I've read through every thread on replacing these, I haven't seen where anyone suggests putting sealant on the threads to keep them from leaking.

The various VW parts sites state: "We suggest installing these switches with a hydraulic fluid safe pipe sealant. Do not use teflon tape"

Is everyone installing these dry or what are you using? I had this on my to-do list already due to the warning light issue, while driving it yesterday the pedal went to the floor and the rear most switch is leaking. I was going to replace them today anyway......lucky timing I guess.

I'm guessing Loctite 565 or 545 is going to be the most common suggestion.

This stuff says it's hydraulic safe:
http://www.oreillyauto.com/site/c/de...0802&ppt=C2392
http://www.oreillyauto.com/site/c/de...&keyword=59214

The last one is the only stuff available locally.

 

It's a tapered "NPT" fitting so I've never used a sealant.

I'd wager that a substantial leak is going through the switch body.

 

I did mine some years ago now, and didnt use any sealant, never leaked. Just dont tighten TOO much - apparently you can crack the cylinder casting. I replaced the reservoir grommets when I got the car (13 years now) and again couple of years ago, so watch out for them degrading to the point of leaking. Cheap from MB dealers - ATE part.
jp 83 Euro S AT 56k

 

Never used a sealant on them before and have never seen one leak.

Thanks for posting this thread though, it reminds me I have a customer to call to have these replaced.

 

Cool, that's what I thought but wanted to be sure.

When these are delivered new they have some kind of red sustenance on the threads. I received these from a local repair shop, they ordered a brake master for a 911 which came with the 3-prong switches installed. This particular car needs the two prong so he removed these and set them aside for me. With no "red stuff" on the threads, I wasn't sure if I should add anything or not.

That's what it looks like. When I removed the plug it was soaked in brake fluid.

 

The new switches come with a dab of sealant on the threads similar to what's found on new timing belt tensioner bolts. On reinstallation, you can use Teflon thread sealing compound (Oakley, white tube with gray printing, in the plumbing aisle at Home Depot). Hylomar works almost as well.

Pipe threads seal by pulling the threads hard against one face in a tapered thread arrangement. The metal "thread" is a single groove that spirals down the lentgth of the tapered part of the fitting. To get a good seal, you just need to block fluid flow down the backside of that thread in just one spot along it's length.

Teflon tape will work, but is dangerous if done wrong. For most tapered threads, your first wrap of tape is folded just past the small end of the fitting. But that risks having that first fold cut off as the fitting is assembled, with shreds of tape now loose in the system to interfere with hydraulc sealing in the piston cups and the caliper seals. So start the first wrap of tape one thread back from the end, so there's no chance of a scrap of tape getting loose inside. I'm not a fan of tape until we get into bigger (maybe 1/2" NPT fittings and larger) in hydraulic systems, and then only when a shred of tape lose inside won't cause separate problems.