Thetford valve rebuild

[mkeith54]

I just finished rebuilding both valves on my 75 Argosy rear bath and thought I'd share the experience.


Tools needed:


Drill with 1/8" bit (for drilling out any rivets that need to be removed
#2 Phillips screwdriver
Stubby #2 Phillips screwdriver
#3 or #4 Phillips screwdriver.
medium common screwdriver
pliers
Pop rivets and tool


Parts needed
2 Thetford valve repair kits


1. The first step is gaining access to the valves, in my case I had to drop the belly pan for about three feet forward starting at the trunk.


2. Next, starting with the gray water valve loosen the band clamp on the out let of the gray tank. This allows the plastic pipe that goes into the tank to rotate which you'll need to do later.


3. Disconnect the pull rod handle or extension from the pull rod. Remove all the small screws in the body of the valve except the two where the pull rod goes in.


4. At this point the valve will separate into two halves. If your black water valve is screwed into the black tank and the pipes join with a small rubber slip connection, stop on this valve and proceed to the black valve.


********** WARNING *****************
THE BLACK WATER SYSTEM CONTAINS THINGS REALLY, REALLY BAD TO YOUR HEALTH.
Rinse the black tank several time and use some soap to help loosen the bad stuff from the tank. I used a cup of bleach and filled the tank with hot water and let it set for a couple of hours. Drain the tank.


5. Disconnect the pull rod handle or extension from the pull rod. Remove the 4 large screws holding the valve to the bottom of the tank and loosen the band clamps on the rubber slip joint. Working from the uphill side, slide the valve and waste line from the tank and remove from the trailer.


6. Remove all the small screws except the two by the pull rod. separate the valve halves and clean with a strong bleach water solution.


7. Remove and discard all rubber pieces. Install new rubber parts and reassemble.


8. Reinstall the black valve reversing the instructions above.


9. Remove old rubber parts from the gray valve and install new rubber parts.


10. Reassemble the gray valve and install both pull rod extensions.


11. Tighten all the clamp loosened and the check them again.


12. Fill both waste tanks with clear water and check for leaks, if every thing worked there are no leaks.


13. Raise the Belly pan back into place and rivet it up.



As an addendum to my note on rebuilding the valves I would like to add the following step:


NOTE: It is important to remove _all_ rags, plastic bags or other items placed in the drain line to prevent critters from entering prior to closing everything up... Don't ask how I know. Rebuild valve not twice, but three times because water did not flow out, finally I remembered the Wally World bag with the rag inside that we had slid into the waste line.


Major embarrassment.

[BobbyW]

mkeith54;

Great detailed post mkeith54. This has been asked many times and this is the best instructions on the Thetford valves. Thanks for sharing your discoveries. This is what makes AirstreamForums so great.

-BobbyWright

[Inland RV Center, In]

Excellent detailed info. Now you know why most owners choose to replace those valves. Saves a lot of time and headaches. The greatest hazard of rebuilding slide valves is that plastic is inherently unstable, in that it can and sometimes does change dimensionally, especially when one screw or bolt is tightened more than another. Keep in mind that the original valves lasted 25 to 30 years, that's not bad!!
Rebuilds usually last a couple of years or so.
Granted, exceptions do exist.

Andy
inlandrv.com
airstreamparts.com

[mkeith54]

I would have changed the valves, maybe even put electric valves except for the fact that the valves appear to be glued on to the tanks. If they fail in the future i'll have to cut them off and replace them.

Mike

[Inland RV Center, In]

Mike. Airstream usually has the valves bolted to a flange.
Glued up construction stopped in the early 60's.

Andy
inlandrv.com
airstreamparts.com

[Gkiesel]

I can tell you for fact that Argosy glued those valves in 1976. I'm livin the dream. Thanks. george

[3boyscamping]

When rebuilding the valves, where does the large and thin O ring go?

All of the other O ring locations were easily determined.

[Gkiesel]

I believe the large diameter, thin o-ring seals the two halves of the valve body.

[Inland RV Center, In]

Originally Posted by 3boyscamping

When rebuilding the valves, where does the large and thin O ring go?

All of the other O ring locations were easily determined.

Generally speaking, rebuilding dump vales is not a cost saving venture.

Plastics shrink in time. Therefore you will be rebuilding a valve that is many years old.

Unfortunately, the proof of the pudding is that the success of the repairs, is not known until the valve is reinstalled and tested with the tank.

If, for whatever reason, that valve leaks, then you must start all over again.

The known lack of longevity of valve repairs, in spite of some exceptions, is really then, not worth the effort.

If the old valves lasted 25 years or more, you certainly got your moneys worth. A rebuilt valve, will historically, not last maybe just a few years.

Then of course, you know when it will leak. It certainly won't be in your driveway.

Andy

[Gkiesel]

I would have to agree with Andy on this one. It was alot of work, at least on the Argosy to get to the valves, and the valve bodies themselves appeared slightly warped. I did not want to have to do it all over again and felt the better way was to replace the valves completely. Thetford valves are very expensive though, approx $65.00 a piece. The Valtera's are way cheaper but I doubt they will last 30+ years like the original valves did.

[Overlander & Sea]

I just finished a rebuild on our '61 Thetford bass slide valve. The information and pictures from forums member wagsrp were very helpful. Purchased the o-rings and seals from a local hydraulics store and replaced the screws with stainless steel ones. The orginal lasted 46 years, time will tell on the rebuild.

[maccamper]

Excellent list by mkeith54. I have both of my tanks on the ground since I am replacing the framing and sheet metal around the holding tanks. I knew the grey water tank valve leaked, and since it had a stainless steel cover it had to be replaced (they have discontinued the repair kit). We recently purchased the trailer, so I had no idea how long the all-plastic valve on the black water tank had been in service.

That black water valve got a new set of seals, since it was just sitting there anyway. The point I would add to mkeith54's list is when you have the two halves of the valve are apart. I think you need to make sure every bit of dirt and grit is cleaned out of the inside of the valves, even if it is up in the slide recess and appears to be out of the way. The inside should be pristine before the valve is put back together.

I am new to trailers, but have seen enough problems in home plumbing to know that even very small amounts of dirt and grit can scour plastic and greatly shorten the life of rubber seals. A little extra time and effort here should make the rebuild last much longer.

[dlowrey]

Originally Posted by Gkiesel

I can tell you for fact that Argosy glued those valves in 1976. I'm livin the dream. Thanks. george

Ditto....

I just took off the black tank dump valve on mt '77 Argosy. The valve half is glued to the outlet pipe. No clamps here...

Does anyone know if rebuild kits are still available for the Thetford dump valves? If so, where can I get one?

I REALLY dont want to have to put a new one in, as I now also have to replace a 4" Y fitting, reducer to 2" for the gray tank, and everything else that is attached to the valve...

Thanks!

Dave

[Gkiesel]

I do believe that rebuild kits are still available, but I really don't know if i would recomend it. It is alot of work just getting to the valves, I wouldn't want to have to go in there again if it starts leaking. New valves are pricey, $60+ dollars plus the sweep 90's, reducers etc. if you go for it, do them both economy of labor and all that. Also it's a good time to por -15 the frame rails up to the axles while the belly pan is removed. Good Luck, George.