No-hub coupling on stack leaking - how do I replace it?

Question

The no-hub coupling on my stack is leaking. It has a rubber liner with a corrugated metal covering, per northeast Ohio plumbing codes. See below for the type of coupling that is currently in place. The leak is in the area where the metal cover overlaps itself. It seems that the rubber underneath that area has rotted away.

It connects a 4" vintage 1928 iron stack pipe with a newer 4" PVC section that leads to the basement. {The connection was done prior to us buying the house in 2005.} The coupling is at floor level with the main floor of the house, and is easily accessed through a small hole cut into the wall.

I have tried a few fixes. The plumber that located the leak (and charged $470 to do it, yet didn't fix it) tightened the band on the bottom of the connector (the PVC section) where it's leaking. He also put a chunk of epoxy putty on the leaking area, which just diverted the leak. I have since removed the putty.

I bought a roll of 1" wide neoprene and tried putting it over the metal covering and under the bottom clamp to make a seal, but that didn't work. I bought a new clamp and replaced the old one, but no matter where I put it, the leak remains. I had thought about removing the bottom clamp. prying up the metal just enough to be able to slip the neoprene under it, but I'm saving that as a last resort, since it will probably ruin the metal covering.

Is there a way to replace just the coupling without tearing the PVC part of the stack out? The cast iron pipe is fine. Until I take the old connector off I won't know how much of a gap there is between the cast iron pipe and the PVC pipe. From what I can tell by feeling the connector it's probably about 1".

The plumber said tearing the pipe out was the only alternative and quoted me in the area of $2000 for the repair, which would include ripping up the wall where the stack is located, cutting into the old pipe a few feet above where the cut currently is (why?) and replacing the PVC all the way to the basement where the clean-out is. I can't afford that. I'm pretty handy and have done plumbing work on sinks with PVC. I could probably tear out and replace the PVC section myself if need be. Just hoping there's an easier fix.

Any suggestions would be greatly appreciated. TIA

Answer 1

The easiest solution to do this job where you don't have mobility for the pipes is to use a pair of them on a short section of pipe you can remove. Of course, you have to be sure the upper pipe is properly supported, first.

So, make a cut 8-12 inches down the pipe from the current joint (since you have PVC below, and PVC is easier to cut - though if cutting the cast iron works better cut out a section of that and use PVC to replace it.)

(I have been there, I have done that.)

Slide the remains of the old coupling, loosened, onto the short section of pipe, and remove it by pulling sideways. Clean everything up well, and put two couplings on the short section of pipe (unless other constraints mean it's too short for that, in which case, slide one fully onto the fixed pipes) slide the short section into place, and slide the new couplings into place, then tighten them.

Answer 2

There's a nice write-up of the procedure to replace an existing coupling at plumbingsupply.com. I'll summarize it here:

1. Loosen or cut the pipe clamp bands. Remove them and the corrugated shield section.
2. Remove the rubber section (probably by cutting and tearing it).
3. Clean the ends of the pipes. The new coupling needs relatively clean, smooth surfaces so that it can create a leak-free seal.
4. Loosen the pipe clamps on the new coupler; remove the clamp-and-shield section. Slide it onto the lower section or pipe, or fully open the shield so that you can wrap it around the pipe.
5. Work the rubber coupler section onto one pipe and then the other. This is definitely the hardest part! It's possible that you'll need to cut a small amount off the end of one of the pipes to increase the clearance between them. Use the new coupler as a guide to ensure you don't cut away too much, leaving too large a gap between the pipe ends.
6. Slide the shield assembly up into place and tighten the clamps.

Sometimes the rubber piece really doesn't want to slide on one or both pipe surfaces. Lubricant helps, but don't use anything petroleum based because it can break down the rubber over time. A water-based lubricant like dish soap or personal lubricant is a good choice.

You asked why the plumber wants to open the wall and make a second cut in the one pipe. The reason is that it helps the installation of the couplings. Instead of cutting the gap larger as I described above, one can create two cuts as your plumber wants to do. The necessary gap for inserting the coupler can be split into the two couplers when the job is done -- this way, both couplers have more overlap/coverage than a single coupler could have had.