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Answers to all your Jeep questions

Posted in How To: Tech Qa on June 15, 2016
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Dana 300 Dilemma
A friend of mine runs a Toyota 4Runner with a 4.7:1 ratio low-range transfer case. Now all my buddies are jumping on the dual transfer case bandwagon. These are all East Coast rigs with small-block V-8 engines. Some have four-speed manual transmissions and some have automatics. We have some rocks, lots of trails, and some tight gnarly off-camber hills. I really don’t see the big need for an Atlas transfer case, but my buddy wants one for his CJ-7. He is asking me a ton of questions because apparently I'm that guy. It’s a typical CJ-7 with a throttle-body V-8, SM465 manual transmission, Dana 300 transfer case, 4.56 axle gears, and 42-inch Super Swamper tires. Do you see the need for an Atlas, or would he be better off doing suspension work to make it more flexible? It’s on leaf springs right now.
Ken Basile

Half the fun in owning a Jeep is having the ability to modify it the way you want to. It’s not at all unusual to see completely overdone Jeeps on easy trails. Ultimately, if it makes the owner happy, who cares? However, in my opinion, the 42-inch tires are a bit much for a stock Dana 300, especially when backed up to a V-8 engine and an unforgiving manual transmission with a granny low First gear. The 1 1/8-inch-diameter, 26-spline rear output of the Dana 300 is generally the first weak link to let loose. You’ll want to make sure that the driveshaft never binds, which can be difficult to control on a leaf-sprung CJ. A binding driveshaft is what causes most output failures. Given the build specs of this Jeep, I’d consider installing the Advance Adapters ( heavy-duty 32-spline Dana 300 rear output shaft kit. Novak Conversions ( and JB Conversions ( also have heavy-duty rear output kits. If you want to really beef up the Dana 300, you can add a JB Conversions heavy-duty 32-spline front output too. At some point, you’ll start shearing teeth off of the gears of the Dana 300, but it will really depend on the driving style and type of terrain that you regularly go wheeling on. For the ultimate in durability for this application, the Advance Adapters Atlas transfer case can be the way to go. The gears and case are much larger and better able to take the punishment dealt out by 42-inch tires, a V-8, and a manual transmission. Atlas transfer cases are available with several different low range ratios including 1.5:1, 2.0:1, 3.0:1, 3.8:1, 4.3:1, and 5.0:1. Choosing the right ratio for this Jeep will be tricky. The current crawl ratio in the Jeep is 78:1, which is probably fine for most general trail situations. I'd probably shoot for a crawl ratio that hits no lower or higher than about 80-90:1 with the transfer case shifted to low and transmission in First gear. This would dictate an Atlas with a 3.0:1 low range ratio. The 3.8:1 and lower ratio transfer cases would be better options for serious big-rock wheeling. Anything more than about 100:1 with a healthy V-8 and a granny low manual truck transmission is sort of a waste. You rarely need that much gearing.

Flattie T-Case Query
I’m building a CJ-3B with a Ford 302 V-8 engine and an NP435 manual transmission. I plan to run 35-inch tires with lockers front and rear. I'll be running a flanged, offset Dana 44 rear axle from a ’70 CJ-5, and a Dana 30 in the front with 3.73 gears for now. Later on, I'll go with 5.38 gears when I can afford an overdrive for the Spicer 18. I'm not really building a full crawler, but it will be an on- and off-road hot rod that will likely see smokey tire burnouts. Do you think a Spicer 18 transfer case will handle 350 hp? Would I be better off getting a Dana 300 and swap to a centered rear axle before I order an adapter? How much longer is a Dana 300 over a Spicer 18? Everyone tells me I'll eventually blow the 18. Also, everyone tells me to run a large-hole Spicer 18 with the 1 1/4-inch intermediate shaft. But, I noticed that you are running the small-hole Spicer 18 with the 1 1/8-inch intermediate shaft. I plan to run about 4 inches of lift with a spring-under suspension and a double-cardan driveshaft, but will all this work? What's the downfall of tilting the transmission down for improved rear driveline angles?
Dan Yoder

