This Jeep section deals transfer cases used in the 1941-1979 Jeep vehicles and Scouts. The purpose of this information is to provide the needed help with stock part identification, conversion parts needed, and general information on what to expect when dealing with these drivetrain components. D20 & D18 Power Flow
Dana 18 Transfer Case
The cast iron Dana 18 was an offset transfer case used from 1941 to 1971. Although compact in size and relatively light in weight, the transfer case was quite reliable. The initial units were a twin stick design that featured a 2wd-4wd shifter with second high-low shifter. Later models would be offered in a single style shifter only; however, many have been and continue to be converted to twin stick configurations. There was also an interlock detent pin between the two shifter rails. Over the years many Jeepers have removed the interlock to obtain another shifting option of a 2wd rear low only. The low range for the Dana 18 was standard with a 2.46:1 low range.
The 5 bolt pattern on the front of the Dana 18 can best be described as the state of Texas. The front indexing hole can further I.D. the year based on diameter ranging from the early 3.15” to the later 4”. Sm hole Dana 18 Lg hole Dana 20
The rear yoke was a 10 spline flange style yoke with a 10 spline 1310 Non-CV up front. A drum parking brake was also common on the rear of the transfer case.
The Dana 18 was the only cast Iron offset transfer case used by Jeep. The offset configuration was a passenger side drop with the exception of early prototypes. To clarify offset: Early jeeps were basically built with both front and rear axle pumpkins shifted over to the passenger side. The Dana 18 design utilized both front and rear yokes offset to be in line with the axle pumpkins. It is quite easy to I.D. this feature as the front and rear drive shafts would also be in line with each other.
Since the transfer is clocked down on the passenger side, the front and rear drive shafts sitting bellow the transmission. This clearly offers better angles for both the front and rear drive shafts and hence better angles. This is a big advantage for the shorter wheel based jeeps.
The “offset” clearly has its advantages, unfortunately the offset also creates a challenge for the Dana 18 and the transfer case is not impervious to failure. The offset design creates a torque load on the intermediate shaft and bearing. The increase load on the idler shaft coupled with the helical gears wanting to travel can cause failure. The failures can begin as a mild leak or can be as catastrophic as the Dana case cracking in half. Jeep initially used a small ¾” idler diameter shaft followed with civilian model upgrades of 1-1/8” in 1946 and 1-1/4 in 1955. Another design change to the “large hole” Dana 18 would further add strength to the case as the casting and manufacturing procedures were significantly improved upon.
It should be noted, Dana 18 failures are somewhat rare and many could have been avoided with proper maintenance. In no way should the Dana 18 be considered weak, as we have seen this transfer case easily handle V-8 power. There are limits though and there have been a few individuals that are clearly exceeding the expectations of what the Dana 18 can handle.
Following the retirement of the Dana 18, Jeep would introduce a transfer case known as the Dana 20. It was actually marketed as the “silent transfer case”. This was obviously in reference to the noise issues some were having with their Dana 18s. The problem again was with the power flow. All of the power and load had to go through the intermediate gear in order to reach the offset outputs for both the front and rear differentials. As Americans increasingly drove more and more 2wd highway driving, so to their intermediate gear, its shaft, bearings and thrust washers were wearing constantly more as well. Even a slight amount of wear on the intermediate gear bearings and thrust washers could create “gear whine” both under load and at a coast as well. Simply replacing the shaft offered little relief as the wear on the I.D. of the gear and bearing allowed for a thump or wobble. This bouncing all around created continued wear of all parts concerned. Since the problem generated from the intermediate gear and bearings bouncing around under load, the fix was simple, keep it from bouncing to begin with. For over 25 years Advance Adapters has offered a tapered roller bearing kit for both 1-1/8” and 1-1/4” intermediate shafts. These kits use tapered roller bearings and a new shaft that aids in increased support and significant the noise reduction.
One of the best features of the Dana 18 is the PTO port in the rear of the transfer case. This feature was extremely popular for rural Americans wanting to use their vehicles around farm, field and forest. An incredibly large amount of aftermarket implements were offered including not only winches but log splitters, water pumps, and numerous other agricultural tools.
