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Overdrive Automotive Transmission Ratios
by Jeffrey Diamond
Last revision: January 19, 2017
Here are some of the more common 4-speed (overdrive in high gear) automatic transmissions. In all cases, 3rd gear is direct (1.00:1 ratio, as in the original 3-speed on which these are based) and 4th is overdrive with the driveshaft turning faster than the engine. This involves a certain degree of risk as to driveshaft speed, which would not be present in a car with the same over-all ratio achieved with 1.00:1 high gear and equivalent axle ratio for the same RPM vs. MPH.
The transmissions are grouped by manufacturer. The “base” is the original transmission case type from which the OD transmission was developed.
The column next to each gear is the percentage of engine RPM recovered after the shift into this gear. Actual RPM will always be slightly higher due to converter slip. Note that the transmissions with the highest torque in 1st gear (largest value for “1st”) also have the worst engine speed recovery, and require the widest power band for successful use.
For comparison, the popular Gear Vendors overdrive ratio is .78:1, which has less effect on engine speed than any of the factory transmissions but can be used in any gear. This has the effect of “splitting the gears”, viz. creating an intermediate ratio between each pair of the original gear ratios.
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4-Speed Overdrive Ratios |
Trans | Chrysler | GM | Ford | Toyota |
Gear |
500 |
Shift % |
518 |
Shift % |
4L80 |
Shift % |
200-4R |
Shift % |
4L60/65/70
700-R4 |
Shift % |
AOD |
Shift % |
AODE |
Shift % | A340E |
Shift % |
1st |
2.74 |
2.45 |
2.48 |
2.78 |
3.06 |
2.40 |
2.84 |
2.804 |
2nd |
1.54 |
56% |
1.45 |
59% |
1.48 |
61% |
1.57 |
56% |
1.63 |
53% |
1.47 |
61% |
1.55 |
55% |
1.531 |
55% |
3rd |
1.00 |
65% |
1.00 |
69% |
1.00 |
68% |
1.00 |
64% |
1.00 |
61% |
1.00 |
68% |
1.00 |
65% |
1.000 |
65% |
OD |
.69 |
69% |
.69 |
69% |
.75 |
75% |
.67 |
67% |
.70 |
70% |
.67 |
67% |
.70 |
70% |
.705 |
71% |
Base | 904, 999 | 727 | TH400 | TH250 | TH650 | C4 | (NA) |
For reference, here are some common automatic transmissions, note the internal ratios are quite different in some cases. |
2 & 3-Speed Ratios |
Trans | Chrysler | GM | Ford |
Gear |
999 |
Shift % |
727 |
Shift % |
TH650 |
Shift % |
TH400 |
Shift % |
PG |
Shift % |
PG |
Shift % |
C4 |
Shift % |
1st |
2.74 |
2.45 |
2.52 |
2.48 |
1.82 |
1.76 |
2.46 |
2nd |
1.54 |
56% |
1.45 |
59% |
1.52 |
56% |
1.48 |
61% |
1.00 |
55% |
1.00 |
57% |
1.46 |
59% |
3rd |
1.00 |
65% |
1.00 |
69% |
1.00 |
66% |
1.00 |
68% |
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1.00 |
65% |
See these Victory Library booklets |
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