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Rebuild Your Dana 20 at Home

Posted in How To: Transmission Drivetrain on February 27, 2018
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The Dana 20 transfer case is a medium-duty, gear-drive unit that was manufactured from about 1962 to 1979. It is a part-time, manual-shift t-case that was found in Jeep, GM, Ford, and some International Harvester vehicles. The cast iron housing helps contribute to its reputation as a robust and reliable transfer case.

We had a Dana 20 from an old Jeepster with a TH400 transmission that was in need of a little TLC. It had a lot of years and miles on it, and was popping out of gear on occasion. It was time for a home workshop rebuild of this unit. We contacted Novak Conversions for advice. The company assured us that a Dana 20 rebuild was straightforward, and Novak offers a master rebuild kit with online instructions for the process. This kit includes the company’s special hardened intermediate shaft, and we also opted to install Novak’s new billet rear-bearing cap that shims internally using an O-ring for sealing.

With our Dana 20 pulled out of the Jeep, we did a little external cleanup and then tore into the rebuild. Follow along as we freshen up a 50-year-old transfer case and ready it for many more wheeling miles. We completed the rebuild using mostly common mechanic tools on a home workbench, and did use a press to remove and install a couple of bearings. We also used feeler gauges, pullers, and a dial indicator during the process.

All our gears looked to be in good shape, so we proceeded with the rebuild to replace wear items with the Novak kit. This article is not meant to give you comprehensive instructions to do a Dana 20 rebuild. The factory service manual provides far more detail of the process. However, the information here should give you a good idea what’s involved as far as parts, tools, and some techniques go.

Here is the master rebuild kit from Novak Conversions. It includes all the necessary bearings, seals, gaskets, thrust washers, and Novak's case-hardened, triple-alloy intermediate (or idler) shaft. This kit is compatible with Jeep and most IH Dana 20 transfer cases.
We started disassembly by removing the bolts securing the rear output assembly. Make sure not to damage the somewhat-fragile cast iron output shaft assembly housing by hammering in a screwdriver and prying away. If yours is stuck on with silicone, have patience and work it with a razor blade or sharp, thin chisel around its circumference until it’s free.
Unbolting the bottom oil pan cover reveals the guts of the Dana 20. You can see here that someone had been in this transfer case previously and sealed it with liberal amounts of RTV silicone. Fortunately no metal chunks or concerning debris were in the pan.
Next we removed the bolt and lock plate securing the intermediate shaft. Using a brass drift, we drove the slightly tapered shaft out of the case towards the rear.
With the intermediate shaft removed, the intermediate gear, 48 roller bearings, three spacer washers, and two thrust washers could all be pulled from the case.
If you don’t have an impact wrench, remove the front output nut while holding the yoke with a large pipe wrench. We have also made and used yoke holders that bolt to the yoke. The pipe wrench works fine but may leave a few teeth marks in the yoke. We then pulled the front seal behind the yoke and removed the shifter linkage assembly from the case.
It was time to disassemble the front output section. The rear cover plate was unbolted and the rear bearing race removed. Then the front output cover was removed. Pulling the front bearing off the front output shaft can be a bit tricky with a puller setup, and you'll want to take care not to force too hard and risk cracking the cast iron case. During this process, the rest of the internals can be removed, including the two shift forks and their detent components.
Many times you can get a yoke to slide off its shaft with a few taps of a hammer, but we had to use a simple puller on our rear output assembly. With the shaft pressed free, we drove the old bearing races from the housing to start the rebuild.
After inspection and cleaning, the assembly started with the bare case to place the front shift rod and fork. Note that during disassembly we found it handy to reassemble each shift rod with its fork when set aside to easily know the proper orientation upon reassembly. The front sliding gear was dropped onto the front shift fork.
A new rear bearing was pressed onto the front output shaft.
The front output shaft was reinserted into the case and mated through the front sliding gear and front output gear.
With the front output shaft residing in the transfer case, the front bearing was pressed onto the shaft. Then the matching front and rear bearing races could be tapped into the housing.
The front output cover got new shift rod and output shaft seals. On the back side of the housing, new shift rod cover thimbles were tapped into the housing using a bit of sealer to keep them leak-free.
The front output cover was installed onto the housing using a new gasket and sealer. Bolts on all the housing castings were torqued to 30 lb-ft. There’s also a proper sequence to assemble the shift rods, detent components, and a detent rod into the case.
The stock Dana 20 transfer case uses a steel rear cover (right) for the front output section. Shims placed under this cover set the endplay of the assembly. Novak now offers an upgrade to the factory method. The kit uses a billet aluminum plate (center) with an O-ring seal and internal shims to rid the issue of combining shims on the fluid sealing surface.
We placed the Novak cover in place over the rear bearing of the front output and checked clearance with a feeler gauge. We added to that measurement to determine the shim thickness needed under the cover for proper shaft endplay.
With the Novak rear cover tightened in place, we used a dial indicator to check shaft endplay. We had to make a shim adjustment and reassemble to arrive at the final recommended endplay of 0.002 to 0.005 inch.
The front bearing on the rear output shaft was pressed off the shaft using a bearing separator and it was replaced with a new one.
Here are the components in the rear output assembly. The shaft rides on two tapered-roller bearings. The speedometer drive gear rides between the two bearings. Shims next to the gear set the endplay of the shaft assembly, which is specified to be 0.002 to 0.005 inch with the yoke torqued to 175 lb-ft. We had to change a few shims with our new bearings to get the proper endplay. Luckily, we had a few in our spare parts pile.
With the low-range shift fork and gear reinstalled into the case, the rear output assembly was bolted back into position.
The intermediate gear rides on 48 roller bearings set in two rows. We positioned them inside the gear vertically using chilled petroleum jelly to hold them in place along with the three bearing spacers. Petroleum jelly, unlike some heavy greases, will easily dissolve harmlessly into the gear lube once the transfer case is in use.
We also used petroleum jelly to stick the two thrust washers to the internal case sides while we dropped the intermediate gear into the case. We installed the Novak hardened shaft with well-lubricated O-rings on each end. We tapped it into the case using a block of wood, making sure all the roller bearings stayed in place. Then the shaft lock plate was reinstalled.
Our last step in the rebuild was to reseal the oil pan with a fresh gasket and sealer. It's a good idea not to overtighten the pan bolts and warp the pan edge. We also added a bit of sealant on each bolt that mates to open threads in the case were lube is present. After we reinstalled the shifter linkage assembly and did a quick function check, our Dana 20 was ready for many more miles of use.

Sources

Novak Conversions
Logan, UT 84321
877-602-1500
http://www.novak-adapt.com

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