03 Detroit 60 series 12.7 Jakes rattle like metal on metal? like hammer inside?

Check the upper stack mounts, could be a bad bushing and it’s rattling right by your head where it mounts above the door.

 

Detroit jakes sound like someone beating on an old soup can at the best of times lol.

 

If stage 1 & 2 feel the same, after checking wiring/switch I'd go to the solenoid. The one Series 60 we had would go through a jake solenoid every 9-12 months.

 

The fan problem is common. My 92 WS w/Cat had that problem, it had a Bulletin, the fix was to move the fan solenoid further away from the fan, to the firewall. My 99 Classic did it, it had a bulletin upgrade harness for the fan solinoid. I forget exactly, but had to crimp a couple connectors, and install them into the pigtail on the harness, took me years to find a Dealer ( Freightliner Youngstown) that knew what I was talking about. I spliced the harness myself. They even loaned Me the fancy crimp tool. Truck did it since almost new, for years, had read about the upgrade, but no one seemed to know anything. My newer 01 has had the same problem. Not sure if it needs the same upgrade, but I don’t think so. I think it has something to do with the power distribution module. Something they added in 2000, from what I understand. It’s a 4”x6” box that sits in the bottom of the fuse panel, says PDM right on it. It controls the function of 3 or 4 previous sensors that were eliminated. One of its functions has to do with the fan. I know that’s pretty vague. But it’s a start. All 3 Trucks, different causes. I was going to change my PDM, but I think my fans working correctly now. I’m pretty sure yours has a PDM. I’ve replaced so many things, A/C pressure and fan switches, coolant sensor and pigtail, rebuilt fan. All things that were needed. I can’t remember exactly what I suspect fixed the fan. But I think it’s working right finally, not sure yet. I may still need to change the PDM, the harness to mine has a broken wire, just haven’t fixed it, since the fans been working right. Fan will come on with defroster on, due to A/C compressor running, and high pressure fan switch, that’s normal. Anytime the A/C is on for that matter, especially when idling, or going down the road, if overcharged. I try to only do one repair at a time, so not to get lost in the diagnosis. Jakes are supposed to be like you said. 1st switch-1 jake, 2nd - 2 jakes. Both together= 3 jakes. Should be able to HEAR the difference if working right. Maybe the wastegate is opening and causing the different sound and boost? I can’t tell you how many times I’ve imagined a rod knock on my Detroit’s. It’s over my head, but sometimes it sounds like it does when it’s cold. Lots of spark knock. Seems to happen when it’s real hot outside. So it’s something with timing and temperature readings, atmospheric sensor maybe? I don’t know. The Jake noise? Aside from an exhaust manifold leak? Heat shield, around elbows, or on crossover, for A/C lines, pipe cracked at the Y weld, bad flex pipe, or a part of the old muffler inside the y pipe/cross over, no telling. I once blew an injector and at the same time, the y pipe split wide open. Fixed the pipe, but it still ran terrible and was a lot louder. Doubt you have an injector problem, if it’s running decent. Check the y pipe, good. Make sure nothings stuck in there, like part of the old mufflers. They rot out. Sounds like they left a Jake unhooked. Maybe the harness is bad. They’re known for bad injector harnesses, pretty common. Might as well put a new one on, if everything’s hooked up right already, while they’re in there, would at least rule it out, they’re only about $150, pretty simple to change yourself, and inspect the 4 small screws that hold the injector solenoids together, they’re known to break, sometimes they just come loose and fall out, and seep fuel. Injectors either blow a tip, and run terrible, or leak fuel from a cracked solenoid. I had one break, and ran it 60 miles, put 10 gallons of fuel into the oil, it was squirting fuel like crazy. Other injector problems are the cups get damaged, and leak. They have a crush washer that can be used in the seat, to seal up damaged seats, otherwise you have to remove head to change them.
Make sure the cac hoses are tight, along with the 1” hose from intake to compressor, they’ll fail and leak at the compressor, where it’s hot. it’s hard to get to, hard to see or hear a small leak. Once it’s bad enough you’ll hear it, boost will fall off, a lot.

 

I don’t know how many miles you have, but the bearings on the bottom end are known for looking like new even at 1,000,000 miles. I checked my receipts. I paid $241 a yr ago from Local Freightliner in Detroit area. My mistake. Injector harness # 23526101. Engine harness was $318, part# 23522323. Don’t know your part #s but you can try SAE Auto in Redford Mi. @ 313-817-1722. They have about the best prices on OEM Delphi parts. Others on EBay are $240-$300, claim to be OEM, not sure I’d trust them. I trust ArkValley on eBay, theirs is $300. So you’re in the ballpark, at $385 Canadian.