RESTOR­ING AN NP242

RESTOR­ING AN NP242 FULL/ PART-TIME T-CASE WITH YUKON

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

A good-as-new 242 with the Yukon kit from Randy’s World­wide.

THE NP242 TRANS­FER CASE was in­tro­duced in 1987 and pro­vides the op­tion of both ful­land part-time func­tion with four oper­at­ing modes. The medi­um­duty trans­fer case is built us­ing a cast-alu­minum hous­ing. It is quite sim­i­lar in de­sign to many other New Process chain-drive cases, how­ever, an added dif­fer­en­tial as­sem­bly on the main­shaft al­lows for high-range 4WD use un­der any con­di­tions. And, like all the other trans­fer cases, it has tra­di­tional, locked mode for typ­i­cal part-time high-range and low-range 4WD op­er­a­tion.

Weight of the NP242 is about 85 pounds, and the Jeep unit has a driver­side front out­put. High-range gear­ing is

1:1; low-range is 2.72:1.

These trans­fer cases are quite durable when used un­der rea­son­able con­di­tions. Long-term, se­vere use can cause the drive chain to stretch and the syn­thetic pads on the shift forks to wear. One of the com­mon causes of fail­ure is ex­ces­sive wear due to lack of lu­bri­ca­tion. The

NP242 uses an in­ter­nal oil pump to move lu­bri­ca­tion where needed. When fluid lev­els in­side drop due to a seal leak­age or other rea­sons, the case can run hot and start to wear parts pre­ma­turely. Once the trans­fer case is opened up for re­pair, a mag­net in a pocket at the bot­tom of the hous­ing can be ex­am­ined for signs of metal wear and de­bris.

We com­pleted our re­build us­ing mostly com­mon me­chanic tools on a home work­bench, and did use a press on a cou­ple of bear­ings. To do the job your­self, you will want a good set of flat-bill re­tain­ing ring pli­ers, a large socket for the front yoke, and likely an in­ter­nal-type bear­ing puller. The Yukon kit from Randy’s World­wide pro­vides re­place­ments for the com­mon wear items. While in­side, you’ll also want to in­spect for chain dam­age or ex­ces­sive wear, pump con­di­tion, and the con­di­tion of all in­ter­nal gear com­po­nents in­clud­ing the an­nu­lus gear in­side the front case.

1

Here is the Yukon re­build kit. It in­cludes re­place­ment bear­ings, seals, thrust wash­ers, shift fork pads, O-rings, and the gas­ket used to mate the NP242 to the trans­mis­sion.

2

We started the dis­as­sem­bly at the front out­put by re­mov­ing the yoke. An im­pact wrench will usu­ally spin the nut right off while you hold the yoke, but if you don’t have one this can be done with a bolt-on flange tool or the yoke can be held with a large pipe wrench. Then, we un­bolted the alu­minum ex­ten­sion hous­ing, re­moved the main­shaft snap ring, and un­bolted the re­tainer hous­ing shown here. This ex­poses the oil pump.

3

Next, we re­moved all the bolts that se­cured the rear case to the front case and sep­a­rated the two halves. The de­sign­ers pro­vided spe­cific pry points on most of these hous­ings to keep you from hav­ing to pry against the ma­chined seal­ing sur­faces.

4

With the rear case and oil pump as­sem­bly re­moved, the snap ring se­cur­ing the drive sprocket was re­moved from the main­shaft. This al­lowed re­moval of the sprocket, front out­put shaft, and chain.

5

The main­shaft was re­moved from the hous­ing. Here you can see the type of dif­fer­en­tial as­sem­bly that is added to some New Process trans­fer cases to make them ca­pa­ble of full-time

4WD op­er­a­tion.

6

The ex­ter­nal shifter lever and the shift de­tent com­po­nents were re­moved to al­low for low-range shift rod re­moval. The ser­vice man­ual rec­om­mends pulling a roll pin from the shift rod us­ing a No. 1 screw ex­trac­tor. This can be trou­ble­some, and we weren’t suc­cess­ful pulling the pin out. In­stead, we ma­nip­u­lated the mode fork as­sem­bly and shift sec­tor to al­low our­selves to work the as­sem­bly out while strate­gi­cally pry­ing as needed. Then the shift sec­tor could be pulled from the hous­ing.

7

Turn­ing our at­ten­tion to the in­put side of the

NP242, we re­moved the front bear­ing re­tainer and the in­put snap ring be­hind it. The in­put and low-range gears were pulled from the hous­ing. Some­times these can be sticky and re­quire a light push from a hy­draulic press, but of­ten a few taps from above with a ham­mer and drift will drop them free of the in­put bear­ing race.

