 06:04:54 PM »

So I am finally biting the bullet and shelling out for a modern master and stainless brake lines...

I've search the forum quite extensively and now believe that a stock master is a 14mm piston and will work but may feel soft.

Many people seem to be using 5/8 masters (15.875mm) and are happy with the feel (more bite). Which I am taking as less lever travel and a hard feel...

If that is all correct. What do you recommend for a master?

I'm thinking this one:

http://www.dimecitycycles.com/vintage-caferacer-cafe-racer-bobber-brat-chopper-custom-motorcycle-brake-parts-black-aluminum-nissin-hydraulic-front-brake-master-cylinder-perch-lever-kit-17-651-b.html

JohnG · « **Reply #1 on:** May 26, 2013, 07:22:36 PM »

I converted my '76 750F from single to dual disks (all stock parts). I had planned to use a different master cylinder but was so happy with the results that I left it with the stock master. My original plan was to use the master from a '78 Gold Wing (and actually got one and refurbished it).

So I would suggest you try the stock master and see how you like it. Go from there.

John
PS I have the 750F calipers which have pistons a little bigger than those in the K calipers

flybox1 · « **Reply #2 on:** May 26, 2013, 07:58:55 PM »

I picked up an aftermarket 14mm MC off eBay for about $50. Works great. Firm feel. Very similar to the unslanted one sold by slingshot.
Guess it depends on if you want that stock look. I didn't really care, but am happy with it.

scottly · « **Reply #3 on:** May 26, 2013, 08:30:47 PM »

I'm guessing you are talking about a '78 K with dual 42.8mm calipers? A stock 14mm MC will work fine, but may "feel" a bit soft when bleeding. It's not really an issue when riding, as you won't be clamping down that hard on the brake lever in order to stop.

Don R · « **Reply #4 on:** May 26, 2013, 10:02:04 PM »

What John G said. Same pressure, more travel. I can make the front tire squeal if I want to. It does feel softer until you lean on it excellent control. I have a rock hard master cyl on my K0 (single disc)and am not as comfortable with it.

shinyribs · « **Reply #5 on:** May 26, 2013, 10:39:38 PM »

My bike has an F and an A caliper on the front. Both are the 42mm piston. I thought the front brakes felt horrible with the stock m/c,which I really wanted to retain.I wouldn't even leave with driveway with that setup it felt so bad. I ended up using a 2006 zx6 m/c (robbed from another project) and am very happy with the brakes. Rock solid lever feel with very good modulation. They fit 7/8'' bars,but admittedly look out of place. Using a matching clutch perch fixes that. They can be found cheap on ebay. I paid $55 shipped for the m/c and clutch perch with the levers pictured. M/c needed a kit,that was $18. Hope this helps. Good luck!

EDIT: Just looked back up at your link to DCC. That appears to be a standard Nissin 5/8'' m/c.(Same as I mentioned aboove) The lever on there,I've seen those local for about $10. Honestly,I've never bought anything from DCC...since I always find it elsewhere considerably cheaper.

shinyribs · « **Reply #6 on:** May 26, 2013, 10:56:13 PM »

Here's one for $75 shipped. Lever and res. included. Not a bad buy,but with some searching you'll likely find one cheaper.

http://www.ebay.com/itm/2001-99-01-02-Kawasaki-Zx600-Zx6r-Zx6-Ninja-GENUINE-FRONT-BRAKE-MASTER-CYLINDER-/321100816015?pt=Motorcycles_Parts_Accessories&hash=item4ac3199e8f&vxp=mtr

scottly · « **Reply #7 on:** May 26, 2013, 11:20:00 PM »

Quote from: shinyribs on May 26, 2013, 10:39:38 PM

My bike has an F and an A caliper on the front. Both are the 42mm piston. I thought the front brakes felt horrible with the stock m/c,which I really wanted to retain.I wouldn't even leave with driveway with that setup it felt so bad.

