The transmission on this 1983 R80ST is serial number Z 078854. According to Robert Fleischer’s article on transmissions, the range of transmission serial numbers in 1983 was from Z 074700 to Z 084299, so mine is the original transmission as it is within the range for 1983.
Here is a short video that summarizes how I do this work.
VIDEO: 1983 R80ST Remove Transmission
What To Remove Before Removing The Transmission
In preparation for removing the transmission, I removed the battery and battery box; the swing arm, rear drive and monoshock; and the air box and pulse air components.
Drain The Transmission Gear Oil
I remove the transmission fill plug and the drain plug. Unfortunately water comes out with a very thick goo of gear lube. The speedometer cable is missing from the bushing on the rear of the transmission. Although some cloth was put in the hole in the bushing, since the bike did sit outside, water got into the transmission through that bushing.
Remove Clutch Throw-out Arm
On the back of the transmission is the throw-out arm that works the clutch. I need to pull the transmission backward off the clutch splines to remove it so I need all the clearance between the transmission and the frame I can get. The clutch throw-out arm on the back of my transmission is caked with hardened gear lube and dirt so I clean it with engine cleaner before I start work. It is likely the seal inside the transmission input shaft (part# 23 12 1 242 522) that is supposed to seal the push rod was leaking.
On the 1983 transmission, the throw-out arm is secured with a bolt, nut and washer. It pivots in a boss cast onto the back cover of the transmission.
I remove the 6 mm bolt, nut and washer to release the clutch throw-out arm from the boss.
An adjusting bolt on the clutch throw-out arm fits into a rubber bellows. The bolt is used to adjust the free play of the clutch lever on the handlebar. The adjusting bolt presses on a bearing assembly that in turn presses on the clutch throw-out rod. The clutch throw-out rod presses on the center of the clutch diaphragm spring to separate the clutch plate from the clutch disk. I remove the throw-out arm adjusting bolt from the rubber bellows.
The rubber bellows is secured by a metal strap that I remove. Under the bellows is the clutch return spring. Mine is bent so I will replace it
I use a magnet to remove the throw-out bearing cup and the ball bearing race under it. Since the clutch throw-out rod rotates, the bearing allows it to do so with out damage to the stationary throw-out arm.
Remove Transmission Foot Shift Mechanism
The foot shift mechanism consists of an adjustable linkage that attaches to the transmission shift lever and the foot shifter.
The foot shifter is attached to the frame with a pivot bolt.
The linkage has a cup on each end. The transmission shift lever and the foot shifter have a bolt with a ball on the end. The cup fits over the ball and is retained with a wire clip.
I remove the wire retaining clip from the cup on the transmission shift lever ball with a screw driver. The wire pivots out of it’s groove and then I pull it down out of the small holes drilled into the side of the cup on the linkage.
I use a screwdriver to pry the cup off the ball.
Next I remove the pivot bolt so I can access the other end of the adjustable shift linkage that is attached to the back of the foot shifter.
I remove the other end of the adjustable shift linkage from the back of the foot shifter in the same way I removed the adjustable shift linkage from the transmission shift lever.
Remove Transmission Mounting Bolts
I already removed the upper left bolt and upper right nut when I removed the air box.
I remove the bottom left Allen bolt and wave washer with a cut-down 6 mm Allen wrench as its a tight fit between the bolt and the boss for the transmission shift lever.
The bottom right transmission Allen bolt goes through the engine bell housing and is secured by a nut and wave washer. There is a flat washer under the bolt head
Remove Transmission From The Frame
The transmission is loose from the engine. I pull it back and expose the clutch push rod. I push the clutch push rod back into the transmission and pull it out of the back of the transmission. Then I remove the transmission through the left side of the frame.
The transmission input shaft has splines that mate with splines on the clutch plate. These need to be lubricated with a molybdenum disulfide sticky grease–Honda Moly 60, which is no longer available, or Honda Moly 77–to ensure the splines move smoothly when the clutch engages.
Here’s what the bike looks like now. I just have to remove the engine from the frame. To make that a bit easier, I’ll remove the top end of the engine first to reduce the weight.
2022-01-26 Added missing YouTube summary video link.