8

The low-range-gear as­sem­bly was dis­as­sem­bled and in­spected, then put back to­gether with a fresh pair of thrust wash­ers. A snap ring holds the gear unit to­gether. Af­ter re­mov­ing a few bear­ings and seals from the hous­ings, we in­spected and cleaned every­thing for re­assem­bly.

9

We pressed a new pilot roller bear­ing to the cor­rect depth into the in­put gear us­ing a rod of the proper di­am­e­ter in a press. We used au­to­matic trans­mis­sion fluid for lu­bri­ca­tion dur­ing as­sem­bly.

10

Once a new in­put bear­ing was pressed into the front case, the low-range-gear as­sem­bly was put in the case and we torqued the front bear­ing re­tainer with new oil seal. The re­tainer and all other seal sur­faces on our trans­fer case were sealed us­ing RTV sil­i­cone.

“One of the com­mon causes of fail­ure is ex­ces­sive wear due to lack of lu­bri­ca­tion”

11

The shift sec­tor was re­placed in the hous­ing along with a fresh O-ring and the ny­lon outer bush­ing. New pad in­serts were in­stalled on the low-range fork, then the fork and its hub were en­gaged to the in­put gears and the shift sec­tor.

12

The dif­fer­en­tial as­sem­bly had been re­moved from the main­shaft for in­spec­tion and to al­low for re­place­ment of the roller bear­ings. We held the shaft ver­ti­cally while stick­ing each roller to the shaft with chilled pe­tro­leum jelly.

13

Af­ter the roller bear­ing re­place­ment, the dif­fer­en­tial as­sem­bly was re­turned to the main­shaft and se­cured with its snap ring. The shaft as­sem­bly along with the mode fork and shift sleeve were slid back into the case. 14

Here is the shift rod roll pin we men­tioned pre­vi­ously. We drove it out of the shift rod once the shift as­sem­bly was out of the case. For re­assem­bly, it’s nec­es­sary to drive it back into the shift rod through this ac­cess hole in the front case. A rub­ber plug seals the hole when done. Note that, for dis­as­sem­bly, there’s in­suf­fi­cient room in­side the case to sim­ply drive the roll pin com­pletely through the shift rod to free it. The shift de­tent com­po­nents were put back into the case. They drop in from the bot­tom of the case and the de­tent en­gages with the bumps on the shift sec­tor.

15

The drive sprocket, front out­put shaft, and chain were re­assem­bled onto the front case. Our chain was in good shape so we sim­ply reused it. We placed the mag­net back in the bot­tom of the front case for re­assem­bly.

16

The rear bear­ing for the front out­put shaft is blind in the rear case, so an in­ter­nal bear­ing puller is needed for re­mov­ing it. A new bear­ing was pressed into the pocket. The oil pump was fit­ted with a new seal and held on the rear case along with the pickup tube and fil­ter screen.

17

Hold­ing the oil pump in po­si­tion, we fit­ted the rear case back onto the front case us­ing RTV sil­i­cone on the seal­ing sur­face. We torqued all the bolts on the hous­ing cast­ings to 30 lb-ft.

18

We in­stalled a new bear­ing in the rear re­tainer and bolted it in place on the rear case. A snap ring po­si­tions the bear­ing to the main­shaft. Then the rear ex­ten­sion hous­ing re­ceived a new oil seal and was bolted down.

19

A new oil seal had been in­stalled in the front case at the out­put shaft. Fi­nally, the front out­put yoke was slid into place with a bit of RTV sil­i­cone added to the splines. The yoke nut was torqued to 110 lb-ft. Be­fore in­stal­la­tion, the trans­fer case was filled with about 11⁄2 quarts of au­to­matic trans­mis­sion fluid.

20

Here is the com­pleted case ready to be re­in­stalled. A tag on the rear of the trans­fer case lets you know the specifics of man­u­fac­ture. Info in­cludes the model num­ber, as­sem­bly num­ber, se­rial num­ber, and lowrange ra­tio. This case was fac­tory built on Oc­to­ber 12, 1988, and now it has been re­built nearly three decades later.

SOURCE

RANDY’S WORLD­WIDE 800.347.1188 randys­world­wide.com

1

7

3

4

6

2

5

10

8

9

20

12

11

13

19

18

17

15

14

16

Newspapers in English

Newspapers from USA

© PressReader. All rights reserved.