[QUOTE=type25;834208]Is the handbrake master cylinder using its full travel?

Or do you need to adjust the lever pivot ratio to get full travel of the cylinder?[/QUOTE]

Im not entirely sure i understand this. You dont want to use the full stroke of the cylinder. That would be like stepping on the foot brake. And having your foot go to the floor.

It isnt "bottoming out" if thats what your asking. When you pull it, it compress's approx 1/2 to 1/3 of its total travel. (I will have to measure the exact amount tomorrow) As it compress's, it gets firmer and firmer. Until it gets to the point where your arm cannot exert more force. If you use both arms (and i mean really heave on it), you can pull so hard on the lever that the whole frame and floor/dash area that its mounted to begins to flex. But even still the cylinder does not 'bottom out'. But there is no way youd want to try and pull that hard while racing.

If my master cylinder was going all the way to the end, then it could be too small volume to fill the caplipers (and flex in the lines, flex of the caliper body, fluid etc). Or it could be leaking internally. Or a hydraulic leak in the system. Or air in the system.

The adjustment that ive made on the mechanism, mainly adjusts the 'lever ratio'. (I can also adjust where the lever sits relative to the dash etc and how high/forwards the cylinder sits in the cradle etc)

When i say lever ratio, i mean basically changing the length of the lever from the fulcrum (pivot point) to the cylinder. Therefore changing the length ratio between the handle side of the lever to the cylinder side of the lever. This is effectively a force multiplication at the expense of lever travel. So i can multiply the force my arm exerts, but my arm must pull the lever longer.

[url]https://en.m.wikipedia.org/wiki/Lever[/url]

As in if i put 50kg of force into the lever, and my end of the lever is 5 times longer than cylinder ends side of the lever then i am actually exerting 250kgs force into the cylinder, but my side of the lever will move 5cm for every 1cm of movment. (Hypothetical situation.)

When i built my frame, i tried to replicate the ratio as best i could from the handle that came with the cylinder. I actually measured the distance from the pivot to the part that joined the cylinder and measured how long the handle was etc. I based my frame off that, but gave adjustments to go either way incase it wasnt spot on.





So i put force on the lever. This is multiplied by the the lever to give the force on the cylinder. This force is divided by the area of the cylinder. (Converting force into pressure). Pressure is carried down the pipes to the caliper. Pressure is them multiplied by the area of the pistons. (Converting pressure back into force) This force pushs the pads against the rotor. That force coupled with the friction of the pads coupled with the radius of the rotor is what brakes the wheels. That is the basics of hydraulic brakes.

The things i can change are :
The lever ratio. Tried that on both handbrake setups.
Master Cylinder size. Tried that when i changed to the STi cylinder.
Friction co-efficient. Not tried yet.
Caliper piston size. Not tried yet.
Rotor radius. Not tried yet.

The last 2 basically mean new brakes.

Can also change plumbing run and pipe diameter etc. But from a physics stand point, these should not change much. Longer pipe has more space to flex. Larger diameter pipe also has more flex too than thin pipe. Longer and larger pipe also holds more fluid volume which has some small amount of compressability. So in theory, you want the shortest and interestingly THINNEST pipe run you can have.

I cant see how changing the pipe runs, will change anything. UNLESS in doing so, im bypassing some unknown problem with the existing plumbing. Possibly additional restrictor or something?

I want the braking force to exceed the grip of the tyre.
So i could also go a less sticky tyre. Tried that. But not good for racing.
A smaller diameter tyre. Not really practical.
A smaller width tyre. Not really practical.
Less weight over the rear. Already stripped the interior and run on empty everywhere.

I had issues with a replacement hydraulic handbrake lever assembly that I quickly knocked up years ago.
Initially I wanted to have a fairly short throw on the lever, however I was unable to lock the brakes as easily as I would have liked, and had was getting quite a bit of tunnel flex. (The bracket and lever assembly itself was very rigid).
I then changed the lever/pivot ratio.
This resulted in being able to lock the rears easily with the trade off being more lever travel.

[QUOTE=type25;834213]I had issues with a replacement hydraulic handbrake lever assembly that I quickly knocked up years ago.
Initially I wanted to have a fairly short throw on the lever, however I was unable to lock the brakes as easily as I would have liked, and had was getting quite a bit of tunnel flex. (The bracket and lever assembly itself was very rigid).
I then changed the lever/pivot ratio.
This resulted in being able to lock the rears easily with the trade off being more lever travel.[/QUOTE]

Yes. I understand that principle. That is the first thing ive tried playing with. On the older twin cylinder setup, i modded it so that it had the most lever multiplication you could get. I shortened the cylinder side of the lever so much that the spherical rod ends on the end of the cylinders actually touched the pivot bolt. Still couldnt make that one work.

