Disassemble

Exploded View Of Type 8, Hummer (ET) Transmission:

1. Remove clutch release bearing, lever and clutch housing.
2. Remove top cover bolts with 10mm wrench and drain lubricant.

Shift Rail Detent Plunger:

3. Remove threaded plug spring and shift rail detent plunger from case.

Removing Interlock Plate Access Plug:

Removing Interlock Plate Retaining Pin:

4. Drive access plug from rear of case, and drive interlock plate retaining pin from case. Lift interlock plate from case.

Removing Interlock Plate Access Plug:

5. Remove roll pin from selector lever arm.
6. Tap front end of shaft rail to displace plug at rear of extension housing.

Removing Or Installing Shift Rail:

7. Withdraw shift rail from extension and case.
8. Lift selector arm and shift fork from case.
9. Remove extension housing bolts and tap extension housing with plastic mallet to loosen it from case so it may be rotated.
10. Rotate extension to align countershaft with cutaway in extension flange. Using a brass drift, drive countershaft rearward until it just clears front of case. Install a dummy shaft in the case and gear until countershaft gear can be lowered to bottom of case, then remove countershaft.

Removing Or Installing Extension And Mainshaft:

11. Lift extension housing and mainshaft from case as an assembly.
12. Remove 10mm input shaft attaching bolts, the input shaft and bearing retainer from case as an assembly.

Removing Reverse Idler Gear Shaft:

Reverse Idler Gear Spacer Location:

13. Remove reverse idler gear shaft from rear of case. Remove reverse idler gear and on 74WT, 75WT and 78ET units, reverse idler gear spacer.

Countershaft Gear Disassembled:

14. Remove countershaft bearing retaining washers, bearings (19 on each end for 74WG transmissions and 21 for 74WT, 75WT & 78ET models), drive shaft and spacer from countershaft gear. 74WG, 75WT & 78ET transmissions have one thrust washer located at each end of the countershaft. The 74WT transmissions have two thrust washers.

Input Shaft Disassembled:

Removing Input Shaft Bearing:

15. Remove bearing retainer and pilot bearing from input shaft gear. Do not remove ball bearing from input shaft unless replacement is necessary. If so, remove snap ring from input shaft, and press shaft from bearing.

Input Shaft Disassembled:

16. Pry input shaft seal out of bearing retainer.

Output Shaft Disassembled:

17. Lift 4th gear blocker ring, from front of output shaft.
18. Remove snap ring from forward end of output shaft and discard it.
19. Position tool T69P-4621A behind 3rd speed gear. Place output shaft and extension assembly in a press and press output shaft out of 3rd-4th synchronizer and the 3rd gear while supporting extension housing and output shaft to prevent it from dropping.
20. Remove snap ring and washer, then slide 2nd gear and blocker ring off output shaft and discard snap ring.
21. Disassemble synchronizer assembly by pulling sleeve off hub and removing inserts and springs.
22. Remove snap ring that retains output shaft bearing in extension housing.
23. Tap output shaft assembly out of extension with a plastic hammer.

Removing 1st Gear Spacer, Output Shaft Bearing, Snap Rings And Speedometer Gear From Output Shaft:

24. Position tool T69P-4621-A behind 1st gear, then place assembly in press as shown in image.
25. The 1st-2nd speed synchronizer and hub are serviced only as an assembly and no attempt should be made to separate the hub from the shaft. The sleeve, springs and inserts may be removed from the hub.
26. Drive shift rail bushing from rear of extension with a 9/16 inch socket and extension. Do not remove bushing if serviceable.
27. Pry shift rail seal from rear of transmission case.
28. Remove remaining linkage from case.