4 Wheel & Off Road - - CONTENTS - Jay Kopy­cin­ski BY EDI­TOR@4WOR.COM PHO­TOG­RA­PHY JAY KOPY­CIN­SKI

A DIY re­build is within reach.

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.

1 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.

2 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.

3 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.

4 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.

5 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.

6 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.

7 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.

8 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.

9 A new rear bear­ing was pressed onto the front out­put shaft. The front out­put shaft was then 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.

10 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.

“It was time for a home work­shop re­build of this unit”

11 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.

12 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.

13 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.

14 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.

15 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.

16 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.

17 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.

18 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.

19 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.


NO­VAK CON­VER­SIONS 877.602.1500 no­

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