Hey everyone, I am rebuilding a 1991 R100 RT transmission myself this winter and wanted to enlist the help of the form. With 89k miles it developed a skip in first gear. Within 200 miles from the first occurrence that skip deteriorated into the eventual loss of use of first gear entirely. When shifting into first gear the lever moved smoothly and seemed to engage but when letting out the clutch a terrible chattering sound comes from the transmission. All the other gears were working 100% with no slippage, skipping or chattering.
I have opened the gearbox and removed the innards to find no obvious damage or excessive wear. Shift forks are straight and in great condition with no wear on top or bottom surface. No broken teeth. No broken dogs, although a few of the corners of the 4th gear dogs are mildly rounded (this is the splined gear that engages with 1st gear to make the bike move in first). The only issue I have seen is that there is excessive play in 1st gear itself and there is about 0.98mm of space between 1st gear and the washers on either side of it. It seems as though the rear bearing on the output shaft crept backwards to create this gap. With that much of a gap it's possible for 1st gear to cock at a slight angle which could be preventing the 4th gear dogs from fully engaging. Thereby producing that chattering sound as the dogs skip by the windows cast in 1st gear.
These things are kind of difficult to describe in words but I'd really appreciate any feedback on this theory or anyone's similar experiences. I've done a lot of research and this does not seem to be a common problem. The only root cause I could imagine is improper shimming when the transmission was professionally rebuilt 2 years ago. The problem at that time was a failing front bearing on the output shaft.
I have opened the gearbox and removed the innards to find no obvious damage or excessive wear. Shift forks are straight and in great condition with no wear on top or bottom surface. No broken teeth. No broken dogs, although a few of the corners of the 4th gear dogs are mildly rounded (this is the splined gear that engages with 1st gear to make the bike move in first). The only issue I have seen is that there is excessive play in 1st gear itself and there is about 0.98mm of space between 1st gear and the washers on either side of it. It seems as though the rear bearing on the output shaft crept backwards to create this gap. With that much of a gap it's possible for 1st gear to cock at a slight angle which could be preventing the 4th gear dogs from fully engaging. Thereby producing that chattering sound as the dogs skip by the windows cast in 1st gear.
These things are kind of difficult to describe in words but I'd really appreciate any feedback on this theory or anyone's similar experiences. I've done a lot of research and this does not seem to be a common problem. The only root cause I could imagine is improper shimming when the transmission was professionally rebuilt 2 years ago. The problem at that time was a failing front bearing on the output shaft.
