For disassembly, start by removing the side cover for internal inspection (previous page). Then remove the clutch release arm and front cover (save the bearing shims). Remove the top cover and remote shift extension assembly. Remove also the steel spacer plate beneath the remote shifter housing (first picture) as you will need extra space to rotate the remote control rod before the rear housing can be removed.

On the front lever of the remote control rod you should find a 2-piece split bronze bushing held together with a thin wire retaining ring (picture at right). Treat this like precious jewelry, as it has been unavailable as a replacement part for decades. These bronze bits may last indefinitely, but they are easy to lose. If you buy a used gearbox it may be missing the remote shift assembly, or the split bushing may be missing. The current substitute replacement bushing is molded from white plastic (Nylon or Delrin), and may be expected to break up from age deterioration in less time than anyone would like (several years if you're lucky). The original bronze part gives a nice crisp feel to the shifting motion. The nylon part (when it is working) gives a slightly softer feel to the hand lever. If the part is missing or broken (quite common for the nylon part) the lever motion gets very sloppy, and it may tend to get caught in a position of extreme motion for 1st, 2nd or reverse gear. The hand lever may even get trapped so it is stuck in gear and cannot be returned to neutral. The solution then is to remove the remote shift housing to reset the mechanism, and hopefully install a good split collet so it won't happen again.

Addendum 2005: One of our fellow hobby enthusiasts has recently produced a small batch of these split bushings, exactly as original issue. See article GT-120 (Split bushing for gearshift).

Check the bore holes in the remote shift extension housing where the rod slides in the aluminum housing. They should be a very close fit with little or no perceptible clearance. The ones inside of the main part of the gearbox are usually perfect. The rod in the remote control tower on the MGA gearbox can be a different story. This one is exposed to road dirt from underneath (remote control housing being open on the bottom), and the aluminum bores can get pretty sloppy. This housing can be bored out and bushed as standard machine shop procedure (if you can't find a good used one at reasonable price).

Also, check the spherical aluminum surface where the shift lever seats in the remote control tower. Somewhere way past 100,000 miles this surface gets badly worn, and the shift lever action gets sloppy. The flat top surface of the spherical part should sit about flush with a flat surface inside the housing. You could have the small bearing holes sleeved for repair, but fixing the worn spherical surface is more expensive. A reasonable fix here is a new (used) aluminum part. This is less of a problem with the 3-synchro MGB gearbox, as the remote shift mechanism is enclosed underneath on that unit. A badly worn ball socket can also be repaired with a machined insert. See article GT-206 (Remote shift housing rebuild).

The remote shift extension housing is (usually) the only art of the gearbox that may need any machine work for restoration. The rest of a gearbox rebuild is a fairly simple matter of disassembly, inspection, a few replacement parts, and reassembly.

The picture here shows the spherical socket joint. At either side of the half-ball there is a non-rotation key slot and a round lateral keying pin in the housing. To remove the shift lever you may need to push the pin(s) back a little. Insert a thin blade between the tip of the pin and the base of the slot and tap it in to wedge the pin back just a bit. The slot is not as deep nearer the bottom of the ball, so the pins don't need to be retracted very far to allow the hand lever to lift out. If you're careful to get the pins positioned just right, you can leave them there where they will be effective keys and still allow disassembly. The hand lever is to be held in place by a compression spring, a stamped metal cover, and a large retaining ring.

At the bottom end of the hand lever is a smaller ball which sits in a cylindrical hole in the rear lever. The rear lever has an extension at the back which carries an anti-rattle detent ball and spring secured with a split pin. If you pull the lever out the top, the small ball will likely be lost. That results in a nasty noisy rattling vibration of the hand lever at an engine speed right around highway cruising speed in top gear, which may drive you nuts on the open road. When the unit is in the car, this split pin lies above the gearbox tail housing and propshaft connection where it is generally inaccessible. So if you need to fix this problem, the shift extension assembly should be removed to gain access to the anti-rattle detent parts.


