The not-so-simple task of changing the Thetford cassette seal. (1 Viewer)

Feb 22, 2016
3,613
10,731
York
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41,744
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A five minute job.........yeah right!

Having the van second hand since 2015 we had never changed the cassette seal. Last time we were away, I noticed that a bit of liquid was leaking when carrying it to be emptied it so decided I'd change the seal. A new one was ordered costing £12 from Amazon. This was a pleasant surprise as usually anything to do with motorhomes starts at £500 plus VAT.

The sun was shining so prepared the outside garden table, and laid out the cassette, a cross-headed screw driver, a full silicone lubricant spray, 2 pairs of rubber gloves and a collection of rags, used toothbrushes, and of course, the new seal. I reversed the little plastic sliding cover that the instructions tell you to use as a lever to unscrew the cassette cover to access the workings. That damned cover was screwed in so tight that it was immediately apparent that the little plastic lever wasn't anywhere up to the job. So I got a piece of wood and used that instead. It was a hell's own job to loosen the cover but eventually, it eased and I was able to unscrew the cover from the encrusted (honestly) thread.

It wasn't just poo that covered the workings; it was fossilised excreta, hardened to something they should tip diamond drills with! No question of just wiping it off with a rag or brushing with a little brush. Oh no. This required painstaking chipping away. My neighbour chose this moment to stick her head over the fence and ask what I was up to. I decided lies were preferable so just said "routine maintenance" and carried on.

After taking everything apart and cleaning it by chisel, boiling water, bleach, detergent and a few spells, I was able to put on the new seal and re-assemble. Then came the second most time consuming part; screwing the cover back on. It lined up, the little arrow was on the mark but turn it wouldn't. Like a contortionist, I had one foot pushing the cover down whilst trying to turn the cover (again with the piece of wood) the approximate two inches to the 'closed' mark on the cassette. The damned thing wouldn't budge. I checked the washer, checked it that it was level, nothing under the catching cassette flanges was obstructed. Just at the point when I was about to go and order a £500 replacement cassette from Amazon, the cover moved reluctantly into the locked position. Luckily it all works now and the little plastic cover, that used to be quite loose and rattle now is a snug fit. It moves up and down easily enough as required but the seal is much better.

But what a struggle. I wish, when people say a job is a five minute job, they wouldn't. It's the precursor to a horrible, dirty and demoralising day-long saga. Happy days and good luck. I decided against posting photos of my handiwork on the basis it offends against bad taste. :giggle:
 
2

2657

Deleted User
Recently went through almost the same procedure, didn't replace the seal, with similar problems.
I used a vinegar solution in a partially successful attempt to dissolve the crystals, then managed to over tighten one of the screws and broke the 'boss', luckily managed to glue back in place.
It all looked so easy on the demo video......using a nice new cassette!!
 

Kannon Fodda

LIFE MEMBER
Feb 26, 2019
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But what a struggle. I wish, when people say a job is a five minute job, they wouldn't. It's the precursor to a horrible, dirty and demoralising day-long saga. Happy days and good luck. I decided against posting photos of my handiwork on the basis it offends against bad taste. :giggle:
This thread is worthless without pics :D

But any handyperson will know that to understand the real time needed for a task is to take that original estimate of minutes and convert it to hours.
 
Mar 16, 2016
1,072
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Norfolk
Funster No
42,019
MH
Hymer S520
Insert 2 bio capsules, fill with hot water, leave for 24hrs stirring occasionally, empty and flush with cold water and there you have a squeaky clean cassette........... Simples!

20180916_112321.jpg


Pete

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2

2657

Deleted User
Insert 2 bio capsules, fill with hot water, leave for 24hrs stirring occasionally, empty and flush with cold water and there you have a squeaky clean cassette........... Simples!

View attachment 429696

Pete

If bio capsules do that to the inside of a cassette in the state mine was then I dread to think what they would do to clothes :Smile:
 
OP
OP
Ingwe
Feb 22, 2016
3,613
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York
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Recently went through almost the same procedure, didn't replace the seal, with similar problems.
I used a vinegar solution in a partially successful attempt to dissolve the crystals, then managed to over tighten one of the screws and broke the 'boss', luckily managed to glue back in place.
It all looked so easy on the demo video......using a nice new cassette!!
Yes, I've noticed the demo vids all use a brand new, pristine cassette.

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Jan 19, 2014
9,395
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29,757
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Elddis Accordo 105
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since 2014
I changed the mechanism on ours recently, there were no unpleasant build ups inside at all, just looked a bit tired and screws a bit rusty. Always used bleach in it 👍😎
 
Nov 19, 2019
793
2,605
Funster No
66,935
MH
Challenger 287GA
Exp
Since 2020
We have a much older 200 series toilet/cassette in our van. Much older and also much smaller!! We bought a fresh-up kit and decided to give the old cassette a full going over to get it nice and squeaky-clean. I think Colonel Kurtz summed it up best..."The horror...........the horror" !!!!
 

Pete5996

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Sep 18, 2016
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I've treated myself to a 'Fresh-up' kit for my C250 which has, coincidentally, arrived today. There was an offer on the Thetford Cassette Cleaner so I've started the cleaning process on my existing cassette - I'll let you know if it's as good as they say....🙂

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Popeye

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Sep 5, 2011
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This thread is worthless without pics
I expect the pics turned out $hite.

