1.
I would start by
checking and replacing the
transmission mount AND the
engine mount as well (especially focus on the left side engine mount).
There`s a chance that these wear-item parts of the unit reached a point where the overall alignment is not 'comfortable' anymore for the tranny, the engine, or both. Bad mounts can make shifting into 2nd/1st very hard or "impossible" at times.
I`ve been there multiple times when my mounts were badly worn, sometimes invisible though, and I could slowly, gradually feel the tranny not wanting to be shifted into 2nd, more and more as months passed by, until I finally installed a new tranny mount/Left engine mount/or both.
BTW. I never, repeat,
NEVER shift into 1st gear
when the car is still rolling. I put the shifter into 1st gear only after a complete stop. This may sound as crazy as it sounds but this is how I do it, maybe it helps, (maybe it doesnt help) to reduce unnecessary wear in my m46 tranny.
Plus, the 1st gear is simply way too short anyways.. and I hate to hear when/if the engine doesnt like the 1st gear coming from a rolling stop.
Indeed, my shifting troubles , started either in 1st or in 2nd gear, usually when I slowed down and tried selecting 2nd or 1st gear at a stop sign or traffic light... appeared most of the time if the car was still rolling.
Multiple times these issues disappeared right after I installed a new tranny mount but often my car wanted the engine mount to get replaced as well.
2.
Also, check the
fluid level in the tranny but I doubt that it is that what`s causing your shifting troubles this time.
Although, my tranny once had only HALF of the fluid that was supposed to be in there but it did not cause symptoms you were describing.
Adding fluid definitely helped with the smoothness of the gears, especially when I replaced all of the fluid (and even topped it up above the high mark, just by a little).
3.
Other times, my shifting (into 1st or 2nd) troubles were also caused by extremely worn
shifter bushings which really made sense to me when I went under the car to inspect them. They looked shot. Immediately after adding those two little plastic craps, shifting gears felt 'night-and-day' and shifter slop disappeared. It used to wobble a lot, even at idle.
make sure to not strip the hex-head down there. Easy, fun project with good results when/if they happen to be worn, definitely worth a check, and won`t hurt the check...
These 3 things come to my mind as things to check, because it literally costs nothing to check on them. Parts are cheap and fixing these 3 seems to be a very easy thing to do even if you only have just a few hours to work on your car.
What is the history of your car, the tranny, and, do you 'gently abuse it" sometimes?
Let`s hope that your shifting troubles are not caused by an internal failure and wear. These m46 trannies are very durable if cared for. Usually they do last at least as long as the engines do.
There are exceptions
Use the proper fluid if you decide to change it.
Report back to us after you found the source of the problem!
4.
Small
adjustment is also possible near/under the
shifter, done from inside the car but it is mainly for making a comfy 'track' for the shifter (when I adjusted here it took the 1st gear better, especially the Reverse--- the bracket was limiting the shifter from reaching out
enough to the left side towards the Reverse gear)
I would
not do this unless very very obviously necessary. Maybe see all else first and try to figure it out without thinking
this adjustment will make any difference.
5.
Clutch cable adjustment
See the clutch cable unit under the car, it is easy to figure out what to do. As the clutch wears, you may need to readjust the cable here.
Questions to ask from yourself;
Have your shifting problem developed somewhat slowly and
gradually (throughout at least a couple of weeks of driving),
OR is it something very `new` to you?
How does the clutch pedal feel compared to how it used to feel? etc
Any changes in that, anything to mention about how and 'where' it engages?
Does it ever 'throw out' 1st or 2nd gear sometimes? Once engaged, does it hold it really well even at higher revs in a moving car? etc.
Without overthinking much, I would strictly focus on 1,2,3,5.
My clutch pedal used to feel kind of soft and only engaged at the very bottom of the floor (at the very end of the pedal`s path) so I never really liked it but it is what it is, cable adjustment somewhat helped, it improved a slight bit.
If you cant figure out what is grinding, do not use the 1st gear at all. Grinding has no benefits