Master Cylinder Ratio Chart

[Nerobro]

Now... there is a problem with smaller bore master cylinders. Scarily enough, it's possable to have to small of a master cylinder. For instance the stock master cylinder on a single disk GS550 won't move the calipers on a GS850 far enough to contact the disks, much less brake. The master cylinder off a seccond gen 550 will but the feel is off due to most of the lever travel being sucked up moving the pads. Though... it's easy to lock up the front tire. :-) My 80 550 is running 650 calipers with the stock MC.

I still need to get those measurements I promised....

[AOD]

Nero, you are right in what you said, but it's because you were moving calipers designed for two calipers (two pistons) to a bike with one caliper (one piston)

The ratio goes to hell at that point!

[AOD]

Bump to this topic....I've now had some experience with it to add a few comments.

While the brake work I did on the stock master cylinder, calipers, and stainless lines on the 1100E resulted in a nice firm lever, I still really never liked the feel.

This past winter I redid the entire front end on my '71 CB500F (both brakes and suspension) because it was shot. Based on my experience with the GS, I knew I wanted to use the stainless steel lines and Ferodo Platinum pads, but I wanted something different on the master cylinder, because the 'on/off' wooden feel of a large bore master cylinder is no fun.

I found a new aftermarket replacement master cylinder for a Kawi EX250/500/KLR650 on Ebay for a song, $40. I checked and the those Kawi bikes all used a single rotor brake system, so I knew I'd be very close with my CB500F, because it's a single disc too. (What I did not know is the caliper side for the EX500.)

I lost the email with the Kawi EX250/500 master cylinder bore size, but it's near 1/2" or slightly smaller and I imagine it will work fantastic on any single piston / caliper GS.

The result? Fanastic brake feel. I have to pull the lever a bit farther than before, which was almost scary at first (thought I had no brakes!) but once you're on the brakes you can adjust for ever so slight braking to full stopping power. It's awesome.

I encourage this upgrade to everyone, but it is going to require some work on your part to find the appropriate ratio to target and then the right master cylinder. Micheal Moore from Vintagebrake.com is a great source of info - call him up.







~Adam

[8trackmind]

Good job Adam!
I gave up on this thread a long time ago. Kind of gets old when everyone parrots the same SS line, brake pad song over and over. I guess it's hard to look at something old in a new way.

Heres where I ended up.







It's running Galfer SS lines from a Kawasaki ZG1000, sintered metal brake pads and a 14mm bore master cylinder off a single disk bike. It has very little lever free play and stops great.
I have at least 10,000 miles on this mod now, so anything that was going to fail, should have done so by now.

[robertob]

Cool brakes but that lower strap & spacers scare the crap out of me!

As for brakes this is all pretty well-known stuff. Any of the race car design books can walk you through the calculations.

Deceleration speed in gs is brake force at the contact patch times the tire's coefficient of friction at the road times area of the contact patch times tire lateral load (including the effects of weight transfer).

Brake force at the contact patch is pad friction times the diameter of the midpoint of the pad swept area.

Pad friction is pad friction coefficient (mu) times pad pressure.

Pad pressure is hydraulic pressure times area of pistons.

Hydraulic pressure is braking force from your hand times the lever ratio times the master cylinder piston area divided by the caliper piston area MINUS flex in the caliper mount, master cylinder mount and lines.

So assuming the same amount of "squeeze" from your hand:

Larger disc rotor: more brake force
Larger pad (radially): more brake force
Larger pad (circumferentially): less brake wear (no effect on stopping power)
Stickier pad: more brake force
More caliper piston area: less hydraulic pressure
More master cylinder area: more hydraulic pressure
Stiffer calipers: less wasted movement
Stiffer lines: less wasted movement
Stiffer caliper mounts: less wasted movement

Most people don't realize that multiple pistons are used to keep the disk rotor temperature more consistent across the surface as well as keep pad wear even. They allow you to run more piston area within the same pad width envelope.

[8trackmind]

Cool brakes but that lower strap & spacers scare the crap out of me!

Come up with something better and I'll use it instead.

[robertob]

You could have someone mill a nice flat bracket for not a lot of money. Use 6061-T6 or stainless steel if you want to make it really bulletproof. Or you could probably make it yourself out of a flat piece of stock and a drill press.