The Spicer 18 is an incredibly durable and adaptable transfer case. However, you have to keep in mind that it was originally designed to handle the 60 gross horsepower produced by a 134ci L-head four-cylinder engine. Don’t get me wrong, I’ve seen Spicer 18 transfer cases somehow survive fire-breathing big-blocks and paddle tires and live for years behind a healthy V-8, but I’ve also busted the small coarse 10-spline rear output shaft idling along on a trail. Manual transmissions transmit a lot of shock loading to a transfer case, there is no real cushion when you dump the clutch and hammer the throttle. Keeping a Spicer 18 transfer case alive takes at least a little bit of driver finesse. If you plan on hammering the throttle, smoking tires, and making regular long high-speed road trips, you should start stacking Spicer 18 spare parts like cordwood or swap to a stronger transfer case. Upgrading to a Spicer 18 with a 1 1/4-inch intermediate shaft is more of a durability upgrade than an ultimate strength upgrade. The intermediate shaft and intermediate bearings in the Spicer 18 are the most wear-prone components. The intermediate shafts don't break, they simply wear out. Once this happens, the intermediate gear is free to move out of square with the rest of the transfer case, the gears no longer mesh properly, and one or two teeth get busted off. After these broken parts cycle around in the transfer case for a while, none of the gears inside are salvageable. Of course, the 1 1/4-inch intermediate shaft has a little more surface area and better bearings, but it still wears out. If you make regular long highway drives you'll likely want to replace the intermediate shaft and bearings every few years, regardless of the intermediate shaft size. Advance Adapters ( offers a tapered bearing intermediate shaft upgrade kit for the Spicer 18, which will increase its road-worthiness, but the kit requires some simple machining. Herm the Overdrive Guy ( offers complete rebuilt Spicer 18 transfer cases in all variations. If you don’t want to think or worry about it, get the Dana 300. If you don't mind driving with a light foot and will go through it every few years, go with the Spicer 18. Also, you won’t be able to add an overdrive unit to the Dana 300, so you’ll probably want to stick with more highway-friendly axle gears if that is a concern.

The more common long-output Dana 300 measures in at 11 5/8 inches from the mating surface to the yoke face, while the Spicer 18 measures about 9 1/4 inches from the mating surface to the center of a CV yoke. The Spicer 18 adapter for your application is around 3.5 inches and the Dana 300 adapter is usually 3 1/4 inches to 4 1/4 inches depending on the manufacturer. One advantage the Dana 300 has is that some adapters allow you to rotate the transfer case up or down slightly for body and front driveshaft clearance. As you have alluded to, the real bummer with switching to the Dana 300 is rear driveshaft angle. The Spicer 18 rear output is not only offset, it’s several inches lower than the centered rear output of the Dana 300. The swap can cause driveline angle issues. You won't be able to run a lot of lift with the Dana 300, unless you lower the transfer case. I think your combination of parts is doable, but you will have to pay special attention to driveline length and angles. I think your best bet is to mock it up before buying anything. Add the Dana 300 and adapter length and mock up some sort of yoke to figure out the driveshaft angles. Rotate the pinion of the rear axle up to help you work it out. Use a short piece of tubing or broomstick to mock up a driveshaft and calculate the angles. Worst case is that you have to drop the transfer case a bit to make it all work.

Tilting the engine and transmission down for improved rear driveline angles does just the opposite for the front driveshaft. The front driveline angle at the transfer case will get steeper. You also decrease ground clearance under the middle of your Jeep. Watch the fan and radiator clearance up front when tilting the engine and transmission assembly. The good news is that since your Ford engine has the distributor in the wrong (joke) location, it won't hit the firewall. It gets tight real quick with a V-8 under the hood of a flattie. I always push the motor back as far as possible. The high-hood of the CJ-3B will give you more room to work with than other flat fender Jeeps, especially when it comes to fitting the carburetor or fuel injection and a proper radiator.

J-Truck Guidance
I have stumbled across a ’71 J-20 with a six-cylinder and a three-speed transmission. It looks like there is very little rust, and it has a clean interior. I am going to go look at it. What would be the main areas of concern to closely inspect? Thanks in advance.
William Lawson

After fiddling with different models of Jeep J-trucks for a little more than a decade, I’ve come to the conclusion that they are really easy to turn into capable trail rigs. They aren’t exactly fullsize trucks so they fit on tight trails more easily than the trucks from the Big Three manufactured during the same era. Another advantage is that you can keep the center of gravity incredibly low and still fit big tires. The wheelwells seem like they were made to be cut out for tire clearance. A properly built J-truck on 37-inch tires sits around a foot lower than a comparable fullsize truck. Now, on to the bad. Rust is a huge issue for J-trucks, even in the southwest. Most Midwest and Northeast FSJ pickups rusted away decades ago. The window gaskets on most trucks have long since rotted, allowing water to leak in. This causes the stamped-steel window mounting lips to rust. The water eventually works its way inside and puddles up on the floors. Lift the carpet or vinyl flooring and see how bad it is. You can also crawl underneath to look for floor holes and hack repairs. If the rust is isolated to the middle of the floors, you can easily repair the damage. Companies like BJs Offroad ( offer weld-in replacement floor panels.

