Gurgling from shower drain when flushing new toilet

[HealingDr1]

I recently remodeled a small bathroom. The small shower has been done for a couple of weeks and I've been using it with no problems. I installed the new toilet (and new toilet flange) yesterday. When I flush the toilet I hear water gurgling from the shower drain.

I replaced the old toilet flange and I believe the opening was 4 inches in the previous flange and the new flange opening I installed is 3 inches. I used a Korky waxfree seal and only used the thin piece of the seal because I couldn't get the toilet to sit flat with just the thick piece or a wax ring. A wax ring was used on the previous toilet.

A rubber coupling couples some pvc pipe and the toilet flange to cast iron. This connection must be secure because the toilet has been used multiple times and there is no water coming to the first floor(toilet is on second floor).

Could my change from the 4 inch opening flange to the 3 inch opening flange be causing this? Thank you!

 

[Terry]

It may be that the new toilet flushes much quicker than the old one, perhaps siphoning the p-trap on the shower. Looking down, is there water there? The water in a p-trap is what seals you against smells from the waste lines, "sewer gas".

 

[Sponsor]

 

[HealingDr1]

It may be that the new toilet flushes much quicker than the old one, perhaps siphoning the p-trap on the shower. Looking down, is there water there? The water in a p-trap is what seals you against smells from the waste lines, "sewer gas".

There is water but I looked down the shower drain when flushing the toilet and it is definitely pulling water. Is there anyway to fix this?

 

[hj]

YOu either do not have a vent for the shower drain, or it is clogged.