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Answers to all your Jeep questions

Posted in How To: Tech Qa on May 23, 2017
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Rear Disc Conversion

I remember seeing a closed knuckle disc brake conversion article in Jp. What about a disc brake conversion for the rear of an FC170?
@chris_moon82
Via Instagram @cappaworks

Front disc brake conversions usually require a careful mix of factory components or custom built and machined parts. Fortunately, all of the early closed knuckle Jeep front axles utilize similar parts and bolt patterns, so the front disc brake conversion can be performed on all of them with easy-to-find factory pieces. You can find more about the conversion on fourwheeler.com.

Rear disc brake conversions are typically much easier to perform, even on an oddball rear axle. The more popular Jeep models enjoy lots of aftermarket bolt-on rear disc brake kits from companies like TSM (tsmmfg.com), EBC Brakes (ebcbrakes.com), TeraFlex (teraflex.com), and Herm the Overdrive Guy (hermtheoverdriveguy.com). I’m not all that familiar with the backing plate bolt pattern used on the FC170 rear axle, however I suspect it could be the same, or at least very similar to the other Jeeps of that era. If not, you can always assemble your own custom conversion kit using weld-on caliper brackets from RuffStuff Specialties (ruffstuffspecialties.com). The RuffStuff universal caliper brackets are designed to mount ’75 Chevy 3/4-ton 4x4 front calipers and 12.5-inch diameter rotors. You may be able to find a rotor that properly seats on the flanges of your rear axleshafts, although some machining of the rotor may be required for a proper fit. Longer wheel studs will also be required. The steel brake lines on the rear axle will need to be modified to accept flexible braided stainless or rubber lines to accommodate the floating calipers.

T-Case Pop Out

What causes these Dana 20 and 300 cases to pop out of gear (primarily downhill) and what is the real fix for it?
@pottersmachine
Via Instagram @cappaworks

The first time your transfer case pops out of a gear can be a harrowing experience. There are several older gear-driven transfer case designs that are more prone than others to pop out of gear. These include the Spicer 18, Dana 20, and Dana 300. The design of the later chain-driven transfer cases like the NV231 and NV241OR Rubicon transfer case makes them less likely to pop out.

Anyway, the problem can be caused by several things, but typically stems from worn internals, more specifically the bearings and bushings inside, not the shift linkage. Once the bearing surfaces become worn, the gears get cocked slightly sideways under load. If cocked sideways enough, the gear can walk out of position and into neutral. You’ll find that this only happens in specific shifter positions, such as low range on the Spicer 18. The short-term fix is to simply sling a bungee cord around the shifter to help hold it in place until it can be repaired properly.

Start by inspecting the shift detent springs. In most cases you can access them without removing the transfer case. Use a small telescoping magnet to remove the springs from the bores. Sometimes older springs become collapsed, weak, or even break and can’t hold the transfer case in gear. Omix-ADA (omix-ada.com) offers new replacement shift detent springs.

If you remove the transfer case to rebuild it, also inspect the shift rail detents. Older transfer cases may have worn detent notches. You may be able to get in there with a file or small grinder to modify the detents for better shift engagement.

Engine Swap 101

What factors help you decide the engine height when doing an engine swap? What options help reduce driveline angle when putting an automatic transmission into an early CJ-5 or flatfender? What is the best combination of function/price for a CJ headlight swap to get rid of the deep buckets and maximize radiator space?
@arsenalproducts
Via Instagram @cappaworks

You have touched on only a few of the most common issues when doing an engine swap in an early Jeep. Properly locating a swapped-in engine under the hood of a CJ-5 can be a bit of work, and near impossible in a flatfender. The actual height you choose for the engine in the engine bay is pretty easy, however you do have to keep every component in mind including exhaust routing, driveshafts, steering shaft, radiator, fan, air intake, oil filter, and so on. On my most recent flatfender engine swap I got down to moving the engine 1/8-inch at a time to find the optimum position. This is a little excessive, but no matter how much you think it through and plan, there are always going to be compromises. I wanted my engine to be as close to the firewall as possible. This created some clearance problems with the exhaust but offered much more room for the radiator, fan, and front accessory group. Ultimately, there is no ideal location for a swapped-in engine. It’s more of a trial and error sort of thing. Mock up everything into place and tack weld the new motor mounts to the frame. Temporarily install the engine, transmission, and transfer case. Check for clearance around everything. It helps to have the suspension and axles already in the Jeep so you have a better idea of where you need oil pan and exhaust clearance. I’ll even go as far as using an inexpensive piece of PVC pipe to mock up a driveshaft and calculate the U-joint angles at ride height and full droop. Only after everything checks out do I fully weld the motor mounts to the frame.

Automatic transmissions and early short-wheelbase Jeeps typically don’t go well together. Even with a well-placed V-6, your rear driveshaft could be about a foot long, which doesn’t leave much room for suspension travel or much of a lift. You can lower the entire engine, transmission, and transfer case assembly to improve driveline angles, but you’ll decrease ground clearance and you may limit suspension uptravel due to axle or front driveshaft interference with the oil pan and bellhousing. The other option is to tilt the rear of the engine down to bring the rear transfer case output more in line with the rear axle. However, this will increase the U-joint angle at the transfer case front output. Locating an engine in an early Jeep frame is a delicate balance that takes time to figure out.

