Guided Tour of a Ratchet-Top Four Speed Transmission

Tom Johnson
Tom Johnson


They’re not as easy as five-speeds or later four-speeds, but the ‘39-’78 jockey-lid/ratchet-top transmissions aren’t that hard to work on. The biggest gotcha is that they require tools most home mechanics don’t have. I contacted Jim’s USA for two biggies that I needed and couldn’t jury rig or borrow- Shift Fork Gauge #96384-39 and Main Seal Remover/Installer #95660-42. I also ordered Jim’s Master Rebuild Kit #35125-37 and a bag of .0004 oversize rollers (more on that later). A clutch-hub puller is necessary too, and something to keep the mainshaft from turning as the puller draws tight. It’s tempting to wedge a long screwdriver between two of the hub studs, but doing that usually breaks one. An old friction disk bolted to a muffler support or piece of flat stock works much better, with commercial versions of that tool available from Jim’s and other sources. 

The shift fork gauge is pretty much indispensable for early four-speeds, the seal tool slightly less so, depending on how good you are at changing seals with a hammer and screwdriver. And, unless you’re working in a shop with a vast inventory of obscure little parts on hand, you’ll want the Master Rebuild Kit, too. It eliminates having to go through a catalog and find every last little bushing, lock ring, and gasket you might need, not to mention the midnight SNAFU when you discover the only truly indispensable parts were back-ordered and didn’t arrive with the things you could probably have gotten by without. The rebuild kit is a major convenience, but doesn’t include quite everything necessary for a rebuild because of size issues- you’ll also have to buy a bag of rollers in the correct size and a countershaft endplay spacer. For me, Jim’s is the source for specialty tools and items like the rebuild kit- always has been, always will be. There was a time when few H-D dealers would even talk about selling specialty tools to a civilian. Jim Thiessen solved that problem all by his lonesome, singlehandedly opening a market that no one else knew existed. 

They aren’t exactly cheap, but those tools and parts are reasonably affordable, especially considering the labor savings they make possible. A bigger problem is sizing the main bearing race, which the main drive gear and bearing rollers ride in on the sprocket side of the transmission. The race will need careful measuring at the very least, and machining if it is worn or damaged to the point that it requires oversize rollers or has to be replaced. A micrometer is recommended for measuring the outside diameter of the gear, which is then subtracted from the inside diameter of the race to determine the roller size required. One of the pros I spoke with felt that a T-gauge/inside micrometer in the right hands would be ok for measuring the race, but agreed with the other that a dial bore gauge is best- no calipers! I bought my bore gauge from Enco for a hundred bucks, and a cheap 1-2” outside micrometer for the gear should only run another 30 bucks or so- less on E-Bay, if you’re a gambling man. That leaves the machine work. You’ll need a press to replace the race, if necessary, and a lapping tool to size it. It’s conceivable that sizing could be accomplished with an inexpensive cylinder hone, but a hone wouldn’t provide for keeping the race concentric with the bore for the bearing on the kicker side of the transmission. To size the race correctly, Jim’s lapping tool #1023-TL, or something similar, would be necessary. Lapping tools are pricey enough (think two carb kits at typical street cost) that most home mechanics would do better turning their cases over to a friendly shop for the machine work and then assembling everything at home. 

You’ll want to use a shop manual as a reference unless you build enough ratchet-top four-speeds to know your way through them by heart, so I’m going to concentrate on covering the highlights and passing along a few tips. 

• Removing a transmission requires more time than knowledge or skill, but it’s important to remember that the clutch hub and sprocket nuts have left-hand threads, meaning you turn the nuts clockwise to loosen them and counterclockwise to tighten them. I use an air-impact wrench to remove the nuts, but torque them by hand during assembly- it’s too easy to damage a seal, or worse, with an impact tool. 

• After removing sprocket nuts with a hammer and punch forever (a punch damages the nuts less than a chisel), I bought a sprocket-nut socket from Fab Kevin seven or eight years ago. I didn’t consider it cheap until the first time I used it. 

• With the sprocket off, you should find a small, L-shaped piece of metal in the keyway on the spacer that surrounds the main drive gear. That’s- tah-dah- the main drive-gear spacer key, which is the easiest part in the world to lose or forget about. 

