Brake Lever Travel – Stock vs Smaller Master Cylinder

[eyewinder]

As part of a brake system overhaul on my 1980 Special (caliper and rear master cylinder rebuilds + new stainless steel lines), I'm looking to replace the front master cylinder with a smaller bore model. This is my first motorcycle and since the brakes were shot when I purchased the bike, I have no point of reference as to how a working stock 14mm MC feels or functions.

I've read a ton of posts on this forum, reviewed the front master cylinder ratio chart (http://www.vintagebrake.com/mastercylinder.htm), and have talked to Michael Morse at 650Central about the switch to a smaller MC. However, I'm still left wondering about the actual lever 'feel' I can expect when everything is reassembled.

I'm looking for some objective comparisons between the stock and upgraded brakes, as the ratio 'sweet spot' appears to be partially related to personal preference.

Can anyone tell me the range of lever travel on a 14mm vs 11mm MC, assuming the same stainless lines are used? Put another way, what would be the distance from the lever to the bar when approaching wheel lock?

At the moment, I'm considering a 12mm Brembo MC from Bevel Heaven, as they also have a matching clutch lever (with mirror mounts on the clamps). Any insight would be greatly appreciated!

 

[5twins]

I'm probably going to be the dissenting voice here but I think the stock one works fine. The experts say it's too big and many say it has a "wooden" feel, whatever that means. I think it works and feels fine. I have a pretty much rock hard lever feel once I pull through the freeplay, and the harder I pull after that, the harder it stops. My buddy replaced his MC with one from 3M (the brake "expert") and frankly, I think it operates like shit. The lever feels like it's connected to a rubber band. I also replaced my pads with what 3M says are about the best available. They work worse than the stock ones I replaced. So, I'm not buying into the "replace the MC, replace the pads, replace the disc ...." hype anymore. For this bike, I think well sorted stock stuff is just fine. You do need to replace the line, that's all I really think needs doing.

 

[fredintoon]

hi eyewinder,
FWIW, 5Twins is relating his personal experience with his XS650 front brake while 3M sets up brakes for a living.
What's fact instead of opinion is that swapping to the smaller m/c means the lever has to move further to put the brake on.
My own personal experience is that the '77 & newer XS650 stock front brake works OK but with a smaller m/c it works WAY better
and that it's longer lever travel gives you more control of how hard the brake is being applied.
And oh yes, stainless brake line is just about essential.

 

[retiredgentleman]

I have used the stock 14 mm M/C with the stock front caliper (38 mm piston) and rotor. The braking was good, but I did find the change from no braking to full braking to be a bit too quick. In other words the modulation was not the best.
If you do the math, the ratio is 1134.12/153.9 = 7.37
Michael Morse recommends a ratio of 12 to 14 for a single piston caliper.
In order to get into that area, you would have to use a 10 mm M/C, which has a ratio of 1134.12/78.5 = 14.4

So, it would seem its best for you to use a 10 mm M/C. If you used a 12 mm M/C, it will be an improvement (ratio of 10), but it would not be as good as if you used a 10 mm M/C.

This information is not what you are doing, but it may be of some interest. I installed a 4 piston Brembo caliper on the front of my bike. At first I tried using the stock 14 mm M/C, but the change over from no braking to full braking was just way to quick. I was locking up the front wheel much too easily, which was bad (poor modulation). That was using a ratio of 20.98.
MMM recommends a ratio of about 27 for 2 piston or 4 piston calipers.

To improve things, I bought a 12 mm Brembo M/C. That gave me a ratio of 28.6, which made a really big improvement. Now I have great modulation, which gives more control over how you brake.

I think the ratios that MMM suggests are ball park correct. Of course we are all individuals, and what I think is good brake modulation may not be what you or someone else prefers.

 

[eyewinder]

5twins – That's an interesting perspective. Considering that my stock master cylinder is not worth rebuilding, would you recommend that I find another one at the stock size, or do you think there are some benefits to dropping the bore size slightly, perhaps to 13mm or 12mm?

fredintoon – Are you using an 11mm m/c on your bike? Could you give me a rough idea about how far your lever travels? Is it still firm as the brakes are applied harder, or does it have some springiness in comparison to the original?

