Brake Hoses

I needed to replace the dead brake hoses at the rudder pedals. The parts are cheap and the process is easy enough. Aeroquip has a sheet you can download which shows how to assemble 303 hose and fittings. The EAA also has a nice video. I realized after I got the parts that I don't own a mandrel for assembling 1/4" hose. It's easy enough to pay a local A&P shop to assemble and test the hoses or buy ready made hoses. I wanted to assemble the hoses. Everything I read on line said that the do it yourself mandrels you can buy (about $80) are too small a diameter to hold the hose open well during assembly.  They make them undersized to fit well in used fittings for disassembling old hoses. The solution was obvious, make my own mandrel.  I got out my box of drills and used them as plug gauges to find the inside diameter of the hose fitting, 0.170" goes, 0.172" is a no go.  McMaster-Carr has 36" sticks of drill rod for about $3 so I selected 0.168" rod to make the pin for the mandrel.

 I cut off a piece of rod about 6" long.  By chucking it in the drill I tapered about 3/4" on one end with the belt sander and then polished it.  For a holder I got a 1/4" AN 815 union out of the recycle bin as well as an AN818 Nut and AN819 Sleeve.  It took some light pounding to drive the pin through union.  The ends get squashed down when the fittings are tightens installing the lines in use.  This same idea was used to with the nut and sleeve to squeeze the one end to hold the pin in the union.

The tape on the hose is so I can see how long I need to cut the other end of the hose to get the same length hose as the old hose.  It also allows me to see when I'm done that the hose is still fully in the socket.  For a small hose like this it's easier to use a socket wrench to screw the socket onto the cleaned up end of the hose.  I use the belt sander to get a nice clean square end and blow the debris out when done.  Remember the socket has left hand threads, snug it down and back it off 1/4 turn.

My camera caused this picture to rotate. I've turned off auto rotate so it won't do this again.  The important thing here is I use some assembly oil, it's supposed to be slicker, to lubricate the inside of the hose and the threads on the nipple so it doesn't gaul the socket.  After you tighten the nut and nipple on the mandrel oil the mandrel pin.  You'll need to clean the the oil off the mandrel before you do the next fitting because the nut has to be tight enough not to spin while screwing the nipple into the socket. I also rinse out the hose when all done with a little mineral spirits.  The oil is green so it's easy to see when you've rinsed it clean.  A couple tablespoons of spirits will clean from each end.

Push the mandrel into the hose and hand thread the nipple into the socket as far as you can so you're sure the threads are engaging well.  Then just wrench it in to leave the right gap, 1/32" - 1/16", between the nut and socket.

The fittings add 1-1/16" to the length of the hose so wee need to cut the other end 1-1/16" short of our 11" length needed.

With a short hose like this it's easy to look through it to make sure there is no bulge or cut flap in the inner hose.  These 2 came out great.  Now I just need to pressure test them and we'll have 2 excellent "Owner Produced Parts" to install and so note in the log book.  Good fun!