In the last issue, we went through some of the steps necessary to keep your Big Twin, four-speed transmission shifting smoothly and staying oil tight. This time we'll deal with looking over the ratchet top for problems that would cause hard shifting or oil leaks, plus we'll show how to align or time the ratchet top to the gearbox. The gaskets we used came from the same gasket/seal set from last issue, which we bought from V-Twin. One of the keys we have found over the years to smooth shifting is careful assembly, double checking your clearances, and making sure all lock tabs are secure. But above all else, don't forget to put oil in. You won't believe how many people rebuild their transmissions, put them back in the bike, shim and align it to the engine, and then forget to fill them with oil. Don't be one of them.
Note: This article is a companion to last issue's article on fixing the oil seals and kicker covers. In the last photo we have not attached the kicker cover to the transmission; we usually save the kicker cover for last. We have included as much information as possible to fit on these pages, this information is meant to augment your service manual, and the service manual will have all the torque specifications you need.
The same 1975 Harley-Davidson four-speed ratchet top transmission from the Four Aces Cycle Supply project bike. | 
First thing to do before disassembly is to clean the outside of the transmission and drain the oil into a clean container. A can of spray degreaser liberally applied before removing the trans from the bike is the best start; once removed from the chassis, clean any dirt or grease from the outside so that you can examine the trans for any problems. We're using compressed air to clean the ratchet top screw so we won't round out the internal hex. | 
A complete inspection of the outside of the transmission revealed certain facts, such as a groove worn into the right front edge of the top (A), caused by braided, stainless steel oil line rubbing the softer aluminum. On later model transmissions, there is a serial number (B) stamped into the right front face of the case. This number is tied to the VIN number of the bike. |
Since our trans was so cruddy, we carefully loosened all of the ratchet top screws (two or three turns) and used the compressed air to blow away any dirt that was lingering under the screw heads. | 
We had to use a hunk of wood and a mallet to gently tap the ratchet top free of the transmission case. The last person who had the trans apart glued both sides of the top gasket, making it tough to remove. The top is connected to the case with two solid dowel pins; don't use a screwdriver to pry the top from the case. | 
Once the ratchet top has been removed, check the shift drum and the channels that move the shifter forks. Look for any deep groves or dings that would hamper the movement of the forks. |
After scraping the gasket from the ratchet top, we clamped the top in our bench vise between some soft jaws and removed the shift arm and cover. Once again, we cleaned the countersunk Allen screws internal hex before removing. | 
Next, we removed the six countersunk Allen screws that held the ratchet housing to the top. Five of the screws thread into the steel plate and the sixth screw (arrow) is a through hole with a nut underneath. | 
This is the heart of the ratchet mechanism: the pawl carrier (A) rotates on the gear shifter shaft (B) and the shift pawls (C) catch the groves in the shaft (B), turning the shift drum gear in either direction. The return springs (D) do just that-return the pawl carrier to the neutral position, ready for the next shift. |
We removed the return springs and found that they were broken. Next, we cleaned the entire cover again in the parts washer, and then followed with a spray of brake clean. We used a razor blade to remove the gasket from the gear shifter adapter plate. | 
A small rectangular stone with some 3-in-1 oil was used to smooth any dings or burrs on all of the gasket surfaces. A light touch is all that is needed here; you'll be able to tell when the surface is flat by observing the strokes of the stone giving a "flat or dull" finish to the aluminum. | 
One of the most overlooked components of the ratchet top is the shift drum detent (A). The detent is a spring-loaded wedge that holds the shift drum in position once it has rotated to a new gear selection. On the right side of the drum is a series of "valleys or cams" (B) that the detent rides in. As you shift, the drum rotates one of the cams and forces the detent against the spring in the detent bolt, then once the gear has been selected, the detent rides back into the valley, preventing the drum from further rotation. |
The detent bolt is threaded into the front of the ratchet top and secured with a lock ring. To remove, bend the lock tab back and unscrew the detent bolt. | 
To help the shifting of the transmission gears, the movement of the detent should also be smooth. We like to smooth out any scars on the "cams" of the shift drum allowing the detent to ride smoothly up and down the valleys as the drum is rotated. Here we're using a small 3M cylinder mounted to a die grinder to polish the end of the drum. | 
The detent itself is also polished; we used the same 3M cylinder to polish the tip of the detent and our cordless drill to spin the outside of the detent against a Scotch-Brite pad. We spun half the detent, then reversed it in the drill to polish the other end. |