Rebuilding The TC Gearbox - An Overview

As noted in the “The TC Gearbox” article I considered the gearbox to be the ultimate “black box” mechanism. I really wanted nothing to do with this complex set of gears and shafts. However, once I committed to the rebuild project and began to understand its workings, the rebuild was like a 3 dimensional puzzle with nicely machined parts fitting together in a very compact space. I must compliment the engineers who conceived of, and designed such wonderful pieces of machinery.

My set of references included The Blower Manual, the TC Instruction Manual, the MG Autobook One by Kenneth Ball Brown, a paper titled The Gearbox Fitted to the XPAG by Neil Cairns, all the articles in the TSO CD on gearboxes, as well as, studying illustrations in both the Moss and Abingdon Spares catalogues. This paper is a report of what I learned and hopefully I can pass along some tips I acquired while doing this project. I would also like to thank Lawrie Alexander who reviewed this text and answered numerous e-mails during the rebuild.

In the following please refer to the TC Gearbox illustrated in the Moss Catalogue on page 12. The numbers in parentheses (nn) refer to the illustration numbers.

Special Tools Used

In addition to the normal set of Metric and Whitworth wrenches, hammers, screwdrivers, and drifts I added a few “special” tools to aid in the rebuild of the gearbox. Like all my special tools, I got them at the local home improvement store. This included:

1. A ¾” wooden dowel 7 ½ inches long to act as the temporary layshaft
2. A plastic (or metal) pipe coupling with an inside dimension of 3 ¼ inches and an outside dimension of 3 ½ inches, and 3 inches high. This is actually a plastic drain pipe coupling used to connect two sections of pipe.
3. A modern type 3 to 4 inch hose clamp
4. A number of large flat washers

My Transmission Stand

In order to rebuild the gearbox is necessary to completely remove it from the car. Once removed place the gearbox on a good working surface, the unit is not too heavy and can be moved about without too much difficultly. Moss and Abingdon sell a part that fits in the drain hole that you can then mount in your vise. I did get one of these and gave it a try. I ended up not using it for it for the following reasons:

1. My vise is mounted at the end of the bench and made working difficult.
2. Since the bracket is screwed into the drain plug, the gearbox had a tendency to turn when working on it.
3. It raised the entire gearbox up too high.
4. I lost the use of the vise when working on the gearbox.

Items I replaced

The following items were replaced because I could and since the gearbox was apart it seemed like the right thing to do. Although I ordered a set of synchromesh springs (Ill. numbers 77 & 92) I did not end up using them – see text on Synchromesh

1. Remove the eight bolts holding the bell housing and slide the housing off. Between the bell housing and the front of the casing will be the front Guard Plate (61) and Spring Plate (62). These sit in a circular cutout in the back of the bell housing.
2. Undo the six nuts (119) holding the remote gearbox cover and slowly lift up the cover. Keep some pressure on the cover as the springs (21) at the rear will have a tendency to force up the back end. Be careful not to lose the three springs and balls (21 & 22).
3. You can remove the Speedometer Housing (108) or leave it in place. To remove it cut the wires holding the two screws (109) and remove the screws. The unit will not just drop out; it is engaged with the rear flange (104) via the Speedometer Pinion (107). I used a very thin screwdriver to wedge between the speedometer housing and the Cover Plate (112) and by gently tapping on the screwdriver the housing slowly moved out.
4. To remove the Rear Flange (104), first remove the cotter pin and rear flange nut (106) and washer (105). I found that putting the drift through one of the bolt holes in the rear flange acted as a nice “wedge” to keep the main shaft from turning while removing this nut. The rear flange can now be removed using a gear puller.
5. Remove the Gearbox Rear Cover (112) by undoing the five nuts (three large and two small) and a single screw on the bottom left hand side of the cover. Note: none of these are illustrated in the Moss catalogue. When you remove the cover there should be a Guard Plate (54) and Spring Plate (55) located in the circular cutout on the inside of the gearbox rear cover.

