Best Thread Sealant For Brake Fittings

Article by Vintage Vinny

After replacing brake hoses on a friend's 1981 Sportster, I noticed a slight weeping of brake fluid from the fittings. So I checked to see if they were tight enough. Yup, they were tight. And they still leaked.

How Tight is Tight?

When brake line flares are over-tightened, it damages the soft metal they're made of, and then your problems get worse.

There should be a voice in back of every mechanic's head that says, "They shouldn't need to be this tight."

What Didn't Work

Before I learned about hydraulic line sealant, I tried wrapping Teflon tape around the fittings, but after sitting overnight, the weeping came back.

And when I removed the brake hose, I noticed the brake fluid was dissolving the Teflon tape!

So, Teflon tape doesn't seal brake fluid. Not only does it not stop the weeping, the pieces of tape could become dislodged and clog passages in the brake caliper.

Other Hydraulic Sealants

Most mechanics have a tube of blue or red Loctite in their tool box, but are they compatible with brake fluid? I went to the Permatex website to find out, and learned that neither the red or blue sealants are compatible with brake fluid.

Out of all the hydraulic sealants that Permatex makes (and there are many), I found that only one that safely works with brake systems. Permatex 54540 sealant.

Permatex 54540 sealant is specifically designed for use with hydraulic line fittings, brake fittings, and transmission fluid fittings. It also works well on PTO fittings and air compressor fittings.

It's Purple!

Out of the bottle, it comes out purple in color.

Permatex 54540 sealant for brake fittings

All it took was a few drops on the threads, then I re-tightened the fittings, and the leak stopped.

Once it dries, it leaves a purple-red tint on the threads.

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The Brand New Bottle Was Half Empty!

Yes, it's supposed to be that way. The reason why it's half-empty when you buy it is, it needs to be shaken up before use.

For a small 1.22 oz bottle, it's expensive, but it works so it's worth the money. And none of the local auto parts stores had it. I tried the local AutoZone, Advance, and NAPA stores--nobody had it in stock, so I had to order it online.

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Are Permatex and Loctite the Same Company?

I used to think they were both the same company. Turns out I was partially correct.

Loctite actually owned Permatex for a long time, then they split around 2002. Since then, the two companies have been offering nearly identical products. Although there's not much difference (if any) between the two brands, it's important to get the right product for your needs.

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