I have a m-21 trans and when i stick the yoke all the way in untill it stops i have about 3/8in of shaft showing. Then i pull it out to install the drive shaft and it comes out 1in. The total amount of the shaft showing is 1 3/8in. Is this to far out of the tailshaft? Its 1in out from when it was all the way in. I know ppl say 3/4 to 1in is good, but is that total, or from when you stick it all the way in till it stops and then pull it out the 3/4 or 1in. Any help would be appriciated, i need to know if i need a new driveshaft or not as soon as possible.

thanks,

Lucky,
Let me explain some driveline geometry first. If you had the car jacked up and placed on stands---------------WITH THE REAR STANDS UNDER THE FRAME, AND NOT UNDER THE AXLE HOUSING, then the axle housing would hang down to its lowest point of up-down travel. At this lowest point of travel, the yoke will be pulled out from the rear of the tranny the farthest distance. Then, when the housing is raised to its highest level, the yoke will go into the tranny the farthest.
Inside of the tranny tail housing is a bushing which the yoke rides in. Use something to insert into the tail housing (piece of wire, etc) with a hook on the end. Use this to reach into the tail housing to locate the inside edge of the bushing so that you can determine where where the inside edge of the bushing is in relation to the end of the tail housing. With the yoke at the position where it will be pulled out from the tranny at its farthest travel, the end of the yoke still needs to be beyond the inside edge of the bushing. If you determine that it will be in beyond the inside edge of the bushing, they you will be OK. Of course, you do not want the end of the yoke to be just right at the edge of the bushing, but if it is at least 1/2in or so past it, that would be best.