Engine Speed at 60 MPH with various Rear end ratios:

    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.


 
 

(Above)  Chevrolet 4 speed crash box above 31 - 47.  Spur cut gears.  No syncromesh.

(Below)  Clark 5th over will fit 31 - 47 Chevys.






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 Ratios



 
 
 
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.
 
 



Identification Numbers !!
Engine Casting Numbers >
Production figures >
Paint Chips  >
 Back to Trux >>
 Back to Carz >>
 Back Home >>>

Repair tips