1. Clip the wires holding the selector shaft lock bolts (20) and remove the bolts.
2. Remove the selector shafts (1, 2 & 4). If the shafts are sticking, you can use a drift to drive them through. I found that removing them through the front of the gearbox worked much easier. Be careful not to let the Stop (8), Steady (9) and Selector (10) fall into the casing as you remove the shafts.
3. The forks (5, 6 and 11) can now be lifted out.
4. Remove the two balls (22) that are on either side of the middle selector shaft.

1. Remove the first motion shaft nut (64) and lock washer (63). Note this is a LEFT hand thread. To keep the shaft from moving I wedged a wooden hammer handle in the gearbox.
2. Remove both the first motion shaft bearing (58) and the rear main shaft bearing (51). The method I used was to strike the end of either the first motion or main shaft with a plastic-tip hammer. After a few blows the bearing on the opposite end began to move away from the casing. If you are lucky the entire bearing will pop out. If not you may have to use a drift from the inside to give it a nudge.

3. Remove both the front and rear bearing guards (52 & 59).
4. Remove the first motion shaft (56) from the front of the main shaft (50). There is nothing holding it in place, but it may be a bit sticky. Be careful not to lose any of the thirteen needle bearings (57).
5. The main shaft can now be removed. To do this, slide it back as far as it will go and angle the front slightly to the left, then lift the front end up through the box. On the left hand side near the top you will see a notch in the casing (see photo) that will allow the shaft to exit. Once the end of the shaft is clear of the casing, the entire shaft along with gears, sliding hubs and striking dogs can be removed.

1. Take out the cotter pin holding the nut (17) in place; remove the nut, washer (16) and Fulcrum Pin (15). This will allow you lift out the Reverse Gear Link (14).
2. Remove the Lock Bolt (18) and slide the Reverse Selector Shaft (3) out the back of the casing. The Reverse Fork (7) is now free and can be lifted out.
3. Reverse Gear (95) is also free and can slide off its shaft out the back of the casing.
4. Undo the Locking Bolt (98) and the Reverse Gear Shaft (96) will slide out of the back.

1. Now raise the laygear to its original position and use the original steel shaft to drive the wooden shaft out so that you can check the end float. This is the measurement between the laygear thrust washer and the case at one end, when the other end is pushed hard up against the case. From what I have read this should not exceed ten thousandths (0.010"). If it does, the thrust washers should be replaced.
2. After checking the end float, you can remove the laygear assembly by, once again, installing the wooden shaft then lifting the unit from the box.
3. Before you lift up the laygear unit, look at the holes where the layshaft goes through the casing (both front and rear), you will see a small notch. Now look at the thrust washers, you will see pins on the outside of the washers. The only way to remove the laygear unit is to navigate the pins through these notches.

1. Remove the cotter pin.
2. Slide out the plunger and spring.
3. In the perpendicular shaft you will find a ball and another spring (not shown in the Moss catalogue). These are there to keep the face of the plunger in alignment with the face of the reverse gear selector.

1. Scoring of the shafts, look for grooves where the shafts go through the casing, check the notches used by the balls that lock the shafts in place.
2. Reinstall the shafts back in the casing holes without the balls and check for a smooth operation. Then try it again with just the two balls that reside on either side of the center selector shaft. Finally try with all five balls installed.
3. Look for wear on the forks; they need to be at least ¼ inch thick. If they are too thin the striking dogs will not fully engage the conical protrusions on their associated gears. This may cause “popping out of gear.”
4. I would recommend just replacing the five balls (22) and three springs (21) since this seems to be the primary reason many gear boxes “pop out of gear.”

1. Clean the splines so the clutch disc will ride smoothly, and check inside the end where the needle bearings go to make sure it is clean and not scored. Also, check for any broken teeth on the helical gear or the conical protrusions.

