One master cylinder for both?

[Drizzle]

I'm doing my best to keep the handlebars clean on my X and also I'm cheap. But I want to be safe and have functional brakes. So I was thinking, why not put in a double banjo on my foot master cylinder and run both front and rear brake off of it? I would probably put a proportioning valve on the rear disk to lower pressure some and I would only be running one disk up front. I have the the lever type master cylinder. Has anybody tried this and/or does it seem safe and effective?

 

[fredintoon]

I'm doing my best to keep the handlebars clean on my X and also I'm cheap. But I want to be safe and have functional brakes. So I was thinking, why not put in a double banjo on my foot master cylinder and run both front and rear brake off of it? I would probably put a proportioning valve on the rear disk to lower pressure some and I would only be running one disk up front. I have the the lever type master cylinder. Has anybody tried this and/or does it seem safe and effective?

Hi Drizzle,
my best answer is Yes, but - - -
You see coupled brakes on the big cruisers.
What they do to get around the two separate independent braking systems rule is to couple one of the dual front brakes and operate the other with a handlebar lever.
Legalities aside, a coupled proportion-valved set-up will work OK but perhaps not with that master cylinder.
Assuming your m/c is the right diameter to work the rear caliper it most likely won't be big enough to work a rear and a front caliper together.
Go to Vintage Brake's site to see 3M's chart on optimum m/c vs caliper ratios and pick a bigger one.
[edit] just re-looked at your pics, suggest you go with stainless brake lines and trust that you plan to add a fork-brace.

 

[Word Man]

Bad Idea. Without being able to regulate the amount of braking going to the back (as compared to the front), you will one day lock the real wheel and go down in a turn. Yes, manufacturers like Moto Guzzi have been linking brakes for a long time, but they are properly proportioned to avoid exactly the scenario described above. Finally, most modern big bikes with linked brakes are ABS.

 

[Brian902]

Proportioning valves are available.

Stock car guys use them all the time.

http://www.summitracing.com/int/search/part-type/brake-proportioning-valves

 

[pamcopete]

You have to be able to lock up the rear wheel with the rear wheel brake on a motorcycle and put the bike down when the only other option is to slam into the vehicle that just did a TIF and left you two car lengths to make a decision. That happened to me and the result was severe road rash but no broken bones.

 

[Drizzle]

Thank you for your advice. I do plan on replacing the lines with braided but am waiting on what size to make them. I am reluctant to put a brace on due to half the people with them say it's too stiff with them. Other half say they like them. Idk. Thought about getting one cause they look cool. As far as replacing the m/c, I welded tabs for it and would hate to cut them off and do it again. Brand new m/c darnit. I will take a look at the specs of my cylinder and look at that website you suggested.

 

[Drizzle]

You got the right idea but I think I found cheaper ones.

 

[Drizzle]

First off you should almost never brake in a turn. Gyroscopic momentum will upright the bike and you will run off a cliff like I did when I was a teenager. As for locking the brake up, I planned on utilizing a proportioning valve to lower pressure to the rear brake. I'm second guessing the idea though due to feel like you expressed earlier.

 

[Drizzle]

Eh? Add a m/c? What would the cable for it engage?

 

[Word Man]

You have to be able to lock up the rear wheel with the rear wheel brake on a motorcycle and put the bike down when the only other option is to slam into the vehicle that just did a TIF and left you two car lengths to make a decision. That happened to me and the result was severe road rash but no broken bones.

Do you honestly believe you can scrub off more speed using your body as a friction material that you can with good brakes and tires?

First off you should almost never brake in a turn. Gyroscopic momentum will upright the bike and you will run off a cliff like I did when I was a teenager. As for locking the brake up, I planned on utilizing a proportioning valve to lower pressure to the rear brake. I'm second guessing the idea though due to feel like you expressed earlier.

If you understand counter steering, you can brake in a turn. Yes, it upsets the suspension. Yes, you are correct insomuch as it is better not to. But yes, you can brake in a turn. But even in a straight line, locking the rear wheel at 70 is going to be damned hard to control. Especially when the side of that truck is coming at you fast.

And without a proportioning valve (or ABS system) to compensate for the rear wheel getting lighter and lighter as you brake as hard as you can, or unless you bias the linked system so much to the front that it is almost impossible to lock the rear wheel, a linked system is not going to allow you to stop as fast as a non-linked system.

I'm not trying to be a kill-joy here. It's your skin and bones. And I'm not necessarily the one to talk, I've definitely been known to ride in jeans and a T-shirt. But if it were my skin and bones...

 

[Word Man]

Here is a Moto Guzzi proportioning valve. Note how it has a mechanism that links to the swingarm so the amount of pressure to the rear wheel decreases as the back of the bike rises.

http://www.ebay.com/itm/98-Moto-Guzzi-California-V11-BRAKE-PROPORTIONING-UNIT-/200642110748?hash=item2eb733a51c&vxp=mtr

 

[fredintoon]

Ooh! I love meddling with other folks design concepts.
OK then, it's mostly about getting a clean look but the bike still gotta stop, eh?
How about this:-
use backwards levers like it was still 1927.
The backwards levers make it easy to hide the cables inside the bars.
The clutch cable still works the clutch like always and sneaks out from inside the bars someplace it don't show.
The cable from the brake lever also sneaks out and operates a hydraulic m/c that's hidden under the tank. My '74 BMW had a cable/hydraulic hybrid front brake like that.
The BMW also had a twistgrip with more parts in it than there were in the engine that allowed the throttle cable to run parallel to the bars rather than sticking straight out like everyone else's which would also tidy up the look.
Only one problem fitting a used BMW twistgrip.
The "we are BMW so we gotta be different" design mantra has them using 22mm bars instead of 7/8" (22.2mm) bars like everyone else.
Means you have to emery tape 0.004" off your 7/8" bar's surface to fit the bastard.
BTDT.
Takes effin' ages.

 

[jbenedict]

Compromise. Cable type front brake lever with the cable going under the tank to a master cyl and then the hydraulic line out and down to the front caliper. Less handlebar clutter like he wants.

This is the standard mechanism for BMW airheads from 69 to sometime in the early 80s. It works well. My only objection is checking of brake fluid. There is a float switch monitoring the level by lighting up a bulb in the gauges but the tank has to come off to top off the fluid.

It is not necessary to use the BMW twist grip and switches to use the undertank MC. Might have to make a custom cable but you should be able to use any cable-operating lever and twist grip you choose.

 

[Drizzle]

Yeah I'm not going with any of those ideas. Reversed levers wouldn't look right with what I'm doing and I don't want to add a m/c to the frame or whatever. I'm just going to put one on the handlebars and be fine with it. I am definitely keeping the rear brake on this thing. A lot of braking power can be utilized with the rear brake on these things. I almost never touch it on my sportbike. Thanks for the feedback though.

 

[jbenedict]

Yeah I'm not going with any of those ideas. Reversed levers wouldn't look right with what I'm doing and I don't want to add a m/c to the frame or whatever. I'm just going to put one on the handlebars and be fine with it. I am definitely keeping the rear brake on this thing. A lot of braking power can be utilized with the rear brake on these things. I almost never touch it on my sportbike. Thanks for the feedback though.

Cool. There are a lot of types and sizes of m/cs available so you have your choice of sizes and shapes. I certainly agree with having a rear brake.

Post some pictures when you get that far...