Brake Lines

Complete 16th December 2006

The brakes on an RV-7 are hydraulic. I chose to install brakes on both sides, as I hope to share the flying with colleagues with right-seat pilot experience, and it just seems natural to me to allow for all possibilities. Images 1 and 2 show the setup for left and right brake-pedal assemblies respectively. Image 3 shows the left rudder bars with brake cylinders attached, ready for brake lines. The large black lines (image 4) run over the top of the rudder bar assemblies and connect with two angle unions which traverse the firewall. These will eventually supply the brake slave cylinders via lines down the gear legs. All the other high pressure leads are actually made from "Parker" plastic line connecting to brass angle fittings. Each line end has a small brass furrule that fits inside the line ID, and a tapered brass collar that fits over the lines. Image 5 shows one of these thinner white lines connected to the right master cylinder. When cutting these lines you have to be careful to allow enough length so that there are no repetitive stresses or wearing actions imposed as teh rudder pedals are moved throughout their full arc os movement. This is quite hard to get right. You do not want brake lines wearing and then leaking brake fluid inside the cabin. The final image on this page shows the finished result which seemed to work OK.

The next trick you have to learn is how to construct these plastic line end fittings. Image 6 shows some of this line and pairs of end fittings - threaded nuts, collars and ferrules. First the ferrule goes in the line. It helps to use boiling water (image 7) to soften the line first, and then you can puch the ferrule into initial position by hand (image 8).

1. left pedals

2. right pedals

3. left pedals

4. black main lines

5. connected

6. end fittings

7. Heat it first

8. Initial position

To get the ferrule all the way into the line, i pressed down on a wooden tabletop (image1). Image 2 show everything in position ready to attach to the brass angle connector. You have to PUSH the nut hard toward the end of the line to move it into a position where it will "take" on the connector thread. It is quite tough to do this. I tightened only one or two threads, and the torque required to do so suggested a good tight fit. I will test with brake fluid when the time comes.

The brake fluid reservoir is bolted to the right hand forewall on the engine side (images 4 and 5). You have to cut a hole 4 1/2" inboard for the plastic reseroir connector (image 5), and use washers as spacers so that the top lip of the reservoir does not foul the angled part of the upper firewall. Image 6 shows one of teh two (L & R, image 7) low-pressure plastic connectors to this fitting.

The final image shows the whole shebang completed. Note how the lines to master cylinders are all parallel and vertical, insuring minimum interference with each other as the pedals are moved.

1. push into line

2. all in position

3. brake reservoir.

4. engine side

5. reservoir connector

6. ready to screw in

7. cabin side

8. ready to go (stop)