From under the top cover, remove the interlock arm assembly. This may be a bit of a puzzle the first time you do it. Pry the bracket from the top of the box and lift it up slightly. Rotate the remote control shaft to raise the selector lever. Move the interlock arm a bit to the side to disengage it from the three selector slots, pull it back to slip it away from the selector lever, and it should lift out easily. If at first you don't succeed, fiddle a little more. It does work (eventually). Be sure above mentioned spacer plate was removed to allow free rotation of the remote control lever.

An item to check at this point is security of the interlock arm on the mounting bracket. Refer to Confidential Service Memorandum MG/269. A loose rivet here can result in jamming in gear as the interlock arm may move to the right and hang up on the thicker part of the selector lever. If the interlock arm is loose it can be remedied by tightening the shoulder rivet.

The input bearing does not need to be removed from the input shaft unless the bearing will be replaced. Likewise the large retaining ring on the OD of the input bearing does not need to be removed (not ever). If you want to remove the large nut holding the front bearing, it will be more convenient to remove the input shaft first, and work the wrench later on the workbench when the input shaft stands alone (unless you have a really large and very long tube socket).

But you do need to remove the rear flange nut on the 1600 type gearbox. If you don't find it convenient to hold the flange while removing the rear nut, you can shift the gearbox into two gears at once to lock up the mainshaft (after the interlock arm has been removed). Move one shift rod to engage 1st or 2nd gear, and another shift rod to engage 3 or 4th gear. Then go ahead and wrench off the nut to remove the rear flange. Shift it all back into neutral afterward. NOTE: The late model MGB gearbox does not use the interlock lever, but has interlock detents at the front end of the shifting rods.

Remove the speedometer drive spindle housing and small gear from the bottom/side of the rear housing. If left in place this may interfere with removal of the rear housing on the 1500 type gearbox, because of the locktab washer at the back of the helical speedometer drive gear (but may not interfere with the 1600 type gearbox). Also remove the shift extension spacer plate from the top of the rear housing (mentioned twice before). If left in place this will interfere with sufficient rotation of the remote control shaft.

Next remove bolts and part the rear housing from the main housing. One nut on the top stud cannot be fully removed until the rear housing is withdrawn slightly. If it's a little stubborn it may require a little whack with a plastic faced dead blow hammer, or a gentle thump with a 2 pound hammer and a bit of wood in between to protect the aluminum housing. Rotate the remote control shaft to move the selector lever downward out of engagement with the selector slots. Then the rear housing may be pulled off to the back. If you have trouble here, refer to removing the top spacer plate (repeat over and over) and the speedometer drive spindle.

If the selector lever does not quite clear the bottom gate, check to see if the tip of the bolt securing the lever on the shaft might be touching the housing. I have heard of this condition only once so hopefully it is rare. Loosening the pinch bolt a turn or two may be enough to solve this issue. A longer term solution may be to shorten the tip of the bolt slightly.

The rear housing carries the rear bearing and the rear seal, which are more conveniently removed after the housing is off. For the 1600 type gearbox, remove the rear seal first, then remove a large circlip and withdraw the ball bearing (but only if it needs changing).

Now referring to the MGA 1500 gearbox. This gearbox has a sliding spline joint where the propeller shaft mates to the rear of the gearbox. Inside here is a bi-metal bearing like a big copy of a kingpin bushing, bronze inside of a steel liner. To check this one you shove the drive shaft front yoke in to the normal working distance and try to wiggle it. When new the working clearance is just 0.002 inch like a crankshaft bearing, no perceptible clearance with oil in it. If the yoke can wiggle more than a few thousandths of an inch, it's a problem. It probably won't self-destruct immediately in normal use, but it can cause a vibration in the drive shaft at speeds over 30 MPH. But what's also nasty is that it beats up the rear seal in short order and the oil leaks out. In one case when mine got especially loose, a new rear seal was completely shot in two weeks. Adding oil daily will save the gearbox but leaves a big oil puddle where you park. Enough about the problem. For the repair check out Replacing the tail bushing.