If you never left the driveway, then you have no idea how the 14mm MC really worked.

shinyribs · « **Reply #8 on:** May 26, 2013, 11:30:03 PM »

lol My driveway is right at 1/2 mile long. I made down to the bottom of the first hill and said ''no way!''.

scottly · « **Reply #9 on:** May 26, 2013, 11:37:42 PM »

Quote from: shinyribs on May 26, 2013, 11:30:03 PM

lol My driveway is right at 1/2 mile long. I made down to the bottom of the first hill and said ''no way!''.

Why?? I'm serious.

Viktor.J · « **Reply #10 on:** May 27, 2013, 02:34:38 AM »

Quote from: shinyribs on May 26, 2013, 11:30:03 PM

lol My driveway is right at 1/2 mile long. I made down to the bottom of the first hill and said ''no way!''.

Did you bled the brakes properly, new lines etc?
I have new staneless lines, EBC brake pads and stock MC. It's not perfect but much better then stock and def. not "unsafe". Many ride like this.

I agree with the others. complete the setup and try the stock out. If you dont like it then change.

Bodi · « **Reply #11 on:** May 27, 2013, 05:30:15 AM »

The problem I found when using a stock SOHC4 master on a dual disc setup was what I expected but worse. With a single disc in a "panic stop" grip I could pull the lever about halfway to the bar. And of course the brake was incapable of a stoppie or locking the wheel on dry pavement.
With the dual disk setup the lever came to the bar with more braking felt but still no stoppies. It was scary to be pulling the lever close to the bar for normal traffic braking, realizing there wasn't much in reserve for emergency use.
With a larger bore mc the lever feel was stiffer, but maximum squeeze was again about 1/2 way to the bar and was to be avoided at speed unless I wanted to do an endo.
I used one from a late model sportbike, I think it's a Kawasaki but I picked it on looks out of a bin full of assorted M/Cs at the bike wrecker and don't know the actual model.
In theory the smaller bore will give twice the braking for a given lever pressure: lever travel will be doubled as well. With well bled steel brake lines the lever travel could be tolerable and the stock master could work. With the stock rubber lines I don't think it will be acceptable, the lines swell under pressure and take enough fluid doing that to have the lever against the bar before maximum braking is achieved.
In general going to steel lines (steel braided hose) you get a very different lever feel, the mushy feel due to the rubber lines - that you never noticed i- s suddenly obvious once it's gone.

Xnavylfr · « **Reply #12 on:** May 27, 2013, 05:55:09 AM »

Your THEORY is flawed!!!
If your PUSHING piston(MC) is for instance 1inch and your calipers have 4 1inch piston (WORKING pistons) then you divide the PUSHING piston size by the working piston size. In this calculation you will need to apply 4 times the power to the MC to get the same power at the calipers. Sounds to me that your brakes aren't bled good! and you have air in them.Air compresses and fluid won't.

Xnavylfr(CHUCK)

Viktor.J · « **Reply #13 on:** May 27, 2013, 06:07:22 AM »

Quote from: Xnavylfr on May 27, 2013, 05:55:09 AM

Your THEORY is flawed!!!
If your PUSHING piston(MC) is for instance 1inch and your calipers have 4 1inch piston (WORKING pistons) then you divide the PUSHING piston size by the working piston size. In this calculation you will need to apply 4 times the power to the MC to get the same power at the calipers. Sounds to me that your brakes aren't bled good! and you have air in them.Air compresses and fluid won't.

Xnavylfr(CHUCK)

I'm not sure of what you mean there's a chance that i missunderstand you. But If the area of the MC is 1/4 of the active piston size you get 4 times higher pressure at the active piston. That's the whole principle of hydraulics.
Since the pressure is constant due to incompressible media and pressure are defined as force on a area F/A the force acting on the bigger piston is Pbigger= (Fsmall*Abigger)/Asmall. Thats the basics of pascals principle and the working fork on a hydraulic brake system.

to be clear.

