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Saturn Overdrive



This unit will work as bolt overdrive / gear splitter in vehicle equipped with the Dana 18 transfer case. These cases came in early jeeps and scouts (with the offset rear differential). This transfer case can also be made to work in American powered Toyota Land Cruisers, and Land Rovers. I mounts onto the BACK of the Dana 18 and adds no additional length to the drive train, lending itself to very short wheelbase vehicles or where a transmission conversion is requiring a short T-case system.

The benefits are maximized by using a "granny tranny" with very wide ratios. On of the primary drawbacks to these transmission is that the gears are so far apart that you may be looking for a gear halfway between 1st and 2nd. The Saturn works as a gear splitter (See gear splitter data above) as well as an overdrive.

By using available 3.15 gears in the Dana 18, the Saturn overdrive and a granny tranny such as the SM420, SM465, NP435 or T18, 16 forward gears are available. with a SM420 (7.02 1st gear) and 4.88 axles a crawl ratio of 108 is achieved. This system can also be used with an NV4500. The resulting double overdrive allows even lower axle ratios without sacrifice of highway drivability.

Crawl ratio example demonstrating 16 forward gears: (Shown using 4.88 gears)

Dana 18

SM420

Saturn

Axle

Crawl Ratio

Hi

1.0

4th OVR

1.00

in

0.75

4.88

3.66

Hi

1.0

4th

1.00

out

1.00

4.88

4.88

Hi

1.0

3rd OVR

1.70

in

0.75

4.88

6.22

Hi

1.0

3rd

1.70

out

1.00

4.88

8.30

Hi

1.0

2nd OVR

3.57

in

0.75

4.88

13.07

Hi

1.0

2nd

3.57

out

1.00

4.88

17.42

Hi

1.0

1st OVR

7.05

in

0.75

4.88

25.80

Hi

1.0

1st

7.05

out

1.00

4.88

34.40

 

 

 

 

 

 

 

Lo

3.15

4th OVR

1.00

in

0.75

4.88

11.53

Lo

3.15

4th

1.00

out

1.00

4.88

15.37

Lo

3.15

3rd OVR

1.70

in

0.75

4.88

19.60

Lo

3.15

3rd

1.70

out

1.00

4.88

26.13

Lo

3.15

2nd OVR

3.57

in

0.75

4.88

41.16

Lo

3.15

2nd

3.57

out

1.00

4.88

54.88

Lo

3.15

1st OVR

7.05

in

0.75

4.88

81.28

Lo

3.15

1st

7.05

out

1.00

4.88

108.37