• If you don’t own a compressor and air wrench, the usual trick for removing the clutch-hub, sprocket, and starter-gear nuts is to jam the transmission by putting the bike in gear, then cramming a rag or wooden wedge between the chain and sprocket and/or having someone apply the rear brake. If that seems more trouble than it’s worth, consider saving the nuts until the transmission is out of the bike. Then you can lock the shafts by removing the lid and engaging two gears at once, followed by loosening the nuts with a breaker bar…after bending back the tabs on the lockwashers, of course. I’ve never had a problem doing this with American-made gears, but don’t know about Asian imports- you’re on your own with them. 

• Removing the transmission and baseplate as a unit is usually the way to fly if the oil tank’s in place, because the transmission case studs won’t often clear the baseplate. 

• A mechanical impact driver like the one shown in Photo 3 is great for loosening stubborn screws and screws with damaged slots. Penetrating oil or heat from a propane torch may help too. This should go without saying, but never forget that an open flame around gasoline fumes is a loaded weapon- it can put an end to you, your garage, and your motorcycle forever. 

• Encouragement from a soft mallet or a hammer against a block of wood will break the lid loose if you didn’t overlook one of the 12 screws that hold it down. After it’s off, note the top hats, aka, “shifter rollers,” shown in Photo 4. Keep them in a prominent place to avoid forgetting them until the transmission is back in the bike and doesn’t shift right. Been there, and it sucks. 

• With the lid off, you can remove the retainer screw shown in Photo 5, then tap the shift-fork rod out the sprocket side of the transmission with a skinny drift inserted from the kicker side. The first few taps may require a fair amount of force because of resistance from the shaft seal. When you remove the forks, inspect them closely and replace if bent or otherwise damaged. Note that the two forks are not interchangeable. 

• When working on a transmission, keeping the subassemblies together will simplify reassembly and help avoid SNAFU’s. Notes and digital photos aren’t a bad idea for the elderly and terminally forgetful. 

• Before going farther, you’ll want to shake the end of the mainshaft up and down to get a feel for the amount of clearance between the shaft, main drive gear, bearings, and race. Better yet, use a dial indicator. Recommended play is .0005” to .002”. As a backyard point of reference, .001” is barely perceptible- you almost need your imagination to feel it, and even then you shouldn’t be quite sure that the shaft actually moved. No seal will ever stop an oil leak caused by excessive wear, and note that oil will leak past the mainshaft until the sprocket nut is installed to snug the main drive gear spacer against the seal. 

• The countershaft comes next. Remove the cap on the sprocket side of the transmission, shown in Photo 8, followed by the lockwasher, 7/8” nut, and lockplate on the kicker side. The nut is a conventional right-hander and should be no problem getting off with a ratchet or breaker bar if you lock the transmission by engaging two gears at once. 

• Keeping the transmission level, tap the countershaft out towards the sprocket side of the case. The countershaft gear assembly will be slippery unless it’s bone-dry and rusty, but you should be able to lift it out with a pair of Channel Locks once the shaft’s clear. There should be 44 loose roller bearings inside the assembly, or 43 if oversized rollers were used. (Standard roller diameter is 0.125”.), so keep it level as you remove it. Even so, you’ll probably hear a light clank when the gear comes out of the case. That’s the countershaft endplay spacer falling into the bottom of the case on the kicker side, although it sometimes sticks to the gear. While you’re looking for the spacer, check for loose rollers inside the case, then count them to be sure they’re all there. Disassembling the countershaft gear is a breeze, but throw the lock rings away so you will never be tempted to reuse them. A lock ring that’s been sprung even a little can come loose, teaching you what it’s like to lock the transmission up at highway speeds with the old “two gears at once” trick. Been there too, and it really sucked. 

• There are alternatives, but you’ll have to replace the main seal and spacer before removing the mainshaft, or after it’s back in, if you use a seal installer/remover like Jim’s. I forgot, and had to reinstall the mainshaft for the photo of the seal tool. The alternative is to hammer a screwdriver into the old seal and wrestle it out, which can be vastly more frustrating and timeconsuming than it might sound. 

• Remove the mainshaft retainer plate on the kicker side of the transmission, then tap the mainshaft through from the sprocket side. (My ‘69 Shop Manual says to tap it out with a soft mallet, but a press is nice if you’re careful.) You’ll be able to move the shaft just far enough to free the sealed bearing from the kicker side before third gear bottoms against a boss in the bottom of the case. 