You’ll likely find that none, or few of the gauges work. I’d recommend installing some aftermarket gauges even if they appear to be functioning. Interestingly enough, the most questionable things I have seen on J-trucks have been owner-made modifications, especially to the wiring. I usually remove anything that looks remotely wrong to avoid electrical shorts and unexpected battery drain. A lot of J-trucks have been poorly maintained, and anything with a major leak has probably run without fluid for some time.

The ’71 you are looking at will likely be a J-2000, not a J-20. The J-20 moniker wasn’t used until the ’74 model year. It will have the 258ci AMC inline-six engine. The three-speed transmission should be the T-14A and it will be backed up to a Dana 20 gear-driven transfer case. Up front you’ll find a closed-knuckle Dana 44 axle with drum brakes. Another drum-braked Dana 44 will bring up the rear. The factory carburetor and ignition system on the 258 and the three-speed transmission are the only real bummers in this combo. If the truck still has the original steel fuel tank, it will likely be rusty inside. Inspect and replace the fuel filters and take a look at the inside of the fuel tank prior to running the engine if it has been sitting unused for some time.

Overall, the ’74-and-newer J-trucks are more desirable than the ’73 and earlier trucks. They have better brakes, a tighter turning radius, stronger front axle assemblies, and there are more aftermarket suspension lift kits available for them. The ’73-and-earlier trucks could be considered more collectable in some circles, especially the ’63-’70 Gladiator trucks with the rhino grille. However, the AMC engines found in the ’71-and-newer trucks are generally more reliable and easier to find parts for than some of the oddball engines found in the ’70 and earlier trucks.

Dana 30 Trussing
I am trying to upgrade the Dana 30 on my ’01 4.0L TJ Wrangler. I have already gotten rid of the Dana 35 rear axle and installed a G2 Dana 44. The entire suspension has been upgraded with a 4-inch short-arm mutt lift kit with parts from TeraFlex, Rusty’s, Skyjacker and M.O.R.E. To get a better crawl ratio, I tossed an Atlas with a 4.3:1 low range ratio on the back of the NV3550 manual transmission. Tom Wood’s driveshafts are fit fore and aft. I only run 33-inch Goodyear tires on steel 15-inch Cragar Soft 8 wheels. As for traction, the rear has an Eaton ELocker with disc brakes. I have already purchased RCV 30-spline axleshafts for the front along with Alloy outer axle tube seals to keep out crud. A new Eaton ELocker for the 30-spline shafts is on the way along with custom inner axle seals from Seals-It. I have been told that with this combination I can’t use any axle sleeving to truss the assembly. I can’t see why, if the inserts are shortened up to account for the inner and outer seal lengths, set to the proper location and welded in as designed. Any comments other than why waste the money on the Dana 30?
Jim Smith
Newark, DE

Adding the internal axle sleeves only marginally increases the strength of the axle tubing. Real strength comes from increasing the tubing diameter or adding an external truss. There is no reason you can’t cut the inner sleeves to allow for the seals. However, the areas without the sleeves will still be susceptible to bending. Rather than go that route, consider an external weld-on truss. Artec Industries ( offers a very heavy-duty front axle truss assembly that should accomplish what you are trying to do much better than the tube sleeves.

3.6L JK Swap
I have a ’15 Jeep Wrangler Unlimited with the 3.6L V-6 engine and six-speed manual transmission. What engine is compatible to swap in place of my original? What would I need and is there a kit?
Daoud Rahmati
Via email

Unfortunately, the only engine that will affordably mate up to your factory transmission is another 3.6L. The most common engines to swap into the ’12 to current Jeep JK Wrangler are GM LS V-8s and Chrysler/Dodge Hemi V-8s. When making this kind of a conversion, the transmission is also swapped out for a much larger and stronger assembly. Many different companies can perform an engine swap for you. AEV ( offers kits to install either a 5.7L or 6.4L Hemi V-8. Bruiser Conversions ( offers kits to swap in the GM 5.3L LC9 engine or the 6.2L LS3.

When making an engine swap like this there are lots of hidden costs that many people forget about. These include cooling, exhaust, fuel system, air conditioning, driveshafts, and so on. If someone does the complete conversion for you and supplies all the parts, it wouldn’t be uncommon for the V-8 swap to cost up to $30,000 or more, depending on the engine and other components you select. Ultimately, there really isn’t a budget engine swap that you can make to the current Jeep JK Wrangler.

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