Early Bronco Transmissions - General
- Automatic Transmissions
- Ford C4
- Ford C6
- Ford AOD
- Chevy 700R4
- Manual Transmissions
- NP435
- T18
- T19
- NV4500
- Stock 3-speed
There are a few different kinds of trannies that can be put into an EB. You have the choice of automatic or manual. Then you have the choice of overdrive or not. Then, if going manual you also must decide if you want a granny low or a granny low with overdrive.
First, decide if you want manual or automatic. If your engine runs well and doesn't stall often, the automatic is terrific offroad. The only there's really a need for a manual offroad is in some very rare downhill sections, but some smart braking will do you just right. A downside to the automatic is the fact that your RPMs on the highway may be a little higher (200-400 RPM) because of TC slippage.
Automatics
C4
First, there's the C4, which is likely the easiest of swaps since you can get stock EB parts to do the conversion. Some people don't think the C4 is strong enough, but if you drive wisely and don't put more than 300 or so horsepower to it you should be fine.
C6
Strongest of the old-school light truck Ford transmissions. Bulletproof, but heavy and several inches longer than the C4 (drive line mods required).
AOD
You can also go for the Ford AOD transmission, which comes behind the late model Mustangs (and other cars). This is a great transmission if you do certain modifications to it first. You must use some larger servos in it and a better oiling system to make them good for the EB. Ford Motorsports makes a low gear kit for this transmission (not a granny low, but almost a 3:1 first). This transmission also has one hell of an overdrive in it, which will make highway cruising very pleasant. However, you must have the correct axle gears to make the OD useful.
Chevy 700R4
Checkout Kincade's writeup on http://www.700r4inaford.com/
Manuals
Next, we have the manual transmissions. You must decide what you will be doing with your EB before you decide on a specific manual tranny, whereas with automatics you are pretty much OK regardless of what you do. If you plan on four wheeling with a manual, a granny low is strongly recommended. If you don't have one, you will be burning up clutches, breaking parts, and just getting aggravated! Anything below (above numerically) 5:1 is considered a granny low. If you don't plan on doing much rough four wheeling, you will likely not find a need for a granny low, and may want to look at an overdrive option (Ratio < 1).
NP435
The New Process 435 is a four-speed 'truck' manual transmission with granny low. It was made by New Process Gear from 1964 to 1993. They are found in GM trucks until 1972, Ford trucks until 1992 and Dodge trucks until 1993. The 435 is an excellent heavy-duty truck transmission designed and used in ½, 3/4 and 1-ton trucks.
It is probably the easiest (and therefore most popular) of the manual transmission conversions. The one you want is from 1978-83, 2 wheel drive Ford Truck. They have the 28 spline square tail pattern. If you get a 4wd tranny, you'll need to swap out the tail shaft.
General Info:
- Granny First Gear (non-synchro)
- Very Strong (ie heavy :)
- May be hard to shift for some (very heavy action).
Install Notes:
- An adapter is required.
- Need to cut the transmission tunnel if you don't have a body lift.
- Need to bend the shifter out to clear the dash.
- If you need to lower the tranny a bit, you can swap the upper & lower bushings.
Specs:
- Make: New Process Gear
- Length: 10.7"
- Weight: 135 lbs
- Case: Cast Iron
- Top Cover: Cast Aluminum
- PTO Port: Passenger Side
- Ratios: 6.68, 3.34, 1.79, 1 (All Ratios :1) (Ford)
NOTE: There are at least two different height top covers and two different lenght pins that engage the shifter cover. Also, some come with a reverse switch and some don't!
-Rob Wilson
CAUTION: Improperly towing any vehicle with the NP435 transmission will cause the very prompt destruction of third gear bore and the mainshaft journal due to insufficient oiling.
If you must flat tow, you may set the transfer case in full neutral and place the NP435 in any gear to prevent mainshaft spin. However, The stock Bronco Dana 20 has the oiler on the rear output shaft as well.
Preferably, you may wish to disconnect the rear drive shaft. Rear axle lockout hubs may be a worthwhile addition for this reason.
T18
The Borg-Warner T18 four-speed manual transmission was manufactured from 1966 through 1989. It is a heavy-duty truck transmission designed for 1/2 tons through 1 tons. The T18 is fully synchronized in the second through fourth gears. All gears are helically cut except first and reverse, which are spur gears. The T18 is not quite so popular because you have to modify driveshafts (unlike the NP435).
General Info:
- Gearing: 6.32, 3.09, 1.69, 1.00 (Jeep and IH versions had a 4.02 first gear)
- First gear is non-synchro.
T19
The Borg-Warner T19 is similar to the T18 in appearance. This four-speed transmission is different from the T18 and others in that it usually features taller gearing and a synchronized first gear. It was introduced in Ford trucks in the 1968 model year. T19s are harder to find, but are a great tranny if you find one. Also, the T19 is not quite as low as the first two, but it is below 5:1.
General Info:
- Synchronized first gear
- Three gearing options were available for the Ford T19.
- 4:02:1 first gear was the most common on the T19A.
- 6.32:1 first gear on rarer Ford 500-800 series HD trucks.
- 5.1:1 was made for two years (1983-1984) on the T19.
NV4500
The New Venture Gear 4500 is a heavy-duty five speed manual transmission. It is found in Chevy trucks from 1993 and Dodge trucks since 1995. Though it has it roots as the New Process 4500 four-speed beginning as early as 1972 in Dodge trucks, its current incarnation as we know it today is quite different. It is a granny (5.61) low with overdrive (.73?) 5 speed. It is also bulletproof. They are hard to come by and expensive ($1200-$2500). Check with Advance Adaptors as they have an excellent adapter kit (Can include transmission) for the conversion from the three speed. It moves everything back about 5" so drive line work is needed, but that is a good time to add CV joints if you don't have them. The clutch can be problem if you have 10" clutch/flywheel as the required 11" (Chevy)clutch may not fit your bell housing or starter offset and will require replacing flywheel and pressure plate with the larger size 167 tooth. If you order the kit and already have an NV4500 make sure you check the output shaft on the transmission as there are 23 and 29 spline shafts. The second thing is the top loader as there are three different styles depending on year to make the nice looking shifter attach correctly.
General Info:
- Length: 18.9"
- Weight: 195 lbs.
- Case: Cast Iron
- Top Cover: Aluminum
- PTO Ports: Both Sides
- Gearing: 6.34, 3.44, 1.71, 1, .73, R 6.34 or, 5.61, 6.04, 1.67, 1, .73, R 5.61
Stock 3-Speed
Lastly, there is the stock 3-speed. They are strong, they are cheap, about the only beef I have with them is that first gear is too high rock crawling(extreme), and that pesky column shift. But they are plentiful... they are cheap... they are strong. Keep it for a while, you might enjoy one of the last of the column shift trucks in the United States :)