I have a upright piano and its sustain pedal did not work for a long time (you have to press very hard to get a bit of sustain), and the cause is found to be three loose screws that fix the pedal in place, which allows it to move without moving the vertical component. After I replaced these screws with much longer screws, the sustain pedal works perfectly. However, after some time (couple months), the effect of sustain becomes uneven across the keyboard. Basically, C5 is completely sustained (maximum effect) just with a light touch on pedal. On the other hand, C3 is barely sustained with full pedal. What are some possible cause of this problem? Can I fix it myself without specialized tools?
I had this problem before with my piano, which is very old and sustained the notes way too long, as well as the sustain varying across the keys.
The mechanism in which the hammers are attached to is attached to the soundboard at the back of the piano case, usually using a big knob that can turn. Although I'm not sure whether it is like this on other pianos, my problem was that the knob was not screwed tightly enough.
Hope this helps.
Take the front panel off and look at the dampers as you depress the pedal. It seems that the ones at the treble end are lifting fully away from the strings, the ones at the bass end are not. Maybe the entire action can be aligned better by following @MrNiver632's suggestion above. Maybe the pedal effect can be increased by adjusting a nut on the screwed rod at the actual pedal.
You can't cause much damage by attempting these two adjustments! If they don't work, however, I suggest you call in a piano technician.