With the STi cylinder, i have 4 levels of adjustment and they still arent enough. But on the more extreme settings, the lever has way too much travel. Im sure in theory if i took it to the extreme and built a frame with an ever higher ratio it might work. But the lever/handle would be so long, and id have to pull it from the dash into the back seat area ro make it work. Like that old saying "give me a lever long enough and ill move the earth"

I dont think its a problem with the lever ratio. Im still thinking its more a problem with the area ratio of the master cylinder to caliper piston.

Changing the ratio of MC to caliper is a bit like changing the lever ratio. If you have bigger caliper, then the brakes work more per unit of force input, but the trade off is the MC travels further in order to fil larger calipers.

Bram...you have Brembo's on your car, yes? The setup you bought from me was fitted to STI Brembo's and worked perfectly...so theoretically it should be the same in your car.... there must be something different in the way you have set it up.
Did you chat to MMS?

Id be fucking the ABS off bud , thats the main difference . Have done at least 10 of these setups when I was at PBMS . None with ABS never had one issue . Done 2 of my old Datto 1600s no issue . S13 Silvia for a mate no issue . Tx3 turbo rally car no issue . Gemini using hydraulic drum brakes No issue .


None had ABS and None used the factory proportioning valve all had Willwood or AP manual adjustable valves.

[QUOTE=amtrapid;834222]Id be fucking the ABS off bud , thats the main difference . Have done at least 10 of these setups when I was at PBMS . None with ABS never had one issue . Done 2 of my old Datto 1600s no issue . S13 Silvia for a mate no issue . Tx3 turbo rally car no issue . Gemini using hydraulic drum brakes No issue .


None had ABS and None used the factory proportioning valve all had Willwood or AP manual adjustable valves.[/QUOTE]

It is something i want to avoid if possible. I cant say its not the problem until i either solve the problem elsewhere, or remove the ABS and it does or doesnt solve the problem.

But theoreticaly it shouldnt be the ABS. The important stuff is everyrhing between the HB MC and the rear brakes. Everything before the HB MC is effectively just a reservoir for the HB MC. Look at how a master cylinder works. They have an in and an out. The in is just a resivoir, the out is the circuit to the brakes.

I could unscrew and block off the input to the HB MC and just put a simple resivoir in its place, totoally bypassing EVERYTHING before the HB MC and i can guarantee it will still be the same.

The only issue i can see the ABS could have is because it has a individual circuit for each wheel, you need to use a twin/tandem MC, so you keep both sides independant. But, i am using a group n tandem master cylinder designed specifically for cars so they can keep diagonal split dual circuits (part of the group n regulations). So that should be a null issue.

[QUOTE=nauli;834220]Bram...you have Brembo's on your car, yes? The setup you bought from me was fitted to STI Brembo's and worked perfectly...so theoretically it should be the same in your car.... there must be something different in the way you have set it up.
Did you chat to MMS?[/QUOTE]

Yes. The brembo 2 pots.

If that is the case then it could only be one of a few things.

A plumbing issue. - i have plumbed it in an un-conventional way.
A pad compound issue. - i do have street pads, i would presume most race cars use race pads.
A lever/mechanism issue. I did try and replicate the important dimensions when i built mine? But who knows.

I havent spoken to MMS yet. I presumed they would be shut over the break.

Some more details on the lever ratios etc.

The original handle that came with the cylinder has 43mm from fulcrum to cylinder. And 300mm long handle to fulcrum. That is a lever ratio of 6.97:1 (basically 7:1)

My frame has 4 hole positions on the frame and 7 hole positions on the lever so can adjust quite a number of different ways. The shortest distance from fulcrum to cylinder is 40mm and the longest is 75mm. My lever and Hoonigan handle is 400mm long when at the 75mm hole and 435mm when at the 40mm hole. So that can give me a lever ratio of anywhere between 10.87:1 and 5.33:1. As said, i tried to replicate the ratio seen on the original handle and have adjustments to go either way.

[QUOTE=Bram;834225]Yes. The brembo 2 pots.

If that is the case then it could only be one of a few things.

A plumbing issue. - i have plumbed it in an un-conventional way.
A pad compound issue. - i do have street pads, i would presume most race cars use race pads.
A lever/mechanism issue. I did try and replicate the important dimensions when i built mine? But who knows.

I havent spoken to MMS yet. I presumed they would be shut over the break.[/QUOTE]

Bram, I would say either plumbing or mechanism.....