• A lock ring secures third gear on the shaft. For me, getting that weasely little bastard out of the way is the only hard part of working on a four-speed. The trick is to pry it up from the bottom and away from the gear at the same time. I use a rightangle scribe and a small flat-blade screwdriver with a bent tip, while a couple of pals I checked with just use scribes. Prying on the lock ring enough to spring it makes working it out of the groove and over the shaft a little easier. 

• With the lock ring loose, you’ll be able to slide the mainshaft through the gear and out of the case, but note that there’s just enough room for the low/second gear to clear the opening. 

• To finish up, slip the main drive gear and rollers out of the bushing. The gear may require coercion from a press or soft mallet. Again, 44 is the magic number unless the rollers are oversized. 

Next we’ll cover assembling the Ratchet-Top Four Speed Transmission

So far, I took my four- speed apart to change the speedometer drive gear. This part will cover freshening up the things that need it and putting everything back together. I’m just going to focus on the highlights, and strongly recommend following the procedures outlined in an H-D Service Manual. For the record, my transmission is a ‘46 model that got a Pan ratchet lid a few years ago. Others in the ‘39-’78 year group are similar, but not always identical. Early and late ‘76 transmissions have different countershaft bearings, for instance (Thanks, Shane.), and you may notice that my Knuckle case has a stand- alone vent fitting in place of the drilled screw that later four- speeds use. But enough trivia.

• Besides the tools that most of us already have, you’ll want access to a bore gauge for measuring the inside diameter of the main bearing race; a lapping tool for fitting the race to the rollers, if necessary; 0-1” and 1-2” micrometers; and a shift fork gauge. Although somewhat optional unless you have to replace the main bearing race or countershaft inserts, a press is handy too. I bought “Big O,” my 20-ton hydraulic press, on sale cheap at Harbor Freight. I should have gotten one sooner. My micrometers and dial bore gauge are Enco items, also bought on sale. My shift fork gauge, along with every other specialty Harley tool I own and didn’t make, came from Jim’s. If you have any interest in H-D projects that require specialty tools, you’ll want to click up www. or call 805-482-6913 and order a catalog. In addition to the tools, you’ll need more bushings, lock rings, and gaskets than I’m even going to think about looking up, all of which are included in Jim’s Master Rebuild Kit. The kit also includes a countershaft, shift-fork shaft, and top hats (shifter rollers), but you’re on your own for new bearing rollers, a countershaft endplay spacer if the existing one doesn’t work out, shift fork shims, and replacements for damaged or worn-out parts. This has nothing to do with patriotism or politics, but I would strongly recommend buying American- made transmission parts. Almost any problem in a transmission, either with parts or assembly, can put you on your head before you even know something’s wrong.

• A through inspection is the first step after disassembly. The main things to watch for are bent or broken shift forks and damage/excessive wear to splines, threads, gear teeth, and engagement areas on gears and shifter clutches. Edges should be crisp, not rounded or dull. You’ll also want to look for pitting or corrosion that could indicate a problem with surface hardening.

• We stopped at the main drive gear last time. The bearing surface on mine measured 1.629” in diameter, compared to 1.88” for the i.d. of the  race, as shown in Photos 1 and 2. The difference of 0.251” indicated an ideal clearance of .001” after deducting .250” for the combined diameter of two standard, 0.125” rollers. That seemed odd, considering the gear had felt a little loose, so I measured six of the rollers. All were worn down to.122” to .123”, which bumped clearance into the .004-.006” range- too much. Since the bore gauge indicated only a couple of .0005” wear spots in the race, I didn’t worry about lapping it- I could restore clearance to .001”-.0015” by installing new standard-sized rollers. I found a set (Sonnax #HDBR0001, 0.162” x 0.125”) at a local shop. After installing the thrust washer on the gear, I smeared a coat of grease around the race to hold the 44 rollers in place (usually 43, with oversizes) while I finagled the gear into place as shown in Photo 3. It felt great, with minimal drag and no perceptible play- very cool, but no great surprise since I measured the new rollers to make sure they really were 0.125”. Even the best manufacturers make mistakes, especially in packaging, so it’s always a good idea to measure critical parts before installing them- exactly what blueprinting an engine or transmission is all about.

