You finally get your old 6 cylinder Chevy together after years of restoration and with a smile as big as a clam you head for a meet 20 miles away.  The leprechauns tap dancing under the valve cover are music to your ears.  About a mile down the road the temp gauge starts to move up to normal and you floor it for the freeway on ramp.  You have plenty of acceleration in high gear of your Deluxe sedan until you hit 50 MPH.  All of a sudden the babbit starts beating and the leprechauns start tapping on your head  to see if they can loosen some fillings.
    Back in the "good old days" when your car was new, most roads weren't designed for over 50 MPH so the cars were built thusly.   Using the chart below you can see what the engine speed is at 60 MPH for your rear end ratio and tire size.  If the engine has to lug or over rev, your fuel mileage will be horrible.   A 3.55 to 3.08 ratio is good for 6.00 X 16" tires depending on vehicle weight.

    Math= Wheel Diameter X Pi = circumference in inches. Divide into 63360 Inches per Mile. = Wheel revs per mile. (60 MPH = 1 Mile per minute). Times Rear End Ratio = Engine rpm @ 60 mph. . . . 2200 RPM is a quiet engine speed for 60 MPH.
 

Application>			4.11 w/OD		57Turbogld	Power Glide	37 Std GB	Econo  1/2 Ton	54  1/2Ton	1/2 Ton  GC	Deluxe GA	41 3/4 ton	41  OneTon	ton&half	2-Speed Hi	Ton&half H- Duty	2-Speed low
Tire  Size	Outside  diameter	Wheel  Revs / Mile	Rear 2.87	end 3.08	Ratios 3.36	3.55	3.73	3.82	3.90	4.11	4.22	4.56	5.14	5.43	5.64	6.17	8.22
4.00X8	16”	1260	3616	3882	4234	4474	4700	4813	4914	5181	5317	5746	6476	6842	7106	7777	10361
	24"	840.8	2413	2589		2985		3195		3456				4566			6911
	25"	806.7	2315	2485		2864		3066		3316				4381
	26"	775.7	2226	2389		2754		2947		3188				4212
	27"	747.1	2143	2301		2652		2838		3070				4056
6.00X16	28"	720.3	2067	2219	2420	2557	2687	2737	2809	2960	3040	3285	3702	3911	4062	4444	5921
6.50X16	29"	695.4	1996	2142		2469		2642		2858				3776
7.00X16	30"	672.3	1929	2071		2387		2554		2763				3650
7.50X16	31"	650.6	1862	2004	2186	2309	2426	2472	2537	2673	2746	2967	3344	3533
600x20	32"	630.3	1809	1941		2238	2351	2395	2458	2590	2659	2874	3240	3422	3555	3889	5181
6.50X20	33"	611.2	1754	1882		2170		2322		2511			3142	3318		3771
7.00X20	34"	593.2	1702	1827		2106		2281		2438				3221		3660
7.50X20	35"	576.2	1654	1775		2046		2190		2368		2627	2961	3129	3250	3555	4736
8.25X20	36.5"	552.6	1586	1702		1962		2100		2271				3000		3410
9.00X20	38"	530.7	1523	1635		1884		2017		2181				2882	2993	3274	4362
	39"	517.1	1484	1593		1836		1965		2125				2808		3190
10 X 20	40"	504.2	1447	1553		1790		1916		2072				2738		3111
14 X 20	48"	420.2	1205	1294						1727				2282	2370	2593	3454
			2.87	3.08	3.36	3.55	3.73	3.82	3.90	4.11	4.22	4.56	5.14	5.43	5.64	6.17	8.22

    There are various ways to get a higher gear in your old Chevy.  None are cheap or easy.
    1.    You can install a higher rear end ratio. (lower numerically).   Patrick's in Casa Grande, Az offers 3.55 for 40 - 54 half tons.  33 - 39 have spiral bevel gears and different lengths drive line but could be made to fit.  1950 - 54 Power Glide rearends will bolt into  37 - 54 passenger cars.  This is another cut to fit on older cars and Hypoid vs spiral bevel on 33 - 36.
    2.    An overdrive auxiliary transmission is another option.    Truxtell offered an overdrive inserted in the torque tube of a 41 - 54 passenger or half ton.  Many private entrepreneurs have inserted Borg-Warner  and custom made overdrives in the torque tube.    If you bolt your Brownie to the frame as instructed, overdrive will rattle your fillings out.      I butted a 3 speed backwards in my Limousine and adapted to torque tube.  The gear whines a little but is way too hi in second and ridiculous on low.  Second over = 0.595.  Low over = 0.34.
    3.    An overdrive main transmission is another way.  The Clark 5 speed will bolt up to 41 and newer trux.  I have never seen one with a torque tube out put for 31-40 trux. It's quiet in 4th direct and has gear noise in 5th over.  It's not much over.
             One pipe dream I had is to take low gear in a 3 speed and make  an overdrive out if it. This would only work on 37 - 39 half ton 3 speed transmissions.   (see butchered 3 speed below right) 0.686 is a bit hi for anything but a deluxe (4.22) coupe with a 235.
 