When I spoke to 3M, there were a few things he mentioned that made me question dropping all the way to an 11mm master cylinder:
- some mechanics may consider the brake lever with an 11mm m/c too soft when doing safety/certification
- if he wanted to, he could probably squeeze the lever all the way back to the bar
- more than a few racers don't like his preference for lever feel

 

[eyewinder]

retiredgentleman – If I'm not mistaken, isn't the stock piston on the later calipers 38mm? This would put a 12mm m/c at a ratio of 10.03, an 11mm at 11.93 and a 10mm at 14.44? Of course, these are just numbers and anything within a reasonable range will function – just with different levels of modulation/feel...

I'm afraid that my inexperience is playing a big part here (still working on getting my licence – haha). Without any working brakes to compare with, I may have wing it and hope that I like the feel of the end result!

 

[Max Midnight]

I think your last paragraph sums the situation up.
From the above posts you will have concluded that Mr 5Twins like a hard or firm feel to the brake lever whilst Mr Retired gentleman prefers a softer feel. Neither is right or wrong; it's a matter of personal taste.
The only way you are going to find out if you like it 'hard' or 'soft' is from experience and the only way to get that is by riding the bike.
If you get an OE m/c and ride with that then you will be able to form an opinion based on your experience and thus be able to have an opinion on what you like.
Assuming that the OE hoses are serviceable then I would start with them on the bike. Once you have developed the feel of them then change to the steel lines. This will make the lever feel firmer giving you another perspective.
From this you should be able to decide if the OE m/c goes on e-Bay or not.

 

[eyewinder]

Thanks Max, I think you are correct. My own opinion will have to be formed on this one... Unfortunately, neither the OE master cylinder nor the lines are serviceable, so I probably will never know what the original 'baseline' was. I'm hoping to make the best guess/decision possible on the first attempt!

It stands to reason that a larger OE 14mm m/c will be significantly 'harder' than the stock setup when paired with modern stainless lines (due to lack of line flex/expansion), so I will likely take an intermediary step to one that's a bit smaller, perhaps to 1/2" (12.7mm) or 12mm bore.

 

[gggGary]

Stone stock will be fine for a first time rider, that will change if you run harder as experience allows. I run a stone stock system vs. a 10mm MC, SS line, 650 central vesrah pads, mikes rotor, michelin sport bike tire on a wide rim back to back all the time (pair of plated insured 79's) Hands down the modified system wins for me. Nothing wrong with stock system if you are an "out for a cruise" type rider like 5twins. If you run with a fast crowd and sometimes get to a tight corner going way too fast, only one of those systems can save your bacon. (survived to 61 so far and that's still me LOL)
A bit of background; IMHO these early disk brakes were a transition from guys used to running no matter what you did at the lever the drum brake would "gradually slow the bike". Through the next 40 years expectations about how a front brake should work and act have changed, 100% for the better. Big fat cruisers still ship with brakes that are more suggestions of slowing than stop on command systems. Sport bikes now have SERIOUS incredibly controllable stopping ability. I am in the middle of upgrading a Royal Star Venture to sport bike calipers with a more suitable tire. Those big ole barges can boogie pretty good and do need better brakes for the way I want to ride them. Yet another XS650 with an upgraded fork, double disks and 4 piston calipers will most likely get done this year. THAT will bring up other short comings in frame and handling. But hey this stuff is my hobby! I also have an FJR gentleman's express this year. Sure is interesting swapping riding these very different bikes.

PS in a rare show of restraint I did that front brake upgrade one step at a time test riding each change. order was, rotor, pads, ss line, then MC. Hands down the biggest change was the smaller bore MC (you have to use a SS line). As you have intuited the small bore MC trade off is power vs travel.
Hint; some Yamaha scrambler, dirt bike MC's are 10mm and virtually plug and play.....

 

[retiredgentleman]

retiredgentleman – If I'm not mistaken, isn't the stock piston on the later calipers 38mm? This would put a 12mm m/c at a ratio of 10.03, an 11mm at 11.93 and a 10mm at 14.44? Of course, these are just numbers and anything within a reasonable range will function – just with different levels of modulation/feel...

I'm afraid that my inexperience is playing a big part here (still working on getting my licence – haha). Without any working brakes to compare with, I may have wing it and hope that I like the feel of the end result!

I recommend you try a 10 mm M/C. Gary gave you a good idea there, to maybe buy one from a Yamaha dirt bike.

 

[aldo5468]

I just measured my stock front caliper piston from my 78SE, and it appears to be 34 mm.
I recommend you try a 10 mm M/C. Gary gave you a good idea there, to maybe buy one from a Yamaha dirt bike.