It's just that the more rigid the caliper mounting the better. Since the upper mount + spacer are not tied to the lower mount strap there is a lot of room for movement. The spacer gives the caliper a lever to bend the strap since the two mounting points are not in the same plane.

Add to the fact that it appears to be a piece of 1/8" CRS which has all the fatigue resistance of a coat hanger wire, you have a recipe for cracking.

I'm pretty anal when it comes to brakes but I understand that everyone has their own risk tolerance/pursuit of perfection level.

Come up with something better and I'll use it instead.

[8trackmind]

You could have someone mill a nice flat bracket for not a lot of money. Use 6061-T6 or stainless steel if you want to make it really bulletproof.

I haven't had any problems so far but...If it needs to be stronger, then I need a better bracket. Can you make one?

[robertob]

I haven't had any problems so far but...If it needs to be stronger, then I need a better bracket. Can you make one?

I could but only after I make mine I appreciate your work finding the calipers. I think Dan (salty monk) is doing the same conversion...

[8trackmind]

I could but only after I make mine I appreciate your work finding the calipers. I think Dan (salty monk) is doing the same conversion...

Next question: Would you make 'em?
I can give you the measurements. I'll even volunteer to test them for you. (since I seem to have no fear whatsoever)

[salty_monk]

Watch this space... I have the bracket design & some prototypes on the way. Once tested I'll feed back & we'll see how many others want them on here & Oldskool suzuki to see if it's feasible to get a big lot made up.
The prototypes I'm having made are Aluminium, they should be T6.
I may well have a set I can send you to test.

Your strap doesn't scare me as such... but you do need to keep an eye on it for stress cracks & I would be happier if it triangulated to the other bolt hole as well so stop any possible rotation.

What thickness did you use for the strap?

Dan

[8trackmind]

1/8 inch. Same as the caliper bracket itself. It has not moved, or cracked in the year they've been on there. All the real nasty forces are on the upper bracket anyway.
I was checking them daily for the first two weeks, then monthly. I've stopped the bike from 100 mph + occasionally, and from 70 mph daily. Nothing has happened. I trust them, but they are on the ugly side. Something that looked a little less homemade would be nice.

If you end up having some made, I would love to try a set.

[AOD]

It looks like someone made this really easy for us...

http://cgi.ebay.com/ebaymotors/FRONT-BRAKE-MASTER-CYLINDER-GS1000-GS1100-GS1150-VS700_W0QQcmdZViewItemQQcategoryZ35592QQihZ001QQitemZ110245374329QQrdZ1QQsspagenameZWDVW#ebayphotohosting

Back on page 3 of this thread I stated the GS1100E master cylinder was a 5/8" bore. Using the chart on http://www.vintagebrake.com/mastercylinder.htm with (2) 38mm single piston calipers, the ratio comes to 11.46.

Single piston calipers are much happier in the 14:1 to 12:1 range. Disc and wheel diameters, as well as hand lever ratios, must be considered.

A 14mm bore master cylinder puts you at a ratio of 14.73 - closer to the mark.

I'm pretty tied up with things now, so if someone wants to call Michael at Vintage Brake and run that by him, I think it will help confirm this replacement master cylinder is the real deal.

~Adam

[posplayr]

OK I did

so if someone wants to call Michael at Vintage Brake and run that by him,

We talked about it , he seemed a little distracted (he was trying to write up the order or pads). We also discussed surfacing the disks and as we were finally ending the conversation he lights up and said "wow you are really going to notice the upgrades". OK So now I'm really looking forward to it. \\/ Safety First :-D

83 GS1100ED brake upgrades
FERODO Sintered front
FERODO PLATINUM rear
Fresh surfaced rotors
New 14mm Master Cylinder (looking for someone else to verify)
New Slave cylinder kits

Existing SS lines

Posplayr

[AOD]

With 70% of the braking power coming from the front brakes...why not run the Platinum pads? It's what I used, they're better than Vesrah organic (Kevlar) pads for sure and stock Suzuki.

I don't have any experience with the sintered Ferodo. If Michael Moore says they're soft and sticky...I'd worry less about it.

~Adam

~Adam