Mansfield toilet mechanism leaks, but new seal doesn't fix

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Well-Known Member
May 15, 2008
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My house has toilets with a common Mansfield mechanism. There's a white plastic tower that is lifted by a lever from the handle, that dumps water into the bowl, then the moving part of the tower falls back down to the circular seal and the flow stops.

I've had (many, over the years) seals fail. Replacement is easy. But now I've got a toilet that acts like the seal has failed, in that water very slowly runs into the bowl, and if the water supply is shut off, this drains the tank down to the level of the seal (technically to the level of the lip of the thing the seal goes around). But replacing the seal doesn't fix it. I looked at the bottom of the moving part of the tower. Clearly if it were cracked or there was a chip in its lip, that could cause the same thing. But it looks fine.

Any idea what is going on? What should my next move be? I can post photos if needed.
I have had good luck and recommend the Fluid Master brand of parts. Here is the whole kit or you can buy just the flapper or fill assemblies.

Sounds like you need a new flapper. Sometimes you get a bad one that won’t seal right.
Yes, always post pics.

Also post the info printed or molded on the back of your tank wall.

If the seal on the flush valve is not the problem, it could be the seal between the flush valve and the hole it mounts to in the bottom of the tank.

So water might be leaking out under the whole thing.
If you have that tower style of flush valve, there are at least two styles.
Black is 1.6 gals, and white is 3 plus gallons per flush.

Just buy the correct new flush valve, and try just swapping out the tower part that lifts up and down.

Be sure to clean off any gook or minerals off the seat of the old valve.

If the valve still leaks, make sure the flush lever is letting the tower sit freely and flat on the base.

If all looks good, you probably have to pull the tank and change out the base of the valve.

You will then probably need a new tank bolts and washers set, and the correct tank to bowl gasket for your toilet.
Ok, the tower is white, but the tank says Mansfield 102 1.6 gpf. I didn't quite get that in-frame of my picture though.
I have made sure the bottom of the moving part of the tower is clean (it already was - we have very soft water in suburban Seattle). There doesn't appear to be any reason for the tower to not sit flat on the seal. Indeed, I've been testing without the lever attached and even tried lightly pressing down on the moving part to try to get better contact with the seal. So your idea that water is going around the seal the other way (through the groove the seal sits in) does seem reasonable. I haven't tried cleaning that groove yet. That will be a tricky reach, but I'll give it a shot. (The (red) seal was out when I took that picture)

Here's the moving part of the tower
Not the groove the seal sits in.

I meant the rubber seal between the flush valve and the china.

That is a common source of leaking.

Sometimes you can try a quick and dirty fix for that, by drying the tank, cleaning around the rubber gasket and china connection, and applying a bead of flexible marine sealant or pure silicone.

The best repair is to pull the tank off and change the whole flush valve.

But first, buy the new flush valve and try changing out the moving tower part.

A decent picture of the tank info would help.

Also some wider angle shots of the tank innards.

There are other ways water could be getting out.
>I meant the rubber seal between the flush valve and the china.

Ah. However, an important clue is that the water drains to the level of the top of the lower rim of plastic - in other words, to the upper rim of the groove the seal sits in. The water then stops draining. So it seems highly unlikely it's the rubber seal between the plastic and the china - that's lower down.

I do note that the tank, or at least the lower rim of plastic, isn't quite level. The water is *exactly* at the rim on the low side, while the high side is dry Not by much, maybe a half millimetre at most. Could being just that bit out of level be the problem?

There isn't going to be a good picture of the tank info. Some characters are illegible or obliterated
The following is what I can get out of it, with question marks standing in for characters I can't read.

No 102
1.6 gpf ?? lpf
msp? No ?03

The first ? might just be a copyright or trademark symbol.
I can do the math to figure out that the ?? in front of lpf is likely 6.0.
The ? after the msp might be just a period.

It's hard to get wider angle photos - the tank is under a ledge (an extension of the countertop around the sink). Countertop people call those "banjo" counters.
Ok new photos.