MOONDOGNYC · « **Reply #14 on:** May 27, 2013, 06:55:09 AM »

Quote from: Viktor.J on May 27, 2013, 06:07:22 AM

Quote from: Xnavylfr on May 27, 2013, 05:55:09 AM
Your THEORY is flawed!!!
If your PUSHING piston(MC) is for instance 1inch and your calipers have 4 1inch piston (WORKING pistons) then you divide the PUSHING piston size by the working piston size. In this calculation you will need to apply 4 times the power to the MC to get the same power at the calipers. Sounds to me that your brakes aren't bled good! and you have air in them.Air compresses and fluid won't.

Xnavylfr(CHUCK)

I'm not sure of what you mean there's a chance that i missunderstand you. But If the area of the MC is 1/4 of the active piston size you get 4 times higher pressure at the active piston. That's the whole principle of hydraulics.
Since the pressure is constant due to incomprehensibility and pressure are defined as force on a area F/A the force acting on the bigger piston is Pbigger= (Fsmall*Abigger)/Asmall. Thats the basics of pascals principle and the working fork on a hydraulic brake system.

to be clear.

Dude....simply put, you forgot to carry the 2....

Viktor.J · « **Reply #15 on:** May 27, 2013, 07:03:45 AM »

Quote from: MOONDOGNYC on May 27, 2013, 06:55:09 AM

Quote from: Viktor.J on May 27, 2013, 06:07:22 AM
Quote from: Xnavylfr on May 27, 2013, 05:55:09 AM
Your THEORY is flawed!!!
If your PUSHING piston(MC) is for instance 1inch and your calipers have 4 1inch piston (WORKING pistons) then you divide the PUSHING piston size by the working piston size. In this calculation you will need to apply 4 times the power to the MC to get the same power at the calipers. Sounds to me that your brakes aren't bled good! and you have air in them.Air compresses and fluid won't.

Xnavylfr(CHUCK)

I'm not sure of what you mean there's a chance that i missunderstand you. But If the area of the MC is 1/4 of the active piston size you get 4 times higher pressure at the active piston. That's the whole principle of hydraulics.
Since the pressure is constant due to incomprehensibility and pressure are defined as force on a area F/A the force acting on the bigger piston is Pbigger= (Fsmall*Abigger)/Asmall. Thats the basics of pascals principle and the working fork on a hydraulic brake system.

to be clear.

Dude....simply put, you forgot to carry the 2....

I'm just explaining the principle behind hydraulic pressure systems.
If you reefer to the second caliper you can pretend that A2 is the size of two calipers, that's not really a problem. The problem with stock MC and dual discs as I understood is not the diameter of the MC its the volume it moves (or more the volume it doesn't move). Since we now have two calipers we need to move more fluid, the volume is constant. This is done be increasing the diameter of the MC or longer stroke (moving more fluid). And since larger diameter means less difference in areas and more pressure force needed at the leverage. Therefor the problem would not need to be the diameter of the stock MC piston, Isn't this one of the reasons why modern bikes have radial Mc besides less flex in the MC ? It provides small piston size = small pressure att leverage , radial = long stroke

If you increase the diameter or ad a double piston the principle is the same, but that's one "side" of the problem. since the volume is fix you can easily calculate how many mm one caliper piston moves for every 1 mm the lever moves. And then you understand that if you increase/double the area for the caliper the distance it travels for every leverage mm will decrease, the pressure on the caliper area will however increase.

Xnavylfr · « **Reply #16 on:** May 27, 2013, 07:17:02 AM »

NOPE not wrong!!! If you look at a BOTTLE HYDRAULIC jack, you will notice the pump PISTON is much smaller than the surface of the ram piston. That's why it take you so many pumps to move the ram up 1 inch. If you have a brake system, for instance , you have a 1" bore MC piston and 4 1" caliper pistons, you will need 4 times the amount of pressure on the MC to equally apply all 4 calipers. The working power at the MC will be divided by the 4 calipers. If this system was reversed you would only need 1/4 the power at the MC to LOCK the calipers down HARD, because the power applied by the MC would be multiplied by 4.

I KNOW my HYDRAULICS Theory , I worked as an AIRCRAFT HYDRAULICS MECH for over 40 years!!

