Straight Cessna 170 project

[IdahoPilot]

Hey, Just thought I would post some pics and show everyone the progress we have made so far on the 170 project in my school. And see it as a whole.

The windshield is in permanently, and all exterior lighting is wired up and ready to go. I just finished building new flexible brake lines, and rebuilding the master cylinders. And the pedals are in. Next we are going to install the headliner, and remove unneeded wiring as we will not be installing radios at this time.

Any input would be appreciated. Thanks

Totally forgot to post the pictures. They are on flickr at this address.

http://www.flickr.com/photos/pilot89/67 ... hotostream

IdahoPilot

[n2582d]

It looks like you're making good progress on the 170! One word of caution though. I saw in your pictures that the 170 you all are restoring has the old style serrated shaft master cylinders and that the parking brake cables are still there. I'd encourage you to show your school instructors this link concerning the serrated brake master cylinders and the parking brake. This is just one of many links on the subject. Just do a search on this site using "parking brake". The owner of the 170 would be well advised to update the master cylinders and get rid of the parking brake system all together. Unless of course the school needs more rebuild projects!

[IdahoPilot]

It looks like you're making good progress on the 170! One word of caution though. I saw in your pictures that the 170 you all are restoring has the old style serrated shaft master cylinders and that the parking brake cables are still there. I'd encourage you to show your school instructors this link concerning the serrated brake master cylinders and the parking brake. This is just one of many links on the subject. Just do a search on this site using "parking brake". The owner of the 170 would be well advised to update the master cylinders and get rid of the parking brake system all together. Unless of course the school needs more rebuild projects!

I checked out your link. Holy cow! I may have to talk them into removing the cables. I was thinking this system was a little sketchy.

[Bruce Fenstermacher]

IdahoPilot,

While I noticed your ring shaft master cylinders it just occurred to me the advice you are being given about the parking brake cables is not quite correct. You see the ring shaft master cylinders use a completely different system to engage the parking brake than the trouble parking brake system. The ring shaft type system can not be activated accidentally as the newer system can be.

Compared to those that have the later smooth style master cylinders there are few today who have the ring type master cylinder and so many of the folks familiar with the 170 may have never seen the parking brake system for them and assume it is the same as the troublesome system for the improved smooth shaft master cylinders.

SO.. the good news is there is no trouble leaving this parking brake system intact. In fact I have one which is why I'm familiar with it and mine is still and will remain connected.

Now the bad news. There is a Service Bulletin (SB) that suggests those ring type master cylinders should be replaced by the later design smooth shaft master cylinder. It seems they had a tendency to snap at the rings. Now as a SB is not mandatory but it should be considered. My partner and I are not replacing our ring shaft master cylinders. He has been flying the airplane with these for 45 years and sees no reason to change them now. I personally don't feel it an airworthiness issue because brakes shouldn't be used in the flight and I can't see how if a shaft broke while in flight it would be an issue. Of course I could be somewhere and it be very inconvenient taxiing should a master cylinder shaft snap.

If you should decide to replace the master cylinders with smooth shaft master cylinders DO NOT install them with the levers on them that the parking brake cables attach to which means the parking brake system can not be active. It is these levers that are activated by the firewall, not the cables or the fact the cables are attached to them though the cables being attached may aggravate the accidental activation of the system by the fire wall.

[IdahoPilot]

Idaho Pilot


If you should decide to replace the master cylinders with smooth shaft master cylinders DO NOT install them with the levers on them that the parking brake cables attach to which means the parking brake system can not be active. It is these levers that are activated by the firewall, not the cables or the fact the cables are attached to them though the cables being attached may aggravate the accidental activation of the system by the fire wall.

So what is the difference between the notched type and ring type? I understand its the lever on the master cylinder that causes the porblem. But what makes this type safer?

[Bruce Fenstermacher]

First, I would call the ring type and notch type one in the same. There are rings around the master cylinder piston shaft which form notches for a flat metal lever to be slid into. This is spring loaded in the off position and moves perpendicular to the piston shaft by the cable being pulled to engage a notch in the piston shaft and hold pressure in the master cylinder. The levers are not in a position nor to they protrude far enough to be pushed into engagement by the firewall.