One savvy Seattle Washington Jeep dealership would specially outfit jeeps they sold with PTO devices and other innovative offerings to suit their customers’ needs. Dealership owner Arthur Warn who would later start Warn Industries developed numerous aftermarket products including an overdrive unit commonly known as the Warn All Range. Since more and more jeeps were seeing highway use, this product saw great success. When the Dana 18 was discontinued many of the PTO products including the Warn Overdrive were also retired. The Warn All Range saw new light in 1991 when Advance Adapters purchased the tooling, engineering data, and inventory from Warn Industries. The components we manufacture today are the same as the old Warn components. We have incorporated a few upgrades on the units we sell today, but these units are all still interchangeable with the original Warn overdrive. The new overdrives are known today as the Saturn Overdrive. More additional information can be found by clicking here. Saturn
Indexing: The Dana 18 transfer cases were indexed to the stock transmission by either a bearing or bearing retainer. Early jeeps equipped with either T90 or T84 transmissions used a bearing to index the transmission to the transfer case. These are commonly known as “Small Hole” Dana 18 transfer cases. When the T86 was introduced around 1965 the transmission was indexed by an index hub where a bearing fit inside it. These indexing retainers were 4” in diameter and were used with “Large Hole” Dana 18 transfer cases. It should be noted that most of our adapters utilizes these indexing retainers. This allows our adapters to be used on both small and large hole transfer cases. Likewise most jeep transmissions used behind the Dana 18 can be interchanged by simply exchanging the one retainer for another. There were also a few transmissions that actually had a built in hub on the adapter like the T-18 and therefore are the exception to the rule.
Gears and Splines: During the 30 year span of the Dana 18, Jeep would use several transmissions. The spline count of the transmission output shaft and tooth count of the input gear would slightly vary. As the figure below indicates the output shaft of the jeep transmission enters the front of the transfer and the input gear is then retained with a nut. In a factory configuration the differences are non-important. The differences can be critical however when it comes to: transmission interchangeability, Saturn Overdrives, low range gears and transmission conversions.
The six spline output shaft was the most predominately used. This was the factory configuration for most transmissions used during this time period. They include T84, T90, T86, T85, T89, T98a, and the T18. These transmissions commonly used a 26 or 29 tooth input gear. There were also some very early 27 splines gears found in MB Jeep Universals 1941-1945. The MB model is a dual lever shift control, can be identified by the small intermediate gear idler shaft that is only .750" in diameter. This MB transfer case is marginal for V8 power, so we suggest that you limit your engine size to a V6 or change the transfer case to the later model Dana 18. This transfer case uses an input gear with 1-3/8" 6 spline. We offer a special Saturn overdrive unit for use with this transfer case. drive gears
In 1969 Jeep introduced the Buick Dauntless V6 and with it the T14 transmission. This transmission used a 10 spline output shaft with a 29 tooth input gear. Do to the minimal amount of years this application was used, some aftermarket parts may be limited. The Saturn Overdrive is available for this limited application as are several of our transfer case adapters.
1971 saw the last production year for the Dana 18.
Dana 20 Transfer Case
The Dana 20 was the end product of some rather simple yet innovative design changes to the Dana 18. The result was a durable and dependable transfer case capable of handling the heavier vehicles and more powerful engines Jeep was introducing.
The early applications were typically Jeep j-trucks and wagons. These vehicles used the TH400 as the factory transmission. Jeep used an oddly engineered adapter to mate the TH400 to the Dana 20. Jeep apparently acquired 2wd TH400 output shafts from Cadillac with a large robust 32 spline output shaft; however, the actual adapter that mated the transmission and the transfer case was a flimsy cast adapter which was heavily prone to failure. Advance Adapters offers a replacement adapter kit to correct this faulty design under PN50-0500.
The Dana 20 would eventually find its way into the CJ models as well, with complete replacement of the Dana 18 by 1972. Unlike the TH400 version of the Dana 20, the manual transmission applications remained with the typical 6 spline output shaft as used on the Dana 18. These transmissions would include T14a, T-15, T18, & T-150. As mentioned previously the TH400 was the only automatic Jeep would use behind the Dana 20. It should also be noted that International Harvester also utilized the Dana 20 in some of their smaller 4wd vehicles. The manual transmissions used by I.H. were the T18/T19 and their Dana 20 transfer cases were identical as with Jeep transfer cases including the 6 spline output shafts. I.H. also used the Torque Flight Automatic with the Dana 20, This Dana 20 was unique as the output shaft of the transmission was actually 23 spline.
