Sealing leaky NPT fittings

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Clone TIE Pilot

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Aug 14, 2011
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Having issues with both the brake booster fitting and HVAC fitting leaking vacuum. Tried using pipe dope for gas lines and it didn't work. Any ideas?
 
some of the best pipe thread sealant i've used is oatey/hercules megaloc. you will probably need to goto a plumbing supply store to get it.

is the connection you're referring to actually a threaded (npt) connection? your description of brake booster and hvac vacuum -- i cannot think of where a threaded connection is... i thought they were mostly all barbed connections.
 
You could try Teflon tape on the threaded portion, are you sure you are matting 37 degree fittings to each other?
Any question of the quality of your fittings?
 
You could try Teflon tape on the threaded portion, are you sure you are matting 37 degree fittings to each other?
Any question of the quality of your fittings?
if you're referring to a 37degree flare fitting --- DO NOT USE TEFLON TAPE....

the joint is made a the flare / bevel surface, not the threads. the threads are not designed to be the seal on a flare joint.

teflon tape and pipe thread sealant are for NPT / tapered pipe threads.
 
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Both fittings are original GM fittings that came on the engine. I always heard not to use Teflon tape on vacuum fittings because the fuel vapors in the intake would dissolve it.
 
The brake booster fitting is flare to NPT in the back of the carb baseplate. Its thin casting where it screws into and you to be careful about not overtightening the fitting and cracking the baseplate. The HVAC fitting is a 90 degree hose barb to NPT fitting that screws into a thick boss on the back of the intake manifold, between the carb and dist. Both fittings are leaking vacuum around the threads.
 
As far as thread sealer I have always used ARP
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As far as thread sealer I have always used ARP
View attachment 160005
Anything like ^^^^ works. 592 Thread lock/ pipe sealant. Any product that contains liquid ptfe Teflon will seal a threaded component including a head bolt, vacuum, fuel, diesel Fittings, etc.
 
Anything like ^^^^ works. 592 Thread lock/ pipe sealant. Any product that contains liquid ptfe Teflon will seal a threaded component including a head bolt, vacuum, fuel, diesel Fittings, etc.
Right up to 15000psi 1/2" NPT fittings, and acid service to 28% HCl for the equipment at work. Good old 592 Liquid Teflon.
 
When I have a NPT fitting that leaks I will wrap it in Teflon tape and then a coating of thread sealer. I have done this many times in high temp water jackets and I know my dad did the same thing when he worked maintenance in a factory.
 
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