• Taking things a little out of order, I removed the drive gear to inspect the bushing inside and replace the seal in the sprocket end. Clearance between the shaft and bushing was .001”. That saved having to replace the bushing, although the Jim’s kit included one. The seal popped out easily with a screwdriver, but the replacement seemed a little flimsy for tapping in with a hammer, even my little mini-whacker. Big O took care of that as shown in Photo 4, although the vise would have worked equally well. Continuing inspection of the mainshaft assembly, I found that the kicker-side bearing felt brand new- it spun freely with no slop, grabby spots, or ugly grinding noises. Acknowledging the risk, I left everything on the mainshaft in place, including said bearing- an iffy move that’s not recommended, considering the work required to go back in and replace it if it fails. Next, I reinstalled the rollers and gear in the case and started the mainshaft assembly on its way in from the kicker side (See Photos 5 and 6.) If you were here last time, you’ll know to have second gear waiting inside the case, on the drive side of the ridge on the bottom, and the lock ring and mainshaft shifter clutch on the ready. 

• The main and countershaft shifter clutches are not interchangeable. Mine being Andrews parts, the one for the mainshaft goes in with the letters “A/P” facing the main drive gear, while stock clutches are stamped “HIGH” on that side. (Countershaft clutches can go either way.) Slide the shaft through second gear, then work the lock ring and shifter clutch over the end before pushing the shaft on through to the drive gear. A coat of grease will make sliding the lock ring over the shaft easier, and be sure to treat that bad boy like a friend, not your worst enemy. You’ll be less likely to spring it if you’re patient and slowly rotate the shaft as you work the lock ring over it, moving the ring towards the groove evenly and a little at a time. If you have any doubt that the lock ring is strangle-hold tight in the groove, rip it out, buy a new one, and start all over. If it ever vibrates loose, the transmission will lock-up and cause you and your motorcycle grievous bodily harm…or at least a lot of inconvenience. 

• The kicker-side bearing is a press- t in the case, so you’ll need to ease the mainshaft assembly home with a press or soft mallet after seating the lock ring in the groove and making sure the shifter clutch slides freely on the shaft. The problem with seating the mainshaft with a mallet or hammer, although that’s SOP in older Service Manuals, is that even light tapping can tweak the shaft and damage the balls in the kicker side bearing, old or new, and shorten its life. I’ve never had a problem with tapping the mainshaft home, but the potential exists. Use a press if you can. • Finish the mainshaft by installing the retainer on the kicker side of the case. Don’t forget the oil slinger, and be sure to use Loctite on the screws. Occasionally you hear someone ask if they really need the slinger. The answer-only if you want to lube the kickstarter ratchet gear and keep the bushing and gear from seizing on the shaft, snapping off the stop pin on the back of the crank gear, and letting the kick arm spin around to beat the back of your leg black and blue. Checking transmission fluid from time to time is another good way to avoid that.

• The countershaft assembly comes next. You’ll want to replace the shaft or rollers if either is worn enough to provide more than .002” of clearance between the shaft and countershaft gear. The gear may be worn too- a good automotive machine shop should be able to hone it for oversized rollers. I replaced my old countershaft with the new one in the Jim’s kit, so shaft wear wasn’t an issue. The rollers were a different story- they measured .122-.123”- the same as those from the mainshaft. (I got the old rollers from one of the big distributors before I realized how heavily they rely on struggling countries in the Far East, even for critical parts like bearings.) After placing the retainer rings inside each end of the countershaft gear, as shown in Photo 7, I coated the bores in the shaft ends with grease, installed 22 new std. rollers in each end, followed by the thrustwasher that goes on the sprocket side of the gear (Photo 8), and slid the shaft through. I was surprised to find a slightly sloppy t, despite the three dimensions having added up to a clearance of .001”. I tried the .0004-over rollers from Jim’s, and they snugged things up nicely. All 22 of the .0004+ rollers t inside the gear.

• Next up is measuring countershaft-gear endplay. With the retainer rings, bearings, and thrust washer in place, followed by the countershaft endplay spacer shown in Photo 9, I lowered the countershaft gear into the case and slid the shaft through, using grease to hold the spacer in place. Mine stayed put, but if you run into problems, try weaseling the spacer between the gear and case when the shaft’s halfway through. Then push the shaft home, install and tighten the nut, pull the gear out from the spacer as far as possible, and measure the clearance between the two with a feeler gauge as shown in Photo 10. Endplay spacers are available in .074, .078, .082, .085, .090, .095, and 100” thicknesses. My endplay was .010” with the existing .095” spacer, exactly in the middle of the .008-.012” range called for in the manual. I’ve been told that .008-.009” is too tight and will blue the spacer. 

