Dana 300 Transfer Case - Gearbox AnatomyPosted in How To: Transmission Drivetrain on June 1, 2000 Comment (0)
(Editor's note: This is the first installment in an ongoing series. Starting this month, as time permits, we'll focus our attention in each issue of FW on a single transmission, transfer case, or axle that was popular in a variety of past OE truck and Jeep applications, and which still holds appeal to truck builders today. We'll examine their componentry, talk to experts about their strengths, look for any obvious weak links, and recommend strong fixes when applicable. This month, we look at a very stout t-case that saw widespread use in Broncos, Jeeps, Scouts and other 4x4xs throughout the '60s and '70s, and which is still in demand today.)
The Dana Spicer Model 300, which we will refer to as the Dana 300 throughout this story, is probably one of the most significant transfer cases ever developed and sits high atop the list of bulletproof transfer cases. You may have heard about it in shops, on the trail, or on a junkyard dig. So what makes a Dana 300 so significant? For this story, we contacted Four Wheeler tech guru Willie Worthy for some insight and incorporated website reference material from the experts at Novak Conversions, a company that has specialized in Jeep powertrain conversions since 1967.
The first thing to know about the Dana 300 is its history. The Dana 300 was a replacement, as well as a direct descendant of the much-loved Dana 18 transfer case, and as such uses many of the same components, including the very strong all-gear design. The biggest difference between the Dana 18 and Dana 300 is the Dana 300's centered rear output through the port where the power take-off (PTO) was located on a Dana 18. This was done to make the Dana 300 more efficient (think direct drive in two-wheel drive), as well as to make it much quieter than the Dana 18 it replaced. The other benefit of the centered rear output meant that a centered rear differential could be used instead of an offset rear differential, which allowed manufacturers to use the same rear axle on both two-wheel and four-wheel drive models. There were some conversions that changed the centered rear output to a Dana 18-style offset rear output so that the stronger 3000 could be used in place of the 18 on older vehicles. Jeep, IH, GM, and Ford all used versions of the Dana 300.
Other benefits of the Dana 300 include its very compact dimensions, light weight (less than 100 pounds), and a cast iron case that is much stronger than the Dana 18 case. Notably there was a single-speed Dana 21 model that was used behind automatics in some fullsize Fords.
Both front and rear output yokes are 1310. Earlier output shafts were 10-spline, while later versions used a 26-spline. According to Novak, this was done for the speed of manufacturing because the 26-spline shafts could be roll-forged instead of machine-cut like the coarser 10-spline. Because the shaft size is similar, both shafts are equally strong, and neither version is prone to breakage.
The common gear ratio was 2.0:1 in most model 300s, although the Bronco version and the Dana 18 had the desirable 2.46:1 ratio that could be swapped into Jeep Dana 300 cases with the Dana 18's gears, the Bronco's sliding gear, and some know-how. There are still low-range gearsets that run deeper than this that are available in the aftermarket today.
The Dana 300 featured two-wheel high, four-wheel high, and four-wheel low operation. A shift interlock pin prevented the transfer case from being operated in two-wheel low, though aftermarket twin stick conversions and modification of this interlock were common and allowed this extra mode, along with front axle-only operation in either high- or low-range.
The Dana 300 has exceptional strength for its size. Worthy believes that a stock Dana 300 can easily handle power ratings up to 350 horsepower and 350 lb-ft of torque, while Novak says they regularly see them handling big-block power and deep compound gearing without failure. Novak also reminds us that the Dana 300 was used successfully in the Jeep J-4000 1-ton trucks. Breakage usually occurs because of shock loads to the drivetrain from an aggressive driver, a worn intermediate shaft, or worn bearings.
If there are any drawbacks to the Dana 300, it would have to be the standard 2.0:1 low-range gear ratio and the fact that the centered rear output shaft does not allow it to be clocked for improved ground clearance and driveline angles the way a Dana 18 can be with its offset output. Also, the Dana 300 gears are unbalanced, and Novak says that while it is rare, breakage could occur because the helical front seat can produce significant side loads against the case.
Mel Wade at Off Road Evolution in Fullerton, California, had an old Dana 300 in his shop and offered it up as the sacrificial lamb for this story so that we could get a better look at its internals. We headed down to Fullerton, where we plucked an old Dana 300 out of the junkpile and let it die a hero.
Also be sure to check out the excellent history, parts, and rebuild guides available at www.novak-adapt.com.
Model 300 in Popular Production Vehicles
1969-'73 Blazers (some)
1962-'79 Fullsize J-series
1967-'73 C101 and C104 Commando
1972-'79 CJ-5, CJ-6, and CJ-7
Dana 300 Quick Hits
Similar to Jeep, but used a left-side front output shaft and/or a lower 2.46:1 (or 2.34:1) low range.
Not as common as the NP203 or NP205 and only used with three speed manual transmission.
Had twin sticks from the factory up to '69.
Avoid the problematic remote style "J"-shift versions.