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March 2007 4x4 Tech Questions - Tech Line

Willie Worthy | Writer
Posted March 1, 2007

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Question: I have recently purchased an '86 Chevy D30 pickup. It is a military truck and it even has a tag stating "Property of the U.S.A." It has a 6.2L diesel, and due to its military heritage it has some unique features such as dual alternators, a plug-in fuel filter, oil cooler, 4.56:1 gearing, and a lot of unique wiring.

I would like to know where I can get more tech info on this truck, maybe even some tech manuals. Parts stores don't list D30 as a vehicle option. Do you know if it is the same as a K30 for the most part?
Rick Carroll
Chatham, MI

Answer: Yes, your truck is basically a K30 with the exceptions you have noted and a bunch of military-only items. And yes again, the wiring is quite unique with its dual electrical system that has two 12-volt alternators and dual 12-volt batteries. Troubleshooting that maze of wiring, should you have a malfunction, could be a real nightmare.

Tech manuals are available, though it takes (in typical military fashion) about 14 of them to cover the truck. It's referred to as an M1008 series cargo truck in military lingo. I think that your best bet would be to order a CD from

Question: I have a '79 Bronco running a 400M V-8 and C6 trans. It has a Detroit Locker in a Dana 44 up front, and a 9-inch with a posi in the rear. I'm currently running 3.55:1 gears in both. I'm putting a 6-inch lift with 15/38.5-16 Boggers and I want to change the gears to a 4.10:1 or so, but I've been told I can't without putting in a new Detroit. Is this true?
Name unavailable

Answer: Yep, you will need a new Detroit in your 44 to make use of those new lower gears. You're in luck with the Ford 9-inch, however, as it will take the lower gears. You may have to do some slight grinding around the pinion support for clearance but it's no big thing. Also, I sure would consider a 4.56:1 gear ratio with those big Boggers, and if you don't drive it much on the street, maybe something in the 4.89:1 range.

Question: I have a Jeep Cherokee with a rebuilt I-6 engine with 20,000 miles on it. For the first 10,000 miles, it did not leak oil, but then it started to leak at the rear main seal. My mechanic has replaced the rear main seal seven times already, but it still leaks! He also replaced the oil pan. He said the crankshaft is worn and it leaks because I used 10W-30 synthetic oil. The engine is still under warranty, but I really don't want to replace it again. I heard from another guy about an offset or double-lip rear main seal. If these exist, please tell me where I can buy them.

Answer: I doubt very much it's leaking because you're using a synthetic lubricant. Yes, I have seen some high-mileage engines leak oil out the rear main seal and other gasket areas that had been using a straight petroleum oil and then switched to synthetic. The detergent action of the synthetic loosens up all the crud that had kept it from leaking in the first place. In fact, the synthetic lube should prevent excessive wear to the crank seal area.

The problem as I see it is that the crank seal area was improperly ground from the remanufacture of the engine. I did some checking and couldn't find any double-lip seal or offset seal for your engine.

In reality, the only way you're going to solve the problem is to have the engine rebuilder replace the engine with one that the guy who did the crankshaft hopefully did a better job on.

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