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Your Top 4x4 And Off-Road Tech Questions Answered Here

Posted in How To: Tech Qa on February 3, 2017 Comment (0)
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Ford Diesel Swap

I have a ’77 Ford F-250 with a 351M two-barrel V-8 engine, NP435 four-speed manual transmission, NP205 transfer case, Dana 60 full-float rearend with a limited slip, Dana 44 frontend, 4.11 axle gearing, and 35-inch tires. I may be getting my hands on a ’87 Ford with a naturally aspirated 6.9L diesel mated to a T-18 or T-19, I’m not sure. I believe it also has an NP205 transfer case, along with a Dana 60 King Pin front axle and a Sterling 10.25-inch rear axle. Should I swap the engine, tranny, and transfer case? Or would I be able to use the NP435? I also have a ’01 ZR2 that I daily drive to college and an old crappy ’02 S-10 4x4. Everything has 400,000-plus kilometers on it, so it leaks fluid everywhere. I wanted to keep the stock axles under the ’77 Ford and swap the Dana 60 and 10.25-inch Sterling under the S-10, rebuild its 4.3L V-6, and swap in an NV3500. Any input is appreciated!

gigz21
Via Instagram @cappaworks

The Ford 6.9L IDI diesel is quite a pig. You probably won’t be very happy with this diesel swap into your ’77. In new condition, the 6.9L IDI makes only 155-170 hp and 318 lb-ft of torque. You could make significantly more power with even a slightly modified 351M.

The ’87 6.9L IDI F-250 and F-350 trucks came with a BorgWarner T-19 four-speed manual transmission. The C6 three-speed automatic was an option. In 1988, the five-speed ZF S5-42 replaced the T-19. The T-18 could be found in the F-150 trucks of this era.

Now, if you aren’t concerned about the low power output of the 6.9L IDI diesel, you can swap just the engine into your ’77 truck. You can mate the 6.9L to the NP435 using all factory Ford parts. However, some people who have made similar swaps say that the wide ratio gaps of the NP435, which were designed for a gas engine, do not compliment the 6.9L diesel. Of course this will depend on application and personal preference, but it is something to consider. You might just be better off slinging the entire ’87 engine, transmission, and transfer case into the ’77 truck.

Wrangler Wiggle Wobble

I have a Jeep Wrangler JK with new ball joints, a new track bar, and a fresh alignment with new tires. It has a wobble in the steering at 60 mph only. The tires have been balanced three times, and the wobble is still there. I even tried adjusting the toe out to 0.32-inch.

@azjag64
Via Instagram @cappaworks

Chasing down a wobble in the steering can be time consuming and frustrating on any vehicle. Few 4x4s are as prone to wobble in the steering as much as the Jeep JK Wrangler. There are many things that can contribute to the problem, and sometimes it’s a combination of issues, which by themselves wouldn’t matter much, but when compounded, a steering wobble surfaces. More often than not, the steering wobble on a JK comes from worn track bar ends, loose track bar hardware, worn ball joints, or worn unit bearings. A fresh track bar and ball joints is a good start, but not always necessary. Another culprit is the steering stabilizer. The factory unit hangs down fairly low and can become damaged, leaking all of its fluid out. If the steering stabilizer looks wet and oozy, it should be replaced.

Typically, I set the toe-in of any solid-axle 4x4 to 1/4- to 3/8-inch. However, I have found that some JK Wranglers have fewer handling issues when toed out up to 3/8-inch. You may have to experiment a bit to find the best setting for your application. Not all Jeeps are set up the same, so different toe-in or toe-out may be needed.

Having said all of that, I don’t think your problem is chassis related. I have a suspicion that you may be running too much air pressure in your new tires, causing them to roll sort of bulbous, which would decrease the contact patch. This can lead to wander and a steering wobble, especially on older or uneven roads. If you are running the original sized and load rated tires, you should be running the air pressures designated in your owner’s manual and on the driver side doorjamb sticker. You should be nowhere near the max psi rating noted on the tire sidewalls.

