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Login to post Forums » Grassroots Motorsports » Is teflon tape okay for use in a brake system?

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June 20, 2011 11:22 p.m. Wonkothesane Reader

I just got a new clutch slave cylinder for my Rx-7, and when I went to bleed it tonight, it was leaking a bit where the soft line screws into it. It only leaks when the bleeder valve is closed and near the end of the pedal travel, and this is after tightening it in a vice (well, the slave was in a vice, I was wrenching on the line), so I know it's tight.

Is it okay to use teflon tape around this fitting, is there some other form of sealant that's okay, or should I return it and try again?

Thanks.

Edit: Yes, I know this is about my clutch system, but I figured the brake fluid would be the problem here, and I wanted the keyword search to find it.
June 20, 2011 11:38 p.m. fasted58 HalfDork

teflon tape or pipe dope is not intended to seal, never depend on it for that !!

your soft line or slave cylinder is at fault
June 21, 2011 1:39 a.m. Travis_K SuperDork

Try again. If it's leaking there is something wrong.
June 21, 2011 9:34 a.m. iceracer Dork

The flare is probably cracked.
June 21, 2011 9:55 a.m. Wonkothesane Reader

I'm pretty sure it's not the soft line, since it's a < 2 year old stainless line, and it wasn't leaking there on the old slave. I just got a replacement for that slave on the way. Thanks for the help!
June 21, 2011 10:14 a.m. dollraves Reader

FYI: Brake fluid will dissolve the Teflon tape.
June 21, 2011 10:48 a.m. curtis73 Dork

Not to mention that the threads have nothing to do with sealing a flared fitting. They simply mechanically press the flares together.
June 21, 2011 11:34 a.m. Wonkothesane Reader

Doll - Thanks for the confirmation, that's pretty much what I thought.

Curtis - Good point, I think the hole in the slave was just tapped too deep from the factory.
June 21, 2011 11:34 a.m. Giant Purple Snorklewacker SuperDork

What they said. Brake fluid dissolves teflon tape. Sealing the thread won't help because that is not where the seal is. It is the flare. Either the line is deformed or the nipple inside the cylinder is (or its the wrong flare).
June 21, 2011 11:58 a.m. curtis73 Dork

Wonkothesane wrote:

Curtis - Good point, I think the hole in the slave was just tapped too deep from the factory.

That's what SHE said.
June 21, 2011 12:14 p.m. Wonkothesane Reader

curtis73 wrote:

That's what SHE said.

I was thinking that as I wrote it..
June 21, 2011 12:16 p.m. amg_rx7 HalfDork

Hmmm... Lotsa people use teflon tape on the Miata rear brake junction box. Seems like they all leak if you don't and teflon tape is the fix.
June 21, 2011 12:24 p.m. Teh E36 M3 HalfDork

I've used teflon tape between an aluminum an-pipe thread adapter and a wilwood brake caliper without issue.

That said, for your issue, I would echo the above comments about the flare being the issue.
June 21, 2011 12:26 p.m. 44Dwarf Dork

Aftermarket calipers and masters have pipe threads often. Everyone I've ever seen says not to use tape. CNC brand masters tell you before filling the master to use red or green loc-tite thread sealer on the fitting and do not over tighten.

Now if your talking a flare fitting its more likely that some one used a standard 3/16 line where there should be a metric line! The thread is so close and often will work just fine but the metric tube nut has some extra length to it before the treads.

44
June 21, 2011 12:31 p.m. erohslc Reader

Hmm, nothing dissolves real teflon (except maybe hydroflouric acid). If you have 'teflon tape' that dissolves, then it's suspect.
June 21, 2011 12:47 p.m. Wonkothesane Reader

In my case, the leak is shown in this picture, at the "1 [SST]" connection.

Graciously hotlinked from miata.net, so it's not Exacccctly the right pic.
June 21, 2011 1:14 p.m. Giant Purple Snorklewacker SuperDork

erohslc wrote:

Hmm, nothing dissolves real teflon (except maybe hydroflouric acid). If you have 'teflon tape' that dissolves, then it's suspect.

