A strong attempt has been made to condense a tremendous amount of information into a coherent table, below. This chart's primary purpose is to assist individuals with interchange and compatibility information. All Dana 18 / 20 gears that are not spur cut teeth are cut on a ~30 degree, left-hand helix.
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Dana Model |
Pressure angle, in degrees | Drive Gear: Dana & Jeep #'s | Gear teeth x Spline count | Intermediate Gear: Dana & Jeep #'s | Gear teeth counts | Front Output Gear | Gear teeth count | Front Sliding Gear: Dana & Jeep #'s | Gear teeth count | Rear Sliding Gear: Dana & Jeep #'s | Gear teeth count | With Transmissions | Idler Shaft Diameter | Jeeps | Years | Low Ratio |
| 18 | 20 | 18-8-7, A-1510 |
27t x 6 | 18-5-1, A-999 |
33t x 23t | 18-8-2, A-989 |
27t | 18-8-1, A-988 |
37t | n/a | T84 | 3/4" | MB, GPW | 41-45 | 1.97 | |
| 18 | 20 | 18-8-19, A-1510 |
26t x 6 | 18-5-6, unknown |
34t x 21t | 18-8-18, A-989 |
26t | 18-8-17, A-988 |
39t | n/a | T90 | 3/4" | Earliest CJ2, using last of 3/4" intermediate shafts | 41-45 | 1.97 | |
| 18 | 20 | 18-8-19, 937339, (a) |
26t x 6 | 18-5-7, 642189 |
34t x 21t | 18-8-18, A15044 |
26t | 18-8-17, A15045 |
39t | n/a | T90 | 1-1/8" | All. CJ3B before s/n 541-2506. Military M38 & M38A1 | 46-54 | 2.46 | |
| 18 | 20 | 18-8-23, 809297 |
29t x 6 | 18-5-9, 809293 |
39t x 18t | 18-8-24, 809291 |
29t | 18-8-22, 809290 |
33t | n/a | T90, T86 | 1-1/4" | CJ, Early Style Pickups & Wagons. Four cylinder to '71, V6 to '68. Both new & old body style built between '62-64. CJ3B built after s/n 541-2506. | 55-71 | 2.46 | |
| 18 | 20 | 18-8-50, 947382 |
29t x 10 | 18-5-9, 809293 |
39t x 18t | 18-8-24, 809291 |
29t | 18-8-22 809290 |
33t | n/a | T14 | 1-1/4" | CJ with Buick V6. | 68-71 | 2.46 | |
| 20 | 20 | 18-8-31, 937339, (a) |
26t x 6 | 18-5-10, 933736 |
34t x 20t | 18-8-18, A15044 |
26t | 18-8-28, 933735 |
31t | 18-8-26, 933742 |
31t | T98, T18, T90 | 1-1/4" | Late style Kaiser J series Pickups & Wagons. Also '76-'79 CJ's with T18 | 62-79 | 2.03 |
| 20 | 17.5 | 18-8-46, 946574, (b) |
26t x 6 | 18-5-16, 946786 |
34t x 20t | 18-8-28, 933735 |
26t | 18-8-28, 933735 |
31t | 18-8-26, 933742 |
31t | T18, T15, T89, T98 | 1-1/4" | Late style Kaiser J series Pickups & Wagons. Jeepster | 66-79 | 2.03 |
| 20 | 20 | 18-8-40, 940472 |
26t x 15 | 18-5-10, 933736 |
34t x 20t | 18-8-18, A15044 |
26t | 18-8-28, 933735 |
31t | 18-8-26, 933742 |
31t | TH400 | 1-1/4" | Late style Kaiser J series Pickups & Wagons | 64-79 | 2.03 |
| 20 | 17.5 | 18-8-43, 946785 |
26t x 15 | 18-5-16, 946786 |
34t x 20t | 18-8-44, 946784 |
26t | 18-8-28, 933735 |
31t | 18-8-26, 933742 |
31t | TH400 | 1-1/4" | Jeepster | 66-72 | 2.03 |
| 20 | 17.5 | 18-8-49, 947339 |
26t x 10 | 18-5-16, 946786 |
34t x 20t | 18-8-44, 946784 |
26t | 18-8-28, 933735 |
31t | 18-8-26, 933742 |
31t | T14 | 1-1/4" | Jeepster, CJ | 67-74 | 2.03 |
| 20 | 17.5 | 18-8-55, 5354506, (b) |
26t x 6 | 18-5-16, 946786 |
34t x 20t | 18-8-44, 946784 |
26t | 18-8-28, 933736 |
31t | 18-8-26, 933742 |
31t | T150 | 1-1/4" | CJ | 76-79 | 2.03 |
| 20 | 17.5 | 18-8-56 | 26t x 23 | 18-5-16, 946786 |
34t x 20t | 18-8-44, 946784 |
26t | 18-8-28, 933737 |
31t | 18-8-26, 933742 |
31t | TF727, 904, 909 | 1-1/4" | IH Scout | -79 | 2.03 |
| 20 | 20 | 18-8-33 | 29t x 6 | 18-5-9, 809293 |
39t x 18t | 18-8-24, 809291 |
29t | 18-8-35 | 33t | 18-8-37 (c) | 33t | 1-1/4" | Bronco | 66-72 | 2.46 | |
| 20 | 18-8-24 | 29t x 6 | 18-5-21 | 39t x 18t | 18-8-24, 809291 |
29t | 18-8-57 | 33t | 18-8-58 | 33t | 1-1/4" | Bronco | 73-74 | 2.46 | ||
| 20 | 18-8-64 | 29t x 6 | 18-5-21 | 39t x 18t | 18-8-24, 809291 |
29t | 18-8-66 | 33t | 18-8-65 | 33t | 1-1/4" | Bronco | 75-77 | 2.46 | ||
| 20 | 20 | 26t x 6 | 18-5-10, 933736 |
34t x 20t | 18-8-18, A15044 |
26t | 18-8-28, 933737 |
31t | 18-8-26, 933742 |
31t | SM465 | 1-1/4" | Chevy Blazer | 70-72 | 2.46 | |
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a. Yes b. Special seal area machined into the front face of gear for T150. Interchanges when not used with T-150. |
Intermediate gear bores are identical for 1-1/8" and 1-1/4" applications. | c. The Bronco gear used for Jeep Dana 20, 2.46:1 conversions |
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The 1-1/8" transfer cases can be precision line bored to accept 1-1/4" intermediate shafts and their larger contingent of bearings, resulting in quieter operation and longer gear bore, shaft journal and needle bearing life. This is a service that is provided on request.
A potential problem exists on these gear interchanges. It is possible to assemble an 18-8-31 gear in a non-compatible transfer case. They both have a 26 tooth 1-3/8" 6-spline gear but the tooth form is 2-1/2 degrees different and it will run noisy and hot and destroy the transfer case in short time. As much alike as these Model 20 cases are, there are some combinations that are not compatible unless all the helical gears in the case are changed.
Sources
- The Novak Archives
- Willie Worthy
- Bob Hutchins
- Dave Martinez
- Herm Tilford