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July 2009 4x4 Truck Repair Questions - Tech Line

Willie Worthy | Writer
Posted July 1, 2009

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Solid Axle Swap For New Ram 1500?
Question: I have a 2006 Dodge Ram 1500 with the Hemi, and I've done all the performance mods, so now I'm looking to tackle the suspension. I've looked high and low for a good suspension, and the only one I've found that I like is the new kit from KORE Offroad, which is $2,500 just to raise the front two to three inches. So I was thinking of ditching the dreaded IFS and going with the Dana 44 out of the new JK Rubicon. I don't know the track widths of either of the two axles, so I don't know if it would fit, but since the 44 is set with selectable-lock high pinion and 4.11:1 gears, it's already a great choice. The other options would be custom, or the new Power Wagon axles, but either would be expensive and the Power Wagon axles are hard to find.
Sam Dosch

Answer: While at first this sounds like a great plan, when you dig deeper into it, you will find all sorts of problems. While I should actually do some measuring (but again, that is something that you could also do), my gut feeling is that the track width is too narrow. The second problem with this idea is that the JK axle tubes are not really strong enough to handle the weight of the heavier pickup. The tubes, as well as the "C" yoke, have been known to bend.

Yes, you could swap out to a solid axle from an earlier Dodge truck, but you'd better have a handle on your fabrication skills as it would take a bit of work to make it all come together. Not that it wouldn't be possible, but I know of no company that makes a direct conversion kit.

Yep, it's expensive to raise the new breed of IFS trucks, as there is a lot of design work involved to keep the proper geometry of the system. If it's not right, problems such as excessive tire wear and poor handling can be the results.

Wants To Mate NP 208 To SM 420
Question: I have an SM 420 transmission from a 1951 GMC pickup, and I want to know if I can put the transfer case off of my 700R4. It's an NP 208 from a 1985 Chevy K-5 Blazer. Would I need any adapters?

Answer: I spent a considerable amount of time searching for such an adapter, and came up empty-handed. The early SM 420 transmission is short and compact as well as offering a very low First gear. There are some downsides involved in such a conversion, even if you should find an adapter.

First, the transmission is, well, old, and most likely pretty worn out, so a complete rebuild would be in order. (Just as a note: Novak Conversions offers completely rebuilt units.) Second, it shifts like an "old truck transmission." Third, the gear ratios are very wide-spread, leaving some pretty big gaps between gear changes. Due to differences in lengths (the 420 being about 10.5 inches long and the 700R4 being 23.4 inches long) you would definitely require longer driveshafts.

Your 700R4 has some advantages over the 420 in that it has a fuel saving overdrive gear, and in reality, when you count in the multiplying factor of the torque converter, almost as low a starting-out gear.

Just as a note for you guys with CJ Jeeps: The compact length of the 420 makes for an excellent swap for short wheelbase vehicles. Bolt it up to a Dana 18 transfer case, and add a rebuilt Warn or present Advance Adapters Overdrive unit, and you can almost split the gears perfectly, giving you eight forward speeds in high-range alone.

Chevy 1/2- and 3/4-Ton 10-Bolts: The Same?
Question: I would like information to help me decide which front axle to use on my '89 1/2-ton 4WD Suburban. I purchased a set of used 3/4-ton axles to upgrade for the strength and brakes. Unfortunately, after the sale, I found the 3/4-ton front 10-bolt tubing bent. As we all are on a tight budget, which is the next best route? Have the tubes in the 3/4-ton replaced, or transfer the gears, diff, knuckles, spindles, and so on to the 10-bolt 1/2-ton axle? Is the tubing size/thickness the same on the 10-bolt 1/2-ton and 3/4-ton? Thanks-I have been a subscriber since the early '70s, and I am often disappointed with the criticism some of your readers provide. Does this help to get my question answered?
Jeff Cranfill
Ione, CA

Answer: Yes, I've always thought that it was a big joke for GM to use a 10-bolt for a 2500 series (3/4-ton) vehicle. While I have never measured one, it was my understanding that the axletubes are a heavier wall thickness than those of the 1/2-ton version, but I was wrong. According to the guys at Off Road Design, both versions of the 10-bolt use the same-size axletubes. They do tell me that the Dana 44s that were used did have a heavier tube.

Keep in mind that in 1987 (or thereabouts), the inner-axle spline count was increased from 28 to 30 splines. The outer remained at 19 splines. So in reality the only differences between the 1/2-ton and 3/4-ton axles are that you get a heavier hub and spindle assembly as well as larger brakes. Well, and two more lug bolts

To retube or transfer the parts? Tough decision. If you have to pay someone to do the work, it might be less costly to just buy another Dana 44 bare housing. Or better yet, a very pricey Dana 60.

Lifted Ford Leaks T-Case Fluid
Question: I have a '06 Ford F-150 4x4 which I recently raised six inches. I also put 35-inch tires on it. Now it has an oil leak where the rear driveshaft goes into the splined area on the transfer case. I had a new seal installed, but it still is leaking. You can see about two inches on the shaft that used to be inside the case. Any information on how to repair this leak?
Kent Keisling
Harrah, OK

Answer: There could be several things causing the problem. First, it could be a defective seal or improper installation-things like this do happen. Then it could be that the area of the slip yoke that the seal now rides on is not as smooth as the original location and is eating into the seal's lip.

However, I think that the seal leakage is a direct result of the lift kit. The driveshaft has a slip yoke with internal splines that slides over an external splined output shaft that is within the transfer case. When the vehicle was lifted, the distance between the transfer case and the rear end is now longer. As you noted, the slip yoke sticks out of the transfer case an additional two inches. This also means it has two inches less contact area between the yoke and the output shaft. My guess is that there is just not enough spline engagement to keep the yoke from rocking on the output shaft as it delivers power. The seal was never designed as a centering device or support for the yoke.

The solution is to have a new driveshaft built that is equal to the distance that the yoke has extended from the rear of the transfer case. Oh, and just as a note, it's also common for this seal to fail if the driveshaft is made of too light of material where it can actually cause a whipping motion as it rotates, or if the shaft is bent or out of balance. Even the front and rear U-joints being out of phase or operating at unequal angles could, I suppose, cause enough vibration to damage the seal.

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