Corvette Transmission Rebuild

Posted October 24, 2014 by Zip Corvette in Corvette Technical Articles

Is your 4-speed transmission getting hard to shift?  Does it grind whenever you shift gears?  maybe it will pop out of gear when you decelerate.  Have you been hearing a low whirring sound or even a growl?  Well, Bunkie, it is time to rebuild that trusty Super T-10 4-speed transmission.  All of these noises are a sign that something isn’t right inside of that transmission.  Hard shifting, popping out of gear and grinding are symptoms of worn or chipped synchronizing rings.  The whirring or growling sound could be worn bearings.  These problems can all be corrected with one call to Zip Corvette Parts, 8067 Fast Lane, Mechanicsville, VA 23111, (800) 962-9632,  They have a complete 4-Speed Rebuilding Kit available that includes all of the needle and roller bearings, synchronizing rings, washers, shims and snap rings needed.  Please keep in mind that rebuilding a transmission is not for everyone.  You will need specialized tools, a hydraulic press, and an understanding of how a 4-speed transmission operates and is assembled.  You will also need more than average mechanical ability.  But even if you cannot do the work yourself, this article will give you a much better understanding how a 4-speed transmission works and a better understanding as to what is involved with a total rebuild.  For those of you with an older Borg Warner or Muncie 4-speed transmission, most of these procedures done here are the same so this article will also be of help to you.  If you are ready, let’s get started on a Corvette Transmission Rebuild.

Zip Products has a complete selection of replacement gears, cluster assemblies, bearings, synchro assemblies, shafts and seals to complete your transmission rebuild.  Visit for your specific needs.

Click on the images for expanded views – it’s much easier on the eyes. 

Step 1

01: This is the complete Rebuilding Kit that we received from Zip Products.  It includes all of the needle and roller bearings, seals, gaskets, shaft, snap rings, washers and O-rings that you will need for a normal rebuild.  You will also need a hydraulic press, bearing pullers, seal pullers and more than common hand tools.  A shop manual and a unit repair manual for your year Corvette is a must.

Step 2

02: Remove the transmission from your car as per your shop manual’s instructions.  Thoroughly clean the exterior.  After the transmission is clean you can look for the transmission code and VIN numbers stamped into the case.  If the last 6 digits of your VIN number match the last 6 digits stamped on the transmission case, you have the original transmission for your Corvette.

Step 3

03: Drain the transmission then remove the 9 bolts that hold the side cover in place. Carefully remove the cover and shifting forks.

Step 4

04: Mark the shifting forks with their corresponding clutch assemblies. Also make sure you mark which end of the fork was at the top of the clutch assembly. These forks wear with the clutch assembly as they move back and forth so you want them to stay with their respective clutch assemblies. Note: For reference, 1st gear is at the rear of the main case. 4th is at the front.

Step 5

05: With the side cover removed, spin the shaft slowly and look at each gear and synchro ring. You will look for chips in the gears, pits or worn brass synchro rings. If you look closely in this picture you can see how worn this synchro ring’s teeth have become. They have lost their sharp edges and became rounded.

Step 6

06: Remove the retaining bolt and clip and pull the speedometer gear out of the tailshaft of the transmission.

Step 7

07: With the speedometer gear removed check for any worn, broken, cracked, chipped or flattened teeth. If you find any, replace the gear.

Step 8

08: Drive out the lock pin from the reverse shifter boss. (Look carefully at the end of the pin.  You will see that one end is thicker than the other and can only be removed in one direction.  Drive the pin out from the bottom of the boss to the top.)

Step 9

09: Pull the shifter shaft out partially to disengage the fork from the reverse gear.  Remove the 5 bolts that attach the tailshaft to the transmission main case.  Use a soft blow hammer to tap the tailshaft rearward until the reverse idler shaft is clear of the reverse idler gears.  Now rotate the tailshaft to the left.  Turn the reverse shifter shaft to free the fork from the gear and remove the tailshaft.  Clean off any of the old gasket.

Step 10

10: Remove the speedometer gear outer snap ring and then tap or slide the gear off the shaft.  The second snap ring can now be removed.  Here you can see the snap rings and gear are removed from their position on the shaft. (See links at bottom of the page.)

Step 11

11: Here is the reverse gear.  The area of the gear that is being pointed to has been worn through use. This is the grinding noise you hear sometimes when you put the car in reverse.  This type of wear is fairly common and will not hurt.  If the wear was more severe, then the gear should be replaced.

