1986 Chevrolet M1008
6.2L Diesel & TH700R4 Automatic.
Where the truck came from: It was 2003 and I had been driving my 1965 CJ-5 jeep for almost eight years, and was thinking about a new project. I was leaning toward a truck since I was hauling a trailer every two weeks to the local landfill, and I was considering a camper. I was reading my 4wd magazine about HD trucks. They listed the M1008 as one of the bargains; I had been interested in diesels so I thought an M1008 was a good start. The non computerized, non turbo, low tech diesel seemed like a good place to start since I had been doing gasoline engines since the 80's. I went to Ebay and found several M1008's. There was one 1986 M1008 truck in Texas that had a dead engine and a decent body, so I bought it and had it shipped up to northern Virginia. I think that was about the time I joined The Diesel Page. When the truck arrived the first thing I did was a compression test, it failed as I suspected so the rebuilding of the truck began.
Transmission conversion: The truck came with 4.56 gears in the front Dana 60 and the rear 14 bolt full floating axle. At the time the only matching pairs of ring and pinions I could find was a 3.73 ratio, not a whole lot of difference for the money. I decided that the money would be better spent on an overdrive transmission to make it more useful on the street (4.56 x 0.7=3.19), besides going from a first gear ratio of 2.48 in the TH400 to 3.00 in the 700R4 with 4.56 gears sounded like it could handle any size tire. I started by pulling the transmission and the transfer case out of the truck. The input shaft on the NP208 transfer case was set up for a TH400 transmission which has a different spline count than the 700R4 transmission. You can either get another transfer case with the correct adapter, like that out of a Suburban with a 700R4 or change the input shaft in the transfer case and get the correct adapter plate to mount the transfer case to the 700R4. You can find a lot of what you need on ebay and the internet, which makes finding the correct input shaft, the correct adapter plate, and a transfer case rebuild kit somewhat easier. The correct 700R4-6.2L engine flexplate was also purchased. I could have scoured the local salvage yards for the correct 700R4 column linkage, but it was easier to buy a 700R4 cable-column linkage kit from Lokar.com. You spend most of the time with the transmission in drive, so holding it in first gear wasn't that high on my list of priorities. I have control over 2nd, 3rd, overdrive, reverse, neutral, and park - good enough. I installed an OD switch to lock and unlock the torque converter; it stays locked most of the time to generate less heat. The stock transmission cooler in the radiator remains in place, but is supplemented by an aftermarket transmission cooler along with two electric fans. The transmission also has a temperature gauge; I really haven't hauled any large trailers so the transmission temperature mostly lags behind the engine temperature. I use the electric fans when the engine gets above 200°F while on the interstate in the summer.
My only initial complaint about the transmission was its full-throttle shift point. The transmission would stay in first gear and the diesel engine governor would limit the engine RPM before the transmission would shift, (the transmission wanted 4500 RPM to shift, but the engine stopped at 3600 RPM). I took too long getting the truck running and the transmission shop went out of business, so I was left on my own to fix the full throttle shifting problem. I originally thought the transmission shop had put the wrong governor in the 700R4, so I ordered the TCI governor calibration kit. I took out the existing governor and discovered the weights on the governor were heavier than those provided with TCI kit, so the governor was correct. One of the springs in the governor was lighter than the other, so there was at least some adjustment left. The instructions for the TCI kit can be found at: http://www.tciauto.com/Products/Instructions/instructions/326500_inst.htm.
The TCI kit is OK, but if I did it again I would search for a transmission governor calibration kit for diesel engine applications. Since heavier weights produce earlier full throttle shifts and the springs can fine tune the shift point, the only thing to do was put the stiffer spring in. The heavier spring worked, the full throttle shift now happens before the governor in the fuel injection pump limits the engine RPM.
Engine: I pulled the engine and started the disassembly process, and shot lots of reference photos along the way. I was lucky in that the block had no cracks and was a good candidate for a rebuild. I took the block to the machine shop I usually deal with and had the block bored to accept new pistons, and had the crankshaft polished, etc. I just cleaned the camshaft and had new standard bearings put in the block, which would prove to be an annoyance since the oil pressure suffered somewhat from that decision. The only upgrades were the DSG gear-drive timing set, replacing the timing chain, and the installation of a main stud girdle kit.
Glow Plug System: The stock military hybrid 24V/12V system does a fine job when it's working, but I elected to convert the glow system to that used by the civilian models. The instruments in the cab and the lights on the truck were already powered by 12 volts, so converting to a single alternator and 12V starter when you have it all apart isn't too difficult. I purchased the CUCV maintenance PDF off of the internet for $20, which was money well spent. The CD has over 4600 pages on it. After some searching several really good wiring diagrams were found. The 1985-93 glow plug system as described in The Diesel Page's chapter 13 of The 6.2L/6.5L Diesel Troubleshooting & Repair Guide was installed. As part of the glow system conversion I hooked up the original "Wait" light on the dash, and it works great. I have a single toggle switch for the fast-idle and timing advance. Soon after starting the engine, I just toggle the switch off (I live in Mesa, AZ - it doesn't get that cold here). The two Red Top Optima batteries are connected in parallel, using the military style terminal strips, which made the battery connections easy.
