1974 Precision Can o'Worms (Knob Adventures)

Discussion in 'Hardware, Setup & Repair [BG]' started by bmusic, Jun 16, 2020.

  1. bmusic

    bmusic Supporting Member

    Oct 22, 2017
    Los Angeles
    So I thought I would put some different knobs on the 1974 P bass that I got on
    Reverb not too long ago. The brass ones that it came with are sorta cool, but not quite the right match in terms of color or accuracy (the dome, the hex screws).

    Version 2.jpg

    So I bought some Fender flat top knobs and aged them to match the distressed body—first with vinegar, then with ammonia, and then (when those two failed to deliver results) with muriatic acid.


    Finally they were ready, and I took off the brass knobs. Surprise, surprise! The first thing I noticed were the split shafts, which (I’ve just come to discover) are not factory spec (and technically not meant to work with screw-mounted knobs). So these clearly were replaced at some point. Then, when I went ahead and attempted to put on my new knobs anyway, I discovered that one of the shafts is larger—and the threaded part goes way through the pickguard. The knob won’t sit down on the pickguard.


    No worries, right?—I’ll just lower it and mount in place with a second nut. So I removed the nuts and washers, only to find that the pot shaft appears to be screwed into the pickguard rather than mounted with the nut tension. I can wobble it a little bit side to side, but I can’t push it through. So now it becomes a question of “Is the knob idea worth desoldering this pot, unscrewing it and mounting it in a more correct manner? And then the obligatory follow-up question: “As long as I’m at it, should I replace both pots with solid shafts?” It’s not like there’s some degree of vintage accuracy I am trying to protect. The bass has clearly had a lot of work done; I would say only the wood, truss rod, tuners and bridge look original. (And maybe the pickguard screws?)

    Bottom line: the bass plays and sounds fine, and I'm not on a mission to restore in any sense other than making the knobs a little original-ish. So can I just bore out some of the bottom of my knob (on the right) so that it will fit over the threaded part of the shaft like the brass knob (on the left) does?


    And lastly, now that I've become aware of the undersized shaft on the volume pot, I'd love to find a way to make the knob not wobble in an elliptical orbit as I turn it. Like, can you put a sleeve over the smaller shaft and make it into a larger one?
  2. Honestly, quit fighting with the wrong parts. Just replace the pots with a couple of CTS 250k ohm audio taper solid shaft pots along with a relatively period-correct ceramic disc capacitor. Then everything will fit and operate the way it should for less than $20 in parts and 10 minutes with the soldering iron.

    As a bonus, you can probably get decent money for those solid brass knobs with that excellent vintage patina.
  3. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician - Retired
  4. unresolved


    Sep 15, 2015
    SF Bay Area
    Matt Liebenau and bmusic like this.
  5. Slater

    Slater Leave that thing alone.

    Apr 17, 2000
    The Great Lakes State
    As suggested, I would install the proper solid shaft pots just to have the piece of mind of a job done right.
    funkinbottom likes this.
  6. Moral of this tale: leave well enough alone. I think the brass knobs actually look pretty good and to me match the overall wear and vibe of the bass.

    2nd choice , if you’re so inclined, replace pots and caps and use your new knobs.

    I’ve learned for myself if it ain’t broke don’t fix it.
    bmusic likes this.
  7. sissy kathy

    sissy kathy Back to Bass-ics Gold Supporting Member

    Apr 21, 2014
    Arbutus, MD
    You don't need to do any soldering to get the pot out of the pickguard. Take the other pot and output jack out. Now the only thing attached to the pickguard is the problem pot. You can now spin the pickguard to get the pot out. File or ream the hole, add a nut and put it all back together.
  8. bmusic

    bmusic Supporting Member

    Oct 22, 2017
    Los Angeles
    Brilliant. This is exactly the kind of Beautiful Mind solution I was hoping I would come up with, but didn’t. Thank you!!
    sissy kathy likes this.
  9. Lownote38


    Aug 8, 2013
    Nashville, TN
    I would still build a new wiring harness since you found this. What you have there could be so much more cleanly done, and my OCD would win out and I'd clean it up. Split shaft pots on a '74 Precision would always bother me.
    Slater and bmusic like this.
  10. wild4oldcars


    Jan 22, 2012
    Garner, NC
    Ymmv, but every time I try to fiddle with those adapter sleeves, I end up not satisfied with the security of the knob, and end up putting in solid shaft pots anyway. I like to use the set screw as a marker, and not having to worry about where the split is on the knurled shaft is nice. As others have said, it’s probably worth your time to just put in some new pots. I’m personally a fan of the low friction of Bourns, but CTS are fender standard. Also, while you’re at it, why not throw in a stereo jack wired mono for an extra bit of security? That’s a standard and mandatory upgrade on all my passive basses and guitars.
    funkinbottom and Lownote38 like this.
  11. bmusic

    bmusic Supporting Member

    Oct 22, 2017
    Los Angeles
    So (thanks again to sissy kathy) here's the job all done—for now. Looks a little less dolled-up and a little more "right" to my eyes. (But I'll probably keep the brass knobs in case I want to go back at some point.)

    I ordered some of those sleeves and will do that little additional fix. And the seller of those sleeves also had a wiring kit with CTS solid-shaft pots and a .1uf ceramic disc capacitor, so I snagged those for that point down the road where I'm feeling ambitious. It would be nice to have things be correct under the hood (but not necessarily this month, haha).