Step 12

12: Use a soft blow hammer to tap the reverse gear off the shaft.  Then remove the rear portion of the reverse idler gear from the transmission case.

Step 13

13: Remove the 4 input shaft collar retaining bolts and gasket from the front of the transmission.  You may need a soft blow hammer to tap it loose.

Step 14

14: Now remove the front bearing snap rings and washers.

Step 15

15: Use a bearing puller and collar to remove the front main drive gear bearing.

Step 16

16: Shift the 1st and 2nd, 3rd and 4th clutch sliding sleeves forward.  This will allow adequate clearance for the mainshaft removal.

Step 17

17: Next remove the rear retainer lock bolt and slide the mainshaft and rear bearing retainer out of the case.  The front reverse idler gear and thrust washer can now be removed from the case.

Step 18

18: Carefully slide the input shaft out of the case. The inside of the shaft is full of roller bearings so be careful during removal or you will be chasing these bearings all over the shop floor.

Step 19

19: Use a dummy shaft to drive out the shaft of the countergear.

Step 20

20: Remove the countergear and tanged thrust washer from the case. Be careful upon removal because the counter shaft also has numerous needle roller bearings inside of it and these can go everywhere. Be sure to check down in the case for loose roller bearings.

Step 21

21: Carefully check this area of the mainshaft. It rides in the input shaft. If it has pits, scores, gouges, knicks or grooves, the mainshaft will have to be replaced.

Step 22

22: Remove the snap ring from the end of the mainshaft. Slide the washer, synchronizer and clutch assembly, synchronizer ring and 3rd gear from the mainshaft.

Step 23

23: Remove the rear bearing snap ring from the shaft.

Step 24

24: Support the rear bearing retainer in a press and press the mainshaft out of the bearing.

Step 25

25: Remove the rear bearing to rear retainer snap ring and remove the bearing from the plate.

Step 26

26: Slide 1st and 2nd gears, synchronizer, clutch assembly, synchronizer ring and all washers from the mainshaft. Keep all of the respective gears in order. It is important to keep each clutch assembly with its gear assembly. You should also note which direction the clutch assembly faces. It can be assembled in either direction, but it will only work in one direction. (NOTE: In some instances you may have to press this assembly off the shaft.)

Step 27

27: Thoroughly clean the mainshaft, cases and gears. Clean off any gasket material. Check each gear for chips, cracks, heat discoloration or excessive wear. If any of these characteristics appear, replace the gear. Check the cases for cracks. Look for burrs on areas where bearings fit. A small file or sandpaper will usually repair any damages of this type.

Step 28

28: Synchronize hubs and sliding sleeves are selected assemblies and should be kept together as originally assembled. Mark the relation of the outer hub to the sleeve and its direction. Remove the two snap rings and push the sleeve out. The keys will also fall out. Thoroughly clean the hub and sleeve assemblies.

Step 29

29: After the assembly has been cleaned, start the re-assembly.  Place the keys into position on the hub.  Now while holding the keys in place, slide the sleeve down into the hub.  With the hub, sleeve and new keys in place install the new snap rings.

Step 30

30: Pry the old oil seal out of the tailshaft housing. A seal remover or a large flat blade screwdriver will work.

Step 31

31: Use a bushing puller to remove the tailshaft bushing.

Step 32

32: Now install a new bushing and seal. A seal and bushing tool such as this makes installation a snap.

Step 33

33: Starting from the rear of the mainshaft, assemble the 2nd gear. (The hub of the gear faces the rear of the shaft.) Install the 1st and 2nd gear synchronizer clutch assembly. (The clutch sleeve taper is toward the rear. The hub to the front.) Also install the synchronizer ring. Make sure the ring fits all the way down into the hub and locks into the key.

Step 34

34: Position the 1st gear sleeve onto the shaft and push it down into place until the 2nd gear clutch assembly and sleeve bottom against the shoulder of the mainshaft. Install the new thrust washer. You can sure see the difference between the old and new.

Step 35

35: Install the new rear bearing and snap ring into the retainer and slide it down onto the shaft. Use a brass drift to tap it down into place. (In some instances you may have to press the bearing down onto the shaft.) Remember to put a new gasket onto the rear retainer.

Step 36

36: Install 3rd gear, 3rd gear synchronizing hub, and synchronizing gear into place. Remember the taper of the synchronizing clutch assembly falls toward the front of the transmission. Now install the 2nd synchronizer gear and snap ring.

