'77 center bath black tank sagging

[CA_Tallguy]

Can someone tell me what supports the black tank on a center bath 70s trailer? Is it just the belly pan? I am replacing my valves and I kind of think that my black tank is sagging a bit. The belly pan has a little bulge there but not a whole lot.

It seems like a lot of weight to just sit on a flat piece of sheet metal. It appears there could be a little foam insulation between the tank and pan and maybe there is some sort of stiffening along with that?

Just wondering if there is anything that I should do before installing the new valves. It seems like the drain pipe may have to slope upwards a tiny but to work the way it is. I may be wrong and wrapped up for the night to look at it fresh in the morning.

[perryg114]

A little sag is normal and yes the belly pan supports the tank. That pan is made of heavy gage steel and is a lot tougher than you might think. There is a foam pad under the tank that is slanted to get the water to flow towards the drain. As long as you don't have a rust through situation you should be fine. I am still trying to figure out how to replace the valves on my center bath without major surgery. My valves are between the two tanks.

Perry

[Aage]

The 1977 Service Manual says under "Main & Auxilliary Waste Tank Removal" :

1. Empty tank completely. If tank is not completely emptied it may be damaged during this removal procedure.
2. Remove drain lines
3. Unplug liquid level wires (under nightstand or wardrobe)
4. From under trailer, remove waste tank access panel
5. Support tank with floor jack
6. Remove bolts which secure tank pan to chassis
7. Pan can be slid forward of the axle to remove tank
8. Remove drain outlet from drain tank. It is not necessary to remove slide valve.
9. Lower tank by sliding back and down
10. Apply adequate sealant between support pan flanges and chassis to ensure a proper seal
11. Replace by reversing above procedures

Note: Check replacement tank for leaks by filling with water before and after installation


I can't imagine the belly pan supporting the weight of both tanks filled, but I'm not an engineer.

In any event, the "bolts which secure tank pan to chassis" in number 6 seems to say it doesn't.

In the picture that goes with the instructions, it shows the "pan support main" and a length of U-channel holding up the black tank, and a somewhat flatter pan under the grey tank.

Sounds like a fun job! Good luck!

[CA_Tallguy]

Ahh. Here are those pages. I had looked under drainage but not in the front under chassis.





So I guess this confirms its just the pan and channel around it holding the pan up.

[Aage]

I don't know if your book is different, but be careful to pick up the correct directions for your model. I think you said it is a centre bath: "full bath" is Airstreamese for "rear bath".

[CA_Tallguy]

My book says it is for 1977 excella but I suspect those pages are the same for other similar models. Mine is 31 feet and I think the book is oriented to that length. After you posted info in removal instructions I dug further to find them in my book.