The Dana 20 remained a cast iron transfer case like the Dana 18 and also retained the passenger-side front output. Although compact in size at only 10½” and relatively light in weight, the transfer case was quite dependable. The 5 bolt pattern on the front of the Dana 20 was carried over from the Dana 18 and can best be described as the state of Texas. The front indexing hole was 4”, the same basic design used with “Large Hole” Dana 18 transfer cases. Since the Dana 18 and Dana 20 share the same common bolt patterns and spline counts, Most of the adapters manufactured by Advance Adapters are for use with either transfer case. Likewise the large Dana 18 indexing retainers will also need to be used on the Dana 20 as with the Dana 18. These retainers were not commonly used on factory Dana 20 applications but will be required.
Casting #’s on the Dana 20 can differ; however, most seem to start with C18-15. This commonly leads to misidentification of the transfer case as the number was commonly used on the large hole Dana 18 as well.
The Dana 20 transfer case shifters varied extensively on several models and normally feature a single stick operation consisting of two basic modes, High-Low and 2wd-4wd. The variation of shifters seemed to be based around the multitude of different Jeep models equipped with the Dana 20. The differences were at their greatest when comparing small wheel based too long wheel based vehicles. The shifters were always supported off the front of the transfer case. We have seen on some conversions using large truck transmissions like the Nv4500 where modifications to shifter linkage are required. Our Instruction sheets provide further details for these infrequent alterations. Many Dana 20 t-cases have been, and continue to be converted to twin stick configurations. An interlock detent pin between the two shifter rails can be removed in combination with a twin stick to obtain better shifting options including independent front or rear low only. T.C. Shifter 1 T.C. Shift 1 Top Veiw T.C. Shift 3 T.C. Shift 4 T.C. Shift 5 T.C. Shift 6
The low range for the Dana was acceptable but not envious with a 2.03:1 low range; however, there are aftermarket low range kits available for most versions of the Dana 20. The front and rear yokes were 10 spline much like the Dana 18. Later years of the Dana 20 would introduce a 26 spline. It should be noted that the increased number of splines from 10 to 26 were more likely for reasons of increased manufacturing productivity than strength improvement as the increase is actual diameter was minimal. We have however seen failure of the Dana 20 rear outputs shafts under extreme applications. Advance Adapters offer a 32 spline rear output shaft as an upgrade kit under PN50-3020 or PN50-3020A.
It is fair to say, the Dana 20 made its mark on the history pages of Jeep. The transfer case was strong and dependable, but its compact size did limit its use. By 1979 the Dana 20 was scheduled to be replaced
PN716002 - Small hole index retainer (T90) Dana 18 transfer case
PN716001 - Large hole index retainer (T86) Dana 18 & 20 transfer case
PN716302 - Sealed bearing (307)
DANA 18/20 STOCK GEARS:
TRANSFER CASE INPUT GEAR INFORMATION drive gears
Dana 20 Transfer Case - 26 Tooth x 6 Spline #946574 (18-8-46)
Dana 20 Transfer Case - 26 Tooth x 10 Spline #947339 (18-8-49) Early Jeeps
Dana 20 Transfer Case - 26 Tooth x 23 Spline
Dana 18 Transfer Case - 29 Tooth x 6 Spline #809297
Dana 18 Transfer Case - 29 Tooth x 10 Spline #947382
Dana 18 Transfer case -27 tooth x 6 spline #A10469(18-8-19)
FRONT YOKE & DRIVESHAFT CLEARANCE: On most transmission swaps, we try to allow for proper front yoke clearance. However, the early Dana 18 transfer cases can present a problem. The Dana 18 transfer front yoke protrudes out further than that of a Dana 20. Although front yoke clearance can sometimes be a problem on the Dana 20, it is usually on the early Dana 18 transfer cases with the large diameter yoke only that front yoke clearance issues are found. The large diameter yokes on most 1965 and earlier Jeeps will normally interfere with the transmission pan on most automatic transmissions. This yoke has been discontinued; however, we have had it reproduced. Our PN716407 is the same as the 1966 to 1971 small Jeep yoke.
