Transfer Cases

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  • Transfer Cases

    Jeep CJs have come with some excellent transfer cases. I guess that should be expected. Jeeps set the standard for off-road vehicles and the transfer cases are at the heart of the four wheel drive system.

    The majority of the CJ's came with a Dana 18, 20 or 300 transfer case. These were all compact, and very strong gear driven transfer cases. These were very easy to rebuild.
    In the '70s some CJs came with the Borg Warner QuadraTrac full time transfer case. Although this T-case has a bad rap it really was a revolutionary design that has been copied by drive train companies ever since.

    Spicer 18

    The Spicer 18 is the transfer case that started the four wheel drive revolution. Oh sure there were four wheel drive vehicles long before the Spicer 18. As a matter of fact Ferdinand Porsche designed a four wheel drive car in 1900. These early four wheel drive vehicles were not very good for off-roading. Then in World War II the US government needed a four wheel drive vehicle that could drive over rough terrain. Bantam, Ford and Willys-Overland all produced jeep-like vehicles for the war.

    It was the Spicer 18 transfer case that propelled these four wheel drive vehicles during and long after the war. Even by today's standards, the Dana 18 is an excellent transfer case. It was produced for 3 decades (1940 to 1971), longer than any other transfer case.


    The Spicer 18 was the only cast iron transfer case with an offset rear output. The rear output was on the passenger side. This is one way to tell if you have a Spicer 18. The rear differential is offset to the right side of the vehicle. The only other CJ transfer case with an offset rear output was the QuadraTrac. But the QuadraTrac was an aluminium transfer case that was not produced until 1973.

    The Spicer 18 usually came from the factory with twin shift levers. The right lever would select high or low range or neutral. The left lever would be used to engage the front axle for four wheel drive.


    Only the Spicer 18 had a parking brake on the rear output but not all Dana 18s will have the brake.


    This image is from The Spicer 18 transfer cases are numbered from oldest to newest. All Spicer 18 transfer cases come have a five bolt "Texas" bolt pattern similar to the Dana 18 transfer case. They all expect the transmission to have a gear on the output shaft. This gear fits in the big hole in the front of the transfer case.

    1. The original Spicer 18 transfer case that came in the Willys MB was mated to the T84 transmission. This transmission had shift rails that slid back into the Spicer 18 transfer case. To accommodate these shift rails there are two holes above the bigger hole for the input gear. These Spicer 18 t-cases has a 1.97:1 low range.
    2. In 1946 the intermediate shaft was enlarged to 1 1/8". An oil hole was added near the input gear and the low range was changed to 2.43:1. The two holes for the T84 shift rails were still there although most of these Spicer 18's were not mated to teh T84. This sometimes caused oil leaks.
    3. From '46 to '55 the holes for the T84 shift rails were gone.
    4. From '55 to '71 the intermediate shaft enlarged to 1 1/4" and the low range was 2.46:1
    5. From 1966 on the hole for the input gear enlarged to 4 inches. This gear that mounts on the output shaft of the transmission has 29 teeth. These transfer cases are interchangeable with the Dana 20.


    Spicer 18 overdrive

    There are 3 overdrives for the Spicer 18: Warn, Husky or Saturn. (the Husky overdrive is also known as Dualmatic) They all look similar. Warn was the first to make an overdrive for the Dana 18. Then a company call Husky started to copy the Warn Overdrive. They had to stop production when Warn sued them.
    In the early '90s Advanced Adapters bought the rights from Warn to make the overdrive. AA marketed the drive as a Saturn Overdrive. All 3 of these overdrives have the same basic design but parts are not interchangeable.

    Dana 20

    The Dana 20 was used in CJs from '72 to '79. It was already in use on full sized jeeps since '62. The Dana 20 was based on the Dana 18 transfer case. Many parts are interchangeable. The biggest difference is the Dana 20 (like the Dana 300) now had the rear output centered and therefore the differential is centered on the rear axle. The Dana 20 is another very strong, very compact transfer case. It is considered to be stronger than the Dana 18 because the Dana 20 has a centered rear output meaning the input shaft and output shaft link together to provide the high range.


    (Novak's Twin Shift Levers installed on a Dana 20)

    Unlike the Dana 18 the Dana 20 never came from the factory with twin shift levers but there are several companies that sell twin shift kits for the Dana 20. When installing a twin shift kit it is recommended to remove the interlock pins that ride on the shift rails.


    These interlock pins (also called interlock rods) will prevent you from shifting into 2 wheel drive low. If you remove the interlock pins you can shift the either axle into high or low independently of the other axle. This is nice when you want to do a front wheel dig by putting the front axle in low and the rear in neutral. WARNING: if you remove these interlock pins be careful when shifting. It is now possible to have the front axle in low and the rear in high (or vice versa). Be careful when you shift from 4WD high to 4WD or you may end up with your T-case in high gear and low gear at the same time. Your Jeep won't move and it may be hard to move either shift lever back to neutral.

    I think the easiest way to distinguish the Dana 20 from other transfer cases is by the mounting of the shift lever. The Dana 20 has a tubular bar extending out the front of the TCase. This bar is held on by two square head bolts. See the first Dana 20 pictures for reference. The twin shift levers are after-market but the tubular mounting bar in the picture is OEM.



    The Dana 20, like the Dana 18, has a “Texas bolt pattern” where it mates to the transmission. The transmission has a gear on the output shaft. This entire gear fits into the hole on the Dana 20 in the picture above.

