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How-tos
Photography By: 
Michael Volk

Installing a SYE or Slip Yoke Eliminator Kit may be intimidating to some, but it is actually super easy and can be done with basic hand tools.

What You Will Need

  • 2 quarts of ATF+4 Automatic Transmission Fluid. - Mopar 68218057AA ATF+4 Automatic Transmission Fluid
  • Small & large chisels
  • Small & large pry bars
  • Hammer
  • Snap ring pliers
  • Circle clip pliers
  • Wire brush
  • Brake Cleaner or De-greaser / Solvent
  • 10mm 12 & 6 point socket
  • Extension
  • 7/8" socket
  • 1-1/8" socket
  • 15mm socket
  • 13mm wrench

Tools Required

Instructions

1. Remove the rear output shaft seal guard using a hammer and chisel. This will not be reused so no care is needed here.

Step 1 - Remove Output shaft seal guard

2. Slide off and remove the seal guard spacer to access the constant circle clip.

Step 2 - Remove guard spacer

3. Remove the circle clip with flat blade style circle clip pliers.

Step 3 - Remove circle clip

4. Using a hammer and chisel, remove the rear output shaft seal.

Step 4 - Remove Output Seal

5. Remove the inner circle clip with flat blade style circle clip pliers.

Step 5 - Remove output shaft housing

6. Using a 10mm 6-point socket, remove the five output housing bolts and set aside. They will be re-used later.

Step 6 - Remove output housing

7. Gently pry housing at the large tabs shown and remove. It will be tight because of the original sealant. Discard housing.

Step 7 - NP 231 oil pump

8. Here you will see the oil pump. Take caution and notice orientation.

Step 8 - NP 231 oil pump location

9. Carefully remove oil pump from output shaft by sliding outward and disconnecting filter tube at the six 'o-clock position.

Step 9 - Remove NP231 oil pump

10. Using 10mm 12 point and 15mm 6 point sockets, remove all housing half bolts and set aside. They will also be re-used later.

Step 10 - Remove np 231 housing bolts

11. Locate the two pry marks at either corner of the case halves. Using a flat blade screwdriver, separate the housings at these locations.

Step 11 - Separate np 231 case housing halves.

12. Remove rear case half and set aside.

Step 12 - Remove np231 rear half

13. Using a 1-1/8" socket, remove the front output shaft nut and yoke, then set aside. They will also be re-used later.

Step 13 - Remove front output shaft nut

14. Carefully remove rear output shaft, chain and front output shaft from case as an assembly.

Step 14 - Remove output shaft, chain assembly

15. Separate the rear output shaft from the chain and locate the circle clip that retains the four wheel drive main gear.

Step 15 - Rear output shaft

16. Slide off the 4wd drive gear from the main shaft - taking notice to orientation.

Step 16 - 4 wheel drive gear

17. Install the 4WD gear onto the TeraFlex main shaft in the correction orientation, using the large snap ring and snap ring pliers as shown. Carefully set aside for later.

Step 17 - teraflex main shaft 4wd gear

18. Remove the 4 wheel drive ring and fork as an assembly. Note ring orientation.

Step 18 - 4wd shift fork np231

19. Remove the Low Range drive gear and selector fork. Note gear orientation.

Step 19 - remove low range selector fork and drive gear

20. Using a 13mm socket, remove the shifter linkage from side of transfer case. Save and set aside.

Step 20 - remove np231 shifter linkage

21. Locate and remove the mode selector ball detent and spring using a 7/8" socket. Save and set aside.

Step 21 - remove mode selector ball detent

22. Here you can see a comparison shot of the original (right) and TeraFlex (left) mode selector. The TeraFlex unit has a larger slot and one more detent to accommodate the 2WD Low Range position.

Step 22 - teraflex mode selector

23. Since the cases are empty, now is a good time to thoroughly clean the mating surfaces with a wire brush to remove all old sealant. Also clean with a degreaser so the new sealant will stick. Now would also be a good time to remove the oil pump pickup tube and filter, clean thoroughly as well.

Step 23 - clean np231 case halves

Step 23 - clean np231 case halves

24. Slide the new TeraFlex mode selector into the housing. Secure using the original linkage, washer and nut.

Step 24 - install teraflex mode selector

25. Assemble the new TeraFlex 4WD Fork using the provided slides as pictured (left). Next you can also see the original (left) vs the TeraFlex (right) low range fork. It has been shortened and clearances made to allow for the new 2WD Low position.

Step 25 - Teraflex low range fork

26. Install the original low range gear onto the new TeraFlex fork as shown (left). Install the assembly into the low range gear planetary and the slot in the new TeraFlex mode selector (right).

Step 26 - teraflex 2wd low range gear

27. Install the original 4WD shifter fork and slide into the Teralfex low range fork and then down into the original housings shaft hole as pictured.

Step 27 - np231 four wheel drive fork shaft

28. Slide the new assembled TeraFlex output shaft into the transfer case as shown. Be sure that it seats all the way into the low range planetary.

Step 28 - teraflex np231 output shaft

29. Install the drive chain and front output shaft into the transfer case as shown. Be sure front output shaft is all the way in the output bearing.

Step 29 - np231 drive chain

30. Thoroughly clean and re-install the magnet as shown.

Step 30 - np231 magnet

31. Thoroughly clean out and install the oil pump pickup into the oil pump. Install assembly into the rear case half as shown.

Step 31 - np231 oil pump pickup

32. Oil pump tabs should be on the outside of case as shown below.

Step 32 - np231 oil pump

33. Now this is personal preference but i like to take and install the new output housing dry, just to hold the pump in place during assembly of the case.

Step 33 - np231 output housing

34. Being sure your case halves are totally oil and grease free and then apply a thin layer of black gasket RTV to the front half of case. I prefer to use Permatex® "The Right Stuff®" available at any auto parts store.

Step 34 - np231 gasket maker

35. Now take the entire rear assembly and install over output shaft and seat to front case half. Start with the two over most bolts that have washers where the alignment dowels are, and finish by starting the rest of the bolts in original locations by hand. I like to snug them up tight with a 3/8" impact gun and squish out the sealant. You may want to let the sealant set for a bit, but I have had good luck with no leakage just letting the entire case dry overnight, instead of filling it up with fluid right away.

Step 35 - np231 assembly

36. Remove the rear case bolts and housing to access the shaft. Install the two circle clips and speedometer drive gear as shown.

Step 36 - np231 speedometer drive gear

37. Apply more sealant to the rear case half as shown. Be sure the oil pump is still in the proper location.

Step 37 - np231 gasket

38. Slide the new TeraFlex output housing over the output shaft and on to rear case half. Be sure the output seal is as shown (right). Using a 10mm socket, install the five output housing bolts and tighten. Apply RTV on output shaft threads as shown (left).

Step 38 - np231 teraflex output housing

39. Install and start by hand the output shaft nut and tighten using a 1-1/8" socket (left). Be very careful though as the threads are very fine. I like to use a electric 1/2" impact gun for this until it stops. Finally, let the assembly (right) dry overnight with speedo gear out so air can get in and fully dry the sealant.

Step 39 - Reset Service Interval

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