NV5600 Conversion to

NV5600 Conversion to

Fuller FSO 6406

Fuller has been using a variety of 5 and 6 speed transmissions in mid-sized trucks for many years as well as larger 9, 10, 12, 15 and 18 speed transmission in over the road trucks.

The various transmission options offer a variety of gear ratios depending on

how your truck is setup. If you use a straight 6 speed without O/D and 4.10 gears you will be at 2200-2400 RPM and max at 55-58 MPH. The the 6 speed OD (.73 X 4.10=2.993) gives us a effective high speed ratio of 2.993.

For the NV5600
1st - 5.63
2nd - 3.38
3rd - 2.04
4th - 1.39
5th - 1.00
6th - 0.73 w/4.10's, effective ratio is 2.993

Case Cast Iron

Torque Rating 650 lb.-ft.

Gross Combined Weight 26,000 lbs.

Transmission Weight 360 lbs.

Input Shaft (99-2000) 10 Spline 1.25" dia

Input Shaft (01-up) 10 spline 1.375" dia

The Getrag 56 trans is
1st - 4.23
2nd - 2.53
3rd - 1.67
4th - 1.23
5th - 1.00
6th - 0.79 w/4.10's, effective ratio is 3.239

The Fuller FSO-6406A is
1st - 7.06
2nd - 4.13
3rd - 2.52
4th - 1.59
5th - 1.00
6th - 0.78 w/4.10's, effective ratio is 3.198

With a Fuller set-up, low end pulling (1 & 2) is much better and all 3 transmissions are comparable in 3rd to 6th gears. The lower the effective gear ratio the more top end speed. The NV has a very slight edge.

The Fuller 5 and 6 Speed transmissions come in synchronized and unsynchronized versions as well as final drive at 1:1 (FS series) and overdrive at .78 (FSO series). You can convert a FS series transmission into an FSO with standard off the shelf parts.