Benjamin

Accumulator tanks (bladder tanks/pressure tanks) were used with RV pumps in some cases simply to get enough flow from small single speed pumps, at least for several seconds of use. A larger variable speed pump doesn't need the same storage, and as noted in Tom's first post, a tank can cause issues with the variable speed controls. In most cases, a water hammer arrestor, or a small vertical dead end for an air chamber will absorb the pump output pulse which is a fraction of an ounce and smoothed between three "cylinders". A water hammer arrestor won't let you flush the toilet while the dishwasher is running and someone is in the shower without noticing the pressure drop, the pump will sink or swim on it's own in that case, but a gallon or half gallon of stored water in the pressure tank is not going to make much difference there either.

The basic cause of most pump noise is the pulsating output. These pumps are positive displacement pumps with a pulsating output, not a centrifugal pump like a well pump. Any bit of accumulator near the pump output will help dampen that pulse. The softer vinyl hose absorbs some of that pressure pulse. A tee with a section of pipe going up and capped so it holds air will help also, that would be a tiny accumulator commonly called a water hammer arrestor.

I agree, I would not replace the diode isolator with another one. Upgrade to a modern replacement as noted, if it tests bad. I don't think we can say that yet, the voltage could have been normal expected operation as the result of whatever the failure was, either a battery or wiring issue. Obviously could have been the isolator also. The Duvac system basically means the alternator is reading ("remote sense") the chassis battery voltage after the isolator, and NOT it's own output directly. That gives a very rough division of the control between chassis and house batteries that could lead to this from a simple failure.

Unless you're in a rush, I wouldn't jump to any conclusions on the isolator. Test the batteries first, if the chassis was 10V and the house was 17, which ones were hot? if it was the chassis batteries then some cells shorted internally, if the house batteries were hot, that's to be expected at that voltage and I doubt 30 minutes at 17V hurt them. Get the chassis charged 24 hours, then sit 24 hours and then see what's functioning and not. If the chassis batteries are shorted, then they might heat up unevenly while charging. I don't know what you have in that compartment, but I'd hose the whole thing out, water can't be as bad sulfuric acid.

yes, start at the ignition switch, if that functions, then go to the starter solenoid and relay like I described above. Then you've narrowed the problem down to the middle and can dig into the rest of that thread. Unless you can find a relay roughly in the middle of the circuit, then one test cuts your search in half, and easier than the ignition switch, and cleaner than getting to the starter.

Brakes sticking is common if sitting a while or run in the rain and too cold to dry off. But you were messing with the brakes so there's a possibility something is still applied, only you know if you messed anything up. Easy to do with the internals of some of the valves possibly? Nobody has stated it because it's assumed, but you have to release the parking brakes before prying on the shoes or pounding on the drums. That's why it's critical to chock all the wheels. If you can, have somebody in the seat to apply and release the brakes so you can observe movement of the linkage, it should be tight when applied and loose when the service brakes and parking brake are released. If the linkage does not get release, then you still have air pressure to the chamber.

If you can get to the starter, hook a wire with an aligator clip to the small terminal on the solenoid (either the big solenoid, or the smaller relay) and a test light, then go up front and try to start it. First test the setup on the large battery cable to make sure it works. If you get voltage there or not tells you which direction to go, the starter or the vehicle wiring. Probably have a start relay somewhere, maybe integrated into a control module, the older Allisons sent the start signal through the allison VIM box. I can't tell you exactly what you have on the vehicle side of the solenoid, but you can easily test for start signal voltage at the solenoid then the relay on the starter, and go from there. If the headlights stay on while cranking, then the batteries are fine, or you could check the voltage while trying to crank, but it doesn't sound like batteries.

Looks like that has air drum brakes, is that right? Do you have experience with air brakes? here is the clearest explanation of the slack adjusters that I found: https://transportengineer.com/wp-content/uploads/2017/02/Adjusting-S-Cam-Brakes.pdf You're not likely to have worn out the brakes on a motorhome, but the slack adjusters could sure be sticking enough to affect braking. If the slack adjusters don't go over 90 with full pressure applied by somebody sitting in the driver's seat, then I'd tee into the lines somewhere and run a line to the dash for front and rear applied brake pressure. Some older trucks had those gauges in order to keep track of pressure needed to warn of situations like this. There are other valves that could be affecting pressure, but you'd have to check the pressures to know what's going on. I don't have enough experience to guess.