 

     Above left is stock 37 - 39 3 speed truck trans.  .  .  .  .  .  Above right is an overdrive concept using low gears from another 3 speed. The ratio would be 0.686.
    If you are rebuilding a 3 speed, the countershaft bushings are not available.  If you visit a hardware store, they sell one inch OD by 7/8" ID bushing with flange for less than $5 each.   The flange needs to be shaved to replace the washers.

Below is a list of transmissions that might have found their way into your 37 Chev. Marked in blue are those that are stock and bolt in. (I have never seen a torque tube at the rear of a fifth/Overdrive Clark but the brake and clutch pedals bolt up OK.)  Maple Leaf trux used a 5 speed Transmission and I have no idea if it's the clark or another.

1933 - 72 ton & half differentials will interchange.  (33-39 are spiral bevel.  40 - 72 Hypoid.  33-40 are Torque Tube.  41 - 72 are Hotchkiss.  1940 is only Hypoid torque tube.  Ratios are 5.43, 6.17, and Military 6.67.

1935 -36 Deluxe passenger and half ton & 37 - 39 half thru one ton are identical with 4.11 and 3.82 ratios. May fit 33 - . 34 deluxe. May fit 1940 - 55 half ton.  1940 - 1954  half ton (torque tube) & 1940 - 42 3/4 ton will interchange (hotchkiss). May fit 55 - 64 (?) half  ton (Hotchkiss).

 1937 - 54 passenger will interchange. May fit 1933 - 36 Standard.

1942 - 72 3/4 and One Ton Pumpkins will interchange.
 
 

 
 
 

Transmission	Year		Granny	Low	intermediate	Direct	Overdrive	Reverse
3-Speed	30-31			3.32	1.77	1		4.2
4-Speed	28 - 30		6.165	3.474	1.746	1		6.297
3-Speed	1932			3.05	1.81	1		3.43
3-Speed	33-36 Std			2.802	1.7081	1		2.802
3-Speed	33-36 Dlx			3.02	1.71	1		3.4
Borg W 3	35-36			2.819	1.604	1		3.383
Borg W 4	35-36		6.395	3.09	1.684	1		7.452
3-Sp	37-69			2.94	1.68	1	0.7	2.94
4-Sp	31-40		7.226	3.478	1.711	1		7.148
4-Sp	41-47		7.06	(same)	(same)	1		6.98
Clark  5-Sp			6.06	3.5	1.8	1	.799	6.00
4-speed	48+		7.06	3.58	1.71	1		6.78
Hydro- matic	1954 1/2 ton		3.82	2.63	1.45	1		4.30
Hydro- matic	54 3/4 ton +		4.70	3.03	1.55	1		6.11
HD 3- speed	53 - 64??			3.17	1.75	1		3.76
NVG  4500	1991-93		6.34	3.43	1.72	1	0.74	6.34
Power  Glide	1950-54				1.81	1		1.81
Power- Matic	58?-65? 6-speed	5.3	3.81	2.69	1.94	1.4	1	6.04
Auxiliary
Brownie				2.11	1.26	1	0.83
Chev  transfer Case					1.94	1
GMC  transfer Case				2.63	1.16
Borg-W OD	Most models					1	0.7

 Pumpkins  Differential Carrier Housing Ratios
Year vehicle or Hypoid Pinion : Ring  Ratio Part numbers

