Plumber Expert question (brakes)

[Alexander]

Hello guys

I can’t seem to get rid of a small leak from my newly sleeved master cylinder. The leak is coming from the "Plug Nut". The NUT is super tight.

I replaced the cooper washer and then tried an aluminum washer but nothing seems to help.

My last resort is to try some kind of thread sealant.

Question:

what kind of sealant could I perhaps use that would dry hard?

(I use DOT 5 Silicon fluid, compatibility may be an issue?)

I thought of using Teflon tape, but I an not sure if that will work as it will prevent the nut to seat correctly adding to the leak?. Your kind thoughts and Ideas would be appreciated.

Alex

[Joe Flanagan]

You're sure it's leaking between the nut and the body of the reservoir? If that's the case, the only thing I can think of is really bad pitting. Was it badly rusted? As far as Teflon tape goes, I'm not sure that will stand up to brake fluid but I'm sure there are some folks here who know the answer to that.

[oldmopar]

I would try the brush on type sealer gasket sealer in the tube.

There different type of sealants for different substances.

The brush on or tube type sealant should seal the threads better then the tape. Since the silicone does not affect paint the way dot3 does then it may not eat through the sealant. Only other though if you had a big enough tap & die maybe you could clean up the threads on the plug and mc.

[JerseyHarold]

Run a bead of JB Weld on the rim of the MC then install the copper gasket before it hardens and tighten the end fitting to squash it down into any pits.

[Alexander]

Very sure the leak is coming from the NUT.

JB weld, that seems like a good idea. Any other thoughts on the ideal product to use? should I put some on the threads?

thanks

Alex

[JerseyHarold]

I wouldn't use JB Weld on threads...you'll never get the pieces apart again.

Have you checked the two brake line fittings that screw into the large nut on the end of the MC? The leak might be starting from there.

[HughForrest]

Permatex makes a high-temperature thread sealant that they specifically say is resistant to brake fluid. P/N 59214. It is for sealing threads only, not bad flares!

Brake fluid will eat teflon tape.

[Don Coatney]

I would not use JB Weld on any part of a brake system. Find out where the leak is and make a proper repair.

[Flatie46]

Really the copper washer should do it, is the nut distorted or bottoming out before it squeezes the washer,maybe try a different nut off anthor master cyl. What about where the washer meets the master cyl check it with a strait edge might need filing.

[Frank Elder]

Sounds like a cracked flare...

[Alexander]

I am 100% sure its coming from the nut. I also thought the surface of the master cylinder was maybe pitted or not flat, so I decked it a bit. I have a feeling I have a bad nut, but unfortuanly I dont have another to try.

I hate making making such bogus repair, but in this case I have no choice.

Just wanted to check with you guys what would be the best product to try to seal those threads. Again I am using DOT5 (silicone) fluid which I think is mineral oil based.

Ill try the permetext product.

Thanks guys!

[grey beard]

Alexander,

Methinks you are barking up the wrong tree. If you look very closely at your MS cap plug, you will find a very small vent hole drilled into the side. This vent is necessary for the reservoir to function properly in the system.

When your cylinder is filled completely to the brim and the brake pedal is actuated rapidly, it is normal for some fluid to escape via this exit. Use a clean rag and try to remove about half an inch of fluid from the top, then clean everything up with brakeclean spray and use a new copper gakset. I'll bet you will see the end of your small leakage problem.

They just don't like to be filled completely to the top, or there is a little spillage when the brake pedal is released - but only from the vent.

No big deal, really.

Good Luck:)

[Alexander]

Thanks Grey Beard.

I really thought this would be it, but unfortuantly its not. The nut even leaks while at rest. I think I have a warped nut.

I plan to use some thread sealent this weekend.

Ill report back the results.

Thanks

[grey beard]

Don't unnerstand how a master cylinder cap plug can leak when there is no fluid above or even near it. Methinks something else is involved in this equation . . . What's above this leaking cap?

Also, most master cylinder caps have a tin baffle on the bottom side to deflect splash from the returning piston away from the vent area in the cap. Does your cap have this feature?

Ran into the same problem with my own brand new master cylinder, but this one has a 3/8-inch hose barb threaded into the top and connects to a remote master cylinder reservoir. Couldn't stop the constant weep from the cap area until I took the whole thing apart a second time and had the vent hole - that I had epoxied shut - brazed shut, for a permanent fix. My own MS had a paper gasket underneath the cover lip, but I had to replace it with the better quality copper seal ring. Now it's nice and dry, even with the reservoir two feet above it.

Works for me. God Luck

[JerseyHarold]

I think the cap Alex is referring to is the 'end cap' that screws into the back of the master cylinder that has the front and rear brake line connections.

[Don Coatney]

I think you should listen to what Dave (greybeard) is saying. He is correct!

[Niel Hoback]

Try using two copper gaskets stacked?

[radioguy7]

I would send the question to president Obama, he has all the answers.

[Alexander]

Sorry for the mixup.

I was reffering to the end nut where the 2 lines attach. I think in my case that nut is pehaps pitted or no longer flat. I plan try some thread sealent this weekend.

My intial query was to check what would be the best product, considering I use DOT 5 silicone fluid. Per some of the feed back, I will try permetext high temp.

Thank you all, I let you know how I make out :-)

Alex