You may want to check or change the rear rubber mount. These are only moderately expensive, but good piece of mind to have a new one in there. The MGA gearbox rear mount is a real pain to change, being a press fit steel shell in a thin aluminum housing. Be careful here, as the aluminum monkey ear on the rear housing is easy to break, especially on the 1500 gearbox. Some reinforcing ribs were added to later models to improve the strength of the case around the rear mount casting. You surely can remove and replace the rear mount without a press if you are willing. Check Replacing the rear mount for details.

Shift rods with forks, detent block, and selectors

Inside the box, crack loose the jam nuts and remove three pointed nose screws which secure the bronze shift forks to the shifting rods. Take these screws all the way out. The three shift rods pass through a flat steel block at the back of the main case. This block contains detent balls and springs. It is best to remove this as a complete assembly to avoid disturbing these detent parts. Remove two bolts (a thin wall or 1/4 inch drive socket works here) and pry the detent block away from the main housing. This has to be removed from (or with) two steel dowel pins. Extract the entire assembly (the block and three shift rods) from the back, leaving the shifting forks inside. The forks can then be lifted out individually.

Early gearboxes have an extended tube tail on the 3-4 shift fork, all one piece. Later units make the 3-4 fork smaller, and the extended tube spacer on the 3-4 shift rod is a separate piece. The drawings will be different in different places. The Workshop Manual shows the 3-4 fork and tube spacer all one piece like early units. The Moss Motors catalog shows the 3-4 fork and the tube spacer as separate pieces with separate part numbers like the later units. The Service Parts List shows the tube spacer commencing at (G) A290.

If this is the first time you have opened this gearbox, and you do not know the history of the unit, this is a good time to disassemble the shift rods from the detent block to inspect the detent parts. When you extract the shift rod hold your hand and/or a shop rag over the hole in the detent block to catch the steel ball and spring that will pop out of the hole (or have some spares handy in case you lose these small jumpy parts). When inspecting these parts refer to the following documents:
      GT-202 - Why it Pops Out of 3rd Gear
      MG-241 - Jumping Out Of Gear (csm)
      FT-038 - Incorrect Spring for Shift Detents

Interest here is to measure depth of the hole for the 3-4 gear detent, and length of all of the springs. If you find the hole to be too deep it can be shimmed. If you find the springs to be too short they can be replaced with correct longer springs, or the short springs can be shimmed to equal the free length of the correct springs. These springs are related to the occasional problem of popping out of 2nd or 3rd gear.

Reassembly is easy enough when you know how the bits work. Put any shims in the hole first, then the detent spring followed by the ball. Press the ball down with a flat tip punch to be flush inside the bore, and then insert the shift rod into the bore to cover the ball detent as you remove the punch.

NOTE: The late model MGB (4-synchro) gearbox has a different arrangement of ball detents at the front end of the shift rods. There you will install the shift rods first, then drop a detent plunger into the hole followed by a spring and a bolt. During disassembly you should remove the detent parts before withdrawing the shift rods.

Now take a good look at the selectors (click for larger picture). This gearbox has seen a LOT of usage (maybe 200,000 miles), so the selectors are noticeably worn. The top selector (with the wide stepped face) is for reverse, and shows very little wear. The middle selector (with thin fingers) is for 1st and 2nd gears. The bottom selector is for 3rd and 4th gears. These parts show substantial wear, but oddly enough it was still a pretty slick shifter. A small amount of wear on the selector parts can give it a smoother action when shifting, so don't be too concerned about these parts unless the wear is obviously excessive. If you wanted to put these parts back in service for another 100,000 miles or more, you might patiently weld up the worn surfaces and file or grind them back to flat with square corners. I would do it in a flash if I needed to, but so far I have enough good used parts. Or you might procure another used gearbox for cheap and use the best of the available parts. Photo at right above shows selectors with very little wear.

Remove one special pin-nose bolt (with locktab) securing the reverse gear shaft (left). Slide the shaft out the back of the case, and lift out the gear. Inspect the gear for worn or chipped teeth. Some small chips on the beveled or rounded ends of the teeth is normal and is not a functional problem. This one appears to be low mileage with crisp beveled corners and no visible chips. The pressure faces of the gear teeth should be polished smooth with a little wear showing. If any one tooth pressure face is chipped or spalling (bits missing from the surface), then the gear should be replaced.