Not to be combative but... white teflon tape as used and sold for plumbing is Dupont branded polytetrafluoroethylene. It dissolves in seconds in petroleum based solvents. Gasoline works like a charm. DOT3 Brake fluid is polyethylene glycol-based and so... it might not actually dissolve it but as the root cause of the leak is not the thread interface... it isn't the right answer either.
June 21, 2011 2:02 p.m. Graefin10 Reader

In reply to Wonkothesane:

You referred to the leak occuring @ the "soft line". The diagram you posted doesen't show it as a soft line and calls it a "pipe". Most slave cylinders I've serviced had a flexible hose (soft line) that connected to the cylinder and instead of a flare fitting had another type that used a brass sealing washer between the fitting and the flange of the cylinder. If it's that kind of fitting is the sealing washer missing?
June 21, 2011 2:39 p.m. dollraves Reader

Teh E36 M3 wrote:

I've used teflon tape between an aluminum an-pipe thread adapter and a wilwood brake caliper without issue.

Interesting. I tried using it on the threads for the metal brakeline into the master cylinder on the $2010 GTX...stopped the leak for about a day or two, then leaked again. When we unscrewed the line, there was no teflon tape to be found. Mechanic friend of mine said it was because brake fluid dissolves teflon tape.

Now I have to go home and stick some teflon tape in a small bowl of brake fluid to find out. You know...FOR SCIENCE.
June 21, 2011 2:45 p.m. pete240z SuperDork

curtis73 wrote:

Not to mention that the threads have nothing to do with sealing a flared fitting. They simply mechanically press the flares together.

Curtis has the answer and is the man. And has an awesome 'fro.

Pipe thread is tapered and the threads need a sealing compound or tape.
June 21, 2011 2:47 p.m. Wonkothesane Reader

Graefin10 wrote:

In reply to Wonkothesane:

You referred to the leak occuring @ the "soft line". The diagram you posted doesen't show it as a soft line and calls it a "pipe". Most slave cylinders I've serviced had a flexible hose (soft line) that connected to the cylinder and instead of a flare fitting had another type that used a brass sealing washer between the fitting and the flange of the cylinder. If it's that kind of fitting is the sealing washer missing?

Graefin - That's because the image was blatantly stolen from Miata.net after I google image searched "Slave cylinder." My Rx7 has a hose where the Miata one has a pipe.

Interesting idea about the sealing washer, I'll go take another look at it but I'm pretty sure it didn't come with one, nor had one on the other slave cyl.

Have most of them that you've worked on use a banjo bolt setup like a brake caliper that needs the copper washer on both sides of the fitting?
June 21, 2011 7:01 p.m. erohslc Reader

In reply to dollraves: Breathlessly waiting for the results (I currently have no 'teflon tape' to test it myself.)
I worked for a while as a machinist where we fabricated electronic parts out of solid Teflon chunks, and also fabricated parts out of Teflon sheet. Nothing would touch it, not cutting oil, not mineral sprit, not lacquer thinner, not even the heated tetrachoroethane solvent that we used to degrease.

I suspect that 'teflon tape' used in plumbing is really powdered Teflon in a carrier matrix of some other plastic; such plastic dissolvable in petroleum products.

(and I was wrong, even hydroflouric acid does not dissolve Teflon)
June 21, 2011 8:32 p.m. pete240z SuperDork

I sell s/s hoses for most applications. For all the nastiest applications we go to teflon lined hose. The worst for us is sulphuric acid.....but the teflon hoses are the magic answer to most nasty chemicals.
June 22, 2011 8:44 a.m. AngryCorvair SuperDork

erohslc wrote:

not even the heated tetrachoroethane solvent that we used to degrease.

ah, the good old days.
June 22, 2011 8:52 a.m. spitfirebill SuperDork

I love the smell of TCE in the morning.

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