As you have found, the 7-inch-diamter early Jeep headlight buckets suck up valuable real estate behind the grille, which could be occupied by a more substantial radiator. We have tried several different solutions. The cheapest is to simply cut the backs of the headlight buckets off. It provides up to 1-inch more clearance with the factory halogen headlights and plugs. The halogen plugs will protrude out the back and be the new limiting factor. With the headlight buckets cut, you could switch to LED headlights. Some are narrower than the standard halogen headlights, offering slightly more radiator space. If street legality is not an issue, you could simply remove the factory headlights and buckets and then install some sort of narrow aftermarket off-road light. You can even push them forward so that the backs of the lights are flush with the stamped grille.

CJ Gearing

Is it possible to fit the Spicer 18 transfer case gears into a Dana 20 to get that extra bit of low range gearing? Is it worth it? I have a stock CJ-5 with the F-head four-banger mated to a T-14 transmission. The Dana 27 front and Dana 44 rear axles have 2.73:1 ratio gears. I intend to use it as a normal trail rig that will see mud, rocks, and some steep terrain, but nothing extreme. Is it worth increasing the transfer case low range for normal trail use? I have a CJ-7 with the Dana 300, and it has more than enough gearing. I feel like the Dana 20 low range might not be enough for some of the steep hills on our trails. Is it better to regear the axles?
@danielpineda06
Via Instagram @cappaworks

As you have found, the Jeep Dana 20 has a marginal low range ratio of 2.03:1. Unfortunately, the Spicer 18 is an offset rear output transfer case, so its internals are not the same and it functions completely different than the Dana 20. However, you can use a combination of early Bronco Dana 20 parts and Spicer 18 gears to get the 2.46:1 low range you are looking for. The early Bronco parts can be hard to find and expensive, making it a less cost effective option than you might think, though. It might be quicker and easier to simply purchase the TeraFlex (teraflex.com) Low20 low range gear kit, which converts the stock 2.03:1 low range ratio to 3.15:1, although I don’t think this is the best route for you to take.

Looking at the bigger picture, I believe that the axle ratio that your Jeep has is more of a problem than the 2.03:1 low range in your Dana 20. You’re asking a lot of that small engine with the 2.73 axle gears, especially if you have larger than stock tires. With 31-inch tires I’d be looking for some 3.73 axle gears, with 33s maybe some 4.10 to 4.56 gears, and with 35s maybe some 4.88 to 5.38 gears. The T-14 has a somewhat acceptable 3.10:1 First gear ratio, so I don’t think you really need a transmission swap.

With the Dana 20 and 2.73 axle gears, your Jeep likely has less than stellar on-road performance and a pathetic crawl ratio of about 17:1. This probably causes all sorts of stalling and smoked clutch moments when navigating steep technical climbs off-road. Switching to the 2.46:1 low range gears would only get you a crawl ratio of about 21:1. Going with the TeraFlex 3.15 low range gears would get you a crawl ratio of about 27:1. A change to 4.10 axle gears would get you to a crawl ratio of about 26:1, and improve all-around performance both on- and off-road. Given all of these options, my choice would be to go for the axle gear swap. Unfortunately, no one I know of currently manufactures aftermarket gearsets for the Dana 27 front axle. However, you can regularly find them used on eBay (ebay.com) and on other old Jeep specific websites. Also, Herm the Overdrive Guy (hermtheoverdriveguy.com) offers affordable used and NOS ring and pinion gears for the Dana 27, as well as for other older Jeep axles.

JK Unlimited Up Fit

Will LT255/80R17 tires fit my stock Jeep JK Rubicon Unlimited?
@dishboyjoe
Via Instagram @cappaworks

In most cases, you can up-fit tires on your Jeep one to two sizes without much or any rubbing. In this case, the ’07- current Jeep Wrangler Rubicon models, including the Unlimited, come from the factory with LT255/75R17 tires. These tires measure out to 32.1 inches tall, have a section width of 10 inches on a 7-inch wide wheel, and have a tread width of 8.2 inches. The LT255/80R17 tires measure in at 33.3 inches tall, have a matching section width of 10 inches on a 7-inch wide wheel, and have a 7.1-inch tread width. They are only a little more than 1-inch taller than your factory tires and are about the same width overall. You should be able to fit them on your Jeep on your stock wheels without a problem.

JK Dana 30 Survival

Is a 4.10:1 ratio gear too much for a factory Dana 30 front axle? I have Jeep JK that is currently on 33-inch tires, but I want to get it lifted and install 35-inch tires. I don’t do any off-roading.
@gentle_big_benny_boy
Via Instagram @cappaworks

Because it sounds like this is a street-only rig, I can’t even imagine that you’ll have any issues. The Dana 30 front axle and 4.10:1 ratio gears will survive just fine. However, you might consider some heavy-duty aftermarket ball joints. The stock ball joints have been known to wear out more quickly when combined with larger tires. Companies such as Dynatrac (dynatrac.com) and Synergy Manufacturing (synergymfg.com) offer heavy-duty aftermarket ball joints. The Dynatrac parts are even completely rebuildable.

If you do decide to take it off-road, I believe that the 35-inch tires are about at the operational tire size limit of the Dana 30. Both the JK Dana 30 and Dana 44 front axle housings are notorious for bending under 35-inch or bigger tires. Compounded low-range gearing and bigger tires increases the strain on the Dana 30 internals. To keep everything alive, you’ll want to drive sanely when off-road with this combo.

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