CX500 GL500 650 Global

I have an issue with my master cylinder (MC) leaking at high altitude because of the angle of the reservoir after changing bars. I thought since I had to change my MC anyway I would try to get a better brake feel out of the deal. The modern bikes I have ridden only require 2 fingers to modulate the front brake, my CX requires a mighty squeeze with 4 fingers. I replaced the brake line with a stainless line and it did nothing to help.In my search for a replacement MC I came across this article on www.randakks.com it is in reference to the GL1000 which had a feel like the CX.....hard. The fix for better brake feel is a change in the ratio of the area of the MC piston to the area of the Caliper piston. Both bikes had a stock ratio of aproximately 9:1 and according to this article a better brake feel is achieved at 12:1 to 14:1. Here is a copy of the article:

The problem with the GL1000 front brakes is that the stopping power is excellent, but the lever effort is high and "feel" is quite poor. In fact, GL1000 front brakes are often called "wooden" by riders not familiar with these beasts.

Since I've spent so much time on GL1000 saddles over the years I've adapted to all this. I have normal hand strength, but since the GL1000 lever effort required is so high, I have used all 4 fingers for braking. On modern bikes I ride, I tend to use only 2 fingers for braking.

In the past year, I've considered and implemented many brake improvements on RC-003. After adding stainless steel brake lines, heat treated stainless caliper pistons, better rotors and stickier pads, I began to notice the severe limitations of the stock master cylinder.

The main problem with the OEM GL1000 front master is that the relative size of the master cylinder piston to the caliper pistons is wrong. The master cylinder piston is too large and hence under-leveraged. The 11/16" GL1000 master cylinder piston operates 2-38mm single caliper pistons. Comparing the area of the master piston (239.50 mm2) to the total area of the 2 caliper pistons (2268.24 mm2) yields a master cylinder/caliper piston ratio of 9.47. This is far from ideal!

See: Brake Ratio Chart courtesy of Michael "Mercury" Morse for more background on brake ratios. Michael is an absolute genius with vintage brake matters. He operates Vintage Brake a terrific source for vintage brake information. He is also a Yamaha 650 guru. Highly recommended!

As Michael points out:

"High lever effort and poor front brake feel is very common on '70-80s disc brakes. At the time, the general motorcycling public was not accustomed to the braking potential of hydraulic brakes and the manufacturers really didn't want to hear about locking the front wheel at 100 MPH. Plus, with rubber lines and flexy calipers, the "good" ratios would be perceived as wrong. We had always heard that you needed a very "firm" pedal (lever) from the automotive crowd. With the overly large master cylinder pistons, you don't notice the flex, feel the hydraulic switches, and they are not as sensitive to incomplete bleeding.

The ideal ratio for single-sided caliper pistons is in the 14:1 to 12:1 range. Combine "low" leverage ratios with sticky pads and unpredictable lockup is the result. The high effort require at the lever also results in undesired input to the bars. Disc and wheel diameters, as well as hand lever ratios must be considered as well.

Keep in mind that to a very large extent, leverage ratios are a rider preference item. I have two very fast customers, Daytona winners, that prefer 20:1, instead of my 27:1 preference (for dual-sided caliper pistons). Top modern racers will have a battery of pre-bled MCs on hand, depending on the rotor size and compound they have chosen for THAT particular track. "

No wonder GL1000 brakes feel "wooden!" After some experimentation, I've found a killer improvement for the GL1000. A modern Nissin 5/8" master cylinder absolutely transforms GL1000 braking to near-crotch rocket levels. This unit dramatically reduces lever effort and provides significantly improved feel. The lever is still quite firm, but not "wooden." Max braking near the threshold of lockup is much more predictable and easier to modulate. Best of all, I can now use 2 finger braking on a GL1000!

(I also tried a 14mm unit, but it was a bit over-leveraged. It transmitted a bit more line and caliper flex and felt too "squishy" for my taste.)