Xnavylfr(CHUCK)

Viktor.J · « **Reply #17 on:** May 27, 2013, 07:25:17 AM »

Quote from: Xnavylfr on May 27, 2013, 07:17:02 AM

NOPE not wrong!!! If you look at a BOTTLE HYDRAULIC jack, you will notice the pump PISTON is much smaller than the surface of the ram piston. That's why it take you so many pumps to move the ram up 1 inch. If you have a brake system, for instance , you have a 1" bore MC piston and 4 1" caliper pistons, you will need 4 times the amount of pressure on the MC to equally apply all 4 calipers. The working power at the MC will be divided by the 4 calipers. If this system was reversed you would only need 1/4 the power at the MC to LOCK the calipers down HARD, because the power applied by the MC would be multiplied by 4.

I KNOW my HYDRAULICS Theory , I worked as an AIRCRAFT HYDRAULICS MECH for over 40 years!!

Xnavylfr(CHUCK)

Then we are talking about the same thing and I misunderstood your first text. But you power at the MC is multiplied by 4 (IF we are talking about this example OC) , you said it yourself with the bottle hydraulic jack, how come you could lift a 2000 kg car with one hand ?
Same principle applies on the brakes, You stop a 300 kg moving motorcycle with two fingers so yes, the power applied at the handlebar leverage is increased to the calipers

BTW caps lock/ capital letters on a forum is like yelling in real life

SKTP · « **Reply #18 on:** May 27, 2013, 07:37:07 AM »

So, I'll begood with a 5/8ths right?

754 · « **Reply #19 on:** May 27, 2013, 07:52:39 AM »

FWIW i ran stock with dual 73 calipers and dash 3 lines.. Even chromed them, and was running pods, and felt no ill effects,liked the brakes. And the pods..
First inkling I had that either may be a problem , was 25 years later when I found this forum..

Psychonaut · « **Reply #20 on:** May 27, 2013, 08:03:32 AM »

Front Master Cylinder Ratio Chart

http://www.vintagebrake.com/mastercylinder.htm

Viktor.J · « **Reply #21 on:** May 27, 2013, 09:09:54 AM »

Quote from: SKTP on May 27, 2013, 07:37:07 AM

So, I'll begood with a 5/8ths right?

Probably. assuming you have a similar stroke to the stock MC you'll move more fluid - less travel of the leverage - what most people want and some comfuses with " better pressure, firmer brakes " etc..

70CB750 · « **Reply #22 on:** May 27, 2013, 09:33:35 AM »

The pressure is equal throughout the hydraulic system. Was it the first law of hydraulics? Don't remember.

Oh, it was Pascal's law:

http://www.engineersedge.com/fluid_flow/pascals_law.htm

so if the output area is double, the resulting force equals the area times the pressure, bigger area on slave cylinder, bigger force on the output.

Viktor.J · « **Reply #23 on:** May 27, 2013, 10:00:31 AM »

If anyone still have some troubles, play around with this
http://hyperphysics.phy-astr.gsu.edu/hbase/pasc.html#hpcal

scroll down to " hydraulic press calculation", play around with different MC sizes, different sizes in caliper (nbr of calipers), and see how the resulting pressure increases/decreases as well as the amount of stroke you need.

I know this is a simplification of how a MC works, but hopefully it helps someone to get a better grip around this. At least it gave be a while back.

Over and out

70CB750 · « **Reply #24 on:** May 27, 2013, 10:12:43 AM »

Great link, thanks!

Did you ever fix your front wheel, Victor?

Viktor.J · « **Reply #25 on:** May 27, 2013, 10:25:46 AM »

Quote from: 70CB750 on May 27, 2013, 10:12:43 AM

Great link, thanks!

Did you ever fix your front wheel, Victor?

Yeah I figured since some (not only here) people misunderstand the affect of pressure and travel length and I found this pedagogic tool since my explanations wasn't really going through.

about my wheel, Ill update the thread instead of going OT

JohnG · « **Reply #26 on:** May 27, 2013, 10:47:45 AM »

I just spent some time replacing old Honda brake lines with new ones (still rubber like - not braided SS). There is a very noticeable difference in the feel of the lever. All other things untouched. I mention this because it is one thing you want to eliminate.