I have the tank entirely off the toilet and have found other problems of age that need fixing, but cannot be the cause of the original leak issue.

Here's the photo of the tank info you requested:SAM_3867.JPG
and a couple of shots of the interior of the tank. The pink thing is not original equipment. It's a way of using a bleach disk without having it dissolve in the tank and leave residue or gum up the works. The tube goes into the top of the Mansfield flush tower mechanism.
Note this tank style uses 3 bolts, which seems less common when I search for replacement bolt kits.
Finally, an exploded view of the Mansfield flush tower
Newly discovered problems:
1. The upper black rubber seal is decaying. Still in decent shape, but going bad.
2. One of the three tank bolts had a very very slow leak, and the (white, rubber) washers are decaying on all three, fairly badly on the one that had a leak.

But again, none of the above explains what I was seeing, because they would have drained the tank to a lower level, not just to the rim of the flush mechanism.

I have eyeballed the plastic of the flush mechanism closely and it seems fine. In particular, there are no cracks anywhere and no residue in the seal groove. The black residue you see was accidentally added as I handled it after handling the upper black seal. I took the moving part, placed the bottom flat against a mirror and tried to blow through it - that failed, proving the plastic can form a tight seal against a flat surface.

I bought a whole new mechanism from Home Depot, but discovered the new one is too tall - newer toilets are taller.

One odd thing I noticed was that the threaded base of the tower seemed to be greased up with something yellowish - is that normal or advisable? I could see it improving water-tightness, but the install instructions for the new one say nothing about applying any sort of grease. I think that grease may have been on the lower black seal as well.

Another odd thing relative to diagrams I see online is that the the tank bolts have a single rubber washer inside the tank, nothing between the tank and the bowl, and then a single brass washer, brass nut. Online, I see two-bolt systems where there is another washer and bolt in between the tank and bowl.

I figure I have at least two options
1. replace the worst issue - the bolt washers, clean and reassemble everything, hoping for the best. (Also try to get the tank more level than it was, although it was pretty close to level.
2. Do the bolt washers *and* try to find a replacement Mansfield mechanism of the correct height. Somebody online probably has them.

Which of those, or is there another option you'd suggest? And should I be using any grease?

I think you meant “two nut two washer systems”, not two bolt systems.

Also, sometimes if the flex tubing from the fill valve goes too far down into the overflow tube, it can start a siphon which can slowly drain the tank.
I meant that those two nut two washer systems often seem to only use two bolts rather than the three bolts I have.
The flex tubing was definitely not the issue, it was in less than an inch - just far enough to be secure.

Any suggestions about the rest of it? What do you think the story with the grease is?
The issue of two or three bolts is unrelated to using extra washers and nuts on the tank bolts.
I always add the extra washer and nut under the tank, much more reliable seal.

I have no idea about the grease.

I think you need different advice, we are not staying on the same wavelength.

Good luck.
I hate Mansfield toilets , The problems is parts, where to get them. Yes they are cheap , so my customers will buy them , but when there is a problem they call me and expect me to have all the parts for a toilet that has maybe 5% of the market. I usually carry parts for crane, American standard, Toto and a lot of universal stuff . but for me to carry $100 worth of Mansfield toilets parts that maybe i work on 1-2 a year no. people want me to come to their house and solve the problem fast and for a reasonable price if i have to go running around for parts it is not good.
Well, I figured it out.
At some earlier point, I had used baking soda to clean mold (this is a very infrequently used toilet) in the tank.
Baking soda doesn't entirely dissolve. It leaves behind something like fine grains of sand ... which are enough to hold open the valve by a tiny amount.
I guess I won't do that again.
I had just bought a new seal also, put it into the seat and had even more noisy leak than the old seal. I cleaned off some uneven sticky black rubber that came from another seal below off the bottom of the o seal and flipped the seal from bottom to top, then remounted and it looks good now. Not sure it was the sticky rubber or if one side of the seal should be facing up.