1. Remove the thrust washers from both ends.
2. Push out the temporary layshaft and allow the needle bearings to fall out. Remember there are 30 (15 at each end); be sure to count them.
3. Remove the bottom washers that sit between the needle bearings and the spacing tube (not shown in Moss catalogue.)
4. Remove the spacing tube.

1. Scoring or pitting of any surface especially on the layshaft and the needle bearings.
2. Any broken teeth on the laygear.
3. Worn thrust washers. Since they are out I would just replace the thrust washers. I know they are expensive, but you have already done the hard part, removing the gear box.

1. Insert the spacing tube back inside of the laygear. The tube basically floats in the center and does not actually come in contact with the layshaft.
2. Insert the layshaft (not the temporary one) inside the laygear and through the spacing tube.
3. To replace the needle bearings:
1. Insert one of the bottom washers over the end of the layshaft and make sure it sits solidly on top of the spacing tube.
2. Smear a small amount of grease on the inside of the laygear where the needle bearings will sit (this area should be polished); this will help hold the needle bearings in place while you are replacing them.
3. Hold the laygear on end and insert the needle bearings one at a time. Dipping each needle into your grease will help make sure they all stick to each other and do not fall out when you change shafts.
4. When all of the needle bearings are in, slide the thrust washer over the end of the layshaft with the pin facing the outside and hold it tight against the laygear.
5. Turn the laygear over and repeat the needle bearing installation for the other end.
4. Replace the steel layshaft with the temporary layshaft. Make sure that neither end of the temporary shaft extends beyond the thrust washers.
5. Putting the laygear unit back into the casing takes a bit of doing. Once again you must line up the pins on the outside of the thrust washers. Notice that the two notches in the casing are not in alignment. I did a general alignment on the pins, got one in and then rotated the other end until it dropped in. Allow the laygear to drop to the bottom of the case.
6. At this point you should reinstall the steel layshaft (See Laygear under General Reassembly below) to recheck the end float. If it exceeds ten thousandths (0.010”), even if you have installed new thrust bearings, you should add shims. Once you have checked the float, replace the steel layshaft with the temporary one and allow the laygear to sit at the bottom of the casing to ease the re-installation of the main shaft assemblies.

1. If you have not already done so, remove the two sliding hubs and striking dog units; be careful not to allow the sliding hubs and striking dogs to come apart.

   Before removing these units note their alignment to the main shaft by marking them in some manner.

2. Third Gear:
1. Turn the main shaft on end with the third gear pointing up.
2. Look down into the area where the main shaft exits the end of third gear. Between the splines you will see a very small pin. Now look on the third gear and you will see a small hole behind the conical protrusions.
3. Align that hole to the small pin.
4. At this point you may want to mount the shaft in a vise or other means of holding it up right as the next several steps will take both hands.
5. With the shaft held up right insert a stiff wire into the hole and depress the spring loaded pin.
6. With the pin held down, rotate the collar (81) until the male splines of the collar line up with the female splines on the main shaft.
7. The collar and the gear can now be removed from the main shaft.
8. When the gear is removed the needle bearings (36 for third gear, 22 for second gear) will be released.
9. Remove the locking pin and spring.
3. Second Gear is removed in similar fashion. The major difference is that between the second gear collar and the needle bearings you will find a split washer.

1. Scoring of any surface especially on the main shaft and the needle bearings.
2. Any broken teeth on the gears and / or conical protrusions.

1. Place the shaft on end.
2. Add a smear of grease on the main shaft to help hold the needle bearings in place.
3. Place third gear on the shaft.
4. Insert the needle bearings, again dipping each one in grease as you insert it.
5. Insert the spring and locking pin using needle nose pliers.
6. Align the hole on the gear to the locking pin.
7. Insert a stiff wire and press down on the pin.
8. While holding down the pin, insert the collar and twist it so the male splines on the collar align with the male splines on the main shaft. You should hear a distinct “click” to indicate that the pin has locked the gear in place.
9. Second gear is installed in the same manner except for the following.
1. After installing the needle bearings you need to add the split washer. Make sure that the tabs on the washer do not align up with the hole for the lock pin.
2. When installing the collar (88), the notches need to fit into the tabs on the split washer.

