Hydraulic Handbrake questions

[Mezzanine]

I made my Wilwood conversion over two years ago, and I am only now getting around to making my hydraulic handbrake. I'm making it difficult on myself as I want to make it all fit under the center console and appear stock, which is one of the reasons I've been putting it off. I've worked on it for the last few afternoons and have a nice bellcrank sort of linkage that allows me to use the factory handbrake lever and still successfully fit under the center console. The factory handbrake lever travels about 7.5" and my Wilwood 5/8" bore master has 1.5" of total travel without any fluid. This leaves me stuck with a 5:1 ratio of travel unless I'm willing to give up total travel on the master cylinder. Edited to add: I'm going out to the shop to get my brake handbook to figure out the actual ratio now... All I can tell you is the actual lengths of travel at the moment.

Questions for those of you with hydraulic handbrakes:

1. What ratio does your brake have? (measured from approximately the center of the handgrip)
2. What is the effective travel on your master cylinder in use? Mine is 1.5" without any fluid, and my handbrake can only just manage that full travel. I know that the effective travel will be much less once installed and "wet", but I need some idea how much less.

I'm pretty sure 5:1 isn't enough and I know I could give up some effective travel at the master to increase the ratio. I'm somewhat limited because of the whole bellcrank design and some clearance challenges, but if I don't need that whole 1.5" of travel at the master, I could easily change some ratios to get a little more mechanical advantage.

Use: I'm not looking for a full on drift brake. I just want it to serve as an E-brake and parking brake. Thanks for the help!

[Mezzanine]

OK, depending on how you measure the line of action on the handbrake itself, my overall ratio works out to be between 6.3:1 and 6.9:1.

Forgive the crappy photo and messy car. I'm doing all the mock-up in a parts car and it is kinda nasty in there. Everything you see is just mocked up and tacked aside from the bell-crank pivot mounts. I have not yet fabricated a mount for the master cylinder. That comes after I have the linkage all worked out.

[squaab99t]

OK, depending on how you measure the line of action on the handbrake itself, my overall ratio works out to be between 6.3:1 and 6.9:1.

Forgive the crappy photo and messy car. I'm doing all the mock-up in a parts car and it is kinda nasty in there. Everything you see is just mocked up and tacked aside from the bell-crank pivot mounts. I have not yet fabricated a mount for the master cylinder. That comes after I have the linkage all worked out.

Looking pretty sweet. Nice looking bushings. Might need some nylon or delrin washers between the linkage arms to prevent rattling and galling.
How much travel do you get on the master piston?

Crappy photo is right. Don't you have a degree in photography?

[Mezzanine]

Hey now, no need to bring up that crappy degree. I took the photo with my tablet as I typed my post, so circumstances were compromised to say the least. I have plans to post a build thread at some point. Delrin washers are definitely planned on the linkage.

As it sits now, I get exactly 1.5" of travel on the master cylinder, which is it's full throw. That is from handbrake fully down up to the last notch on the ratchet. There are twelve notches total.

I would prefer to be able to pump the whole stroke, if only to aid in bleeding the system. On that note, anyone have any experience bleeding one of these things? I expect it will be a royal pain to do. Should I put a tee with a bleeder in just downstream?

[squaab99t]

Hey now, no need to bring up that crappy degree. I took the photo with my tablet as I typed my post, so circumstances were compromised to say the least. I have plans to post a build thread at some point. Delrin washers are definitely planned on the linkage.

As it sits now, I get exactly 1.5" of travel on the master cylinder, which is it's full throw. That is from handbrake fully down up to the last notch on the ratchet. There are twelve notches total.

I would prefer to be able to pump the whole stroke, if only to aid in bleeding the system. On that note, anyone have any experience bleeding one of these things? I expect it will be a royal pain to do. Should I put a tee with a bleeder in just downstream?

Well it comes down to math. You know the bore of the master and slaves? Figure out how much volume you move with the 1.5" stroke. Assume incompressible fluid. Divide by the area on the slave and you should get the throw. I think you will have to divide that number by 2 since it is feeding 2 slaves.

[mrazekan]

What about adding some compliance to the system? Then you would not have to exactly match the stroke lengths. There are a number of ways to add a spring to provide enough force o compress the fluid & enough travel for the bleeding of the system.

[Mezzanine]

What about adding some compliance to the system? Then you would not have to exactly match the stroke lengths. There are a number of ways to add a spring to provide enough force o compress the fluid & enough travel for the bleeding of the system.

Please expand, I'm not sure I'm following. Are you suggesting I shorten the travel at the master (for instance) and then add a heavy spring inline that could make up the extra travel when the system is not loaded, i.e. when bleeding?

