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The Novak Guide to
Dana 18 & 20 Gears Interchange 1941-1979

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.

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
18-8-2,
A-989
27t 18-8-1,
A-988
n/a T84 3/4" MB, GPW 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
    a. Interchanges.
b. Same gear profile, except special seal journal machined into the front boss of gear for T150. Ok to use T150 gear on other trans, but not visa versa.
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
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.

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 Novak provides on request. Cost is $74. Contact us.

Sources
- The Novak Archives
- Willie Worthy
- Bob Hutchins
- Dave Martinez
- Herm Tilford