This has us down to the main case with the power transmission shafts and gears only. Next is to push the layshaft out either end of the case. Here, depending on what you have in mind for further disassembly or immediate reassembly, you may want to insert a thin steel rod in place of the layshaft (picture at right) to hold the thrust washers in place. An alternate method is to insert a foreshortened dummy layshaft, 5/8 inch diameter (PVC pipe or wood dowel) and 6-13/16 inches long (which will just fit inside the ends of the case). Once the layshaft has been removed, drop the laygear down into the bottom of the case where it will not interfere with removal of the gears on the mainshaft.

For the next few paragraphs you can decide for yourself whether to remove the input shaft or output shaft first. This may depend some on how tight the main bearings are in the housing, or what success you may have with tapping from inside with a long brass drift and a light hammer. I usually remove the input shaft first, as long as I find it possible. The 1500 and 1600 type gearboxes (and some early MK-II units) use the 10-spline input shaft. Later MK-II units (and early MGB) use the 23 spline input shaft. The input shafts are interchangeable (up to and including 1967 model year) if you use the matching clutch disc.

The next part sounds easy enough, but may require a little tact and understanding (prybar or slide hammer or gentle hammer and big punch). Withdraw the input shaft with bearing and gear from the front. Expect the big ball bearing to be a snug fit in the case, so this may require some encouragement. Keep the shaft and bearing straight during removal to avoid having the bearing jam tight in the housing.

When the input gear comes out, expect a bunch of needle bearing rollers to fall out from the inside. If the assembly is held horizontal, some of the rollers may remain inside the input gear. Many of the rollers will fall into the gearcase. A pencil magnet can help with retrieval. Some rollers might fall on the floor if you're not careful. Count carefully, you should have 18 rollers, don't loose them. They are not expensive, but it's a tough grit if you have to wait for delivery of parts because you lost one roller. And don't even think of trying to reassemble it with only 17 rollers. These rollers are usually in good condition. Measure them with a micrometer (.118 inch diameter), and inspect them with a magnifying glass. If they are smooth with mirror finish they are most likely good to re-use. If they have any visible marks in the surface they are good for the trash.

Extract the mainshaft assembly out the back of the case. There is a thick plate ring mount around the ball bearing which should come out with the assembly. This ring carries an anti-rotation dowel pin which engages the rear housing and must be properly aligned during later reassembly. You may (optionally) use a punch or small chisel to mark the relationship of bearing carrier to case, which may make reassembly easier. The bearing carrier will likely be a snug fit in the case and may need encouragement, but at least the mainshaft assembly comes out in tact with no loose parts, almost.

From the front end of the mainshaft assembly you can slip off the 4th gear synchro ring, the 3-4 sliding hub assembly, and 3rd gear synchro ring. Do not disassemble the sliding hub assembly unless you have a very good reason (and curiosity is not a very good reason). More about this later. Check the brass synchro rings for wear, particularly on the doghouse shaped ears. In many cases these will not be worn much, and you might re-use the parts. The 3rd and 4th synchro rings are the same part number. If 3rd is worn slightly and 4th hardly at all, you might switch places with them for extended service (like rotating tires for more even wear).

Finally lift out the laygear and thrust washers, retrieve any loose bits you may have dropped in the case, and you should be left with an empty gearcase. For the working guts of the unit you now have the input gear (first motion shaft), the laygear (second motion shaft), and the mainshaft assembly (third motion shaft).

Clean the inside of the main gearcase and rear housing sometime prior to reassembly. Also plan on degreasing all nuts bolts and washers and check the threads for free running with fingers only prior to reassembly. Threaded parts with "a hitch in the git-along" can be cleaned up with thread chasers. It is best to do this immediately after disassembly so you have no surprises at assembly time. Replace any damaged fasteners.

