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February 2009 4x4 Tech Questions - Techline

Willie Worthy | Writer
Posted February 1, 2009

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'73-'87 Chevy K-Truck Primer
Question: I'm 15 years old and looking to buy a '73-'87 Chevy 1/2-ton pickup. Is this a good truck to buy? The two purposes of this truck are to get me around and mud racing-I won't be riding on rocks. My plans are a 4-inch lift, 34-9.50 TSLs, and spools front and rear. Will this wear out my tires quicker because they're always locked? I also plan to use new U-joints, 1310s probably, as well as a slip-yoke eliminator and some hop-up parts. Does this truck have a Dana 30?
Cody Giles
Danville, VA

Answer: Well, let's start from the beginning. In 1973 Chevy did a major restyle of its trucks and basically shared the same body and a lot of the driveline components up until 1981, so if you're looking for an early truck, I would stick with these years. But then again, the next-generation trucks aren't that bad up to '87 when they switched to IFS.

One thing that you will surely want to do is buy one of the numerous kits that strengthen the area where the steering box mounts, as this is a notorious weak spot that tends to crack and break.

Forget about spools for either front or rear if you plan on any street driving; they are one of the quickest ways to break axleshafts. With no differential action, the tires must skid when going around a corner, which not only causes a lot of tire wear but handling issues as well.

The front axle is usually a Dana 44 (up to '78), but you may find one under even a truck as late as 1981. Then came what is referred to as the "10-bolt" (number of bolts that hold the ring gear on the carrier). The two are very similar, and GM just seemed to put in what they had available at the time. The 10-bolt is easily distinguished by the squared-off ears on the bottom of each side of the housing. They are nearly equal in strength, but my choice would be the Dana 44.

All the 1/2-ton trucks had the Corporate 12-bolt in the rear up until about 1979, after which they switched to the 10-bolt style. For comparison, the 12-bolt uses an 8 7/8-inch ring gear and 30-spline, 1.28-inch-diameter axleshafts, while the 10-bolt has a smaller 8 1/2-inch ring gear and 28-spline, 1.195-inch axleshafts.

Aftermarket axleshafts for both the front and the rear are available that greatly increase the strength factor. If you go for a true 3/4-ton model, you will get a full-floating 14-bolt rear that is quite strong, and a heavy-duty Dana 44 up front that has stronger axletubes and larger spindles. The 1-ton model will have the very stout Dana 60.

There were lots of transfer cases used, depending on the year and the transmission used, but I think that I would stay away from the NP203 full-time units and go for the pretty-much-indestructible 205. As far as a slip-yoke eliminator kit goes, it depends on what transfer case you come up with. Most likely, you won't need one if you keep the lift in the 4-inch range as the driveshaft is quite long, and this helps to reduce the angle between the transfer case and the rearend. Some late NP205s did have slip yokes as well as the 241s, and kits are available for them if you think you're really going to need one. I would try to stay away from the NP208 transfer case, as they are not as strong as the others, and for mud use, you really don't need the lower gearing that it offers.

For suspension you should consider one of the lift kits that include a shackle flip kit for the rear such as the one from Off Road Design (www.offroaddesign.com). This is one easy way to lift the rear of the truck about 4 inches and still retain the stock springs. By the way, the company's website is full of great information on building Chevy trucks and offers just about anything you will need or think you will need.

As far as tires go, you might think of something a bit wider than those 9.50s. The name of the game in mud is lots of tire contact, but keep in mind that "mud tires" are not the greatest street tires. While they may look cool and offer great traction, they also are hard to balance, noisy, kind of skittish, and wear quite fast. Maybe consider a second set of tires for the street.

GM Axle Tech: Whether To Weld
Question: I have a 3/4-ton '77 Chevy with a 10-bolt Corporate front with a welded front differential. I have popped the front axle U-joint caps off regularly. The last time before I went out wheeling, I welded the caps in 45 degrees, 180 degrees apart, and they still broke. I contacted Warn Industries and they don't offer a stronger upgrade in my configuration.

Please let me know if I have any options. I am thinking of welding the U-joint caps in all the way around.
Larry Abbott
Eaton, OH

Answer: Welding is not the way to go. The steel composition of both the axleshafts and the U-joints does not like to be welded to. Even if you weld the U-joint caps all the way around, it's still going to break right next to the weld in time, and what are you doing to the temper of the needle bearings? What happens when you do break the cross section of the U-joint and have to replace it?

If you keep blowing the caps off, the solution is to machine a groove all around the axle yoke so that it will take a full-circle clip instead of those half-circle clips that came from the factory. The half-circle caps have a tendency under high torque loads to move off the cap. You can have a machine shop do this for you, or actually with a bit of work on your part you could do it at home. You want to make sure you have the proper-size circle clips at hand before doing the machine work.

I also suggest that you make sure you're using the new cold-forged Spicer style 5-760X U-joint and not the older and weaker hot-forged 5-297.

I think that you have by now figured out that the welded front differential is one of the causes of your U-joint problem. I would never recommend anyone ever trying to run a spool in the front, let alone welding up the differential. The U-joint has become the fusible link in the driveline, so the axleshafts are going to be next.

If you're unable to find any quality alloy axleshafts for your axle, you could have some custom axleshafts made, as there are several companies that can do this. They will be expensive but not prohibitive in cost. A couple that come to mind are Moser Engineering (www.moserengineering.com) and Dutchman Motorsports (www.dutchmanms.com).

Wants More Power From 300 Ford I-6
Question: I have an '83 Ford F-150 stepside pickup with a 300ci inline-six motor. I would like to know if anyone makes a tri-power setup for this engine and a dual-outlet exhaust system. The motor is great on gas, but I want more power and do not want to swap out motors and all the other accessories.
Larry Peyer
Torrington, CT

Answer: Maybe if you spent a lot of time searching the swap meets and some Internet sites you may get lucky and find a 3-into-2 setup that someone made. After a lot of searching on my part, I was unable to come up with anything. Clifford Performance (888/471-1161, www.cliffordperformance.net) offers a nice four-barrel manifold, and my choice of carburetion for it would be a 390-cfm Holley. The company also offers a bolt-on throttle-body EFI system.

For the exhaust system, the easiest way to go would be to swap out for a factory fuel-injection exhaust manifold as these flow a lot better. Headers are also available from Clifford Performance. I believe that Hedman Headers (562/921-0404, www.hedman.com) also has some headers available.

If you are really looking for more power and better performance, swapping to the '87-and-later cylinder head lets the engine breathe so much better. Then again, you could just swap out a complete injected motor and its engine wiring harness for your carbureted version and get both better fuel mileage and performance.

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