[MattWatson]

What about adding some compliance to the system? Then you would not have to exactly match the stroke lengths. There are a number of ways to add a spring to provide enough force o compress the fluid & enough travel for the bleeding of the system.

Please expand, I'm not sure I'm following. Are you suggesting I shorten the travel at the master (for instance) and then add a heavy spring inline that could make up the extra travel when the system is not loaded, i.e. when bleeding?

Why would you want compliance in a breaking system? The only thing I can see that adding is decreased cylinder travel until the spring is compressed then normal travel after that, which would make the required handle movement more for the same cylinder travel and less predicatable inital feel.

I guess you could add two pivots on the lever which would then allow you to full travel bleed, and swtich to the other for less travel for day to day use since you would never use 100 travel in normal use unless you had a massive leak somewhere... and then you are screwed anyway since it is sharing the lines with the brake.

As for bleeding, I believe Luke said he bleeds through it like it doesn't exist... so I don't even know that you need to worry about bleeding at all. I'll see if I can find that thread...

[Luke]

Yep, no need to have full stroke of the travel available, the in-line master is through-bled using the main master pedal master cylinder. There is very little stroke required because in a brake system you are not trying to "move" an object like with a normal hydraulic system, you are simply trying to multiply the force. The two opposing piston (slaves) are moving into an immovable object (rotor). So keeping in mind a small expansion of the brake hoses and lines, and the very small space between the rotor and pad that needs to be taken up each time the brakes are applied, the piston travel is actually quite small.
I was able to tuck a hydraulic cylinder with a long push rod under the metal "hump" between the rear seat footwells on a 99 once. With the console and carpet in place you couldnt even tell it was there.

[Mezzanine]

I like Matt's idea of two separate pivot options for set-up, but that got me thinking...If I don't have to worry about achieving a full stroke to bleed, then I am just going to make two different bellcranks that I can swap out easily until I find the right ratio. Besides, even if I did need full stroke to bleed, I could just disconnect the master at the heim joint and manually pump it.

Anyone want to suggest a ratio target? My google-fu has failed me. Luke, I imagine yours is a much higher (less effort) ratio, but can you tell me what it is and what size master you run?

[MattWatson]

I like Matt's idea of two separate pivot options for set-up, but that got me thinking...If I don't have to worry about achieving a full stroke to bleed, then I am just going to make two different bellcranks that I can swap out easily until I find the right ratio. Besides, even if I did need full stroke to bleed, I could just disconnect the master at the heim joint and manually pump it.

Anyone want to suggest a ratio target? My google-fu has failed me. Luke, I imagine yours is a much higher (less effort) ratio, but can you tell me what it is and what size master you run?

I think the ones I have been looking at for my car are around the 1:6 mark, which seems to be similar to the pedal ratios as well. But this will be for an upright rally setup.

What about checking your 'needed' movement in order to achieve lockup then setting that movement as your 2/3 or 3/4 point in your ratchet?

[Jordan]

I run a 5/8" master. It works great as a parking brake or fly-off handle. No problems through bleeding ( just make sure you have the lines hooked up properly, it is sort of counter intuitive). I think you guys are thinking too hard.

[Geoff]

I think you guys are thinking too hard.

ditto

[mrazekan]

What about adding some compliance to the system? Then you would not have to exactly match the stroke lengths. There are a number of ways to add a spring to provide enough force o compress the fluid & enough travel for the bleeding of the system.

Please expand, I'm not sure I'm following....

Why would you want compliance in a breaking system? ...

In cable actuated parking brakes, the multiple feet of cable introduce compliance in the system. The cables stretch as you apply more force. This is why you can continue to pull up on the hand brake lever even after the pads contact. That and the flex in the calipers etc.

With a hydraulic system, though there is still some compliance, swelling lines and flexing parts, it is reduced significantly.

Jordan and Geoff are right. We are over thinking this puppy. But, if it is a requirement to have long travel in the lever to improve the feel of the brake while still being able to go full stroke while bleeding it, a spring makes sense. Under normal use, part of the travel of the lever will be absorbed by the travel of a spring. If the spring rate is chosen properly, the load applied by the spring(s) to the master cylinder(s) would be sufficient to apply enough brake force. When being bled, the springs behave as a rigid member and you can full stroke the master.

But I do be live in K.I.S.S. If there is another option for bleeding then make the system as simple as possible. It looks like there is plenty of experience with doing this.

[Geoff]

This is what I use

http://www.cncbrakes.com/hsb.asp?grp=hsb&subgrp=all&series=412&subseries=

Simple, push and it applies brakes. Bleed straight through it.

The ratchet in the stock handle will be nice to lock it but it doesn't need to be too complicated.