More Info on Transfer Cases
# Chevy/GM New Process 203
This isn't a bad transfer case, but it could be better. Like other chain drive units, the 203 is susceptible to chain stretch, but it won't stretch easily. The low gear ratio is a not the best at 1.98:1. This unit has a right-hand drop. This transfer case, which was produced from 1971 to at least 1980, is a full time unit. There are kits available from various manufacturers to turn this transfer case into a part-time unit. Like the other New Process transfer cases listed here, there's also Dodge and Ford versions of this unit.
# Chevy/GM New Process 205
This very strong cast iron case has all gear construction. It first came out around 1971, and lasted at least until 1990. It was available in both married and divorced styles, both of which had a right-hand drop. The low gear ratio isn't the best at only 1.98:1.
# Dodge New Process 203
This isn't a bad transfer case, but it could be better. This chain drive unit is susceptible to chain stretch, but it takes a lot of abuse to do that. The gear ratio is a not-so-great 1.98:1 and a right-hand drop. This transfer case, which was produced from 1971 to around 1980, is a full time unit. However, there are kits available from various manufacturers to turn this unit into a part-time transfer case.
# Dodge New Process 205
This is possibly the strongest transfer case ever put in Dodge light trucks, with its all gear construction in a cast iron case. It first came out around 1971, and lasted at least until 1980. It was available in both married and divorced styles, both of which had a right-hand drop for the front driveshaft. The low gear ratio isn't the best at only 1.98:1.
# Ford Dana 20
The Ford Dana 20 was produced from 1966 to 1977, and was used in the early style Bronco. Some appear to have made it into a few 1/2 ton (F-100) trucks, but this was not a standard. The very early 1966 model used a different shifter than the standard T and J shifters of the later transfer cases. From 1966 to mid 1973, the T shifter case was used. After that, the J shifter type was used. The J shifter type uses a shift pattern that looks like a backwards J. The T shifter uses a straight pattern, as does the early shifter. The early shifter (very rare) is rather hard to change gears with, and thus Ford/Dana changed the design.
The Ford Dana 20 design has a centered rear output, left-hand front output, and an all-gear design (read this as "strong and hard to break"). The case is made of cast iron, and a sheetmetal plate covers the bottom. This transfer case has two shift rails, one for low, neutral, and high on the front output, and one for low, neutral, and high on the rear output. A pair of metal lockout pins (or "pills") in tubes drilled between the holes for the rails work in conjuction with slots cut in the sides of the rails to provide only the gearing combinations of 2 high, 4 high, neutral, and 2 low. (These are put together by rear high/front neutral, rear high/front high, rear neutral/front neutral, and rear low/front low, respectively.) A linkage piece connects to the end of both shift rails, and then to a shift lever. This linkage rocks back and forth when the lever is moved, as the rails and lockout pins control the rail movement. The high range gear ratio is a straight 1:1, while the low range gear ratio is 2.48:1.
Twin-shifter setups on this transfer case put a shift lever on each shift rail. Most also recommend/require the removal of the lockout pins. This allows for some new gearing combinations, but the driver needs to be careful. The rear low/front neutral is sometimes nice and is the gear combination that most folks are after. If something's happened in the rear of the rig, the front high/rear neutral or front low/rear neutral might be useful. The gear combinations to avoid are rear high/front low and rear low/front high. If all four wheels have traction, these last two gear combinations will either kill the engine (at best), or break something in the drivetrain.
# Ford Dana 21
Definitely not one of Ford's better ideas, this was a single-speed transfer case (in other words, it has two high, neutral, and four high). This transfer case was used only in in some 1969 to 1976 F-100's. Its spline count and bolt pattern differ from the standard Ford stuff. The case on this unit is notorious for flexing and breaking gears and shafts. Parts are hard to find. This transfer case also uses a different input spline and bolt face that the rest of the Ford stuff. I'd recommend avoiding this transfer case; for less bucks and less trouble, there's better options.
# Ford Dana 24
This is a fairly uncommon transfer case. It's a two-speed, divorce-mounted transfer case that was used from 1960 to 1973. If you've got one of these, and it starts having problems, most likely it's the bearings. Some folks have a very high opinion of this unit, and others think that upon its breaking, it would probably be easier to replace the Dana 24 with a divorce mounted NP205 than to find parts for it.
# Ford New Process 203
This isn't a bad transfer case, but it could be better. It's a chain drive unit, so it is susceptible to chain stretch, but it takes a lot of abuse to do that. The gear ratio is a not-so-great 1.98:1, but it does have the Ford standard input and left-hand drop. This transfer case, which was produced from 1971 to 1980, is a full time unit. There are, however, kits available from various manufacturers to turn this unit into a part-time transfer case.
# Ford New Process 205
This is the ultimate beef for a light truck transfer case. It first came out around 1971, and lasted at least until 1980. The Ford version uses the standard Ford input and a left-hand drop for the front output. It's of an all gear design, with a cast iron case. The low gear ratio suffers a bit at being only 1.98:1. This unit will not be the weak link in your drivetrain.
# Ford New Process 208
The 208 is an aluminum cased, chain driven unit. It has the standard Ford input and left-hand drop. This unit has a nice low range ratio, at 2.72:1. This transfer case was supposedly used from 1980 to about 1982 (when the Borg Warner transfer cases supposedly took over), but I've got one of these in my 1984 Bronco.
# Ford Borg Warner 1345
This transfer case is chain driven, and has an aluminum case. It's pretty similar to the NP208 in those respects, as well as the fact that it has the same 2.72:1 low-range ratio. Ford started using this in 1980, and discontinued its use in 1988, when it was replaced with the BW 1356.
# Ford Borg Warner 1356
The 1356 was first used in 1988 or 1989, replacing the BW 1345. Like its predecessor, it's chain driven. However, it has a stronger, magnesium case.