A follow-up to my Post 7251 on 27/2/11 ‘Removing the Thetford C2’

Submitted: Tuesday, Apr 19, 2011 at 04:23
ThreadID: 127332 Views:6059 Replies:6 FollowUps:1
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With the Thetford C2 removed I could give the inaccessible area under the Thetford a thorough clean before the unit was re-installed.
I regret now that having a ‘Senior moment’ I did not think to photograph the entire procedure of removal, service & replacing the Thetford.

Apart from the temporary repairs to the flush pump electrics in W.A., the more important reason for removing the entire C2 was a slight leak.
Each time I emptied the cassette, there was always liquid on top.
This liquid had also found its way under the Thetford, which had created a smell we couldn’t seem to hose out.
I had noted that the ‘blade’ did not always open fully, and when closing it seemed to be out of line with the opening & did not raise as it should.

I was expecting something loose in the mechanism that actuates the blade opener knob.
Now that I had the C2 on the bench (still a bugger to work on) I found nothing loose or worn in the blade opening mechanism.

Also with access to the electrical bits, I was able to re-position the actuator on one of the micro switches so that it made contact again & allowed the flush pump to work as it should. I also hard-wired the temporary flushing toggle switch that I had fitted in W.A. to act as a backup in case the micro switches gave trouble again.
My arms aren’t long enough to service them when the C2 is installed.

After a thorough clean-up of the C2 it was ready to be re-installed in the BT.

The cassette now was the one to be checked.
Manually operating the blade opener knob, I still couldn’t get the blade to rise fully, it seemed to be catching on the side of the opening. I suspected that the blade arm was out of alignment & seeing that all this happens out of sight inside the cassette, I sought help.
Thetford put me onto a small company in Sydney that I would recommend.

Alternate Gas Refrigeration
Unit 20, 14 Holbeche Road
Arndell Park NSW 2148
Contact: Bob Parkinson
02 9672 1664
They also are service agents Engel, Waeco, VF, & Dometic.

They checked out the blade mechanism & found all bits in place & working normally. The culprit turned out to be a worn-out ‘O’ ring on the Blade opener knob. This allowed the Blade opener to be off-centre & causing the blade mechanism to finish up in the wrong place, & not seal against the Lipseal.
The blade not sealing properly was the cause of the leak.

You will find reference to the parts mentioned above in the Thetford Parts List, pages 15 & 16. (See Thetford tab in the Bog Bible)

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Reply By: Spydor - Tuesday, Apr 19, 2011 at 19:36

Tuesday, Apr 19, 2011 at 19:36
Your post has got me thinking. i had a similar problem with a small amount of liquid on top of the cassette after rough roads. i subsequently purchased a brand new cassette. this "almost" stopped the problem. however, i am still getting a slight leak. is this o ring you mention seperate to the cassette and if so where?
any info would be appreciated
Cheers Spydor.
Everybody makes me happy! Some when they arrive, Some when they leave !!

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AnswerID: 582396

Reply By: Boystoy - Wednesday, Apr 20, 2011 at 03:56

Wednesday, Apr 20, 2011 at 03:56
Hi Spydor,
The offending 'O' ring seals the blade opening knob on the cassette. This is the knob that rotates to open the cassette. Thetford won't sell you a spare 'O' ring, you have to buy the complete knob assembly.
If you were to take the 'O' ring off and take it to a bearing supply company, they can check for an equivalent.

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Reply By: jayway90 - Wednesday, Apr 20, 2011 at 08:14

Wednesday, Apr 20, 2011 at 08:14
Just had a similar problem, when I tipped the cassette up to carry it fluid leaked out past the blade control knob. Got a great photographic and explanatory procedure off the Thetford website.
If you look closely at the seal on this knob, it is NOT an "O" ring, but has a lip like an ordinary oil seal. Got a complete new knob from a Caravan parts place at Brendale (Brisbane), cost $10-00, also replaced the main blade seal as it is 6 years old, this cost $21-00.

Would hate to try and do a repair job with out the instructions.
Thomas J.
AnswerID: 582398

Reply By: Kazzie - Sunday, Apr 24, 2011 at 20:43

Sunday, Apr 24, 2011 at 20:43
Dear Neil,
This "blade opener knob" seems to star in a number of probs. We have in the last 12 hours found the blade is not being picked up when the toilet is opened prior to use. Not being picked up on return to close either.
I have removed the mechanism & inspected it: nothing seems to be broken/missing, but the pivoting arm controlled by the blade opening knob won't pick up the blade as it moves. All phillips screws are in the right place, unstripped as to thread & appropriately tightened. Any thoughts you might care to share (polite ones I mean).

Our last BT (4yrs) had a Thetford 40??series cassette. This one's a 402C. It's 2yrs old. So in 6 yrs we've had nothing remotely like this to contend with. Of course it happens in the middle of a 6 day public holiday. Verily, timing is everything.
AnswerID: 582399

Reply By: Boystoy - Sunday, Apr 24, 2011 at 23:00

Sunday, Apr 24, 2011 at 23:00
Hi John,

I know what its like when something goes bung in holiday periods, & I know how lost you can feel.

If you have a copy of the BOG Bible, there is some info on the C402c, but not the repair info you desperately need. The best thing is the parts manual, which shows a breakup of both the toilet and the holding tank.

Possible culprit could be the 'Link' between the shaft & saddle, which appears to actuate the blade opener on the holding tank.

I don't have any experience with the C402, as we have the old C2 model.

Have checked the Thetford web site www.thetford-europe.com but have not found any data that is not in the BOG Bible

If you can hang out until Tuesday best you call Thetford on 03 9358 0700

Good luck

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AnswerID: 582400

Reply By: Mike & Carol - Friday, Apr 29, 2011 at 23:27

Friday, Apr 29, 2011 at 23:27
We stopped using Thetford chemicals and started using Woolworths Home Brand NappiSan which is stronger than the NappiSan branded product.

3 tablespoons of Woolworths Home brand Nappisan to one litre of water, dissolved properly then poured into the cassette and just plain water in the flusher.

Guess what - absolutely no smell from the toilet at all, and when you empty the cassette there is no chemical salt build-up (no more grey flakes). The bathroom does not smell and the cassette does not smell, and there is no adverse reaction in the cassette to the nappisan.

And we no longer use the pink Thetford chemical in the flusher.

Just thought we would pass this on if you really want to get rid of the chemical/urine smell of the Green Thetford toilet chemical.

Happy travelling
Mike & Carol
View photos of our travels on our blog:

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Follow Up By: Uncle Dodgy - Saturday, Apr 30, 2011 at 20:26

Saturday, Apr 30, 2011 at 20:26
We agree Mike & Carol
Nappisan seems to be the go. Some members are even adding dissolved nappisan to the top tank with reported success.
For the benefit of others reading this post, I add;;
Keeping a nice smooth surface on the bowl with Mothers Plastic Polish seems to aid the flushing function.
To help keep skid marks off the bowl, when required, we use five strategicaly placed squares of paper to surround the centre hole. A flush before opening the gate, and its all gone. This method, of opening the gate after use instead of before use, of course requires that the vent in the top of the tank is in good working condition, as any gas buildup in the tank could cause a blow back if you open the gate after the event.
To easily check the operation of the vent valve at some point after you have treated the tank with Nappisan (Nappisan is an oxygenator and can build pressure in the tank if the vent is stuck shut) run a few mills of flush water into the bowl and slowly open the gate. If the vent is working properly there will be no bubbling through the clean flush water.
John & Sharyn
Takin' the long way home - Towing a Bushtracker

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