Does anyone know where I can find information on adjusting the bridge on my upright bass? I want to lower the action.

My recommendation would be to find a good luthier. It's worth it.

I want to adjust the action on my bass too. What exactly will a luthier do? - will he "just shave a bit from the top o the bridge"
The reason I ask is my grandfather repaired a horrible split on the top of my bass perfectly and i think he could sort my bridge out too. (he's a carpenter)

It's not brain surgery to alter a bridge, but it requires care to avoid complications.

The one thing to consider is that if you remove the bridge, it's possible that your soundpost will fall -- are you prepared to put it back, and in the right place??

To try and avoid that complication, lay the bass on it's back (with the back supported, and the headstock not supporting the body-- a dining room table or large couch may do (with the neck hanging off the end). You may even go so far as to stick another bridge or substitute to put some pressue on the belly to help keep the soundpost in place.

If the present bridge already perfectly matches the contour of your bass' belly, then yes, it is the top that will get the trim. If it does not fit the belly, well, that's a problem for another message.

DON'T TAKE TOO MUCH OFF!!! It is amazing how much less than a 1/4" will lower the action -- OK - bassists out there who have shaved their bridge resulting in a too low string height, raise your hands (Bob's hand goes up). Be conservative.

Before the cut put pencil marks at the slots, perpendicular to the bridge attitude. Draw the intended cut with a pencil mark, taking care to maintain the curvature that matches the fingerboard -- or, if it was off, correcting the curve.

After the cut, notch the new string positions, then sand the fingerboard (top) side of the bridge to curve in towards the top- smooth, but leave the tailpiece (bottom) side at 90 degrees (this helps prevent warp). Finish making neat, round slots to perfectly accommodate the strings' widths.

If I can make an observation, I often find basses with the string height at the nut being far too high. Changing that isn't brain surgery either. Just be patient and observe the rule that you can always take more wood off, but putting it back is problematic. Investing in a set of needle files at Home Depot ($8) or Sears ($16) is worthwhile.

One question about making new notches in the bridge for the strings: What is the standard value for the distance between the strings, measured from center to center along the curvature of the bridge? Or what references should be used when positioning strings? Fingerboard width? This is tricky to experiment with...

Thanks for any advices.

Erik

Erik,
somewhere in Bob´s link page there is a link to general bass measurements ( tried to find it to put the link right here but couldn´t ). There are all the measures including string spacing in the saddle and the bridge.
If I can remember right, the distance between strings measured from inside is 24,5 mm ( at least I think mine is ).
That´s easy to measure when you mark the slots to the top.
Trickier thing is WHERE you mark them, and all I could possibly come up with, after thinking it for a while, was to place the bridge directly to the center of the f-holes, have someone to hold it in place an then using a thread between the saddle and the bridge ( the strings were off ) and judging only with my eyes I marked the E-string slot. After that I measured the other string slots.
BTW, fingerboard width varies, and in addition to this, if you have a bewel under the E-string, you have to be careful when positioning the E-string and the A-string.

Bob,
what I have learned about the "falling soundpost case", is
that if the soundpost falls down when you loosen the strings, it was too loose in the beginning, and playing the bass would have caused it to wander out of its place anyway.

Thanks Arto, I have a print-out of that list of measures, and it says string spacing 85mm, which gives about 28mm intervals. My strings are now about 25mm apart measured center to center. I don't have a problem with the existing string spacing, but larger intervals might make it easier to bow as the G and E strings would then also be lowered a bit...?

There is enough space to the edges of the fingerboard (no bevel), and I can also take a bit more off the bridge top. So if I know myself right I won't be able to resist trying it out :-).

Erik

Good luck, Erik and remember that you only can loose the price of a new bridge, as well as the work to setup the new one ;-) But that´s how you learn, don´t you think?
If you don´t want to lower the G & E, you can change the curvature of the bridge top so that they will not come too low. Keep in mind ( if your fingerboard is very flat ) that you have to leave curvature enough to be able to bow...
Everything you do affects to everything ( am I tryin´ to be filosofical of what? ).

I am in the same boat, but I think I am just gonna buy an adjustable bridge. Bob?