1901-1953 Indian Motorcycle – Parts – Accessories

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Chief Overdrive Transmission Case Upgrade

Chief 4 Speed Overdrive Transmission Case Upgrade Instructions for Series 1 cases to Convert to Series 2

The following Instructions are to update an early series I Chief Overdrive 4 speed transmission case to the latest configuration series II Chief Overdrive Transmission Case.

When you are rebuilding your early 4 speed transmission the following steps will be needed so you can update the transmission case so you can use the latest series 2 version replacement parts.

This is the right side of the case

Right side of case:

Equivalents: .156″ use 4mm

.75″ use 20mm

Left side of case:

.156″ use 4mm

.375″ use 10 mm

1.375″ use 35mm

Install Lower Countershaft Bushings

  1. Refer to the case assembly Illustration inside the back cover of the manual.
  2. Install bushing #97 from the inside of the case being sure to line up the anti-rotation pin in #97 with the matching hole in the case. WARNING! — Do not use the 5/16 male thread to pull the bushing in because the thread may strip or pull off.
  3. Install bushing #98 from the inside of the case being sure to line up the slot in the bushing with the corresponding slots in the case.
  4. Drop in the secondary shaft #94 to make sure it will go all the way in and the anti-rotation pin does not hang up anywhere.
  5. Remove #94 and install the o-ring #44 in #98 bushing.


Mainshaft install.

  1. Make sure the case magnetic drain plug is removed. Refer to the “Internals” illustration in the manual for find numbers.
  2. Lube the interior bore of the clutch side countershaft gear (find #49) and place (large gear down) on the bench.
  3. Insert one needle roller bearings (#47) into the bore followed by the spacer (#48) and another #47 needle roller bearing.
  4. Lube the interior bore of the drive side countershaft gear (#50) and place large end down on #49 (rotate if necessary to engage the gear).
  5. Insert two more #47 bearings into the bore.
  6. Place the case, mounting lugs down, on the bench with the primary side flange hanging over the side of the bench and install the countershaft gear assembly in the case making sure you have it the correct way round (largest gear closest to the primary side flange).
  7. Now rotate the case with the tower mounting face up, lube the needle rollers in #14 clutch hub and insert the mainshaft assembly.
  8. Place the large ball bearing (#12) on the final drive gear (#31) and press into the case with the tool from the sketch I sent you.
  9. Turn the case upside down and rotate the mainshaft back and forth until the countershaft gears drop into place and the #47 bearings line up with the case bushings so that the secondary shaft can be inserted and #43 retaining ring installed.
  10.  Lube the seal in #93 bearing retainer, insert spacer #36 in the seal with the groove in #36 spacer to the inside of the gearbox, use some non hardening sealant on the thread side of #93 flange, and one drop of blue Loctite on the thread.
  11. Install #93 retainer in the case and tighten.
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