		Spiral Bevel
Year	Vehicle	or Hypoid	Pinion	Ring	Ratio	Part Numbers
1928 - 29	Pass & 1/2 Ton	Spiral Bevel	11	42	3.82
1927 - 29	One Ton	Spiral Bevel	8	39	4.875
1930 - 32	Pass & 1/2 Ton	Spiral Bevel	9	37	4.11
1930 - 32	Ton & Half	Spiral Bevel	7	38	5.42
1931 - 32	Ton & Half	Spiral Bevel	6	37	6.17
32 option	Pass & 1/2 Ton	Spiral Bevel	9	39	4.33
1933	Dlx & 1/2 Ton	Spiral Bevel	9	37	4.11
1933	Bastard  (standard)	Spiral Bevel	9	37	4.11
1933 - 36	Ton & Half	Spiral Bevel	7	38	5.42
1933 - 36	Ton & Half	Spiral Bevel	6	37	6.17
1934 - 35	Dlx & 1/2 Ton	Spiral Bevel	9	37	4.11
1934 - 35	Bastard	Spiral Bevel	9	37	4.11
1935 Economy	Dlx & 1/2 Ton	Spiral Bevel	11	42	3.82
1936 Bastard	Bastard	Spiral Bevel	9	37	4.11
1936 Economy	Bastard	Spiral Bevel	11	42	3.82
35 - 39	1/2 Ton	Spiral Bevel	9	44	4.89	Part book mentions	#379513
35 - 36 Dlx &	35-39 1/2Ton	Spiral Bevel	9	37	4.11		#602476
35 - 39 Economy	Dlx & 1/2 Ton	Spiral Bevel	11	42	3.82		#602477
1937 - 39	Ton & Half	Spiral Bevel	7	38	5.42
1937 - 39	Ton & Half	Spiral Bevel	6	37	6.17
1937 - 39	Deluxe	Hypoid	9	38	4.22
1937 - 39	Standard	Hypoid	11	41	3.73
1940 - 52	Passngr	Hypoid	11	41	3.73
			#3652285	-595022	#604397
1940-52 Pass	&  53 Sddl	Hypoid	9	37	4.11
1940 - 53	Half ton	Hypoid	9	37	4.11
1940	3/4 ton	Hypoid	9	41	4.56	Torque Tube	Both use same-
1941 - 42	3/4 ton	Hypoid	9	41	4.56	Hotchkiss	ring gear
1939 - 42  2 - Speed	Ton & half	Helical			5.64 8.22
1940 - 55	Ton & half	Hypoid	7	38	5.42	41-72=Hotchkiss
1940-72	Ton & half	Hypoid	6	37	6.17	41-72=Hotchkiss
1941 - 46	Ton & half	Hypoid	6	40	6.67	Military
1946 - 72 (?)	3/4 ton	Hypoid	7	32	4.57
1946 - 72 (?)	One Ton	Hypoid	7	36	5.14
1950 - 54	Powerglide	Hypoid	11	39	3.54
1953 - 54	3-Speed	Hypoid	10	37	3.70
1954 - 56	Half ton	Hypoid	10	39	3.90	Pinion different	on Hotchkiss
1955 - 57	Half ton	Hypoid	9	37	4.11	Over Drive
1955 - 57	Pass	Hypoid	9	37	4.11	Over Drive
1955 - 57	Powerglide	Hypoid	9	32	3.55
1955 - 57	2 Ton	Hypoid	5	36	7.20
56 Vette	3-Speed	Hypoid	11	36	3.27
1957	Turboglide	Hypoid	11	37	3.36
Special Field	Installation	Heavy	Duty	Parts	for use	with 6 lug	passenger	Wheels.
IE., Race	car gears!!
1955 - 57		Hypoid	11	39	3.54
			10	37	3.70
			10	39	3.90
			9	37	4.11
			9	41	4.56
			9	44	4.89
			7	36	5.14
			7	39	5.57
			6	35	5.83
			6	38	6.33

   So after reading all these numbers, What's the right ratio for your car?  Look at the Torque curve of the engine you are using.  (A Honda 2000 that has to spin 7 grand before it sees any torque, & would need a lower  gear.)  Your 37 Chev reaches max torque (170 ft lbs.) from 850 - 1500 RPM. Be careful not to lug the engine with too high of a gear.  Next figure your Aerodynamic drag and rolling resistance.  (Like we all have wind tunnels in our back yard).  It will take about 10 HP to keep your Panel going at 60 MPH and 13 HP for a PU.  Triple that number for a safety factor since the road is never perfectly smooth, no head winds, hills, nor curves.   Your vehicle has mass (similar to weight) that needs to accelerate.
    Bottom line is you want to coordinate tire size and rear ratio to operate at 1900 - 2500 at 60 MPH.