Per Gary and RG, the m/c from Yamaha TW200 is a good example of a 10mm plug-and-play unit that easily accepts the right-hand mirror and front brake switch plug

 

[Paul Sutton]

The front brake on my XS is rebuilt as stock but new stainless brake-lines were added. Although the new lines have removed all spongy feeling I am now unable to set the brake lever to my preferred position because the internally threaded adjuster part on the lever now contacts the master cylinder piston. Previously the sponginess of the stock brake-lines allowed the lever to be pulled in further. Also the brake feels hard to me and not as smooth and controllable like the one on my old RD250B. I am not too sure how I will improve the "feel" of my brakes - personal feelings of what is right or wrong can be a real pain to put right sometimes.

 

[fredintoon]

- - - fredintoon – Are you using an 11mm m/c on your bike? Could you give me a rough idea about how far your lever travels? Is it still firm as the brakes are applied harder, or does it have some springiness in comparison to the original? - - -

Hi eyewinder,
my Heritage Special was my first ever disk brake bike. It's stock disk brake worked far better than the drum brakes on the Britbikes that I owned before.
Then I upgraded to dual front disks for fashion's sake.
I did dual front disks drilled full of holes, new pads, stainless hoses and being cheap, hoped to get away with using the stock m/c.
Much to my surprise, the brake's "feel" with twin disks and the stock m/c was a great improvement.
I had thought that the sudden shift from free lever movement to "hard as a rock" once the pads grip was the way disk brakes were supposed to be.
But it ain't necessarily so.
My dual-disk conversion demonstrated that the stock m/c piston had twice the area needed to work one caliper but was just about perfect to work two
because it turned the single caliper's "hard as a rock" feel into the dual caliper's "controllable resilience" just the way I'd always wanted it to be.
So what I'd look for in a m/c suitable for a single disk is a piston with half the AREA of the stock m/c's.
My memory don't remember the stocker's piston diameter but Pi x (Rsquared) will do the area conversion for you.

 

[retiredgentleman]

Quite right Fred. The stock M/C piston of 14 mm = area of 153.9 mm squared
If a 10 mm M/C is used = 78.5 mm squared
78.5/153.9 = 0.51 which is about 1/2
QED

 

[eyewinder]

Wow, thank you all for the feedback. You've given me a lot to consider!

gggGary – I like your idea of one step at a time. It would be a really interesting learning process. If I were working with a more complete/functional brake system, I'd likely take the same approach. Thanks for the tip about the Yamaha dirt bike m/c too.

retiredgentleman – I was under the impression that all xs650 calipers were the same from 1977 onward... Measured my caliper piston again this evening and it is a hair over 38mm... very strange!

Paul Sutton – Your experience with the stock m/c and stainless lines perfectly illustrates my concern about that combination. Are you thinking of switching to a smaller m/c as well?

 

[Paul Sutton]

Eyewinder, I replaced the old stock brake-lines because they were 36 years old, that is approximately 26 years past their use by date. I examined the old brake-lines and they really were shot, if I pulled them gently one of the ends stretched easily. I suspect the inner pipe was no longer crimped in place. This Spring and Summer I want to give the new brake-lines a good run before I make any decisions about changing things. Clearly 14mm work fine for some and are not first choice for others.

What would be nice to see is a collection of bike models that take 10mm master cylinders so we can perhaps access the second hand market better - thank you aldo5468 for the info regarding TW200.

 

[aldo5468]

Paul, there is a way to identify on the web what other bikes share a particular component, in this case, the m/c used on Yamaha TW200's, but it works for other parts shared by a particular manufacturer, as well. Go on a parts website like boats.net or partzilla. The first challenge is to find a motorcycle model that uses the part for which you're looking - we know Yamaha TW200, but from the "Front Wheel" fiches, early ones apparently used cable-actuated drum brakes, so try later model years until you find one that lists "Master Cylinder". Open the page that shows that fiche and parts list and click on the part number shown, in this case, 4GY-25870-02-00. That brings up another page that shows the different models and years the part was used - in this case, 2000-2004 TW200, TTR 250 and XT225.

 

[5twins]

From my research, it looks like this MC may be an 11mm, or at least that's the number stamped on it. That could be even better than a 10.

If I was in need of a replacement, I probably would try one of these smaller ones.

 

[Paul Sutton]

Aldo5468 - Thank you, I just tried it.

 

[5twins]

Here's the chart from the Vintage Brake site. I've marked the stock 650 sizes .....