Larger aftermarket tires will require a bit of experimentation. To do this, you’ll need to find a wide open flat paved area, like a parking lot or desolate road. Use chalk and make a 2- to 3-inch-wide mark across the tread of a front and rear tire. Drive the Jeep straight forward for 50-100 feet and inspect the chalk lines. If they are only wearing away in the middle, you have too much air pressure in your tires. Decrease the pressure, redraw the lines, and make another pass. Repeat the process until you get even chalk wear across the entire tread surface. With the full cross section of the tread making contact with the road surface, your Jeep will be less likely to have steering wobble at any speed.

4.0L Transmission Options

Are there any manual transmission options other than a rebuilt AX15 for all of us who are keeping their trusty 4.0L inline-six engines on the road?

cvip190
Via Instagram @cappaworks

The AX15 five-speed manual transmission can be found behind the Jeep 4.0L in ’88-’99 vehicles. It’s not a bad transmission, and in most cases it’s worth rebuilding unless you plan to throw significantly more horsepower at it. Companies such as Collins Bros. Jeep (collinsbrosjeep.com) offer completely rebuilt AX15 transmissions. Advance Adapters (advanceadapters.com) offers brand new AX15 transmissions, however they will only fit the ’97-’99 Jeep TJ Wrangler. This AX15 application features a 13-degree tailhousing rotation. An XJ Cherokee requires an AX15 with a 23-degree rotation tailhousing, so these new Advance Adapters transmissions will not simply bolt up. It will lead to install issues with the Cherokee NP231 transfer case shifter.

There are other options too. The five-speed NV3550 found in the ’00-’04 Jeep Wrangler TJ is a great swap. This transmission can easily handle V-8 power. Versions of the NV3550 can be found as a factory option in mid-size and 1/2-ton pickups with V-8 engines, although they cannot be used behind your 4.0L, you’ll need the TJ version.

The NV3550 features a 4.01:1 ratio First gear, which is slightly better for technical off-road work than the 3.83:1 First gear in the AX15. The other gear ratios of the NV3550 are nearly identical to the AX15, so highway driving won’t change significantly.

A more complex and expensive option is to upgrade to the NSG 370 six-speed manual, which can be found in the ’05-’06 Jeep Wrangler. In my opinion, it’s not as durable as the NV3550, but it is a quieter more modern transmission and the six speeds are well matched to the 4.0L. The cost to adapt it in place of the AX15 is generally the biggest downfall. Even though it came behind the 4.0L, there are many engine, clutch linkage, mounts, driveshaft, and sensor changes that need to be addressed. It’s generally a cost-prohibitive swap.

If you plan to significantly increase power in the future via a V-8 engine swap, you might consider the five-speed NV4500. This is a 1-ton-rated transmission that will put up with massive amounts of power and abuse. It’s also much larger than these other transmission options, so you’ll likely have to reroute the exhaust and make other changes to the Jeep for it to fit. The NV4500 never came in a Wrangler, so installation will require adapters. Companies such as Advance Adapters offers complete rebuilt NV4500 transmissions as well as the adapters needed to mate it to most popular engines and transfer cases.

Power Wagon Axle Swap or Not

I have a ’05 Dodge 3500 with the Cummins diesel. I’m turning it into an overlander. I also plan to tow and drive the rig daily. Should I put ’13 Power Wagon axles under the 3500 or just install lockers and gears in my stock axles? I can get the Power Wagon axles relatively cheap. I’m just worried about strength.

@ors01
Via Instagram @cappaworks

If durability and strength are a concern, you need to keep the massive amount of torque the Cummins can develop in mind. Even though the two trucks have similar axles, the Power Wagon lockers were designed to handle a gas engine. Most of the aftermarket selectable lockers available for these axles are stronger and more durable than the factory Power Wagon selectable lockers. It’s especially true when combined with tires that are larger than stock. Also, the Power Wagon 4.56 gears might be a bit deep when backed up with the low-revving Cummins diesel. However, this will depend on the tire diameter you select. You’ll likely want a 35- to 37-inch or bigger tire to comfortably run the Cummins down the highway with 4.56 gears.

Even though you can pick up the Power Wagon axles cheap, there may be some unforeseen differences between the ’05 3500 Cummins truck and ’13 Power Wagon that that could be somewhat costly to accommodate. These differences could include things like suspension brackets, driveshafts, brake line fittings, and more.

