Grinding to 1st gear and reverse from Stop

I have been having this intermittent issue where my car grinds into 1st gear and reverse from stop. L6 motor a745 trans. I researched this when it started happening after a new clutch install and it lead me to overhaul the entire shift linkage. The issue started again after the overhaul. It usually starts happening after the car has been driven for a while at high speeds.

After a long drive today, it started to happen again today. When I got home I thought about it for a bit and I remembered that once after a clutch cable change on my triumph I forgot to take the slack in on the cable adjuster and the bike was grinding like hell. So I got under the car and  tightened the clutch adjuster a few turns and the car was shifting like butter. Is a loose clutch adjustment really the cause of this? Or is there another issue I should be addressing?

If the loose clutch was the issue? Do I periodically need to tighten the clutch adjuster as the clutch wears? Thanks in advance for any help.

I suspect your loose clutch linkage wasn't disengaging your clutch completely, especially when warm. Unless your clutch delaminates (comes apart to the point of getting thicker), your clutch adjustment should need to go the other way. Is your linkage vibrating loose by chance?
JM2C

In big-truck roadranger transmissions, the clutch setup employs a "clutch brake" to stop the input shaft from turning so that the trans can be put in gear because the multi-disc clutches on big truck drag enough that the input shaft would not stop turning otherwise....So here is the trick we use on big trucks when the clutch-brake is worn out.....Start the engine in gear and move between gears without ever letting the clutch out IN NEUTRAL.... result: no grinding!
The clutch on a personal sized vehicle is a single disc and is designed to fully disengage enough that the input shaft will not "freewheel" in neutral while disengaged..... The linkage only needs very slight slack as evidence of full engagement so that it gets the maximum pull towards disengagement...
If you are fully disengaged and the clutch is dragging, then there is something wrong with the clutch assembly (probably the pressure plate assy if there are no strange sounds)……. If your disc linings previously got oiled with trans fluid, they can be very "grabby" after a few friction cycles.... Always replace a disc that's been "oiled" (soiled)….

The basic tests are push down on the clutch pedal with your finger, it should go down about an inch,,,,










Next test is to pull back on the clutch arm,,,,it should move back about an 1/8 of an inch,,,,not be too tight, not be too loose,,,,you could check if your van is getting too groovy,,,,,the shift rods, carburetor and clutch linkage are wearing grooves in their connections,,,,,