Starting system: I began the journey with a gear reduction starter, but after a year and a half it died. I read a post on the bulletin board the other day saying the gear reduction starter is not much of an upgrade, so I elected to install the old style boat anchor style starter from NAPA, which appears to work fine and has a lifetime guarantee. I made the front support bracket from some steel I had lying around.
Tires: Before the sub-prime mortgage and Wall Street implosion and before the gas crisis, a lot of people were buying Hummer H2's and putting expensive rims on them. I read one of the posts referring to how people were nearly giving away the stock H2 rims. He was right - after doing a local eBay search I found four H2 rims with worn tires for $100, if you don't have to pay shipping it's a great deal. I quickly found out the need for a dual steering stabilizer. Most recommend the use of dual steering stabilizers when installing 35" or taller tires. The H2 tires are 34.5" which made the installation necessary. I also installed an add-a-leaf on the 2" lift springs. Now I can go over railroad tracks at 40 mph without a problem (the flat kind of crossing, not the ramp style). The larger tires look good and help offset the rather low 4.56 gears.
Paint: Who cares? The truck lives in the low humidity of Arizona, the sun would bake a paint job in a couple of years anyway. The truck has a nickname "The BUTT" it stands for Big Ugly Tan Truck. My BUTT is parked outside next to the garage; sorry my 67 GTO stays inside the garage. I've had this car since 1981, and it gets preferential treatment.
Temporary setback: 2006-2007: The truck was running, the oil pressure was within limits, but seemed low since all the crankshaft bearing tolerances were very tight, from what I remember the plastic gauge readings for the crankshaft were consistently on the low side. After about 10,000 miles I could hear the #8 cylinder going in and out. Eventually the cylinder went dead completely. I did a compression test on the number #8 cylinder: zero, yea stuck valve. While I was at it I did a compression test on all the other cylinders. The #3 cylinder barely passed, but all the others were around 400 psi. Since I had to take off one head for the #8 cylinder and something was going wrong with the #3 cylinder. I decided to pull the engine and put it on the stand. I pulled the passenger head and one of the valves was stuck open, you could shine a light through the intake side and see. The driver side head #3 cylinder looked like part of the pre-combustion cup broke off and beat up the #3 piston. I had heard a weird ticking sound on that side of the block, it wasn't like a rod knock, but I couldn't figure it out until I saw the piston. I think the piston was rocking back and forth in the cylinder making a ticking sound. The #3 cylinder was all scraped up, so it needed to be sleeved.
I was now living in Mesa, AZ and was far away from my Norfolk, VA machinist. After talking to a local diesel mechanic, he recommended Continental Diesel in Phoenix. I started by taking both heads to them to see if they could be fixed for a reasonable price, and they did a great job. I took the block; beat up piston, and the camshaft to them. I read one of the posts talking about how camshaft tolerances affect oil pressure, so I asked them to look at the camshaft and cam bearings in the block. They sleeved the #3 cylinder, polished the camshaft and, installed different cam bearings. Since the head bolts had been used an unknown number of times, I decided to go with a head stud kit from ARP fasteners. The studs are nice; I'm sure if I ever have to take off a cylinder head I'll have to pull the engine out of the truck. I think pulling the engine out of the truck makes it a lot easier, since everything on the 6.2 is heavy. All of the crankshaft bearings were still good, so I re-used them. The camshaft was the culprit of the low oil pressure; it's now 40 psi at idle. The previous idle oil pressure readings would drop down to 15 psi at idle.
Final State MPG and uses: The truck starts up and has been going since early 2007. I average 16 mpg for city and highway, not bad for a 6000 lb truck with 4.56 gears. I'm an electrical engineer during the day, but have home improvement projects and other automobile stuff I use the truck for. Several loads of sheetrock, a pallet of landscaping pavers, countless trips to the landfill, the truck pulls its weight and is the working member of the vehicles. An eight foot bed is nice; you can get the guys at Home Depot to load the sheetrock and other pallets with a forklift. My wife used to be in the Air Force, she drove an M1008 on one of her tours in Germany. Selling the idea of a M1008 project truck to her was easy. My wife drives and likes the truck too. Eventually we'll put a get a slide-in camper and we'll use it for some Arizona camping. I also use the truck as back-up transportation, such as when my parents are in town and I let them drive my 2005 Hyundai.
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