Step 37

37: Install the roller bearings in the countergear. Use heavy grease (white lithium will work) to install the rollers, spacer, rollers, spacer, rollers, spacer in either end of the countergear.

Step 38

38: Install the tanged washers in either end of the case. Use white grease to hold them into place. Carefully place the countergear into the case making sure the tanged washers do not fall. Slide a wood dowel just slightly smaller in diameter than the countershaft into the case and through the countergear. It should be longer than the case. This will hold the roller bearings and spacers in place inside of the countergear. Now carefully push the new countershaft into the case from the rear. As it is tapped through it will push the wooden dowel out of the front of the case keeping the roller bearings and spacers in place. (Hopefully!) I have had to replace roller bearings back in the countergear more than once.

Step 39

39:  Place the new woodruff key into the end of the countershaft and tap the shaft into place until it is flush with the end of the case.

Step 40

40:  Install the front reverse idler gear and thrust washer in the case. Use white grease to hold the thrust washer into position.

Step 41

41: Again use white grease to install and hold the large 16 roller bearings into the main driver gear.

Step 42

42: Place a new washer on the end of the mainshaft in front of the 3rd gear synchronizing assembly.

Step 43

43:  Install the main drive gear into the case. (Make sure that the roller bearings do not fall.) Align and install the newly assembled mainshaft and retainer. With the mainshaft aligned, install the retaining bolt. Torque to specs. (You did install a new gasket, didn’t you?)

Step 44

44: Place the bearing snap ring on the front bearing. Slide the bearing over the main shaft and tap the bearing into place on the case. A brass drift will work to accomplish this. Now install the new washer and snap bearing ring.

Step 45

45: Install a new oil seal and gasket in the input shaft collar.

Step 46

46: It is very important to align this drain hole in the case with the oil trough in the input shaft collar. This will allow the oil to drain back into the case.

Step 47

47: Use a sealer on each of the input shaft collar retaining bolts. This will help to eliminate bothersome leaks.

Step 48

48: Install the reverse gear onto the shaft. Now install the snap ring speedometer gear and the other snap ring.

Step 49

49: Install a new O-ring on the reverse shifter shaft. Next install the tanged thrust washer on the reverse idler shaft with the tang in the notch of the tailshaft extension.

Step 50

50: Place the 1st-2nd speed and 3rd-4th speed clutch sliding sleeve in neutral position. Pull reverse shift shaft partially out of extension and reverse shift fork as far forward in as possible. Start the extension onto the mainshaft while pushing in on the shifter shaft to engage the shift fork with the reverse gear shift collar. When the fork engages, rotate the shifter shaft to move the reverse gear rearward permitting the extension to mate against the transmission case. Install rear extension housing to case bolts. Install rear extension to rear bearing retainer bolts. Torque all bolts to recommended specification. Install reverse shifter shaft lock pin. (Remember, the lock pin will only go in from one direction.)

Step 51

51: Remove and then install the new shifting fork shaft seals. A soft blow hammer can be used to tap them into place on the side cover plate.

Step 52

52: Install the shifter shafts and detent plates. Stand the cover on one end and move the upper detent to one side. Now align the lower detent with the center boss. Install the sleeve, detent ball, spring, lock pin and second detent ball. Carefully align the upper detent plate and snap the detent ball into the detent. Be very careful. It is very easy to miss the upper detent and have the ball launch into space. Install a new gasket onto the side cover plate.

Step 53

53: Align the shifting forks (They are going back into the original synchronizing assembly, aren’t they?) with their respective synchronizing assemblies. Push the forks into place and install the side cover bolts. I recommend using a sealer on each bolt to stop any small leaks that can occur.

Step 54

54: Put a new O-ring on the speedometer gear and install it back into the tailshaft extension.

Step 55

55: Make sure the forks are all in the neutral position. Now shift each shifting fork shaft while turning the mainshaft. Always remember to go back into the neutral position with each shaft before you shift the next shaft. Without gear lube in the transmission, it will shift hard, but you should be able to get each gear along with reverse. If you cannot get a gear, you will have to pull the cover and find out why. If everything checks out, re-install the transmission, fill with gear lube, and adjust the shifter. You are ready to go. No grinding, growling or noise, just quiet, smooth shifting.

Corvette Turn Signal: 1963-1967 Steering Wheel, Horn Button, Stand & Canceling Cam Install

Source: Zip Corvette Parts
8067 Fast Lane | Mechanicsville, VA 23111 | (800) 962-9632

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