T/C Dana 18 Transfer Cases and Dana 20 Transfer Cases
This Jeep section deals with transfer cases used in the 1941-1979 Jeep vehicles and Scouts. This information aims 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 and 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 a 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 five-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". Small hole Dana 18 and Large 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 transfer case's rear.
The Dana 18 was the only cast Iron offset transfer case used by Jeep. The offset configuration was a passenger-side drop except for early prototypes. To clarify offset: Early jeeps were built with 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 driveshafts would also align with each other.
Since the transfer is clocked down on the passenger side, the front and rear driveshafts sit below the transmission. This 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 increased 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 as catastrophic as the Dana case cracking in half. Jeep initially used a small ¾" idler diameter shaft followed by 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 strengthen the case as the casting and manufacturing procedures were significantly improved upon.
It should be noted that, 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 who 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 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, 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. 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 on 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 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 noise reduction.
These kits are available for Jeep transfer cases 1946-53 (with a 1-1/8" intermediate shaft), or Jeeps 1953-79 (1-1/4") to fit the stock cluster gear. These kits use tapered roller bearings and a new shaft that aid in the noise reduction of your stock transfer case. Machining is required on your cluster gear. P/N 716005 - 1-1/4" Kit P/N 716006 - 1-1/8" Kit
Dana 18 rebuild kit: We offer a complete rebuild kit for the Dana 18 transfer case. Our kit comes complete with bearings and seals. 401801 or we also offer a seal and gasket kit 402018 - SEAL AND GASKET KIT-DANA18/20
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 farms, fields and forests. An incredibly large amount of aftermarket implements were offered, including winches, log splitters, water pumps and numerous other agricultural tools.
One 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 a 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 with 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 utilize these indexing retainers. This allows our adapters to be used on both small and large hole transfer cases. Likewise, most Jeep transmissions behind the Dana 18 can be interchanged by exchanging 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 years 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 vary slightly. 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. However, the differences can be critical regarding 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 use a 26- or 29-tooth input gear. There were also some very early 27 spline gears found in MB Jeep Universals 1941-1945. The MB model is a dual lever shift control, which 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 limiting your engine size to a V6 or changing the transfer case to the later model Dana 18. This transfer case uses an input gear with a 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. Due to the minimal number of years this application has been 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 was 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 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 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 that was heavily prone to failure. Advance Adapters offers a replacement adapter kit to correct this faulty design under 50-0500.
The Dana 20 would eventually find its way into the CJ models as well, with a 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 and T-150. As mentioned previously, the TH400 was the only automatic Jeep that would be used 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 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.
We offer a tapered roller bearing kit for 1-1/4" intermediate shafts. These kits use tapered roller bearings and a new shaft that aids in increased support and significant noise reduction. This kit is available for Jeep transfer cases 1953-79 (1-1/4") to fit the stock cluster gear. These kits use tapered roller bearings and a new shaft that aid in the noise reduction of your stock transfer case. Machining is required on your cluster gear. P/N 716005 - 1-1/4"
Dana 20 rebuild kits: We offer a couple of rebuild kits for the Dana 20 transfer case.
402001 - REBUILD KIT-JEEP D20 TCASE 1973-79 (bearings, gaskets and seals)
402018 - SEAL AND GASKET KIT-DANA18/20 JEEP TRANSFER CASE
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 on the multitude of different Jeep models equipped with the Dana 20. The differences were at their greatest when comparing small wheel-based to 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 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 was more likely due to increased manufacturing productivity than strength improvement as the increase in actual diameter was minimal. We have however seen failure of the Dana 20 rear output shafts under extreme applications. Advance Adapters offer a 32-spline rear output shaft as an upgrade kit under 50-3020A.
