I've owned my 4003 for around 9 years and someone else owned it for around 7 years before I bought it. I never made any adjustments as it was setup pretty well and in the 4 years I was gigging with it nothing much changed. However, since moving to the US around 5 years ago, the bass has seen much less action and has sat on the stand (alongside my 360) going through seasonal heat and humidity changes.

I first noticed that the bow on the 360 had increased and made the necessary adjustments to get it feeling right again. The 4003 had a similar increase in bow and when I popped the cover I found that the 2 truss rods looked very uneven (see pics). There doesn't seem to be any perceptible neck twist despite the many years in this state but that doesn't make it right.

In researching I've read that some folk just use the single rod for adjustment and tighten the other just enough to stop the rattle? The guy I bought the bass from had a tech who did his setup and I'm wondering if this is his doing?

I put 1/4 turn into each rod and that has brought things back to an "acceptable" bow but the uneven setup still makes me uneasy.

Any useful comment?

It is my understanding that both rods are designed to work together to keep the neck in spec, not "one to tighten and the other to stop rattling." Because of the differences in wood grain, although generally straight, density, string brand/model/gauge, etc., it is not uncommon when setting the rods that one may be set slightly different than the other. This is all normal, so long as both are tightened, and you check both the G side and the E side to make sure one or the other of the rods doesn't need a further adjustment. And remember they are interactive, so that if one side is straight and the other is bowed, you might need to relax the straight side rod a quarter turn then tighten the bowed side rod so the added force when combined doesn't cause overbow.

Others please chime in and elaborate if I have missed anything.

The whole point of having two truss rods is so that the sides can be separately adjusted. This is absolutely normal and as intended.

Thanks for the reassurance.

I understand the need for individual adjustment but was more worried by the differential between the two. Reading about the "one to tighten and one to stop it rattling" scenario didn't go far to ease my concerns.

Nice to hear from folk who know the score; straight from the horse's mouth so to speak.