In one case I replaced the lines on a 1982 900F that only had 7800 easy original miles. I had rebuilt the entire system but they still felt mushy. Got some new lines (from Slingshot) and there is a very noticeable improvement. The cost was around $75. Essentially the same thing on an '83 1100F with 19K miles. (none of this should be interpretted as my not preferring SS braided . . . )

Other: for anyone who wants it, PM me an email address that will accept an attached file. I compiled a bunch of master cylinder piston diamters and caliper diameters into a table, the product being the ratio of MC piston area to total caliper piston area. You can also toss your own data in and use the same formulas. All data is 70s and 80s Honda; both single and dual disks.

There is one other aspect of this that deserves mention. If you have adding a second disk, careful work needs to go into adding that second caliper so that the faces of the pads are parallel to the disk. If you don't then a bunch of flexing will occur and the lever will feel mushy or disappointing. Careful work with shims and feeler gauges and so on may be required, as well as patience. It is not just a "bolt on".

That said, I have been screwing around with every possible modification on this poor bike for 36 years. The dual disks are the best thing I ever did.

Viktor.J · « **Reply #27 on:** May 27, 2013, 11:23:21 AM »

Quote from: JohnG on May 27, 2013, 10:47:45 AM

There is one other aspect of this that deserves mention. If you have adding a second disk, careful work needs to go into adding that second caliper so that the faces of the pads are parallel to the disk. If you don't then a bunch of flexing will occur and the lever will feel mushy or disappointing. Careful work with shims and feeler gauges and so on may be required, as well as patience. It is not just a "bolt on".

+1 on that John. All kinds of flex is produced and creates a spoongy feeling. A correct spaced second disc, good condition on both caliper and MC, fresh good brake fluid, braded steel lines and a properly bleed systems provides a big improvement and cancels out most of the flex. If he after this still isn't satisfied, then I suggest test different MC sizes (pref. a MC dimensioned for dual discs) and then don't stare blind at the diameter of the MC and diameter ratios, the stroke also plays a part.

Don R · « **Reply #28 on:** May 27, 2013, 11:30:56 AM »

After all that, I went for a ride and my stock M/C is still awesome! I do have aftermarket lower hoses and the stock upper.

scottly · « **Reply #29 on:** May 27, 2013, 12:41:57 PM »

Quote from: SKTP on May 27, 2013, 07:37:07 AM

So, I'll begood with a 5/8ths right?

Yes. In fact, I had a Kawasaki 550 front-end on my bike for a while, and it used a 5/8" master with dual 42.8mm calipers.

shinyribs · « **Reply #30 on:** May 27, 2013, 01:46:32 PM »

^^^ That was pretty much my point. Using the stock 14mm MC with dual 38's may be just fine. But with dual 42's mine was a finger trapper. Full stroke ended up about 1/2" from the grip. And I run really thin grips.

Consider what Honda used on the 77-78 bike with dual 38mm calipers. It wasn't a 14mm master. IIRC, they used a 17mm caliper. Just something to think about.

Like was said earlier, there's much more to MC displacement than just the bore. Just like in an engine. Bore and stroke make up the total displacement. There may be some 14mm masters with the displacement needed to run duals, but IMO, the stock setup is lacking for dual 42's.

And yes, I did in fact complete and bleed the brakes before my test ride. It would be quite ridiculous not to. And the bike has braided lines.

edit- Looked back and the 77-78 F bikes did in fact use a 17mm mc. Stroke?...who knows

shinyribs · « **Reply #31 on:** May 27, 2013, 02:13:18 PM »

Quote from: scottly on May 26, 2013, 11:37:42 PM

Quote from: shinyribs on May 26, 2013, 11:30:03 PM
lol My driveway is right at 1/2 mile long. I made down to the bottom of the first hill and said ''no way!''.
Why?? I'm serious.