• With endplay set, lube the 1st and 2nd gear bushings from the Jim’s kit with whatever lubricant you use in the transmission, place them inside the gears, remove the countershaft and gear from the case, and trial-fit the gears on the countershaft gear. The bushings should oat inside the gears and turn easily, but with no wobble, and the assemblies should spin freely on the countershaft gear. Remembering the bearing retainer rings, slide second gear onto the shaft and install the lock ring, then the shifter clutch, and finally low gear. The retainer rings seat against internal snap rings. You shouldn’t need to replace the snap rings in a rebuild, but you’ll find new ones in the Jim’s kit if you do. In case of confusion about which gear’s which, second has the larger i.d. 

• Keeping the endplay spacer in place is the only challenge in installing the countershaft and gear cluster. If it slips and blocks the opening in the case, you should be able to line it back up with a screwdriver inserted through the opening. Don’t forget to bend the lockwasher ears after you tighten the countershaft nut. I use blue Loctite too. I’ve found more than one lockwasher with a tab broken off, although probably because the last guy reused the old one.

• The shift forks and shaft come next, and a quick check may be all that’s needed. Insert the shaft through the case and forks, then install the top hats and position the forks on the shaft so both shifter clutches are dead center between the two gears they engage, as confirmed with a feeler gauge. Coat the shaft with heavy grease to help keep the forks in place, engage neutral in the lid, and lower it onto the transmission while looking underneath to be sure the slots in the shifter drum engage the top hats. Work the lid down over the dowels until it’s at on the case, then work it carefully back off to avoid disturbing the forks, and check the clutches. If they’re still centered between the gears, +/- .010”, you’re good to go- if you didn’t move the forks, and that’s a big “if” since the lid should be a press- t on the case and hard to get off. If one or both of the forks/clutches is off-center, you’ll need to dismantle the fork assembly and re- shim the fork to put it where it belongs in the carrier. Rearranging the existing shims sometimes works, or you may need more. I got by with a bag of .015’s, but a bag of .005’s would have saved me the trouble of miking all my old shims to find a few skinny ones. (Racers often shim the shift forks closer to second than first and closer to third than fourth, but for all-around street use it’s hard to go wrong placing them dead center.)

• A shift-fork gauge is all but mandatory for centering the forks accurately, no doubt about it. Press it onto the lid, shift the lid into first or second gear, align the channel in the gauge block with the long slot on the drive side of the drum, slide the 3/8” alignment rod through the block until it bottoms in the drum, and tighten the thumbscrew to secure the block. (See Photo 11.) Then remove the rod, shift the lid past third into high, align the channel of the other block with the long slot on the kicker side of the drum, slide the rod through the block, all the way into the drum, and tighten the remaining thumbscrew. Remove the gauge and install it on the transmission case and shifter forks with the top hats in place, as shown in Photo 12. If the shifter clutches aren’t dead center between their respective gears with the gauge in place, realign them as explained above. Making notes of all measurements and the original shim arrangements will save trouble in the event of a SNAFU.

• If you can’t borrow a gauge or scrape up the $100 for one and need to re-shim the forks, try this. Paint the shift-fork shaft with Dykem layout dye, reinstall the shaft and forks in the case, and center the forks and clutches as explained above. Taking extreme care not to move the forks, scribe lines around each side of the fork carriers to indicate the ideal position of the shift forks on the shaft. Remembering the top hats, install the lid in neutral and move the forks to accommodate the slots in the drum as necessary. Carefully remove the lid so as not to disturb the forks. Then scribe new lines, measure the gap between the original lines and the new ones, and re-shim the forks that amount to put them where they belong. Removing the lid without disturbing the forks will be a challenge, so take my word- a gauge is better.

• With the forks shimmed correctly and a new seal on the shift-fork shaft, lube it, pass it through the case and forks, and secure it with the retainer screw on the kicker side of the top gasket surface.

• As far as the lid goes, replacing the pawl and pawl carrier springs, along with the pawls if the sharp ends are rounded at all, would be wise- especially if your motorcycle has aluminum primaries, since they complicate transmission access. Before putting the transmission back in the bike, be sure you can engage all four gears while turning the main shaft, and that there are no odd noises. FabKevin makes an adapter for spinning the mainshaft with an electric drill- a great tool for finding leaks and shifting problems before installation. Remember to re ll the transmission with your lube of preference. I give everything a good soaking before putting the lid on, too.

Tom Johnson
Tom Johnson

It’s been fun. I do love those old loose roller four-speeds.

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