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	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	18-8-46,18-8-55 946574, (b)	26t x 6	18-5-16, 946786	34t x 20t	18-8-28, 933735	26t	18-8-44, 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
		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

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