DIY toilet flange replacement question

[SimpleCycle]

We were having leaking around a toilet, so I pulled the toilet to replace the wax seal.  Turns out the toilet flange is a) totally corroded and no longer usable, b) almost flush with the floor, and c) crooked (about an 1/8th in below the floor surface on one side and 1/8th inch above the floor surface on the other side.

I bought an ABS replacement flange that fits inside the drain pipe and seals when you turn allen screws (like this: https://www.oatey.com/2371311/Product/Oatey-Cast-Iron-Closet-Flange-Replacement) and plan to install that.  The directions say to remove the old flange before installing this one and to fasten the new flange to the subfloor or floor, but there are conflicting opinions on the internet about if this is necessary if it fits with the old flange in place.

My hesitation in removing the old flange is that it will be difficult because whoever installed the tile basically grouted it in and I don't want to damage the floor trying to get it out.  I also am not sure it's necessary because if I install it on top of the current flange it will be appropriately placed with respect to the floor if I shim it on one side to make sure it is level.  If I remove the flange I will have to raise it on all sides to property fit with respect to the floor.

Any thoughts?  Should I just whale away at the flange with a chisel and hammer to remove it, or leave it there?  Seems like sometimes you have to improvise the instructions to fit real world conditions.

[AMandM]

My daughter and son-in-law had a very similar situation. In their case, the replacement wouldn't fit inside the old flange because it was designed to take its place, and also the old flange had deteriorated to the point where its upper edge was all sharp and jagged.
I'm sorry to say that they ended up having to get a plumber to remove the old flange. They didn't have the strength or the tools to do it themselves.

I'm no expert, so take this fwiw. I would probably leave your old flange in place and use a shim. Sounds like it would save a lot of work. Worst case scenario, the leak isn't fixed and you have to remove the old flange after all.

[lthenderson]

I've been in this situation several times and I prefer going the route of using a flange reinforcement/repair ring similar to this:

https://www.amazon.com/Toilet-Flange-Repair-Replace-Broken/dp/B000FHBGEC

It just sits on top of the old one and can be securely mounted in relation to the floor. I find a lot of times if you use what you linked too, the flange will be too thick and might interfere with the bottom surface of the toilet. Also, if it were to shift for some reason, it could start leaking again. With the ring I linked too, you can easily screw it down over tile if need be with a masonry drill bit so you won't have to worry about disturbing the tile.

[bokonon]

You're probably done already, but I vote install the replacement flange inside the old one.

That's what I did.  The replacement is new plastic (water tight and should last forever) and as long as you seat the toilet / wax ring correctly will funnel all the water into the old pipe right through the damaged old flange.  In your case (and mine as well), the old flange acts as a spacer and will make the replacement height where it should be.

I drilled through the old flange (cast iron is very soft, a regular drill goes right through it) and anchored the replacement flange into my concrete slab with tapcons.  Rock solid, should have same effect with wood screws if you're on a subfloor.  I'd use exterior screws.

Hope this helps!