Incontinence of the master cylinder

[ambrose78]

Hey guys,

My existing setup one is a 12mm master with braided line and single brembo caliper. Prior to fitting the braided line and some more aggressive brake pads the braking could only be described as dreadful. Now it is ok but improvements are always welcome.

It has come time to say goodbye to the old master cylinder due to incontinence. It's leaking from everywhere so I'm intending to bolt on a new one to be done with it rather than try and hone, replace bits and hope to fix the leaks as a few posts have suggested this can be a futile exercise.

Looking at what is on offer there are 12, 13, 15 and 16mm master cylinders available. All priced the same.

Is there an advantage to put on a bigger master cylinder on?
Will it provide more effective braking?
Would it allow adding the second disc in the future?

Cheers

[Ben_Carufel]

Hey guys,

My existing setup one is a 12mm master with braided line and single brembo caliper. Prior to fitting the braided line and some more aggressive brake pads the braking could only be described as dreadful. Now it is ok but improvements are always welcome.

It has come time to say goodbye to the old master cylinder due to incontinence. It's leaking from everywhere so I'm intending to bolt on a new one to be done with it rather than try and hone, replace bits and hope to fix the leaks as a few posts have suggested this can be a futile exercise.

Looking at what is on offer there are 12, 13, 15 and 16mm master cylinders available. All priced the same.

Is there an advantage to put on a bigger master cylinder on?
Will it provide more effective braking?
Would it allow adding the second disc in the future?

Cheers

Pete, out of curiosity, what's a new master cylinder go for down there in Aussieland? I presume you'd get it straight from BMW?

[ambrose78]

I'm not even sure what the cost is here - I tend to just head over to motobins. I think at the moment they are about A$135 with the exchange rate.

[Barry]

With a single disc the bigger master cylinder will make the brakes worse in that you will have to squeeze the lever harder down to the reduced ratio of master cylinder area to caliper piston area. A smaller cylinder than stock might be better giving the same braking with less effort at the lever in exchange for a little more lever movement.

I think it's generally accepted that BMW were a bit conservative with Master cylinder / caliper ratios something about not wanting it to be too easy to lock the front wheel (some chance).

 Personally if sticking with a single disc I would go one size smaller on the master cylinder.

It's normal though to use a larger master cylinder piston with twin discs otherwise the brake lever may come back too far and if you are going to do this you will need something like a 15mm master cylinder which would be truly awful with a single disc so I think you would have to do both changes at the same time.

Not sure if this table includes our size of caliper pistons but it gives you an idea how much difference a change of master cylinder makes to the ratios. The chart comes from this web page http://www.vintagebrake.com/mastercylinder.htm where the author recommends ratios in the range 23:1 to 27:1 for opposed piston calipers.

Having done the sums on my single disc 36mm ATE caliper with a 13mm master cylinder we are way below at  a ratio of 15.3:1 which is why we have a very firm brake lever but have to pull relatively hard before anything happens.

The 12mm master cylinder fitted to 81 on single disc bikes gives a slightly better 18:1   

[montmil]

"incontinence"?   Have you tried Pampers, yet?

Monte

[ambrose78]

Thanks for the info Barry. Very informative.

So the lower the first number the heavier the lever? But if it gets too high the lever would be light without enough flow at the other end?

to match the vintage bike reccomendation - a 10mm should give around 25:1 - 26:1

So if I put another caliper and disc on the 16mm would be pretty nice with 20:1.

Think I might look around for a second disc, caliper and hose.


As for pampers - checked the packet and don't seem to be suitable for brake fluid.. good look though..

[bruce_launceston]

Hi Pete, my 84 LS has a 15mm M/C with twin Brembos, the 16mm may result in poor feel. I would stick with a 15 if you can find another disc and caliper.

Cheers Bruce

[ambrose78]

Thanks bruce.

So 15mm master for twins looks to be a goer more or less.

progress so far:
After a bit of net searching I can find a set of brembo calipers.
brand new discs are within reason from motobins.
The exisiting bolts on the wheels are long enough

My main concerns now are the hoses -
 I put on a nice 1 peice stainless steel line that runs to the existing brembo's tube

Is there a hose that can run from the top of the current caliper across to the additional caliper over the mud guard?

P.

[bruce_launceston]

I guess you could order one and a longer banjo bolt, some modern bikes do it that way. The standard R65LS twin disc set-up has a 'y' behind the headlight and 3 hoses. I got a set of 'HEL performance' braided ss lines for mine. They don't use the lower steel tubes. They run directly to the calipers from the 'Y' splitter. Refer to my photo album for pics. It's a pretty neat and simple setup. I swapped the hoses over with the bleed screws so that the hoses don't rub on the front guard.

I also fitted a set of 'semi floating' disc rotors from Munich M/C. $500 the pair and easily fitted yourself to the disc carriers (you will still need to buy two of these but rotor condition wouldnt be important as you grind off the rivets and throw the discs away). They are made in Italy by a company called 'Braking'.

Cheers

[Semper Gumby]

That is a pretty LS Bruce.

[ambrose78]

Hi Bruce,

How do the braking performance of the floating discs compare to the original jobbies?

I take it floating discs are compatible with the existing calipers?

Cheers
p.

[Bob_Roller]

I've got EBC steel semi-floating rotors on my '81 R65 and to be honest, I don't see any real difference in braking in dry conditions, but in wet conditions braking is greatly improved, but I think that may be due more to the EBC graphite pads that were installed when the rotors were installed .

[bruce_launceston]

I don't think you would notice much difference between the floating disc rotors and a pair of GOOD OE rotors but my rotors looked like the edge of a house key. They were badly ridged and had been from very early on. Always suprised me how well thay did work considering the profile. Maybe it was all the extra surface are lol.

I imagine their value is is being resistant to buckling or cracking from heat etc.

They were the same price as new OEM, looked good, and I thought I would use them instead of running the risk of my new rotors ending up like my original ones which I needed to replace.

Yes they are a direct replacement, just bolt them up to your original BMW disk carriers once you grind the top off the rivets and knock the pins out.

Cheers