1. If you just slide the striking dog off the sliding hubs the balls and springs will fly in every direction ensuring that at least one spring and four balls will be lost forever. To circumvent this I used a 3 inch plastic pipe coupling (see Special Tools above) that allows the striking dog to sit on the top of the pipe while the sliding hub will be free to drop into the pipe. Simply put the unit on top of the pipe, center it, and press the sliding hub down into the pipe. If there is some resistance use a plastic headed hammer and gently tap the sliding hub out. When the sliding hub exits from the striking dog, the springs and balls will be captured inside the pipe.

1. Once they are apart take a look at both the striking dog and the sliding hub. Inside of the striking dog are the splines that lock into the synchromesh conical protrusions on the gears (see The TC Gearbox.) On the outside of the sliding hubs are additional splines that the striking dog rides on. With the springs and balls removed the sliding hub should slide easily within the striking dog. Look for any burrs or other anomalies that may hinder movement.
2. The sliding hub should also move freely on the main shaft.
3. Check the brass inserts on the inside of the sliding hubs to see if they have been worn smooth, there should be “cuts” in the brass about every 1/8 of inch or so.
4. Make sure none of the springs are bent. All should be the same length and for that matter all should have the same resistance (I’ll leave it up to you on how to test that). In one paper I read, it said that it should take about 25 pounds of pressure to release the lock-out springs holding the striking dog to the sliding hub. If you choose to replace the springs, as I did, check the length of the replacement springs. The ones I ordered from Moss were about one eighth of inch longer than the originals. I don’t know which length was correct, but when I used the replacements they seemed too strong and I ended up using the original springs.
5. Check the balls for any nicks or burrs or just replace the entire set.

1. Place the sliding hub inside the striking dog making sure that you have aligned the unit using the witness mark made when you took it apart.
2. Put the unit on a flat work surface and place a number of washers under the sliding hub so that when sitting flat the six holes that hold the springs and balls are exposed above the striking dog.
3. Replace the six springs.
4. Place a hose clamp (see Special Tools) around the sliding hub and open it just enough so the clamp rests on the striking dog. The clamp needs to be open enough to allow for the insertion of the balls, but tight enough to keep them in place while doing so. Make sure that the screw devise that tightens the clamp is between two sets of springs.

5. Using a needle nose pliers, insert the balls between the springs and the hose clamp. I found it worked well when I installed the balls opposite sides rather than going around the unit.
6. When all the balls are in place, slowly tighten the clamp until it’s tight against the sliding hub.
7. For the next step the first / second gear sliding hub unit (91) needs to be placed on top of the 3 inch pipe, while the third /fourth gear sliding hub unit (76) needs to be done on a flat surface.
8. With one hand grasp the unit at the hose clamp, then holding it tight against the pipe (or flat surface) with downward pressure, slowly tap the sliding hub into the striking dog using a plastic tipped hammer. At first it will move easily, when the balls engage the end of the striking dog there will be some resistance and the sliding hub will have a tendency to pop back. Hitting the sliding hub a bit harder will convince it to move pass that point. A few more taps and you will feel the balls lock into the notch on the inside of the striking dog.

1. Insert the reverse gear shaft (96) into the casing from the back and secure with its lock bolt.
2. Slide the reverse gear (95) on the reverse shaft with the grooved end toward the front of the gearbox.
3. Place the reverse fork (7) into the groove on the reverse gear and slide the selector shaft through the reverse fork and into the hole in the casing. Secure it with its lock bolt.
4. Place the reverse link (14) into the notch on the reverse fork with the pin facing the inside of the gearbox and secure it with the fulcrum pin, washer, nut and cotter pin.

1. Hold the main shaft with all components (both sets of sliding hubs and striking dogs, second and third gear) in upright position.
2. Insert the main shaft, “back end” first into the casing, allowing the shaft to exit out the back of the gearbox casing.
3. Bring the front of the main shaft down and to the left guiding it through the notch in the front of the casing (see disassemble picture above).
4. Allow the main shaft to rest on the laygear.