All Dana 18 & 20 applications will require the centerline of the drivetrain to be offset 1” to the driver’s side. In many cases, you will be limited on your driveshaft diameter. We offer a complete kit which would include a new stub yoke (weld yoke) bearing cross and U-bolts. This kit also includes the new front transfer case yoke listed above. The complete kit is under PN716009. Front DS clearance
JEEP DANA 18 GEAR KNOBS KIT:
We offer replacement knobs for the Dana 18 twin stick transfer case. PN715643
DANA 18/20 3.15:1 LOW GEAR SETS (6 Spline Input only):
Kits are available for both the Dana 18 and Dana 20 transfer cases. These kits are shipped complete with the necessary hardware and gaskets to obtain the 3.15:1 low gear ratio.
The Dana 20 kit fits transfer cases 1963 to 1979 in CJs, Jeepsters, Jeep trucks, Wagoneers, and 1972 to 1979 Scouts. This is a 5-gear low range kit replacing the stock 2.03:1 gears. A slight amount of internal case grinding is necessary. PN420315.
The Dana 18 kit, PN418315, fits large hole transfer cases only. This 4-gear kit requires the shortening of the shift rod for intermediate gear clearance. A slight amount of internal case grinding may be necessary. CJs 1965 & older will require the use of a case from either a 1966 to 1971 CJ, 1963 to 1979 Wagoneer/pickup (Dana 20), or a 1972 to 1979 CJ (Dana 20). If a Dana 20 T/C is to be used with the Dana 18 components, you will still be able to retain your stock driveshaft offset. For Warn and Saturn O.D. owners, we offer a complete gear set to retain your overdrive using the 3.15:1 low gears, PN418315OD. We also offer just the Saturn Overdrive bowl gear if you have already obtained your low gear set, PN911098.
ADAPTER CROSSMEMBER SUPPORT:
The early Jeep vehicles were equipped with a single channel-type crossmember that mounted directly to the frame rail with two bolts on each side. The mount had approximately a 4" drop from the bottom of the frame rail and provided a pad for positioning the transfer case support donut. The donut gave the transfer case additional support and flexibility which prevents it from splitting. It is important that you retain this donut location with the same type of support. If the transmission mount is moved on the crossmember, then the transfer case mount location will also need to be relocated. The crossmember may need to be positioned downward off the frame rails on certain conversions. This can be easily done by using an aluminum spacer block between the frame rail and crossmember. The original skid plate should be maintained for maximum offroad protection.
In the early 1970s, Jeep started to incorporate the crossmember and skid plate into one unit. This skid plate has been manufactured in various widths and configurations for the different models of vehicles. The crossmember/skid plate combination can be easily adapted for most engine conversions. With a little planning and minor modifications, you can retain the original transmission support location to assure maximum offroad protection. When changing transmissions, it may be necessary to cut away the front portion of the skid plate for additional front driveshaft clearance. The transmission support should be retained in its entirety. The long arm off of the transmission mount must be retained with the rubber snubber in order to limit the movement of the transfer case. Without this rubber donut, the transfer case will be permitted to over rotate and contact the skid plate. The skid plates used have all basically been the same, while the transmission support mount has had numerous variations.
When changing to different transmissions, we have provided a support mount area on the bottom of the adapter housings. This mounting area may not be identical to your original transmission, and a small adapter plate or bracket may be required on certain applications. We offer a crossmember mounting bar, PN716017 that will adapt the new housing to the original transfer case skid plate support mount. The skid plate can be spaced downward from the crossmember if additional transmission and tunnel area clearances are required.
Most of the adapters we manufacture offer a support pad machined on the casting. The location of this pad will normally require you to relocate your crossmember on your frame rails or reposition the rubber mount on the crossmember. We offer a few options to aid you in this area.
