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I am currently playing with a '75 R90/6. I'm thinking of going to a handlebar master cylinder.

Is there any consensus on what size Mastercylinder to use with the 40mm ATE brakes

Motobins seem to stock a variety of sizes from 12mm to 16mm

Thanks Charles

Have you already tried the /6 (single disk) under tank MC with the (2) 40mm ATE's?

George,

I have not tried that option, but even over here good condition ATE M/Cs are not cheap.

Charles

I thought maybe the '75 R90/6 had one.
If you are an agressive rider and like to rush the corners, brake hard and turn in, I would go for the 12 or 13 mm mc to give maximum hydraulic advantage. You will have a little more lever travel than with a 15 or 16 mm mc.

well thats not true

my undetank 13mm is a stopper and my lever does this with no extra work or lever work

all action to lock up is under 1" of travel

Could be the Honda pistion that still working, I used over the german one that leaked

George Ryals wrote:Have you already tried the /6 (single disk) under tank MC with the (2) 40mm ATE's?

I still have my original MC that came with the single brake. Are you saying that using that one will give me more brake than the one for the two brakes?

Chuey

Chuey wrote:

George Ryals wrote:Have you already tried the /6 (single disk) under tank MC with the (2) 40mm ATE's?

I still have my original MC that came with the single brake. Are you saying that using that one will give me more brake than the one for the two brakes?

Chuey

Yes.

Hydraulics are based on the ratio between the surface area of the master cylinder piston, and the surface area of the slave pistons. A M/C that has a poor ratio with the single caliper, will have twice the mechanical advantage with two of those calipers. In a well designed brake system, doubling the slave area would lead to a ridiculously sensitive brake, but, since the original BMW ATE brakes were rather anemic and wooden, it's possible that the crappy ratio with the stock M/C and one caliper might be quite effective with two calipers.

with my first BMW I found with the 38mm, I had like was said two wooden blocks

but as the stock hose was rotten, I replaced with steel braded that went a long way and changed the stock for a set of aftermarket maybe a SBS or Metal splinter pads

and I got a better working disc, later with my Second BMW when I tried the same set up but with a 40mm, I felt who needs a second disc with such a nice brake.... But then I found the pieces to go to mags and a second disc with a second 40mm I could't look back

So, where should Charles go to buy his master cylinder when he figues out what size he wants?

(Sly way to ask my question without bending Charles' topic. It's time for me to upgrade the brakes on my '76 R75/6)





Ken

chasbmw wrote:I am currently playing with a '75 R90/6. I'm thinking of going to a handlebar master cylinder.

Is there any consensus on what size Mastercylinder to use with the 40mm ATE brakes

Motobins seem to stock a variety of sizes from 12mm to 16mm

Thanks Charles

Chas, I used a 13mm h/b unit for my bike. It has 40mm Ate calipers too. I'm very happy with the brakes.

P.S.
Henry says hello!