With all of this in mind, I think you will be better off installing aftermarket selectable lockers and the gear ratio of your choice into your axles.

10-bolt Time Bomb

Is my GM 10-bolt really that weak? It does well for me but I don't slam it on trails.

@purposebuiltlilgreenmonster
Via Instagram @cappaworks

The GM 10-bolt axles came in both front and rear solid axle applications. The GM 10-bolt rear axle has earned a somewhat questionable reputation and is more problematic than the front axle. It’s a 1/2-ton truck axle that will survive just fine in most stock applications. On paper, the 8.5-inch ring gear and 28- or 30-spline axleshafts would seem to make it the equivalent of the venerable Dana 44. However, the GM 10-bolt has a few design features that make it less desirable in the off-road world. Larger tires and abusive off-road driving can lead to costly 10-bolt repairs.

The 10-bolt rear axles feature C-clip axleshafts. When abused, they can break, spitting the wheel and tire off of the axle end. Many 10-bolt axles came with the Gov-Loc limited slip/locking differential. The design and function of this diff make it unreliable with larger tires. The unit requires a specific rpm differentiation between the tires before it locks up to pull the vehicle forward. In abusive conditions, that locking can be enough to cause the small Gov-Loc internals to spit themselves out of the rear diff cover.

Another problem the 10-bolt has is its housing. Larger tires can provide enough leverage to flex and bend the housing. High-mileage and abused 10-bolt axlehousings often develop oil leaks where the tubes are pressed into the cast centersection. Overall, it’s just not an admirable axle design.

If you retain a stock open differential and drive sanely, the 10-bolt is good for up to 35-inch tires. If you want to add a locker, you should consider 33-inch tires the maximum. And if you want a locker and plan to really wallop on your GM 10-bolt, be prepared to swap it out in the near future. Fortunately, a 3/4-ton GM 14-bolt from the same era truck will be a near bolt-in swap. Although, you will need to change the lug pattern up front to match the 8-lug 14-bolt.

M715 Tips

I picked up a stock, clean, not running ’67 M715. All anyone ever says is that it's too big and heavy to go four-wheeling in. I live in Ohio. They also say that the engine, while it was a real technological leap at the time, is a dog by today’s standards. I am thinking it would be really cool to go out west with it and ’wheel out there. Ever had any experience with them? Any tricks to building a fullsize Jeep that I should know about? I have noticed that for the most part they stay leaf sprung. Any special reason for that?

David W.J. Newman
Via facebook.com/JohnCappa4x4

Contrary to what you have been told, the ’67-’69 Kaiser Jeep M715 makes a great four-wheeling rig when properly set up and maintained. It has many advantages over civilian 4x4s. The most obvious advantages are the ground clearance and the massive wheelwell openings. You can fit up to 38-inch tires without a lift. The M715 leaf-spring suspension is very similar to the civilian J-2000 truck of the same era. However, the spring mounts sit lower on the sides of the frame to provide additional lift. This, combined with the bigger wheel openings allows for the larger tires.

Even though the M715 and J-trucks in general are called fullsize trucks, they really aren’t. They are about the same size as a modern-day midsize truck, so they will fit on trails better than most true fullsize Ford, GM, and Dodge trucks.

As far as weight is concerned, a stock M715 tips the scales at about 5,100 pounds. That’s less than a similarly built Jeep JK Wrangler, which can weigh as much as 7,000 pounds. So weight should not be an issue.

Now for the bad. If it’s not running, don’t waste your time on the Tornado 230 inline-six engine. It will be expensive to go through and provide pathetic power. Companies like Advance Adapters (advanceadapters.com) offer the components needed to swap in a common small-block Chevy V-8. It’s probably one of the easiest engine swaps you can make because the factory transmission is retained and remains in the stock location.

You’ll also want to address the brakes. Clean out the lines, remove each drum, inspect the components, and rebuild as needed. Companies like Memphis Equipment (memphisequipment.com) and Surplus City (surplusjeep.com) carry the brake components and other parts you might need to get your M715 going down the road and trail.

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