Brake master cylinder - I don't know what I need to know...
Discussion
Peanut Gallery said:
Just my 2p worth!
The original system - 2 circuits, you mention one for the front, one for the rear - is it not one for Front Right and Back Left, the other for Front Left Back Right? - Yes, I fully understand that if they have been modified this may no longer be the case!
Is the "thing" going to be used on the road? - if so, please stop reading ... . . if not, do you need a dual circuit? - a single, larger diameter master cylinder might be small enough to fit into the gap, and you would not have to have balance bars etc.
I am not a brake expert in the slightest! (well, until I slammed on brakes when I only had my front left wheel doing all the braking - then I very quickly became an expert at swearing - Back right was greasy, the other circuit had popped a seal in the master cylinder)
No definitely front / back split as standard.The original system - 2 circuits, you mention one for the front, one for the rear - is it not one for Front Right and Back Left, the other for Front Left Back Right? - Yes, I fully understand that if they have been modified this may no longer be the case!
Is the "thing" going to be used on the road? - if so, please stop reading ... . . if not, do you need a dual circuit? - a single, larger diameter master cylinder might be small enough to fit into the gap, and you would not have to have balance bars etc.
I am not a brake expert in the slightest! (well, until I slammed on brakes when I only had my front left wheel doing all the braking - then I very quickly became an expert at swearing - Back right was greasy, the other circuit had popped a seal in the master cylinder)
Yes the thing is going to be used on the road lol. If it had been a few years earlier, it would have been single circuit from factory and that would both fit and work, but as you say, not something I'd want for the road!
Davi said:
The rest of the system is exactly as it was
The issue is not the master cylinder - that only defines the displacement. It is the rest of the system which determines the pressure resulting from that displacement.The front and rear slave assemblies are completely different, aren't they? So the chance that they happen to have identical pressure/displacement characteristics is effectively nil.
I'm confused / obviously missing something - if I'm not changing the slaves at all why are they a factor? They are currently fed by two 19.05 x 25mm MC,s, and when changed they will still be fed by 19.05 x 25mm mcs just side by side instead of tandem. Sorry I may well be being totally thick just failing to see what you mean.
At the moment, the front and rear circuits are driven from a tandem master cylinder. The tandem master cylinders I'm familiar with have a floating piston between the two circuits which means they run at equal pressure, but not necessarily equal displacement.
If you replace this tandem m/c with two separate master cylinders driven from a balance bar, that will also give you equal pressure but not necessarily equal displacement. So it's not a completely daft idea. But note that you would need twice the force at the pedal (and half the travel) for a given amount of braking, unless you increase the pedal leverage. Also note that tandem master cylinders have carefully defined failure characteristics which ensure that a failure in either circuit will not disable both circuits. You could achieve similar with a balance bar setup, but only if the balance bar assembly is designed correctly for your specific application.
If you replace the tandem m/c with two separate master cylinders locked rigidly together so they have equal travel, you now get equal displacement rather than equal pressure. That could be (and probably is) quite different to the behaviour of the original setup and could potential throw the brake balance way out.
The only situation where these two options produce the same behaviour is where the original setup you are starting from has both equal pressure and equal displacement on the two circuits. Since the pressure/displacement characteristics are determined by the hydraulic and mechanical design at the slaves, and these are completely different between front and rear, it seems very unlikely that both circuits happen to have identical characteristics.
If you replace this tandem m/c with two separate master cylinders driven from a balance bar, that will also give you equal pressure but not necessarily equal displacement. So it's not a completely daft idea. But note that you would need twice the force at the pedal (and half the travel) for a given amount of braking, unless you increase the pedal leverage. Also note that tandem master cylinders have carefully defined failure characteristics which ensure that a failure in either circuit will not disable both circuits. You could achieve similar with a balance bar setup, but only if the balance bar assembly is designed correctly for your specific application.
If you replace the tandem m/c with two separate master cylinders locked rigidly together so they have equal travel, you now get equal displacement rather than equal pressure. That could be (and probably is) quite different to the behaviour of the original setup and could potential throw the brake balance way out.
The only situation where these two options produce the same behaviour is where the original setup you are starting from has both equal pressure and equal displacement on the two circuits. Since the pressure/displacement characteristics are determined by the hydraulic and mechanical design at the slaves, and these are completely different between front and rear, it seems very unlikely that both circuits happen to have identical characteristics.
Ahhh okay now I see where you're coming from! I was told that the tandem system is equal displacement / pressure so couldn't work out what you meant, my bad! Accordikg to the info I have it's a single assembly front to back providing both circuits but I'll strip the original down and check tomorrow!
Davi said:
The Wookie said:
Risk of dodgy side loads if you don't get it perfect and no guarantee of equal pressure as with different compliance characteristics for the same travel you could easily get a situation where one master cylinder is receiving more force than the other, hence more pressure
The actual manufacture of the pedal assembly is one thing I will have to be careful of, for sure. I'm using most of the original assembly, all I need to do to facilitate the change is shorten the bearing tube on the brake lever in the mill and reinsert the brass bush, the balance bar will then replace the clevisGassing Station | Suspension, Brakes & Tyres | Top of Page | What's New | My Stuff