You will likely find the lay shaft to be worn somewhat where the needle bearings run against it. You should probably replace the lay shaft, but it's a judgment call when you see it. If it doesn't look too bad, and you drive the car in a civil manner (yeah, sure), you may opt to put the original back in. But personally, I thrash the crap out of the thing, and I expect to keep it another thirty years, so I figure a new lay shaft and needle bearings to be a good investment. They're not the most expensive parts in there, and I've done it for multiple gearboxes now, one of which has done enough miles to have the layshaft worn and replaced twice.

The greatest layshaft shaft wear occurs at the smaller end of the gear with the single needle bearing. Some people feeling a little crafty here will shorten the tube spacer to allow for installation of one more needle bearing. This will improve the life of the layshaft considerably, so it may be worth considering. This is a nice modification in combination with installing the improved 2nd gear with steel synchro ring. If you do add the 4th needle bearing, it is advisable to also drill another radial hole in the layshaft to feed oil to the new bearing. Yes, they are oil fed through axial holes drilled from the ends of the shaft.

If the layshaft looks particularly chewed up (which is fairly common) then it's a good idea to also replace the needle bearings inside the laygear. Parts in the picture above are used to mount the laygear on the layshaft. From left to right they are: front thrust washer, circlip, needle bearing, circlip, needle bearing, (laygear), spacer tube, needle bearing, circlip, and rear thrust washer. Original needle bearings may have loose rollers and separate end caps. Replacement needle bearings will most likely be one piece assemblies with the rollers held in assembly by a thin cage. See more pictures and notes under Layshaft improvements

To remove the needle bearings from the laygear you have to extract a circlip from each end of the gear (remove 2 only). The 2nd clip in from the large end of the gear can be left in place. The circlips are a little tricky to remove. They have angled ends, so you can insert a narrow screwdriver blade between the ends and twist to raise one end of the ring. Then slip a second thin blade under the ring to keep it out of the groove. Using two thin blades, work your way around the ring to lift it out of the groove all the way around. This will quite likely permanently distort the ring, damaging it beyond use, so plan on replacing these circlips any time you remove them. Luckily they are easier to install than to remove.

There is a much easier way to remove the circlips. The only reason for removing the clips is to replace the bearings, so we presume the old bearings will not be re-used. Place a small punch against the clip half way around from the tips, and give it a whack with a hammer to break the clip.

If you have to replace the laygear for any reason you should check and/or adjust the end play for the laygear. With the laygear mounted in the housing, nudge it fore and aft a bit and measure the motion in that direction. It should be a small amount, in the order of .002" to .006". If it needs adjusting it is done by exchanging the rear thrust washer for another of a slightly different thickness.

You may also consider replacing the big ball bearing on the input shaft. It's a pretty rugged part, but it depends a lot on its past history of maintenance and such. It is good to check this bearing while running before you yank the engine. See earlier notes on the test drive. Otherwise find more information on bearing inspection under Universal Tech. When the parts are in your hands, try wiggling the outer bearing race. These big ball bearings do have a small internal clearance, so a little wiggle is okay, as long as it turns smoothly without any noticeable scratching sounds. It should be very smooth to the touch when rotated with a little oil in there. If you find a lot of wobble or nasty noises, it's a goner for sure.

Check the working surfaces of the brass shifting forks where they mate with the grooves in the sliding steel hubs. When new these fit almost like crankshaft bearings, just a couple thousandths inch of clearance. After 100,000 miles they get a little loose and wobbly but will usually still work just fine. Don't worry too much unless they're really sloppy. When my original gearbox had about 150,000 miles on it, the forks were working OK. I swapped them out for some younger ones more recently, but only because I had some extra ones laying around and put in the best I had.

Check the front spigot nose of the mainshaft for wear. This should be 0.6455/0.6450 inch diameter (16.4-mm, same as the layshaft), and smooth with a mirror finish. If the spigot bearing surface is rough or damaged in any way, the mainshaft would need to be replaced. The alternative of welding up and re-grinding the spigot surface is likely cost prohibitive. Also run a wire through the front restrictor orifice or blow air through it to verify that the oil passages all the way back to the oil pump spool are clear.

