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Kind of a basic breakdown of the different m939 generations: M939: NHC250 engine, auto trans, 11x20" tires. No CTIS M939a1: NHC250 engine, auto trans, 14x20" tires. No CTIS M939a2: 8.3 liter turbo engine, auto trans, 14x20" tires. With CTIS There are other small differences but that's the big...

Maximum rated temp at the exhaust manifold collector is 1200F with the mostly aluminum alloy pistons in the nhc250, 1150F is safer for extended high temps. The different alloy temps used in the other 855 series engines (335, 350, 400, etc) tolerate higher temps. Backing off the throttle...

Currently non turboed with the pyro mounted into the manifold a little before it's flange on the m816. When driving I keep it below 1150 but if I don't pay attention it will easily go to 1400F (not good). Fuel was turned up before I got the truck, haven't opened the pump to find out what button...

That's the fuel tank plan for it, suburban 40 gallon mounted behind the rear axle once I find one for a decent price ($300 between new tank and sending unit is too much right now). Averaged 18.6mpg cruising at 60mph with the stock 235x85x16 tires at roughly 2400rpm, stepping up to the 37"s will...

Hardest part of the front axle disconnect is deciding where to mount the switch. With the transmission tunnel removed it's easy access to the plumbing. Also with how I plumbed it mine is only disconnected when driving forward, it still engages automatically in reverse. If you want to disable the...

Haha before the m35a2 I had a 87 Chevy 3+3. Worked over 454, sm465 manual, np205, dually with a 9ft long flated sitting on 6" lift and 35"s. Sold it after partway through with a frame off rebuild and have missed having it. New one is an 82 with the 6.2 diesel, th400, np205 dually. Plan is...

I didn't have that problem. With the 4cyl you can move the engine forward if there is a clearance issue. With the 6bt though there is very little wiggle room.

UV rated but the sun still breaks down the synthetic cable over time. Plan is to make a cover for the crane to protect it when not in use and extend it's life. Synthetic cable became approved for cranes a few years ago. This is a test run for using synthetic on one of these trucks and I'm not...

Before I had the wrecker I had a 87 crew cab k30, installed a 4bd2t and nv4500 into it. Complete frame off rebuild. Reinstalled the cab first then the engine/trans after it. Firewall and transmission hump was never touched with the 4cyl and nv4500. a 6bt is TIGHT front to rear and some people...

Excuses excuses haha. Wrecker has currently taken a back seat to project priority since it is mobile again. Sold the house back in Texas finally and bought a truck that is durable enough to survive my uses, 82 GMC 1 ton crew cab. Biggest problem for me with the truck is the total length...

Either the dual circuit upgrade with pinion brakes as parking/emergency brakes, or swapping to air brakes are both good viable options. I went with the conversion to m939 series air brakes because I got the wheel ends (drums, backing plates, shoes, etc) in a trade. Lots of details and pictures...

The 4L80E has been swapped into a bunch of trucks/k5s/suburbans of this body style without body clearance issues. So no need for a body lift or modifying the transmission tunnel. The 4L80E is basically a th400 with an overdrive, a locking torque converter added to it and a computer to control it...

Allison requires either a 1" body lift (minimum) or the transmission tunnel being reworked and the np205 can be adapted to it. Trans absorbs more power than other models. Cost and a much more expensive stand alone computer are big factors. Unless you're cranking up the power above 500ft/lbs...

6.2, 6.5, 4bt, 4bd1t/2t, 6bt are all available with mechanical injection. Reliably the 4bd1t/2t and both Cummins engines are capable of 500k+ miles before rebuild. The Isuzu engines are sleeved, rest of the engines listed are not. 6.2/6.5 I know people with more than 400k on their engines with...

Ah gotcha. With it sitting 12 ft forward it will be snug but should be fine. The chassis are the same on the regular 5 tons. Wreckers and the extra long wheel base trucks got extra reinforcements.

yea that will be fine. The chassis is either 21 or 23ft long if I remember right. If your ISO is 10ft then it's the same size as the dump bed in the pics (minus the cab protector).

The fuel shutoff solenoid on these are simple, doesn't send any info back to the PCB. No clutch safety switch or any tcase safety switch. Sounds like either a loose wire or a bad ground.

The main problem with the 6.2/6.5 is that they really don't like getting over 215F coolant temps and GM kinda screwed up their cooling systems. On the 6.5 the factoy turbos are phenominal at building heat and choking the exhaust flow. With the electronics GM put the PMD right in the intake...

6bt is overkill for a blazer and makes for alot of front end weight. Can build a 6.2/6.5 to make good power reliably. 400-480ft/lbs torque. Smooth operation, truck is designed for that engine, etc. 4bt Cummins or the Isuzu 4bd1t/4bd2t are great swap choices. Easy to crank them up reliably to...

Yea if the stock brake components are there, I'd recommend using them. Have about $900 in fittings/hoses/valves with the air brake conversion on my m816 so far. For a parking brake with the stock hydraulic brakes you might be able to use the factory one installed on the transfercase and rig it...