Yes, probably best to learn to drive it like a truck that the axles and brakes came from instead of a car that it will never be. Using the right gear, and knowing how and why you brake is key. The engine has more braking at higher RPM, and most engines are allowed to spin faster in braking than they will run on their own. The transmission is programmed to handle this automatically, including shifting to a higher gear if the engine speed exceeds the limit. That is when you use the brakes, to keep the engine in the desired gear. Or to slow down enough to get into a lower gear if you've made a mistake and are too high. The reason you slow down firmly then release is because of the drum brakes and cooling. So much of the surface of the brakes is covered by the brake shoes when they are applied, it cuts down on the air contact that cools the drum and shoes. If you apply the brakes firmly only long enough to bring the speed down a few hundred RPM to stay under the engine redline, then release the brakes then that airflow can continue to cool the brakes as long as they are not applied. That's not quite as important with disc brakes, but not enough reason to switch, as disc brakes can't take the heat of a long downhill all that much more than drums, they just fail different. Another thing to do to be nice to your brakes, apply and hold them lightly several times at the top of the hill before you've hit a speed that you need to apply firmly, the cast iron cracks and checks mostly from applying brakes hard when the metal is cold, so warm them up gradually before you need to use them hard.

Michael, I was confusing your boost solenoid with the big boy system because I wasn't focused on your system. That intermittent duty solenoid should work fine for a boost solenoid replacement with intermittent use. You can use a Delco 28SI with the duvac system required with the diode based isolator (the red or blue one with an extruded aluminum housing and three big terminals), as all 28SI's have a remote sense terminal, optional on 22 and 24SI's. Or replacing the diode isolator as suggested is worthwhile also, but not needed to use a delco alternator. The belts issue could be a lot of things. Spin the alternator with the belt removed, it should be obvious if there's anything wrong with the alternator or pulley. Same with the crankshaft pulley, that should spin true with the engine running and no belt installed. Weird things can happen with a failed harmonic balancer or bent crankshaft, but we'll just not think about that for now. The tensioner is the easiest fix, and possibly the most likely issue, spin that by hand feeling for any roughness or play. Same with the water pump and fan drive. The water pump will usually leak before destroying the belt, but you want to check that especially due to the importance of the water pump.

That relay looks suspiciously like the solenoid on any direct drive Delco Remy starter that came on most Cat or Cummins engines up until gear reduction starters took over. It's POSSIBLE that they re engineered the coil to be better suited to this purpose, but I bet they used stock parts and the pulse width modulation allows the intermittent coil to function continuously. Regardless of the coil, the contact end is the same, and looks like the Big Boy gets dirtier than a starter solenoid, but doesn't get as worn down from arcing, so a Big Boy could be a convenient source of parts to get a Delco direct drive starter working in an emergency, or a replacement Delco solenoid could supply parts for a Big Boy rebuild if the plastic was cracked, or the copper bolts twisted off, possibly even replace the coil and all contact parts by swapping the plunger, but I won't promise that. I haven't found any info on how much is interchangeable, other than it's obviously the same design. Michael, did you do your testing with the plunger installed and moving correctly? a coil will draw too many amps and burn out without the correct "core".

Thanks for that info. Cummins removed the filter on the C series sometime around 2010 ish, so they agreed that it was not needed with OAT coolant. Some may say that was cost cutting, cheapening, etc. I bet a lot of RVers keep the filter, even though 100-200,000 miles isn't going to wear out a water pump like an over the road truck could in the old days. Good to know the threads might be there for emergency use.

Exactly, one is a low pressure warning switch, and one is the pressure sender for the gauge. Even with an oil pressure gauge, low oil pressure switch, coolant temp gauge, coolant high temp warning light switch, I still have two or three more senders on my engine for the gauges at the back, and something else still? For the price of the other sender, I'd try one before checking the oil pressure regulator, but check your wiring harness connector to see if you need to buy a sender with the connector included to splice it in.

Aside from something returning water to the tank, air could cause the pump to run constantly only if the air is in the pump and keeping it from pumping. That should flush out on it's own in a few seconds with any water use, UNLESS there is an air leak between the tank and pump and the pump is continually sucking a mixture of air and water? The only other thing I can think of that would keep the pump running constantly with poor pressure is debris getting in the check valves of the pump. The pumps I've seen are diaphragm pumps that are easy to take the pump off with a half dozen or so screws, then look at the rubber flapper valves for debris or damage.

The gunk in the plastic bowl looks like classic bio diesel gone bad. Some of the parts in the metal filter look like they sure could be from a fuel hose. Are there any unnaturally rounded smooth chunks, or bits with a grid from the woven hose reinforcement? Those would be the smoking gun that's it's hose material. The plastic bowl stuff looks like it would be softer dried varnish like stuff, from bio diesel.