Topic: Double disk front master - all suggestions welcome

[Viktor.J]

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]

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]

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]

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]

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]

^^^ 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]

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]

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]

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]

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]

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]

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

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]

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.