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THE GM MUNCIE STANDARD TRANSMISSION

See bottom of page for pictures during rebuild.

The following are the procedures that should be observed when performing this operation. 

Note: before starting make sure you have access to a press. If you have a metal speedo gear then it must be pressed off then on later. You'll need to also press off the rear bearing and 1st gear bushing together using 2nd gear as the pusher in the press. 

Disassembly:

1. Drain the oil into a container. Check oil colour, and also, for metal deposits. This would help in diagnosing defective parts. For instance oil with a bright yellow colour would indicate badly worn synchromesh blocking rings.

2. Use 1/2 inch box wrench and remove seven (7) 5/16 x 7/8 inch bolts that secure shifter side cover assembly to the transmission case. Remove cover and gasket.

3. Use 9/16 inch box wrench and remove four (4) 3/8 x 7/8 inch bolts that secure main drive gear front bearing retainer to the case. Remove retainer and gasket.

4. Manually lock-up transmission (place into two gears) use tool J-933 and remove main drive gear retaining nut. Note: nut is removed by turning clockwise.

5. Place transmission in neutral then shift to 4th gear.

6. Use 3/16 inch drift punch and remove reverse shifter shaft lock pin. Note: pin is removed from the bottom, up, and out.

7. Use pliers and pullout shaft until it jams. This procedure disengages the reverse shifter .from the gear.

8. Use 9/16 and 5/8 inch box wrenches and remove three (3) 3/8 x 11/2 and three (3) 7/16 x 11/2 inch bolts that secure extension housing to the transmission case.

9. Pry back extension housing off dowel pins. Rotate housing while removing to clear the reverse fork from the gear.

10. Remove speedometer drive gear.

11. Remove reverse gear.

12. Remove rear reverse idler gear and shaft.

13. Expand and remove main drive gear outer race snap ring.

14. Use two flat blade screw drivers, insert blades into outer race lock groove and pry out main drive gear front ball bearing.

15. Note: if bearing is a bit tight, drive it out with 7/16 x 8 inch brass punch, from the inside of the case.

16. Remove main shaft, rear bearing retainer, and main drive gear as one assembly from the transmission case. Maneuver as necessary to remove.

17. Use 7/16 x 8 inch brass punch and drive out countergear shaft from the front end of the transmission. Lift countergear out.

18. Remove front reverse idler gear and thrust washer. Remove countergear thrust washers from the case.

         Hydraulic press with 12 Ton bottle jack

Click on thumbnail to enlarge

Shown a Snap-on model 70CP pliers along with part 18 in the parts diagram part # 3831741.

GM Parts book 4.383 67-74 ALL STD 4 SPD / MUNCIE / THIRD AND FOURTH

On The Bench Overhaul

Use varsol and thoroughly clean all parts. Blow dry and inspect for damage, wear, deformity, breakage, nicks, burns, and cracks. Check bushings for scone markings. Check bearings for roughness when turned. Replace part that exhibit to any of these conditions.

Main drive gear overhaul:

Remove 17 needle roller bearings and cage from gear bearing boss. Perform prescribed checks and procedures. Install bearing assembly. Note& use petroleum jelly to retain needle rollers to bearing boss.

Counter gear and shaft overhaul:

Remove one hundred and twelve (112) needle roller bearings, (6) washers, and one roller spacer tube. The steel roller tube I have is almost 5" long Part # 3912195. Perform prescribed checks and procedures. Install roller spacer. 

1. Install the metal roller spacer tube inside the counter gear

2. Cut a broom stick the same length as the counter gear unless you have the tool and insert in the counter gear. 

3. With 1 finger, push the broom stick and steel spacer tube up a bit and insert the 1st washer. Use

4. Insert  your 1st row of  twenty-eight (28) roller bearings around the broom stick. Note the broom stick is used to hold the bearings and washers intack until it's time to place it in the trans case. Later as you insert the counter gear shaft in the case through the counter gear, the broom stick will slide out without the bearings falling out into the inside of the counter gear.

5. Insert the 2nd washer.

6. Insert your 2nd row of (28) bearings.

7. Insert your 3rd washer. That's it for the one side.

8. Flip the counter gear to the opposite end and repeat steps 3-7.

9. Replace thrust washers. (mandatory with overhaul) at each end of the case

 Main shaft overhaul:

Very Important Note: The instances occur during an overhaul operation where the  bearing and shaft, or sleeve, or retainer, fit is fairly tight. As a result, it may  be necessary to use a press to separate the assemblies involved.

1-2 and 3-4 synchromesh assemblies:

           keys in hub detent.