On the other hand the later smooth shaft master cylinder parking brake lever has the piston shaft passing through it, is pinned on one side so when it moves in the direction of the piston shaft , it jambs the shaft which then holds pressure in the master cylinder. These levers are designed to exit off the front of the master cylinder and they protrude far enough that in extreme cases they can contact the firewall environment. The motion of the pedals with the contact to the firewall is in the direction required to activate the lever and jamb it on the piston shaft holding pressure in the master cylinder.

From 10 feet away with a casual glance one might think the systems are the same, but they are not. Looking at the 170A IPC page 42 shows both systems and their different parts for the parking brake lever. The ring type is on the top for the earlier serial numbers and the smooth shaft on the bottom from later models.

170A IPC PG 42 MASTER CYLINDERS.png

PARKING BRAKE LEVER TO BE REMOVED.jpg

Here is the lever part that needs to be removed from the later parking brake system in order to remove the problem with unwanted parking brake activation. Just disconnecting the cable will not solve this issue.

[IdahoPilot]

First, I would call the ring type and notch type one in the same. There are rings around the master cylinder piston shaft which form notches for a flat metal lever to be slid into. This is spring loaded in the off position and moves perpendicular to the piston shaft by the cable being pulled to engage a notch in the piston shaft and hold pressure in the master cylinder. The levers are not in a position nor to they protrude far enough to be pushed into engagement by the firewall.

Ok. So the ring type is safe then. The actuating lever on them will not contact the firewall and cause serious damage? Whew. That's a load off my mind.

[GAHorn]

[..Ok. So the ring type is safe then. The actuating lever on them will not contact the firewall and cause serious damage? Whew. That's a load off my mind.

The early brake master cyl rods are not safe. They have been known to fracture and fail, and in some cases have locked the brakes during landing-brake applications when they jam. This was also described in the old SRAM book the assoc'n produced many years ago. (One of the few reliable reports in that book, as I recall.)

You should plan to replace the old cylinders with new style, and do not retain the parking brake assy. IMO.

[Bruce Fenstermacher]

..Ok. So the ring type is safe then. The actuating lever on them will not contact the firewall and cause serious damage? Whew. That's a load off my mind.

The ring type PARKING BRAKE SYSTEM is safe because it is not the same system used that does cause a problem.

As I've pointed out there is a SB to remove the ring type master cylinders. George and others have and will advise you to replace them. I've already told you my partner and I have decided they are safe enough for us.

Now let me qualify my last sentence. Over the last 12 years I've probably looked at about 300 or more different 170s. I can count on one hand how many I've seen with the ring type master cylinders still in use including mine. Not one of these owners knew there was an issue with the ring type master cylinders or maybe I wouldn't have even seen them. I can't say how many of those I saw have now been replaced but I do know at least one owner said they were safe enough for him and he would not be changing them. So with the opinion of a huge lot of 3 people I know of that think the the ring type are safe for them, I'm not about to tell you they are safe for you. You will have to decide.

[IdahoPilot]

Ahhh. Its all making sense now. I will have to talk to the instructors and see about replacing them. And look up the SB on it. Thank you so much for the info!

[IdahoPilot]

Pushed her out today and did a couple runs. I am attaching some pictures outside, so you guys can see the 170 in the light and a full pic, instead of little parts.


http://www.flickr.com/photos/pilot89/67 ... hotostream
http://www.flickr.com/photos/pilot89/67 ... hotostream

[IdahoPilot]

Latest pictures after reassembly of engine, fabricated new baffle attachments and cowling test fit.

http://www.flickr.com/photos/pilot89/81 ... hotostream
http://www.flickr.com/photos/pilot89/81 ... otostream/
http://www.flickr.com/photos/pilot89/81 ... otostream/
http://www.flickr.com/photos/pilot89/81 ... otostream/
http://www.flickr.com/photos/pilot89/81 ... otostream/
http://www.flickr.com/photos/pilot89/81 ... otostream/
http://www.flickr.com/photos/pilot89/81 ... otostream/