My trans. will not shift into reverse while engine is running without grinding. Have adjusted the clutch and tried going from a forward gear to reverse as suggested in the owners manual.
Neither of which has helped. With engine shut off it will slip right into reverse with no problem.
Any ideas on what the problem could be are appreciated. Thanks.

Dark Red 77,
If the gears are grinding into reverse, then that is telling me that there is still power being transmitted through the transmission. So if your clutch is properly adjusted, try some of these simple troubleshooting checks:

1) Check clutch "spin down" time: With the engine idling, trans. in neutral, foot off the clutch pedal. Proceed to depressing the clutch pedal down. Wait several seconds and shift trans into reverse. There should be no grinding. If it grinds then there is good chance that there is a problem in the clutch disc or pressure plate.

2) Check clutch release: With the parking brake on or wheels "chocked," engine running, depress the clutch pedal down to approx. 1/2" from the floor. Then shift from 1st to Rev. several times. If the shifting is hard or it grinds, the clutch or press. plate is possibly failing.

3) Check all pivot points and bushings from the top of the clutch pedal, to the "zee bar," to the ball stud on the engine, and throwout lever for excessive free play or binding.

Even on my '81 (w/new Richmond Super T10) and a Centerforce clutch unit. Mine is sometimes hard to shift from 1st to Rev. That is due to my pivot bushings are starting to wear out.
How many miles are on your drivetrain and car?
Good Luck! And I hope this info is helpful to you and others.
STW Sarge

Sarge, Thanks for the excellent ideas. Could another possile cause be a worn shifter?

Dark Red 77, It is possible that worn shifter bushings may give you some trouble. That maybe another area to check. I didn't think of that one.
Sounds like a good winter time project to do on the car.
Let us know "down the road" if you find a definite problem. Sarge

Found the problem. One tab on clutch fork was broken off. So the throwout bearing wasn`t releasing the clutch all the way. Ordered clutch kit, fork, fork ball stud, and boot from ZIP today. Shifter still looks good so I`m gonna stay with that for now. Once again thanks for all of the input and ideas.

Good deal! (that you found the problem) To bad it is a slightly costly fix. But when it's all done, it will be well worth it.

Sarge