PN716003 - New rubber support (Jeeps 1941-79)
PN716021 - New rubber support (Jeeps 1972-79)
PN716017 - Aluminum adapter block (used to help retain your stock rubber support)
DANA 18/20 TRANSMISSION-to-TRANSFER CASE ADAPTERS
The Jeep Universals and Scout transfer cases from 1941-79 all had the same Dana 18/20 transfer case bolt pattern. There has been variations to this such as large hole transfer cases and small hole transfer cases, shift linkage, and drive gear variations. We manufacture the complete transfer case product line so that they can be interchanged with the various designs. It is VERY critical that you use the correct alignment bearing retainer when bolting our adapter to your transfer case. In the photos on the previous pages, you will be able to see the differences between a small hole and a large hole transfer case. If the transfer case drive gear can be removed from the front side of the transfer case, then it is a large hole design. If the gear has to be removed from the back side of the transfer case, then it is a small hole design. Small hole designs are limited to only Dana 18 transfer cases, while large hole transfer cases can be either a Dana 18 or Dana 20. The Dana 18 transfer case has the output power OFFSET to the passenger side of the rear axle, while the Dana 20 has the output power directly IN LINE with the transmission.
Alignment retainers: When replacing a T90 3 speed transmission, you must remove the bearing retainer from the backside of the original transmission for installation into the new adapter. The original T90 or T86 bearing must be reinstalled back into this retainer for use with the new transmission. An optional sealed bearing, PN716302, or a non-sealed replacement bearing, PN716312, can be used.
When replacing a Jeep T14, T15, T18, T150 or T98 transmission, you will need to purchase a new bearing retainer, PN716001, or Jeep No. 928477. This retainer is so critical to your installation that, if it is left out, you will have severe damage to both your transmission and transfer case. This retainer must be installed in the backside of our new adapter and then have a 307 roller bearing installed inside the retainer. The bearing must be retained inside the retainer with a large snap ring. The snap ring is furnished with the new retainer. The illustration on Page 22 shows this assembly. There are a few exceptions as to alignment with the T18 and T98 transmissions.
Transfer Case Input Gears: In the Dana 18 and Dana 20 transfer cases, we have seen three different spline sizes and three different tooth counts on the input gears. We have designed most of our kits so that they can be interchanged and furnished with a new shaft having the correct drive spline to match the transmission that is being replaced. This is very helpful since it will eliminate the expense and time necessary to change input gears. There are a few exceptions that will require the purchase of a new input gear. Be sure that the new gear is compatible with your transfer case. There are some cases where Dana has manufactured two 26 tooth gears that appear to be identical, but have a slightly different tooth pitch.
The transfer case input gear is positioned from the bearing that is installed into the rear bearing retainer. If your original transmission has a spacer or bushing between the rear bearing and drive gear, then you will be required to eliminate this original spacer bushing. In order to prevent any error in the installation of your gear, we suggest that you make sure that the gear splines are dead-even with the end of our shaft splines with only the threads for the nut showing.
Output Nut 7/8"-16 Nylock: Each adapter kit includes a new nylon lock nut for your conversion. These nuts are standard Jeep items that are used on most Jeep transmissions (Jeep P/N 8126806). They do not require a cotter pin to lock the nut in position. The nut must be replaced every time it is removed from the shaft. Nuts that are reused could possibly loosen and cause transmission or transfer case damage. These nuts must be used with the original flat washers. The nut must be torqued to a maximum of 75 ft./lbs. in order to prevent bearing pre-load. This same torque specification must be maintained with the Warn, Husky, and Saturn overdrives.
C. Borg Warner Quadra-Trac (1972-1979): This is a chain-driven transfer case used with the AMC Turbo 400 automatic transmission. The Turbo 400 has a 10 spline super-long output shaft that simply slides into the input gear of the transfer case. When changing to a Dana 18/20 transfer case, you will need to use PN50-0500 or PN50-1300, which will require a new Turbo 400 shaft to be installed into your transmission along with the new adapter housing. We recommend using the Dana 18 transfer case since it has the same rear driveshaft offset as the Quadra-Trac. Quadra-Trac TC
We also offer a kit, PN50-2501, to adapt the 700R4 to the Quadra-Trac transfer case. Since this transfer case is a full-time 4WD unit, the front yoke is normally a C.V. style. If installing a 700R to this transfer case, the C.V. yoke may cause interference. The easiest fix for this problem is to change to a standard yoke assembly. The overall length of this combination is identical to the TH400.