Hello
Im in the middle of a bathroom remodel and I found the collar on the 3.5 in main drain that the Vent pipe threads into has broken off. I have no idea how I should fix this.
The 3.5 in cast iron drain comes through the floor to a “T” 1.5 in PVC for the sink branches to the left and above that is the 1.5in straight up vent pipe. The collar on the Cast T where the Vent pip threads into has broken off.
I have a picture but not sure if I can post it on the forum.
What is your recommendation for a fix. Water never really flows over this joint except for rain water down the vent or if the main drain were to clog. My first though was lots of JB Weld. Any help would be greatly appreciated.

What you have there isn't called a "collar" but a cast iron 4 X 1 1/2" threaded adapter. It's leaded into the cast iron tee with lead and oakum.
Since there's no water in the 1 1/2" pipe and since it's a real hassle to replace the adapter I can see no reason, (if it's just cracked and not broken too bad) to caulk it with JB Weld Make very sure you get it air tight so no sewer gas leaks out. Good luck, Tom

It is broken as I can lift the vent pipe striaght up with ring from the cast side still attached.
Would you still say JB weld or other recmoneded epoxy

I don't see where you have much choice but to break out the cast iron adapter and lead joint and replace it. Or if you want to try a "Hail Mary" fix see if you can run JB Weld around the broken edges and clamp them together. After it sets up I would caulk over the edges to make it air tight. I*f you have to replace the cast iron threaded adapter click on back aqnd I'll walk you through it. But try to repair it first. Good luck, Tom

This is a remodel so get a good drill bit and make swiss cheese out of the lead joint and remove that reducing bushing, cut back on the galvanized vent and replace all with pvc. If you need more instruction shout us back. Do this job right no half stepping

This is a remodel so get a good drill bit and make swiss cheese out of the lead joint and remove that reducing bushing, cut back on the galvanized vent and replace all with pvc. If you need more instruction shout us back. do this job right no half stepping

ThomascKeats solution is the best overall repair but it's also the one with the most hassle. If this were anything else but a vent I'd go along with tearing out the 1 1/2" galvanized pipe and replacing it with 2" PVC, however, since he suggests removing the lead joint and converting to plastic you will still to make a joint between the two pipes. This can be done without pouring and caulking a lead and oakum joint using a Duel-Tite Gasket,(see image) and lubricant. But take it from one that's roughed in multi unit condos with Duel-Tites they're not easy to work with. If you decide to replace instead of repair, I can walk you through it step by step. Your call, Regards, Tom

Hint on that gasket, clean out the hub with a wire 4inch coarse wheel attached to your drill, make sure you get the lead out of the groove in the hub. Then greese everything up gasket both sides, inside hub, and pvc. Put your pvc about 1 inch inside the gasket,place it in the hub, put a piece of 6"x6" lumber over the pvc short and whack it in.

hint on that gasket, clean out the hub with a wire 4inch coarse wheel attached to your drill, make sure you get the lead out of the groove in the hub. Then greese everything up gasket both sides, inside hub, and pvc. put your pvc about 1 inch inside the gasket,place it in the hub, put a piece of 6"x6" lumber over the pvc short and whack it in.

Why not just lube the 2" pipe and the inside of the doughnut up, then nail or screw a block of wood to the adjacent stud and lever it in with a 2x4?

Sure beats mangling the glueing surface of the pipe or getting goo all over your paws when the doughnut hops out of the hub the first few times you whack it.:D

Thanks for the good advice guys; this is my first serous plumbing job so I am getting a real education. Step by steps are always greatly appreciated.

So what I am hearing is Swiss cheese the lead joint to get the old cast reducer out of the T. Clean it up real good with a wire wheel. Insert the Dual-Tite or Doughnut into the T. Hammer (or Pry) in 1-2 foot piece of 2.5” PVC into the Dual-Tite. Then couple the PVC to the Galvanized vent.

