Wednesday, November 5, 2014

Brake Line Install Begins - Parking Brake Aft

Because of the instillation of the Matco parking brake, the measurements  shown in the plans no longer applies for the length of brake line tubing required to run between the parking brake and the inboard landing gear attach brackets that the brake lines connect to. This required locating the powder coated U-1203 inboard landing gear attach brackets and temporarily setting them in place so a true measurement can be made. Prior to mounting the gear attach brackets for the brake line measurements, two brake line fittings were installed in each mounting bracket using Loctite 567 thread sealer. The F179CA-4-2 fittings are 45 degree elbow fittings and require being clocked to a 45 degree angle when installed into the U-1203 inboard landing gear attach brackets.
Installing the 45 degree elbow fitting into the inboard landing gear attach brackets.
Both U-1203 inboard landing gear attach brackets with the F179CA-4-2 elbows installed and clocked to 45 degrees per the plans.

After the inboard landing gear attach brackets were readied, the poly brake tubing that will run through the center tunnel from the Matco brake into the center channel was fished through the center channel. An excessive amount of brake line was pulled through the center channel so the brake line could be pulled out the side of the fuselage to make installing the pesky fittings easier.

Installing the compression fittings on the poly tubing is not a piece of cake and ultimately took up a good amount of time to get it ironed out. Unfortunately (well not for Pete), Pete’s RV-9A did not use the poly tubing supplied by Van’s for the brake lines … his RV-9A has all custom built brake lines. As such, I did not have any first hand experience installing the pesky brass inserts into the poly tubing. Van’s suggests soaking the poly tubing in boiling water then installing the brass insert onto the tubing. This method may or may not work, but I have heard folks on the forums complaining that it is still not that easy. However, not having boiling water at the hangar required coming up with another method. To that end, experiments were made on heating the tubing gently using a heat gun on the low setting, but I was not overly impressed or completely happy with the results … so decided to investigate other options. Lacking boiling water, the best overall solution appeared to be spraying a little CorrosionX on my finger and working a drop inside the tubing to coat the inside and waiting until it migrated about 1/2" inside the tubing. A small film of CorrosionX was also placed on the brass insert that is placed inside the tubing … the brass insert prevents the tubing from deforming as the compression fitting is tightened. Those familiar with CorrosionX know it creates a very thin slick film that migrates … a little drop goes a long way.

The brass inserts that are pushed into the poly tubing which prevent the tubing from deforming as the compression fitting is tightened.

After a little CorrosionX was placed in the tubing and on the brass inserts a steel back riveting plate was used to press the brass sleeve into the tubing. Still not a piece of cake but overall this worked well.
Pressing the brass insert into the poly brake line tubing by pushing down on the metal plate.
The brass insert fully seated into the poly brake line tubing.

To facilitate sliding the nut and sleeve for the compression fitting over the area of the brake line tubing with the brass insert, a thin film of CorrosionX was placed on the outside of the tubing then a small open ended wrench and mallet was used to tap the nut and sleeve down over the brass insert until the compression sleeve is 1/8" from the end of the tubing per the plans. Overall this went well and did require very much tapping to slide the nut and compression sleeve into position. Don't forget to inspect the inside of the fitting to insure none of the poly was scraped off to possibly interfere with the proper seating of the fitting.
Gently tapping the compression fitting nut and sleeve down over the area of the tubing with the brass insert by using an open end wrench and a small mallet.
Finished compression fitting for the inboard landing gear attach bracket end of the brake line ... note the sleeve is 1/8" from the end of the tubing per the plans.

Some may wonder about possibly contaminating the brake fluid with the CorrosionX. For starters just a very small amount was used (only enough to put a thin film on the desired areas) and the decision has been made long ago to use synthetic transmission fluid as the DOG Aviation RV-12’s brake fluid … either Moble 1 or more likely Amsoil because it has a higher flash point of 453 degrees … which is a good thing. I truly don’t think any slight CorrosionX residue left behind will affect a synthetic ATF by the time the lines are flushed of possible debris and air during the brake bleeding process. Plus, in a pinch on a Sunday night, it will be far easier to locating a synthetic transmission fluid than it is to locate aircraft brake fluid.