Note: sleeves position in relation to hubs 3-4 synchromesh sliding sleeve and clutch hub long tapered ends both face the front of the transmission. 1-2 synchromesh sliding sleeve long tapered end faces the rear of the transmission, and the clutch hub long tapered end faces the front.

Note the tapered end of the 1-2 gear sleeve points to the rear and the 3-4 gear sleeve points to the front.

In this pic from L to R are:

1st gear, 1-2 sleeve with hub and 1-2 gear syncros and 2nd gear,

3nd gear 3-4 sleeve with hub and 3-4 gear syncros and 4th gear or input shaft 2nd gear

Click on thumbnails to enlarge.

                            <------     M20  ----->

Side shifter cover assembly overhaul

Disassembly:

1. Remove detent cams retaining E ring.

2. Remove detent spring.

3. Remove 1-2 and 3-4 shifter forks.

4. Remove 1-2 and 3-4 shifter shafts and detent plates.

5. Remove 1-2 and 3-4 detent cams.

6. Remove seals and gasket.

7. Perform prescribed checks and procedures.

Overhaul Assemble:

1. Install new shaft seals.

2. Install 1-2 and 3-4 detent cams.

3. Install 1-2 and 3-4 shifter shafts and plates.

4. Install 1-2 and 3-4 shifter forks.

5. Install detent spring.

6. Install detent cams retaining E ring.

Transmission Assembly:

1. Use petroleum jelly and retain one countergear thrust washer to the front of the transmission case. Note: washer tang must fit in groove in case.

2. Place countergear in case.

3. Turn case to rest on its front end and install rear countergear thrust washer (slide into position of lock slot).

4. With the aid of tool J22246, align countergear and install its shaft. Or if using the broom stick method as I did, insert the counter gear shaft from back to front and push slowly, the broom stick will be replaced with the shaft. Position cut away end of shaft to align with its mate lock slot on the rear bearing retainer.(cut facing horizontal with the bottom of the case).

5. Install (front) reverse idler gear thrust washer.

6. Install (front) reverse idler gear in its location in case.

7. Mount assembled main drive gear on to the front end tip of the mainshaft.

8. Install rear bearing retainer front gasket. (Retain to case with petroleum jelly).

9. Place 3-4 synchromesh into 4th gear.

10. Maneuver assembly into case.

11. Align rear bearing retainer dowel pins holes to the case dowel pins. Use a plastic hammer and tap retainer on to case surface.

12. Install main drive gear front bearing, and its outer race snap ring.

13. Slide 1-2 synchromesh into 2nd gear (transmission lock up, 2nd and 4th gears engaged) use tool J-933 and install main drive gear retaining nut. Tighten nut to 40 lb, ft and stake to double lock.

14. Install main drive gear retainer and gasket. "Note! oil passage cutaway in retainer and it must be aligned to hole in case. Install four (4) 3/8 x 7/8 bolts that secure retainer to cage and torque to 24 lb. ft.

15. Slide 3-4 synchromesh to neutral. Leave transmission in 2nd gear.

16. On reverse idler shaft, install roll pin and flat thrust washer.

17. Install rear reverse idler gear into front reverse idler gear (align splines to install).

18. Insert reverse idler shaft assembly into the assembled reverse idler gear train.

19. Position roll pin vertical to align with its mate slot in the extension housing.

20. Install reverse gear (fork hub end must face the rear of transmission).

21. Install speedometer drive gear.

22. Install extension housing gasket on rear bearing retainer (retain with petroleum jelly).

23. On extension housing, move reverse shifter to reverse position. Maneuver housing into position over reverse gear. Observe the gear hub position in relation to its shifter fork. Lineup accordingly and push down shaft to engage shifter fork into its gear hub.

24. Position extension housing on to rear bearing retainer and install three (3) 7/16 x 1 1/2 inch bolts that secure housing to case. Torque bolts to 24 and 35 lb ft respectively.

25. Align reverse shaft lock groove with extension housing boss lock pin hole. Install reverse shaft lock pin. Shift reverse gear to neutral position.

26. Place shifter cover assembly into 2nd gear position to correspond with the 2nd gear engagement of the transmission. Maneuver 1-2 and 3-4 shifter forks into their respective sliding sleeve fork grooves. Install cover. Install seven (7) 5/16 x 7/8 inch bolts that secure cover to case. Torque bolts to 22 lb ft.

27. Manually shift transmission through all gears and check Rotation.

.

Muncie Rebuild Steps  

SIDE EFFECTS OF ANTIDEPRESSANTS