What do you use for lube? Do I need to apply anything to the Dual-Tite to seal it to the T? Are there any pit falls I should watch out for? Any recommendations for supporting the 2.5” pipe from eventually slipping down through the Dual-Tite?

Grease, No compression takes care of that, you will use a 4 inch short of pvc into the 4 inch hub making sure it seats all the way down into the base of hub, then you will glue a 4 inch x 1+half inch reducing bushing to the 4 inch pvc, glue in your pvc vent and attach it to the glavonized pipe with a no hub banded connector. Gluing pvc=cut to lengh, sand gluing area rough, remove burs from the cut. Use purple primer (cleaner) then glue and push pieces together and make one quarter turn to spead the glue and hold for a minute to let it set. Don't put any pressure or move the joint until it has completely set around 3-4 minutes. That's what I do, and I may add never a leak. Don't think that's 2 inch, pipe is measured by inside diameter(ID) not OD

It's not as simple as Growler and Keats make out. If you plan on redoing the 1 1/2" galvanized vent to 1 1/2" PVC there are things you will have to know. First off, you're not going to just take a rubber gasket and jam a piece of PVC it and not expect it to fall right through the gasket into the tee. You say the cast iron's 3 1/2". I think you measured the hub and the pipe's 3" cast iron. First thing to do is remove the lead and oakum joint. You don't have to "swiss cheese" anything, simply take a 3/8" drill bit and drill a few holes down past the lead and into the oakum.. Push a screwdriver under the lead ring and lever it up. Once it's free you can began to peel the lead ring out. Now pick out the oakum and you can pull the joint apart. That's all there is too it.
Now for the PVC part. You will need a 3" Dual-Tite Gasket and a PVC 3 X 1 1/2" bushing, ( you may have to work it down from a 3 X 2" bushing).
You will also need a short piece of 1 1/2"PVC pipe and 1 1/2" slip to female thread adapter plus PVC glue, primer, Teflon Tape and lubricant for Dual-Tite Gaskets.
Take a sharp knife and shave off the first few rings on the gasket and then prime and glue the short piece of PVC into the bushing Lubricate it and follow Growlers advice to seat the PVC into the tee, make sure the PVC seats against the bottom of the hub.. Cut the piece of PVC pipe back just far ernough to slip the adapter over it when you glue it.( If you leave it too long it will lengthen the vent and you want to keep it as close to the original length as possible). Now Teflon tape the galvanized threads and screw on the 1 1/2" adapter to the galvanized pipe. You may now prime and glue the adapter to the short piece of PVC and the job's finished. Good luck, Tom

Can't see below the 4 inch cast tee, If you have room its just easier to cut out the cast tee and go to pvc from there with a no hub banded connector for pvc to cast adapter, if room is available?

Thanks Guys, Im feeling much more confident about this fix

I thought about cutting it off, there is room but there are letters cast into the Pipe on the side facing the finished wall. I can't get a grinder back there to smooth out the surface.

You'll have to forgive me for being naïve but the dual-tite sounded like a reasonable solution. Am I in for a surprise??

One idea I had for pressing the PVC into the dual-tite was to mount a 2X4 about a bottle jack's height over the PVC. Lay another 2X4 over the PVC and use the bottle jack to press away slow and easy.

I gave you a step by step to go with the rubber gasket. There isn't much of anything that I can add to it. Any way you can force the PVC into the gasket is the best way.Good luck, Tom

I gave you a step by step to go with the rubber gasket. There isn't much of anything that I can add to it. Any way you can force the PVC into the gasket is the best way.Good luck, Tom
Am I wrong if he has the room under the tee can't he just snap the cast there and go with the no hub and a pvc tee? Won't that be easier for the diy

Am I wrong if he has the room under the tee can't he just snap the cast there and go with the no hub and a pvc tee? won't that be easier for the diy

Not if he's never used a snap cutter.

Hey Guys
Thanks again for the great advice
I went with the service weight gasket. I was Surprised about how easy this job turned out to be. Using the bottle jack to press the 3" pipe into the gasket worked like a charm.

Thanks Again!!