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
DANA 18/20 INDEXING: Jeep small hole gear assembly Jeep large hole gear assembly
716002 - Small hole index retainer (T90) Dana 18 transfer case
716001 - Large hole index retainer (T86) Dana 18 & 20 transfer case
716302 - 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)
Manual & Automatic Transmission options:
We offer numerous transfer case adapters for the early Jeep and Scout transfer cases. The transmissions and adapters are listed below:
Manual Transmissions:
SM420 GM transmission 10.5" long- 50-2401 adapter kit 4" long to Jeep 6 spline transfer case
50-2402 adapter kit 4" long to Jeep 10 spline transfer case
SM465 GM 2WD & 4WD transmission 12" long- 50-4703 adapter kit .875" long to Jeep 6 spline transfer case
Jeep T18 4 speed 11.87" long- 50-8705 adapter kit 1.0" long to Jeep 6 spline transfer case (large hole index)
Ford T18 4 speed 11.87" long- 50-7201 adapter kit 1.0" long to Jeep 6 spline transfer case (large hole index)
Ford T18 4 speed 11.87" long- 50-7202 adapter kit 1.0" long to Jeep 6 spline transfer case (small hole index)
Ford NP435 4 speed 10.87" long- 50-6102 adapter kit 3.325" long to Jeep 6 spline transfer case
GM NV4500 5 speed 12.375" long- 50-0210 adapter kit 5.87" long to Jeep 6 spline transfer case
GM Muncie 4 speed 10.5" long- 50-0100 adapter kit 6.0" long to Jeep 6 spline transfer case
AMC 1980 and Newer 21 spline output transmission- 50-8601 adapter kit to Jeep 6 spline transfer case
AMC 1980 and Newer 23 spline output transmission, (includes NV3550, AX15, & TR4050)
50-8602 adapter kit to Jeep 6 spline transfer case
Automatic Transmissions:
GM 2WD TH350 21.5" long- 50-3000 adapter kit 1.875" long to Jeep 6 spline transfer case
50-3100 adapter kit 1.875" long to Jeep 10 spline transfer case
50-3102 adapter kit 1.875" long to Scout 23 spline transfer case (Dana 300)
GM 4WD TH350 21.5" long- 50-3001 adapter kit 1.875" long to Jeep 6 spline transfer case
50-3101 adapter kit 1.875" long to Jeep 10 spline transfer case
50-3103 adapter kit 1.875" long to Scout 23 spline transfer case (Dana 300)
GM 2 & 4WD TH400 24.25" long- 50-1300 adapter kit 2.875" long to Jeep 6 spline transfer case
50-1400 adapter kit 2.875" long to Jeep 10 spline transfer case
50-1401 adapter kit 2.875" long to Scout 23 spline transfer case (Dana 300)
GM 2 & 4WD 700R4 23.375" long- 50-6905 adapter kit 6.25" long to Jeep 6 spline t/c (long wheel base vehicles)
Ford C4 3 speed 17.187" long- 50-2900 adapter kit 5.0" long to Jeep 6 spline transfer case (manual value body) 50-2904 adapter kit 6.25" long to Jeep 6 spline transfer case
Ford C6 3 speed 20" long- 50-3300 adapter kit 5.0" long to Jeep 6 spline transfer case
AMC 1980 and Newer 21 spline output transmission- 50-8601 adapter kit to Jeep 6 spline transfer case
AMC 1980 and Newer 23 spline output transmission-50-8602 adapter kit to Jeep 6 spline transfer case
FRONT YOKE and 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 further out than 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 716407 is the same as the 1966 to 1971 small Jeep yoke.
All Dana 18 and 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 in 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 716009.
JEEP DANA 18 GEAR KNOBS KIT:
We offer replacement knobs for the Dana 18 twin stick transfer case. 715643
DANA 18 3.15:1 LOW GEAR SETS (6 Spline Input only):
Kits are available for the Dana 18 transfer cases when using the Saturn Overdrive. This kit are shipped complete with the necessary hardware and gaskets to obtain the 3.15:1 low gear ratio.
The Dana 18 kit fits large hole transfer cases only. This 3-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 and older will require the use of a case from either a 1966 to 1971 CJ or, 1963 to 1971 Wagoneer/pickup. Saturn O.D. we offer a complete gear set to retain your overdrive using the 3.15:1 low gears, 418315OD. We also offer just the Saturn Overdrive bowl gear 911098.
ADAPTER CROSSMEMBER SUPPORT:
The early Jeep vehicles were equipped with a single channel-type crossmember 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 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 incorporated the crossmember and skid plate into one unit. This skid plate has been manufactured in various widths and configurations for 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 ensure maximum off-road 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 the transmission mount must be retained with the rubber snubber to limit the transfer case's movement. 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.
Most adapters we manufacture offer a machined support pad 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.
716003 - New rubber support (Jeeps 1941-79)
716003-HD - Prothane support (Jeeps 1941-79)
716021 - New rubber support (Jeeps 1972-79)
The Jeep Universals and Scout transfer cases from 1941-79 all had the same Dana 18/20 transfer case bolt pattern. There have 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, 716302 or a non-sealed replacement bearing, 716312, can be used.
When replacing a Jeep T14, T15, T18, T150 or T98 transmission, you will need to purchase a new bearing retainer, 716001 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 on the back of our new adapter, and then a 307 roller bearing must be installed inside the retainer. The bearing must be retained inside the retainer with a large snap ring. The snap ring is furnished with a new retainer. 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 to be interchanged and furnished with a new shaft with the correct drive spline to match the transmission 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. In some cases, Dana has manufactured two 26-tooth gears that appear 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 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 50-0500or 50-1300, 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, 50-2501, 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.