Re: 1970 M-20 Issue
To check reverse fork engagement with reverse gear, you could remove the speedometer cable/fitting/gear and put a borescope (android camera) into the hole to look at the fork & reverse gear. Corvette speedometer hole is on right hand side and points toward top of output shaft so you should have space. Use aluminum tubing (home depot) big enough for borescope but small enough to fit in hole to help position borescope. Shift the reverse lever and see if the reverse gear is moving or not and engaged with shift fork.
1. Yes, agree. But you should not be turning the cluster gear and input, 1st, 2nd, & 3rd. Could remove filler plug and see inside main section when you turn output shaft. Also, reverse gear is a helical gear so if driven by engine, it would thrust one way, if driven by yoke spinning in normal direction, it would thrust other way. Also, reverse gear on output shaft has a spiral spline, not straight spline so this would also move reverse gear axially spinning one direction and opposite direction spinning other direction.
2. With all gears truly in neutral and clutch engaged, the output shaft should turn freely. All gears stationary (input, 1st, 2nd, 3rd, cluster, reverse), locked by input gear thru engaged clutch. As you identify, your output shaft does not spin freely so something is engaged. Could check 1st/2nd & 3rd/4th slider position & reverse thru filler plug and speedometer port using borescope.
3. So when shifted to reverse, no movement of output shaft, obviously, this is not kosher. Could be that reverse gear is disengaging when driven by engine side but reverse gear is engaging when driven by yoke side if reverse gear/fork not engaged. On item 2, did you spin it both directions?
To check reverse fork engagement with reverse gear, you could remove the speedometer cable/fitting/gear and put a borescope (android camera) into the hole to look at the fork & reverse gear. Corvette speedometer hole is on right hand side and points toward top of output shaft so you should have space. Use aluminum tubing (home depot) big enough for borescope but small enough to fit in hole to help position borescope. Shift the reverse lever and see if the reverse gear is moving or not and engaged with shift fork.
1. Yes, agree. But you should not be turning the cluster gear and input, 1st, 2nd, & 3rd. Could remove filler plug and see inside main section when you turn output shaft. Also, reverse gear is a helical gear so if driven by engine, it would thrust one way, if driven by yoke spinning in normal direction, it would thrust other way. Also, reverse gear on output shaft has a spiral spline, not straight spline so this would also move reverse gear axially spinning one direction and opposite direction spinning other direction.
2. With all gears truly in neutral and clutch engaged, the output shaft should turn freely. All gears stationary (input, 1st, 2nd, 3rd, cluster, reverse), locked by input gear thru engaged clutch. As you identify, your output shaft does not spin freely so something is engaged. Could check 1st/2nd & 3rd/4th slider position & reverse thru filler plug and speedometer port using borescope.
3. So when shifted to reverse, no movement of output shaft, obviously, this is not kosher. Could be that reverse gear is disengaging when driven by engine side but reverse gear is engaging when driven by yoke side if reverse gear/fork not engaged. On item 2, did you spin it both directions?
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