1. Before installing the first motion shaft you need to add the needle bearings back into the hole at the back end of the first motion shaft. This is done in the same fashion as with the layshaft and main shaft.
1. Add some grease to the inside of the hole where the needle bearings will sit.
2. Hold the shaft upright.
3. Insert the needle bearings into the end of the shaft, again dipping each one in grease as you insert it.
2. Now with one hand hold up the main shaft, slowly bring the first motion shaft towards the front of the main shaft and slide the two together. This may take several attempts depending on how cooperative the needle bearings are in staying in place.

1. Slide the front bearing guard over the first motion shaft.
2. Slide the front bearing, with circlip to the outside, over the first motion shaft and gently tap the bearing in about half way.
3. Slide the rear bearing guard over the main shaft
4. Side the rear bearing, again with the circlip to the outside, over the main shaft and gently tap the bearing in about half way.
5. Continue to tap the bearings in until they are tight up against the casing.
6. On the front of the first motion shaft install the lock washer (63) with the tab into the slot. The replacement lock washer I received from Moss had two tabs, but only one is used. I had to grind off the unused one in order for the lock washer to fit correctly.
7. Add the first motion shaft nut (64); remember this is a LEFT hand thread.

1. Now is the time to raise the laygear assembly. Either by lifting the assembly or by turning the gearbox upside down, being careful to keep the thrust washer pins aligned with their notches, work the laygear back into position so that you can replace the temporary layshaft with the actual one by sliding it in from the rear of the casing. Again this will take a bit of doing, moving the lay unit up and down until it aligns with the holes for the layshaft. When you do insert the shaft make sure that you install the shaft’s locking bolt notch at the rear of the case and facing the bottom of the case.
2. Once the layshaft is in place, replace its locking bolt.

1. Place the first / second gear fork (5), third / fourth gear fork (6) and reverse selector (11) into place.
2. Since it doesn’t matter which shaft is installed first, I will begin with reverse. To identify the shafts, the third / fourth shaft has two side notches with a pin, reverse has one side notch and two top notices, while first / second had one side notch and three top notches.

3. Finally, you need to add the securing wire to each of the lock bolts.

1. If you removed the speedometer housing, reinstall in the rear cover plate. Be sure to wire the two screws together.
2. Insert the rear spring plate (55) into the circular cutout of the rear cover plate.
3. Add the rear plate guard (54) on top of the spring plate.
4. Add the rear cover gasket. I used silicon sealer in addition to the gasket.
5. Place the rear cover on the casing and secure with the three large, two small nuts and single screw.
6. Gently tap the rear flange in into place and allow it to turn as it guides itself into place as it meshes with the speedometer pinion.
7. Install the rear flange washer and nut.
8. Secure the nut with a cotter pin.

1. Add the top gasket, as before I choose to use silicon sealant in addition to the gasket.
2. Install the three selector shaft balls (22) into the holes at the back of the casing.
3. Install the three springs (21) on top of the balls.
4. Looking from beneath, line up the rear of the remote cover with the three springs, press down on the back, and then slowly bring the front of the cover down until it sits on top of the casing.
5. Secure the remote control unit with the 6 lock washers and nuts.

1. Insert the front spring plate (62) into the circular cutout of the bell housing.
2. Add the front plate guard (61) on top of the spring plate.
3. Slide the bell housing over the first motion shaft and up against the front of the casing. As you do so, watch the front plate guard as it has a tendency to slip out of the circular cutout.
4. Secure the bell housing with 8 bolts and lock washers.

Now the only thing left to do is to put it back into the car. Good luck and have fun.

Carl Fritz, Gainesville, Florida, has one small addition:

Shift forks showing too much tip wear can easily be built up by welding, then ground back to a suitable size & shape. Be sure to tell the welder to use a rod with good abrasion resisstamce.