It's a half a mile long because I live smack dab in the middle of a 100 acre farm...

Seriously though,I wouldn't ride it because the brakes were unsafe IMO. The stock lever (which you have to reach pretty far for in the first place) came dangerously close to the grips. I wouldn't rick a panic scenario to see what ''might'' happen.

Regardless, the OP asked for different people's opinions. This is strictly my opinion based upon my personal experience/preference of what brakes should be. YMMV.

Xnavylfr · « **Reply #32 on:** May 27, 2013, 02:30:15 PM »

VIKTOR, and I stand corrected!! you are correct!!
The working force from the MC is MULTIPLIED by the size of the caliper piston size.. I am wrong and accept my torture now!!!..

I had the thought process backwards.

Xnavylfr(CHUCK)

SKTP · « **Reply #33 on:** May 27, 2013, 02:31:46 PM »

Wow. Thanks for all the info...

I think I'm just going to call this guy and buy everything through him...(modern master, stainless brake lines and speed bleeders)

http://www.vintagebrake.com/index.html

I have no interest in stock or period correctness when it comes to brakes...I'm going to lane-splitting on the 405....I just want the best brakes possible without having to do a full frontend swap...

shinyribs · « **Reply #34 on:** May 27, 2013, 02:36:18 PM »

SKTP,do whatever makes you feel the most confident since it is your brakes, your bike...and your butt! But going with a preassembled kit like that will most likely cost you much more money than needed.

lucky · « **Reply #35 on:** May 27, 2013, 02:45:48 PM »

I have a 1978 CB750K front forks and disc. I changed to a Goodrich stainless brake hose and the feel is rock hard now . Not soft and mushy.

The brakes are still not as good a a performance Machine front caliper.
Very expensive though.

Viktor.J · « **Reply #36 on:** May 27, 2013, 11:05:29 PM »

Quote from: Xnavylfr on May 27, 2013, 02:30:15 PM

VIKTOR, and I stand corrected!! you are correct!!
The working force from the MC is MULTIPLIED by the size of the caliper piston size.. I am wrong and accept my torture now!!!..

I had the thought process backwards.

Xnavylfr(CHUCK)

That's alright Chuck, sometimes the fingers are faster than the brain

Quote from: SKTP on May 27, 2013, 02:31:46 PM

Wow. Thanks for all the info...

I think I'm just going to call this guy and buy everything through him...(modern master, stainless brake lines and speed bleeders)

http://www.vintagebrake.com/index.html

I have no interest in stock or period correctness when it comes to brakes...I'm going to lane-splitting on the 405....I just want the best brakes possible without having to do a full frontend swap...

I agree with shinyribs, this may cost more than you get out from it. I don't know vintagebrakes prices but I know they aren't for free

everything in these brakesystems are outdated with 35 years

That means the caliper design, material of the disc, damn even the front forks aren't design for modern braking power. So if you really want modern breaking power I believe a front end swap is the only way, BUT if you want a better braking power the dual disc is the best way to go, then add with the rest of the stuff that I suggested. The money you spend on a new MC may not return the same amount of braking power.

FWIW I emailed vintagebrakes asking what they mean with "more firmer feeling" and then saying you should use a bigger MC diameter to achieve this. Apparently what they mean is "more pressure from you". I don't know about you guys but I didn't understand it in that way and I think this is one of the reasons why many wrongly believe that bigger MC diameter = better braking power.

scottly · « **Reply #37 on:** May 27, 2013, 11:27:00 PM »

With dual 42.8mm calipers and a stock K7 14mm MC, I can pull the lever within 1/2" of the handle bar grip, but I need to use all 4 fingers to do it, and the front wheel would be locked, or nearly so. I've never had to squeeze the lever that hard on the road, and the least of my worries would be pinched fingers... I maintain that in MY experience, a stock MC will work fine with dual calipers. If the 5/8" Kawasaki MC had not needed a rebuild, I would have tried it, but the K7 MC was good to go, so that's what I used.

News:

Author Topic: Double disk front master - all suggestions welcome (Read 4757 times)