Tech article by Jon Hanna (Admin)
Manual Transmission Intro
See also: Automatics

NP435 (NP=New Process) 4 speed manual
1969-1979 Ford F100-F350 pick ups with small blocks and 2 wheel drive. Look for a 28 spline output shaft and square tail housing bolt pattern. The square bolt pattern is the reason you want the 2 wheel drive version. The 4 wheel drive came with a trapezoid or "A" bolt pattern where the bottom two bolts are further apart than the top two. (The exception is a 4 wheel drive with a divorced transfer case, which has the square bolt pattern) It is possible to use a NP435 with a trapezoid tail housing bolt pattern, but your after market adapter choices are more limited and you'll probably need to find a 28 spline output shaft. Chevy and Dodge had their own versions of the NP435, but most adapters won't fit these transmissions.
You can recognize the NP435 by it's single piece, aluminum, bolt-on top cover with the shifter sticking directly out of the top and a fitting on the driver's side for the back up light switch. Most have the letters "NP" inside a circle cast into the cover. The NP435 is sometimes hard to tell from the similar looking T18 or T19. One way to check is with a magnet, which won't stick to the aluminum top cover of the NP435. The NP435 also has the PTO cover plate on the passenger's side. Weight is approximately 120 lbs.
Adapter required?
The NP435 requires an adapter between the transmission and transfer case. There are two styles available; both assume you have a small block V8. One style adapter replaces the 8 cylinder intermediate housing. The second style adapter may save you some money if you can locate the stock intermediate housing and shaft from a 6 cylinder Bronco. This adapter is only 1" thick due to the shorter length of the 6 cylinder adapter.
This is arguably the easiest and least expensive way to get a super low gear transmission into an early Bronco. The "granny low" is a huge help on steep hills (both up and down) as well as slow, technical trails. Installation is very straight forward with no custom fabrication, relocated cross members or new drive shafts required. The NP435 is extremely strong and durable making it a favorite of rock crawlers. The gearing basically makes it very much like a stock 3 speed with an extra low gear added. So if you're comfortable with the 3 speed gear spread on the street, you'll be fine with the NP435 as well. If you constantly wish for another gear between 2nd and 3rd with your current 3 speed, the NP435 won't solve that problem.
There's no speed shifting with this tranny. These are truck transmissions and you know it when you shift. First and reverse are non-synchronized. Because of the top shifter you'll need to cut a fairly large hole in the top of your transmission tunnel, including elimination of the body stiffener channel. Under dash air conditioning is (almost) impossible because the shifter handle is so tight to the underside of the dash.
Cost: (Approximate)
Transmission: $200-400 used and $700 rebuilt
Adapter: $350-500 ($250-300 using 6 cylinder intermediate housing)
Bell housing:
Standard Ford. The NP435 will bolt up to your existing bell housing on small block (289-302-351) engines. The existing Bronco clutch is also used.
Modifications needed:
A body lift is not a requirement, but does make for an easier install. Because the transmission is so tall the shifter tower will come up through the floor. A fairly large hole needs to be cut, including the cross member (or body stiffener) under the floor. Cover plates are available aftermarket or can be made fairly easily from sheet steel or aluminum. The shifter handle needs to be bent to clear the dash. One advantage to cutting a large hole is that the cover plate can easily be taken off giving easy access to the transmission top and transfer case shifter.

Manual Transmission Gear Ratios1st2nd3rd4th5th
Bronco 3 spd (6 cyl)3.411.861.00
Bronco 3 spd (8 cyl)2.991.751.00
NP 4356.693.341.791.00
Toploader (Close ratio)2.321.691.291.00
Toploader (Wide ratio)2.781.931.351.00
Toploader (Overdrive)3.291.841.000.81
NV4500 (Dodge)5.613.041.671.000.73

Automatic Transmission Gear Ratios1st2nd3rd4th5th
Bronco C42.461.461.00
AOD w/ low gear set2.841.551.00.67