Look at third gear and second gear, on the main shaft immediately behind the input gear (and aft of the 3-4 sliding hub assembly). Grab these gears and try to move them around. There should be little or no motion other than normal rotation. These two gears ride on bronze bushings on the third motion shaft, and there is a bronze thrust washer between these gears. If one gear (or both) feels loose and wobbly, the bronze parts inside will need replacing. These bronze pieces usually do not go bad. When the gear is engaged and driving, it is locked to the shaft and the bushing sees no relative motion. Any other time the gear just idles on the bushing with no load. Towing the car on the rear wheels for long distances could wear out these bushings, as they may (possibly might) then be running with insufficient lubrication (if there is insufficient oil in the gearbox). This particular point is the brunt of another discussion about the gearbox lubrication scheme and towing without disconnecting the driveshaft.

A word of caution here, before disassembling the mainshaft. There are two sliding hubs. One called the Sliding Hub And Dog Assembly (or Sliding Hub Assembly 3rd & 4th Gear) is between the input gear and third gear on the main shaft. In 3-synchro boxes the other is the First Gear & Hub Assembly, the big one with straight teeth farthest back on the main shaft. In the 4-synchro boxes the other is called Sliding Hub Assembly 1st & 2nd gear. These hubs are in two pieces, inner and outer parts with splines in between. When you slide off the outer ring, there are three small steel detent balls with springs behind them. Hold the hub assembly low on a work bench and open very slowly. Maybe place a shop rag over the assembly to catch the little balls and springs when they pop out. If you do not find the little bits immediately, search diligently under the workbench and behind everything - they fly a long ways on their own if you don't catch them. It is of course best not to let them get away in the first place, but this is one item that may take you by surprise even when you're expecting it. These springs should have a nice stiff feel, and the balls should protrude considerably above the surface of the splines when unloaded. When in doubt, the springs are fairly cheap to replace. You might want to buy a couple of springs and a few detent balls before disassembly, as these bits could be really hard to find if they go flying. In most cases, if I know the unit was functioning okay before, I will keep the sliding hubs assembled, assuring that the springs and balls cannot fly free or get lost.

The mainshaft assembly must be substantially disassembled to replace bronze bushings or the 2nd gear synchronizer ring. Start by holding the mainshaft in a bench vice, front end up. Lift off the 4th gear synchro ring, the 3-4 sliding hub assembly, and the 3rd gear synchro ring, then exposing what is seen in the picture here. Click for larger image.

Nestled in a recess in the front face of 3rd gear is a special keyed thrust washer. This has an internal spline cut to match the external spline on the mainshaft. The mainshaft has a circumferential groove slightly wider than the thickness of the thrust washer. The washer is pushed over the spline, and then rotated to move the teeth of the internal spline into the groove in the mainshaft to be locked in behind the teeth of the male spline. The washer has a small hole in the face (seen at the front of this picture) to facilitate rotation of the washer during assembly (or disassembly). In this picture, just to the right of that hole there is a spring loaded pin in a radial hole in the mainshaft, centered in the groove of the male spline. This pin pops up to engage the female spline of the washer to prevent rotation, effectively locking it in place.

To remove the thrust washer you need to insert a thin blade between the tip of the pin and the root of the spline in the washer. Pry the spring loaded pin progressively inward, depressing it to the root of the male spline on the shaft. Then rotate the washer until the splines are aligned, and pull the gear forward and off the shaft along with the washer. All of this is easier said than done, so your first time may be a little trying, but have patience and you shall prevail. What you don't see in the picture (rotated out of view) is a small radial hole through the cone flange on the gear. During assembly a pin punch is inserted here to depress the locking pin while the thrust washer is being installed.

This thrust washer was originally available in three thickness (in .002" increments) to adjust end float of 3rd gear. Today a replacement washer might be available only in the thinner of these three numbers. This may be of some concern if you need to replace 3rd gear, where end float is intended to be limited to 0.002" to 0.004". End float might also be increased by wear on the bronze thrust washer between 3rd and 2nd gears. Increased end float of a helical gear increases backlash in the drive train.

