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That jogged my memory. I think that's how I did it, too.

I don't remember. It was too long ago. I still haven't gotten around to putting in my replacement actuator, because I've been fixating on other hobbies and ignoring my green trucks. I'll become re-obsessed with the trucks again eventually. :)

My previous shutter stat repair worked for a while, but after using the wrecker yesterday, the shutter stat valve started venting air out the small hole in the end again. I guess I'm going to need to order a new one after all.

I thought that they were built to run ATF, Allison recommends ATF, and the military used SAE10 motor oil just to simplify their logistics.

I think that I have fixed my shutter stat. I replaced three of the smaller o-rings for which I had the right sizes in my o-ring kit. I didn't have quite the right size for the larger o-ring, and I left the one under the crimped retainer alone. I cleaned out the valve and lubed the o-rings with...

Thanks! I see the part number and supplier for the shutter stat in there. The one I just pulled out is rated at 190F while the one pictured is rated 180F, but I don't think that difference in fan turn-on temp should cause any harm. I got my shutter stat out of the truck, and I'll try to take it...

The sound was still coming from the intake stack when I opened the filter housing, so it must be from one of those vent lines that I finally found plumbed into the stack, hidden behind the filter housing. A leaking brake treadle valve sounds like a likely culprit. Back to the original topic, I...

AHA! Look what I found plumbed into the air intake! I need to trace the lines to figure out what they're for. They were well-hidden, and I didn't find them until I removed the filter, still heard the sound coming from both the intake mushroom and the filter housing, and then felt around behind...

Isn't the fuel tank vent that tube clamped along the side of the intake stack? I verified that the sound comes from the intake mushroom rather than that small tube by plugging the end of the small tube with my finger. I guess I can try loosening the fuel tank lid to see if the sound is caused by...

I ran it again, and that leak sound still sounds like it's coming from the engine air intake mushroom. I popped both the oil fill cap and the coolant reservoir cap after shutdown while it was still making the air leak sound, and neither the coolant system nor the crankcase appears to be...

Sure, here are some pictures. Nothing looks wrong to me, but I'm still new to the world of M939-series trucks. Note that the tach cable and the air supply to the fan clutch actuator are both disconnected and tied off to the windshield washer fluid reservoir bracket, and the air supply line is...

Hmm, it gets stranger now. I disconnected the air input hose at the fan clutch actuator to get that problem out of the way while I look at the other one, and I plugged the dangling hose with a pressure gauge. That pressure gauge tracks the gauges in the cab, the governor cuts out just above 120...

Thinking on it some more, I do not recall hearing either of the pop off valves venting. I still need to fire it back up to take a close look at the pressure gauges. I checked the P2P, and it only shows the compressor and filter restriction gauges tapping off the engine air intake, which makes me...

I'll check on that stuff next time i fire up the truck. If my governor failed and caused an overpressure, then maybe that's what took out the fan clutch actuator at the same time?

Well, that's what I was afraid of. Since the compressor draws its air from the engine intake manifold, maybe I also have an issue in the compressor head that's causing it to leak back into the manifold when shut down? It just seemed like a weird coincidence that both symptoms appeared at the...

Looks like I need to dig into one of these now, too. When I shut down my M936A1 after doing some work on it today, I first heard an air leak coming from the engine air intake. Not the vent tube along the side of the intake pipe, but the actual air intake. It stopped after a minute with a humming...