    The Dana 20 found on Jeeps always had a low range with a gear ratio of 2.03. The Dana 20 was also used in IH Scouts and Ford Bronco's. The Dana 20 installed in the Ford Bronco looked much different than the Jeep version. The Bronco has the front output on the drivers side and used a low range of 2.46. The Ford D20 gears could be installed into a Jeep D20 to get a 2.46 low range. There are also companies such as TeraFlex that make a kit to lower the gearing of the Dana 20 down to 3.15. This kit replaces all the gears and is priced at about $1000.


    Transfer Case Operation: Any gear that is red is transferring power. Any gear that is blue is free-wheeling on it's shaft. This distributes oil throughout the transfer case even when in neutral or 2WD. Black gears are not rotating. When you shift a transfer case there are two gears you are sliding on their shafts. These sliding gears either lock themselves onto the shaft if they are moved to the front of the transfer case. Or if they move to the rear they mesh with the idle gear.
    Four wheel drive low is confusing. Keep in mind the rear output shaft is rotating slower than the input shaft. Power goes from the input gear to the idler gear then back to the sliding gears.
    This image is a Dana 20 but the Dana 300 works the same.


    The Borg Warner QuadraTrac was offered in CJs from 1976 to 1979. It was also offered in full sized Jeeps from 1973 to 1979. It is a full time transfer case and when the factory installed it in a CJ it only came behind the TH400 automatic transmission. It was the first chain drive transfer case and also the first with an aluminium case. These were dramatic departures from the standard transfer case designs of the '70s. One of the problems with the QuadraTrac was the fact that it didn't have any mechanism to compensate for the chain stretching. This made it doubly important to keep it well lubricated. If properly lubricated it is a very strong transfer case.


    Being a full time transfer case it had a limited slip differential incorporated. This allowed the front drive shaft to rotate a different speed than the rear. This was to prevent binding such as when going around a curve or during slippage when off road. The limited slip differential would allow the rear axle to deliver more torque if the front was slipping or vice versa. The QuadraTrac had a vacuum activated switch in the glove box that allowed you to lock this center differential. The limited slip necessitated an oil additive used in axles with limited slip Differentials.


    (Glove box selector knob)

    The rear output of the QuadraTrac is offset to the passenger side. This is one quick way to identify the QuadraTrac. The Dana 18 transfer case also has the rear output on the passenger side but production of the Dana 18 stopped in 1971 and the Dana 18 had an iron case. This offset rear output often causes problems for anyone trying to swap out the QuadraTrac. Since most other transfer cases have a centered rear output it is also necessary to swap out the rear axle. I have seen Jeeps that had a TCase with a centered output and axle with an offset differential. It works but such a set-up is not recommended. The u-joints will be running at a much higher angle than necessary.

    The QuadraTrac came in two versions. The QuadraTrac 1305 did not have a low gear. The QuadraTrac 1339 had planetary gears that provided a 2.57 low gear. The 1339 was the only QuadraTrac used in CJs.


    (QuadraTrac 1339 - Notice the low range unit bolted on the back of the t-case.)


    (QuadraTrac 1305 - Notice the absence of the low range unit.)

    Mile Marker makes a kit that will convert the QuadraTrac transfer case into a part time transfer case. The kit includes a new chain. It will also give a 16% overdrive. Since the QuadraTrac is a full time four wheel drive, normally there are no locking hubs on the front wheels. If you install the Mile Marker part time kit you will be installing locking hubs.


    (Vacuum activation system is used to lock the differential in the QuadraTrac)

    The QuadraTrac is a very easy transfer case to work on. All you really need are a good pair of snap ring pliers and a socket set. The low range unit unbolts from the rear of the QuadraTrac and then the tcase splits in 2 when you remove the bolts.

    There is a plug in the bottom of the QuadraTrac that can be used to check chain slack. Drain the oil and use a screwdriver inserted in the hole to see how much slack there is. It should be no more than 0.5 to 0.75 inches.


    (Checking chain tension)
    Desert Racing: This TCase has been very popular with desert racers. They put some very powerful Engines in front of the QuadraTrac. They like the fact that it has a differential. When you are desert racing you don't need that front drive shaft locked into the same speed as the rear. You are not going to get stuck when you are flying over the dunes. That's another advantage: when you jump an off-roader with a conventional TCase it will experience tremendous shock forces when you land. The QuadraTrac is more forgiving. If you land nose first the differential in the QuadraTrac allows the drive shafts to suddenly change speed up as you slam back to earth.

    Dana 300


    The mounting point for the shift lever is the easiest way to distinguish this Dana 300 from the Dana 20

    The Dana 300 was used in CJs from 1980 until the last CJ7 rolled off the production lines in 1986. This was another strong, cast iron transfer case. The rear output is centered and the low range had a gear ratio of 2.62 to 1. Companies such as TerraLow offer a kit to lower the gearing of the Dana 300 down to 4 to 1.


    The Dana 300 needs the output shaft of the transmission to fit into the splined input hole in the above picture. Compare this to the Dana 20 above. This is a much different design and it should be kept in mind when doing a transmission or transfer case swap.

    The Dana 300 is not only found in Jeep CJs. They were also installed in IH Scouts in 1980. These IH Dana 300 transfer cases were not the same bolt pattern as what is found in Jeeps. The IH Dana 300 had a bolt pattern more like the Dana 20 transfer case.

    The Dana 300 had a single shift lever with a shift pattern like this:
    • 4 Low
    • Neutral
    • 2WD High
    • 4WD High

    When the Dana 300 was first released in 1980 it had a 3.5 inch rear output tail-housing. After that all other years had a 5.5 inch tail-housing.
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