Notice in the picture at right that the sliding 1st gear is pushed back (down) away from the 2nd gear synchro ring (moved into position as though shifted to engage 1st gear). With 3rd gear removed, the bronze bushing and thrust washer (near top) are exposed. These can be pulled off the shaft by pulling forward on 2nd gear. Notice in the picture that there is a hole in the bushing that must be aligned with a radial drill hole in the shaft to admit oil to lubricate the bearing surface. The inside of 3rd gear bushing is keyed to the shaft to fix the orientation of the bushing to assure that the oil hole stays aligned in assembly. The 3rd gear bushing also has castellated ears on the end to lock into the bronze thrust washer, which similarly locks onto the 2nd gear bushing to align that one on the shaft for the same reason, to assure alignment of the oil feed hole for 2nd gear.

Check the thickness of the bronze thrust washer. Parts catalogs may list this part as "interlocking ring". The gears rotating on either side of it bear against most of the side surface of the thrust washer, but not against the tabs which extend inward to key with the bushings. Where the central tabs are not worn you can measure the thickness, and compare that with the thickness farther out to determine the extent of wear on the washer. This wear contributes to end float of 3rd gear at the front steel locking thrust washer. So before you think about looking for a thicker front locking washer, you might consider replacing the center bronze thrust washer.

Measure the OD of the bronze bushings. These should be 1.3115-1.3120" diameter. If the bronze bushings and thrust washer are in good condition they may be returned to service. If any part of the bushing or thrust washer is physically damaged it should be replaced. If the bushings are worn fit new phosphor-bronze bushes (Part Nos. 11G3028 and 11G3029). These were reintroduced at Gearbox No. 24001 to replace the sintered bronze bushings used previously. In reality I have no idea what material is used for currently available replacement parts.

This picture shows the mainshaft with 2nd gear removed and the 2nd gear bushing exposed. This bushing does not need to be removed to exchange the 2nd gear synchronizer ring. The bushing would need to be removed to pull the 1-2 sliding hub off the shaft. It is good not to disturb this bushing if it is in serviceable condition. This bushing has a smooth bore and is not keyed to the shaft, with the oil hole alignment being maintained by keying to the 3rd gear bushing through the thrust washer. It is possible to remove 1st gear from the central splined hub (without removing 2nd gear bronze bushing) if you need to inspect or service the ball and spring detents. Between the 2nd gear bushing and the 1-2 fixed hub there is another thrust washer, which you most likely will never need to remove (except to remove the 1-2 fixed hub).

Beyond the 1-2 sliding hub is a shoulder on the mainshaft, so there is nothing else to be removed from the front. The large ball bearing is positioned against the back side of that shoulder, to be removed or installed from the back end of the shaft. Immediately behind the bearing is the helical grooved oil pump spool (often referred to as "spacer" or "distance piece" in parts lists). Behind that is the speedometer drive gear. For the 1500 type unit the speedo drive gear is retained by a locktab washer and hex nut (seen in this picture). The speedo gear is keyed to the shaft, but the spool is not, so the retaining nut needs to be tight enough to prevent any rotation of the spool on the shaft (so the helical groove oil pump will continue to work).

Remember there are early and mid 1500 gearboxes with different size output splines and different shaft length. The oil pump spool, speedo drive gear, locktab and nut are all slightly different to match the shaft, and are not interchangeable. However, the mainshaft and rear housing can be exchanged as a set to convert from early to mid 1500 model gearbox.

For the 1600 type gearbox the locktab and nut are replaced by a long tube spacer, held in place by the rear ball bearing and output flange and big nut on the back end of the shaft. The oil pump spool and speedo drive gear for the 1600 (and MK-II) type unit are the same as for the mid 1500 unit. Again, the mainshaft and the rear housing can be exchanged as a set for model conversion.

As for the rest of the internal stuff, just be sure that the parts are all there and nothing's broken. The gearbox is not like an engine. No machining is required here, just replace any worn or broken parts and reassemble it. If you have the right parts in hand it can be back together the same day, possibly within a few hours of first cover removal. Taken in small steps and bite size subassemblies, it is simple enough and goes together like tinker toys.