Action Problem

[Definitely]

Just picked up my old bass for the first time in a while, and noticed something that was always there but I never realized until now. The neck has a slight forward bow, and so the action is highest at the first and last frets and lowest in the middle. If I try turning the truss rod and lowering the middle it makes it all too high, any advice on what to do? I know this probably has a simple solution (I'd like to do it myself, instead of getting a pro setup) but I'm new to setups and repairs. Thanks in advance!

[lowendgenerator]

Sounds like you're turning it too much. Small increments, 1/8th of a turn, have noticeable effects on some basses. Remove the guesswork, and get a nice long straight edge. Then you can measure the relief under tension and know how much you're adjusting.

[Foamy]

Make sure you're tuned so the strings have proper tension (but loosen them briefly for trussrod adjustments)
When you made your attempt, you actually set the relief going in the right direction - that's good - you have the adjustability.
Fret at the first fret and around 15 or so, then look sideways at the neck to see how much bow (you have to say "relief" from now on) you have. I like to have it where a single business card can slide out, but 2 business cards will be held when you fret at 1 and 1 15.
Now the relief is set!
The rest is set by the bridge and/or saddles. They are used to lower the "action". That gets tricky. Too low, you can get buzz. Some buzz may be OK. I don't mind a teeny buzz because it doesn't get to the amp. But that's very subjective. Too high, and the bass is a PITA to play.
I start low and raise until it's acceptable.
The nut is the last thing. It ONLY sets action for open strings. Granted, if it is horribly high, it will make fretting the low frets a pain as well. BUt the nut is almost certainly not your problem.
So.....your truss rod works. Good news!
Set the relief as I stated above, then lower the saddles.
If, once you lower the saddles, the action is still too high - do you have a bolt on neck?
You can consider shimming the neck. Very common, very easy, very effective.
You're in good shape - go fix it!

[john grey]

Originally Posted by lowendgenerator

Sounds like you're turning it too much. Small increments, 1/8th of a turn, have noticeable effects on some basses. Remove the guesswork, and get a nice long straight edge. Then you can measure the relief under tension and know how much you're adjusting.

+1

Too often people crank that truss-rod way too much. In changing weather such as Winter it would be a smart move to be very conservative in alterations such as that. It's also a very good idea to subtly mark where you began from.

A great deal depends on the neck construction, strings, tuning, and fret design or problems. The instrument is a "system" of several issues combined to yield a comfortable result.
There MIGHT be instances where truss-rod adjustment ends up being over a 1/4" but it's not a good idea to crank the thing in one sitting. Frets also can be subject to loosening from the tang & the result is a distinct un-even fret height. Approach the adjustment as a system of adjustment (mentally) before beginning to proceed physically.

[JLS]

Make sure you're tuned so the strings have proper tension (but loosen them briefly for trussrod adjustments)

No.

You do not loosen strings, to make trussrod adjustments.

[Foamy]

Originally Posted by JLS

No.

You do not loosen strings, to make trussrod adjustments.

Lot's of discussion about this - both ways.
If ya don't know what you're doing, then why not err on the side of caution?
What is wrong with?
Taking tension off the neck?
Making a small adjustment?
Tuning again?

[lowendgenerator]

Originally Posted by JLS

No.

You do not loosen strings, to make trussrod adjustments.

Why not? Adjusting the truss rod under tension puts undue stress on the moving parts, leading to chewed up truss nuts, stripped threads and broken rods. Slacking the strings for a minute will not harm anything.

[darius8]

I agree, adjusting the truss rod with LESS tension makes it easier to loosen/tighten and to prevent stripping the hex nut.

[Ric5]

Originally Posted by Definitely

Just picked up my old bass for the first time in a while, and noticed something that was always there but I never realized until now. The neck has a slight forward bow, and so the action is highest at the first and last frets and lowest in the middle. If I try turning the truss rod and lowering the middle it makes it all too high, any advice on what to do? I know this probably has a simple solution (I'd like to do it myself, instead of getting a pro setup) but I'm new to setups and repairs. Thanks in advance!

The problem may be low humidity.

Keep the bass in a room with a humidifier. Try to get the humidity between 35% and 50%

[darius8]

Heres my opinion:

Originally Posted by Definitely

The neck has a slight forward bow, and so the action is highest at the first and last frets and lowest in the middle.

Up to here, it sounds like a back-bow

Originally Posted by Definitely

If I try turning the truss rod and lowering the middle it makes it all too high,

I think it's a back-bow and your truss rods needs to be loosened and your bridge saddles lowered,

[Definitely]

Alright, thanks for the advice everyone! I'll try it all as soon as I can and I appreciate the help!

[JLS]

Originally Posted by lowendgenerator

Why not? Adjusting the truss rod under tension puts undue stress on the moving parts, leading to chewed up truss nuts, stripped threads and broken rods. Slacking the strings for a minute will not harm anything.

Lot's of discussion about this - both ways.
If ya don't know what you're doing, then why not err on the side of caution?
What is wrong with?
Taking tension off the neck?
Making a small adjustment?
Tuning again?

I agree, adjusting the truss rod with LESS tension makes it easier to loosen/tighten and to prevent stripping the hex nut.

Sorry, I should have said: Pros don't loosen the strings, every time the trussrod is adjusted.

[Foamy]

Originally Posted by JLS

Sorry, I should have said: Pros don't loosen the strings, every time the trussrod is adjusted.

That was kind of rude.

[DeadHeadSF]

Consider this another vote in favor of loosening strings when making *large* truss rod adjustments. Ok, if it's just a little tweak 1/8 turn, no worries. But if you have a severe bow in the neck (as it appears the OP may have - don't know without seeing it), I would strongly recommend taking all tension off the neck, using a straightedge to do the major truss rod adjustment, then bring strings up to pitch and tweak 1/8 turns from there. This not only gives you a solid starting point (more-or-less straight neck with no tension) but, as others have mentioned, lessens the risk of damage to the truss rod or nut when making a large adjustment.

Just my $0.02, but I prefer to err on the side of caution as well.

[ksandvik]

Originally Posted by darius8

I agree, adjusting the truss rod with LESS tension makes it easier to loosen/tighten and to prevent stripping the hex nut.

Yes, I agree. A truss rod is a mechanical thing so why put additional pressure on it while adjusting it, i.e. loosen the strings while adjusting.

[warnergt]

Originally Posted by Definitely

...The neck has a slight forward bow, and so the action is highest at the first and last frets and lowest in the middle. If I try turning the truss rod and lowering the middle it makes it all too high, any advice on what to do?

Sounds to me like you need a bridge adjustment in addition
to the neck adjustment -- and every piece of advice here
seems to have missed that.

You merely have to follow the logical sequence in the correct
order, getting each bit right before moving on to the next. If
you find yourself jumping back and forth in the sequence
then you are doing it wrong. Follow this sequence:

Relief
Action
Intonation