After fresh brake fluid and hoses, this is probably the best brake improvement you can make on a GL1000. The cost is reasonable compared to the time, effort and expense required to rebuild the 30 year old original master cylinder!

Here's the math for getting the CX into a 12:1 to 14:1 ratio:

The stock CX has a 14mm diameter MC piston and a single Caliper piston diameter of 43mm (according to the service manual) . So the areas of each are 153.9mm2 for the MC and 1452.2mm2 for the Caliper (area=pie x r2), and 1452.2 divided by 153.9 gives you a ratio of 9.4:1...not suprisingly, about the same as the origional GL brakes. In order to get the CX brakes to be in the ideal ratio of 14:1 to 12:1 you would have to find a MC with a piston diameter of 11.5mm to12.4mm. There are a couple available on Ebay sach as: http://cgi.ebay.com/ebaymotors/Front-Br ... 518e1bb79d

(The above link has a 12.7mm diameter (area of 126.6) which would give you a more favorable ratio of 11.4:1 still not perfect but closer. I'm sure someone could find one in that 11.5 to 12.4mm range that would be perfect. The trouble is most of the master cylinders available don't tell you what the piston diameter is. Let me know what you think, and if anyone has experimented with these ratios on the CX)

Interesting stuff.The UK CXs are all twin disc and with 20w fork oil in the forks.I have no issues with stopping power.Also if I have to use excess braking then I'm not riding correctly IMHO.

One of my CXs has old type CB900 brake callipers and that has increased braking power.They are a direct swap but still single piston.

Note:I improved my braking,power and mileage this year for free.I deliberately lost a stone and a half e.g 21 Lbs or 10x2 Lb bags of sugar

I'm not really talking about braking power. If I squeezed hard enough I could lock my front wheel. I am more concerned with braking feel and the pressure required on the brake lever for a given brake effect. I prefer the modern bike feel (lighter) to the vintage bike feel, and was wondering if anyone had found a solution to this. As far as fork oil; I have the 20W and fork dive is not really the issue I am addressing.

uprubicon14 wrote:I'm not really talking about braking power. If I squeezed hard enough I could lock my front wheel. I am more concerned with braking feel and the pressure required on the brake lever for a given brake effect. I prefer the modern bike feel (lighter) to the vintage bike feel, and was wondering if anyone had found a solution to this. As far as fork oil; I have the 20W and fork dive is not really the issue I am addressing.

I understand now.I have a,"Power Lever" on one of my CX,

http://www.bitzforbikes.co.uk/Front_Brake_Lever_%28Black_Power_Blade_Lever%29-ref-8113-155-96.html

but you have to get the ones for your master Cylinder and it's not easy to find them outside the UK as I helped another bloke in the US get some and he eventually had to get one from the UK.

Also there's are universal brake master cylinders that also have adjustable power levers.

So, you have achieved a lighter brake feel with these power levers without messing with the MC/caliper ratios? I like the price tag on those as opposed to a new MC. I still have the leaking brake fluid issue when riding over passes, so I still need to get a new MC with a level reservoir. I think I will try one of the Ebay ones...unfortunately, the ones that have the MC cylinder diameter I want come from China. For some reason I don't associate China with quality. I think I'll keep looking. My bike is at my Dad's place in Nevada (I'm in Minnesota) so, I'm not in any hurry anyway.

Yes,It brings the lever closer to the throttle grip but because of it's,"Dog-leg it doesn't sacrifice the action.The end of the lever where you hand grips is easier to pull.Some of the CX Brake Master Cylinders levers lever design were close to this.The one on my main CX is from a,"B" version although the bike is an,"A"from the ZAB range.It is Oblong MC with two screws.There were three types used over here.

Early type round(Z) screw top.
Oblong type with 4 screws(A)
Oblong type with two Screws(B) type.

You can see the differences on here,

http://www.wemoto.com/home/

put cx500 into the box and then check out the different models/levers.