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MGTF1250Dave
11-06-2003, 09:36 PM
Aloha All,

What is the general thinking on using teflon tape on the threads of brake line connections? I've not seen any evidence of it use when I've taken them apart, so I've never used it when reassembling the fitings. Just wondering if this could cause any problem or if it would be advantagious? Does anyone have an opinion?

Safety fast,
Dave

PC
11-06-2003, 10:01 PM
Teflon tape and other forms of "pipe dope" are used because threaded seals are never precise enough to actually seal. There are always gaps between threads that allow fluid to leak. The dope fills in those gaps. Pipe threaded seals are common because they're cheap, not because they work worth a $#!&. They're especially poor when subjected to vibration.

Brake lines do not seal on the thread. They have a metal on metal conical face seal between the flared end of the brake tubing and a precision formed cone in the mating fitting. The threaded collar presses the flare against the cone. Dope on the threads would have no effect on the seal. Dope on the sealing surface would both leak and cause particulate contamination of the fluid.

High performance seals are always precision faced or swaged or o-ringed or something, never threaded.


PC.
graemlins/hammer.gif

MichaelF
11-07-2003, 01:02 PM
Agreed that thread doping does nothing for the *seal* but it may do something 5 years down the line when you want those threads to release for a caliper or brake piston change. I lightly coat the threads with anti-sieze compound to prevent threads corroding to the fitting. You're right about making sure not to pollute the brake fluid.

Eric
11-07-2003, 01:36 PM
If the flare is seating properly, then there should be no fluid out around the thread, so it shouldn't matter if you use pipe dope, antisieze, tape or peanut butter. If it isn't seating properly, then you need to replace it, as no amount of pipe dope is going to give you good brakes with a leaking flare union.

The antisieze is probably a good idea, although most new nipples appear to be cadmium plated so corrosion shouldn't be too much of an issue. If the nipples are bad, make up a new pipe. Bundy tubing is easy to work with, and flare tools aren't expensive. Just make sure you get the right fittings. Most parts guys look at British brake fittings and assume they're metric. (If it ain't American, it must be metric...) Find an old parts guy. images/icons/smile.gif

11-07-2003, 03:10 PM
Hey guys,
If my memory serves me, the flare used in brake tubing is what they call a "double flare" and these things are a nightmare to get right where they won't leak. I would suggest that if you have a leak to buy pre-flared tubing to the correct length. Torqueing these fittings down is an art form: too little and they leak, too much and they leak and you screwed up. I replaced all the brake lines in my TR6 with nickel-copper tubing that came in kit form, all premeasured and very easy to bend. They say this is nearly as good as steel and certainly strong enough for brakes. Never, never use copper. It will burst. Also, Triumph did start to change to some metric in 1973. The only thing on my entire car that is factory metric is the short tubing from the disc brake caliper to the flex-tube brake line from the chassis. Weird but true.

Bill

Eric
11-10-2003, 01:13 PM
Actually, I believe the American SAE fittings are double flares, the British style are singles. I've made a bunch of them - very easy - and never had a problem with leaks. If you are contemplating doing any work to your brake plumbing, here's a link to an excellent article about brake plumbing do's and don'ts.

https://www.dimebank.com/BrakePlumbing.html

Jerry
11-10-2003, 02:12 PM
Just wanted to let you guys know that NAPA carries the double flare pipe made up in various lengths. They don't have a real long tube but many other lengths under 5 ft. You have to get someone to dig into their books as this is not usually stocked in the local stores. The pipe is a cad plated steel. Quite hard to bend.

Jerry
BN4