Master cylinder specs

[Zzz]

I realize the Gerdes master cylinders from AviPro are recommended/preferred, but I'm having trouble finding the specs on them. Can anyone provide the specifications for the pin-to-pin length and required stroke? It seems like the dependent factor is the design of the BH brake pedal, this would be well documented but it's not called out on the plans.

I could measure the brake pedal travel I suppose but this seems like something users who've installed and tested their brakes would readily know.

Also, I assume the remote reservoir is required because of clearance limitations? Or is it just because those gerdes cylinders don't have an integrated reservoir?

Thanks.

[Mark Goldberg]

The pin to pin length is somewhere around 8". With no pressure on it. These Gerdes new/surplus master cyls do not have internal reservoirs. They require a remote reservoir. They have been pretty good Zane. I believe the most anyone has had to do is replace some o rings. Mark

[fly_n_low]

I use the reservoirs from ACS on the Gerdes cylinders. You can see them in the background in this pic. They work fine and save plumbing.

http://www.foxflier.com/bearhawk/2011/Aug11/P8110024.JPG

[Zzz]

Thanks fly_n_low. I like your firewall blanket. I will have to pick your brain on that later.

The important question for me is actually the pin to pin length of the master cylinder. I know Mark said he thinks it's around 8" but I've seen cylinders in lengths 7.25, 7.5, 7.88, and 8.00". Those are all a little too close to guess.

I've got my rudder pedals set in the fuselage, with brake pedals attached, and measured the distance from the master cylinder lower attach to the brake pedal cylinder attach. It can vary based on what default angle I'd like the brake pedal to rest at in relation to the rudder pedal.

What is the exact Gerdes cylinder model or part number?

Thanks.

[Mark Goldberg]

At the top of the master cylinders is a little clevis end of 7075 AL that we have made. If left at full length the pin to pin is 8". But that clevis end can be cut down which is done as a matter of course on the Patrol and LSA. I think most are leaving it full length on the 4 place. Just a tiny bit of history - Bob designed the plane around the "long shaft" Gerdes. Those are all gone. But with the aluminum clevis end the "short shaft" Gerdes is brought up to the same length as the long shaft. Both have plenty stopping power. Mark

[Zzz]

Thanks Mark.

[Battson]

I've got my rudder pedals set in the fuselage, with brake pedals attached, and measured the distance from the master cylinder lower attach to the brake pedal cylinder attach. It can vary based on what default angle I'd like the brake pedal to rest at in relation to the rudder pedal.

Hey Zane - for what it's worth, I strongly suggest sticking with Bob's measurements per the plans, when it comes to the pedals. I found out the hard way, this arrangement is temperamental and all the lengths / angles need to work together for the whole system to work correctly at full deflection...
The brake pedals can over-cam and lock up the whole pedal assemble if you reposition anything or change the angles / lengths without doing the reciprocal changes to the other parts, which practically means re-welding stuff. Also, you will need to position the pedals as Bob describes in the plans to get full travel.
Just my experience, if you are dedicated to modifying the system I am sure it could be made to work. Otherwise the plans are always your point of reference.

I had an (unlisted) YouTube I would share which shows what I mean, but YouTube wants to play hard-ball right now...
Nevermind - tricked it (I will never surrender to Google+) https://www.youtube.com/watch?v=n_uk9o2N2zQ

With the master cylinders you can get with the kit, you do get minor adjustment with the threaded clevis ends. Overall the brake pedal angle changes quite a lot as the rudder pedals travel anyway.

[Zzz]

Jon, I don't want to modify the system. I'm just looking for an appropriate substitution for the Gerdes cylinder, and nowhere can I find a spec on the pin to pin length. Do you see it on the plans?

[Battson]

Jon, I don't want to modify the system. I'm just looking for an appropriate substitution for the Gerdes cylinder, and nowhere can I find a spec on the pin to pin length. Do you see it on the plans?

I think the plans are drawn to scale?

[Zzz]

I think the plans are drawn to scale?

Doh. Good point. Need to dig out my drafting scale. Or my calculator.

[Phil Leeder]

Hello I'm a mechanic and I would like to worn you guys about those particular brake master cylinders. the return spring has a wide end and a smaller end. The smaller end goes towards the piston. If you make a mistake the result will be dragging brakes. Reason for that is the one way o-ring valve set up is not re-leaved> the ram / piston appears to make full travel as in up and down. But the pressure held by the o-ring is not being released. If your playing with a tail drag-er be-careful. Nothing quite like a surprise like a locked up wheel during a landing.

[Phil Leeder]

Pin to pin. I will be pulling some cylinder out of a lake anfib tomorrow however as I remember it that bird has threads and a adjustable spacer for connecting to the tow brake pedals. Not just that but the static base pivot point is narrow maybe 3/8 inch thick. Not round like a Cleveland master cylinder maybe 5/8 diameter.
Tell you what I remember years back trying to get away from the original north American T6 brakes and wound up using some cylinders out of an old bomber. I just don't remember that much about it anymore. But I remember they look just like what you want. We got them brand new surplus cheap. I'll check and see just what we did for that confederate airforce T6 mucked up like a jap val dive bomber. Oh and now there called the ghost squadron. I hope that's not political. Didn't mean it as such.