I have to say I do my two cassettes every two or three years and have never found it to be more than a 5 - 15 minute job. It takes longer to get suited up than to actually do the job.

AlphaTec_66-320_Model_151_Front.png
 
Last edited:

TheBig1

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Nov 27, 2011
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as above, bio washing liquid or capsules and hot water to soak the crud off before you start, makes for a far less unpleasant job and allows the various parts to be released easier. A good clean, strip down, lubricate and rebuild every year or two at most is good preventative maintenance. Add to that a good clean and coat of car wax to the toilet bowl, saves problems later on

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Nov 19, 2019
793
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I've treated myself to a 'Fresh-up' kit for my C250 which has, coincidentally, arrived today. There was an offer on the Thetford Cassette Cleaner so I've started the cleaning process on my existing cassette - I'll let you know if it's as good as they say....🙂
We used some of that on the cassette of horrors and I must admit I was fairly impressed at the amount of, well, crap, that it got out. I'm new to this so was a bit scared to go with bleach following Thetford's dire warnings of imminent failure and collapse of society itself should i use anything other than their own cleaner, but it was pretty good.
 

Pete5996

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Sep 18, 2016
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Well, the Thetford Cassette Cleaner barely touched it - lots of foaming and precious little action. It didn't appear any different from before. To be fair, there was a lot of calcification inside. I suspect the cassette is probably the original from 2009 and, apart from seal lubrication from time to time since I bought the MH in 2016, I hadn't done more than the usual flush and wash out.

So it was a complete strip-down of all the components and a soak in white vinegar. Half a litre of 23% hydrochloric acid (readily available in supermarkets here) in about 5 ltrs of water and into the cassette for a couple of hours, tilting the cassette appropriately to coat the interior, and it certainly worked! The encrustation just fell off and it's now squeaky clean (y)

Thoroughly washed out, reassembled, rubber components lubricated with silicone spray and it's as good as new. It'll go, in a bag, into the garage as a 2nd cassette for use as and when necessary....

The Cassette Cleaner instructions recommend using it 2-3 times a year, so will probably be fine as a maintenance solution, but don't expect it to deal with years of deposits - IYSWIM! :giggle:
 
OP
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Ingwe
Feb 22, 2016
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I've seen hydrochloric acid in French supermarkets but am amazed it didn't damage the cassette. I'll get some next time we're in France. Of that, we're looking to see if we can get insurance for a lightening trip in November. Without success so far!
 

Pete5996

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I used it at the recommended dilution for plastic pipework, drain unblocking etc, so didn't think it would have any adverse effect on the cassette, which is a pretty robust material.

If I find a blob of plastic in the garage in a month or two, I'll let you know 😁

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TheBig1

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Nov 27, 2011
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I've seen hydrochloric acid in French supermarkets but am amazed it didn't damage the cassette. I'll get some next time we're in France. Of that, we're looking to see if we can get insurance for a lightening trip in November. Without success so far!
sold in builders merchants here as brick cleaner or spirits of salts. Can be nasty stuff to use and not so simple to dispose of legally
 
OP
OP
Ingwe
Feb 22, 2016
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I used it at the recommended dilution for plastic pipework, drain unblocking etc, so didn't think it would have any adverse effect on the cassette, which is a pretty robust material.

If I find a blob of plastic in the garage in a month or two, I'll let you know 😁
I'm sure there was a garage here............🙄
 
6

63720

Deleted User
I found the dribble coming from the cassette in transit was from trapped flush water between the cover and the blade, now I make sure it's fully drained before closing for disposal.
Good tips here, thanks.

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gwyntaxi

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Jun 9, 2009
1,151
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,Swansea
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Mine is the old type with 8 screws, a much easier job. Replaced seals a couple of times.
I replaced mine, C200 the 8 screw type as it was dripping slightly when carrying to emptying point, but even after replacing with a new original Thetford seal it still drips, any ideas, suggestions please.
 
Apr 3, 2019
1,507
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Burstner Travel Van
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Few years now
Did mine the other day. Filled it with with Bio washing fluid and water for a week beforehand.
 
Jan 19, 2014
9,395
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Elddis Accordo 105
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I replaced mine, C200 the 8 screw type as it was dripping slightly when carrying to emptying point, but even after replacing with a new original Thetford seal it still drips, any ideas, suggestions please.
Perhaps some silicone grease round the seal will seal it better.

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Nov 19, 2019
793
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Challenger 287GA
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I replaced mine, C200 the 8 screw type as it was dripping slightly when carrying to emptying point, but even after replacing with a new original Thetford seal it still drips, any ideas, suggestions please.
Check where it is leaking from. I'll bet that it's from the button you depress to allow the contents to drain freely. There's a seal replacement kit available but it's a bloody pig of a job.
 
Nov 13, 2011
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MH
PVC
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Any liquid sitting above the seal will inevitably dribble on the way to the emptying point.
So, for a minute before removing the cassette, open the flap. Close it and away you go, no more dribbles.

As for the OPs crusted up service aperture, sorry but it takes seconds to remove and replace. I would not dream of leaving my cassette without removing the aperture before a good clean. Then a quick smear of silicon lube on the large 'o' ring seal, before replacing back in the motorhome ready for next trip.

Geoff

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