Brake Line Fittings

[bshawco]

From KAI Section 5.22:

"Install compression fittings to plastic tubing using the following steps:

Step 1: Drill #29 the inside of the tube."

I followed this directive and found the brass inserts fairly easy to insert to the plastic tube.

Step 4 implies that the insert should be difficult to install and probably requires putting the end of the plastic tube in boiling water to get the brass insert fully installed.

Am I making a mistake in drilling out the ends of the plastic tubing that will result in leaking brake fittings?

[Scott Hersha]

Brad,
I think if you’ve followed the company installation directives you’ll be OK. When I did mine, I didn’t have that specific instruction, and it was difficult to get the insert in the tubing even after heating it up. I’m guessing the wall thickness on my stretched tube ended up being similar to your reamed tube. The ferrule on the compression fitting doesn’t care what the diameter is as long as it fits, because of its tapered design. It just needs to squeeze down on the plastic tube strongly enough to seal it under system pressure. I hear what you are saying about possibly weakened wall because you’ve removed material, but the the end result is the same with one that is stretched under heat and pressure. The only difference I see is that the way you did it is easier. Just don’t ream the ID past where the insert will rest.

[pazmanyflyer]

Originally Posted by bshawco

From KAI Section 5.22:

"Install compression fittings to plastic tubing using the following steps:

Step 1: Drill #29 the inside of the tube."

I followed this directive and found the brass inserts fairly easy to insert to the plastic tube.

Step 4 implies that the insert should be difficult to install and probably requires putting the end of the plastic tube in boiling water to get the brass insert fully installed.

Am I making a mistake in drilling out the ends of the plastic tubing that will result in leaking brake fittings?

No your not. It's a mix of old and new instructions. The old way was to soften the plastic in water so that the insert will go in. The newer way is removing a touch of material for the insert to go into place. The compression fitting will take care of the seal.

[TS Flightlines]

But the idea is to get the ferulle to compress the tube against the insert to form the pressure sealing. Having a larger ID, or thinner wall provides some 'clearance' or a slight 'void' space between the liner wall and the insert. All things being equal, the ferulle will compress to a known dimension, so the ID of the ferulle will compress similarly. If the ID of the tube has been changed by drilling, so does the the amount the ID will compress against the insert.
It may still be enough to hold pressure for the brakes to work, but after continued pressure cycles it will eventually start to leak.

Be carefull. Mixing and making OR changing the specs will change the way things work.

Tom

[KEG]

Van's instructions are clear regarding the initial tightening of these type fittings (one turn past finger tight I believe). Is there a spec for retightening if you have to disconnect the tubing?