A cylindrical plastic container with spherical ends, maybe 10" long and 5" in diameter, attached behind the right side of the front bumper. It's some sort of pneumatic pressure vessel. At first I figured it had something to do with AC, but both the XJs have it and one of them is non AC. Some sort of vacuum accumulator for 4X4 engagement? Something else?

Whatever it is, I reinstalled it in our build of FrankenJeep II.

 

It's the vacuum reserve storage canister. All the vacuum stuff works much better with it. Why they put it up there were it can be broken easier I don't know.

 

Vacuum reservoir ball .. For heater controls, when you go from, vents, defrost ,floor .

 

Without it, you have to let off the throttle to make them change. It's like shifting gears from the dash to the floor. lol

 

hmm, I never had to deal with it.. All I really know is reservoir is french for (Tank) lol

 

I tried to eliminate them a few times over the years and ended up putting them back. You can move the control on the dash but it won't "shift" the doors in the HVAC until you let off the throttle to create enough vacuum to actually move them. So what happens is every time you want to change from defrost to dash to floor etc. you have to let off the throttle like you are changing gears with a standard trans to get them to move. lol

 

Thanks for the quick answers guys, that makes sense. Although the location is a bit curious, almost like it was an afterthought , and the Jeep engineers said "Oh crap, we forgot about this thing! Where are we going to put it?"

 

That's what I though when I first saw it mounted there too. lol I think they had trouble finding room for it in the engine compartment. I know one thing, life is easier with it than without it. Older cars had metal ones that were basically a large food can with fittings soldered on. Those were probably tougher than these plastic ones. lol

 

If you're lucky enough to have working cruise it also makes that damn near unusable if you remove it. You'll get enough "hold" on the cruise to activate it but not enough to hold your speed.

 

So when the French go to war, they say "Deploy le' reservoir!"....oh wait, sorry, they eat cheese and surrender, my bad haha

 

Huge point you make here. I had forgot about the cruise because even though mine works I don't use it. I don't like how it acts, it is either all on or all off, there is no happy medium and "Float". I can get better mileage manually floating it myself.

I have asked here how to cure this but no one was sure how to do it. In the old days they were adjustable in most vehicles. I haven't had a chance to play with it yet, but I think porting the line for slower flow might help make it accelerate and decelerate slower.

 

Lol, About the only thing they were really good at was making cannons.

 

You might be on to something there, I did notice with mine that it was quite "aggressive" with the throttle when correcting for speed.

 

Glad to hear it isn't just mine. When I first used it I thought maybe I had a vacuum leak that might be causing this very distinct on/off situation but couldn't find any. I even hooked in a "T" to a mechanical vacuum gauge and ran it awhile and all looked good. Part of it is because these torque converters are pretty solid, but it still should not be quite as aggressive it is. It's too much too fast both ways and no advantage in getting better fuel mileage at all. And it really sucks when I am pulling a trailer.