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Thread: 2420 Screws

  1. #1
    Bruno GINARD
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    2420 Screws

    Hi all!

    I own an old pair of 2420 drivers. Some screw ( back) was exchanged for metrics models!

    So, I would like to replace them for original US models, instead of those non-adapted ones.

    Anyone could give me the original size ( inch) for the 4 back screws (rear hood) and ones for the diaphragm fixation on the driver ( 3 screws).

    In centimeters, the 4 are approximately 41 mm X 4 mm (diameter), and the 3 inside the back chamber, for the diaphragm, are 18 mm X 3.1 mm.


    Regards

    Bruno

  2. #2
    Senior Member Guido's Avatar
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    Originally are used

    1/4-20 x 1-1/4 FLH Screws.

    this is a common screw in the states.

    You can go to a screw dealer in France e.g. Wuerth. They should have them.

  3. #3
    Senior Member Guido's Avatar
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    The screws inside I can not tell you. Sorry.

    Are the changed too?

  4. #4
    Bruno GINARD
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    Thanks Guido for those informations.

    In fact, i suppose there are 3 screws to maintain the 2420 diaphragm. My models have only 1, that's why i need the size ( supposed the previous owner was a poor handyman !)

    For the rear chamber, if 1-1/4 is the diameter, how do you translate in equivalent centimeters " 1/4-20 ?


    Thanks

  5. #5
    Tom Loizeaux
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    Metric screws won't work. Not only will the size be wrong, but the threads will not mesh with the tapped holes. Get "INCH" sized screws!

    Tom

  6. #6
    Alex Lancaster
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    Unfortunately, I do not have any 1" 24xx out of cabinets, but if I remember correctly, the screw thread might me numeric, (#6, #8, etc.), In about a week I will have a 2410 driver, and I can tell You exactly.

    Meanwhile, it might be difficult to obtain them in Yr location, but would be available in UK.

    Alex

  7. #7
    Senior Member Guido's Avatar
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    1/4-20 means
    diameter is 1/4 inch (approx. 6mm)
    20 is the number auf "windings" on an inch

    1-1/4 means the screw is 1 1/4 inch (approx. 3,18cm) long.

    I hope this helped.

    I got them from German Wuerth. You have Wuerth in France too.

  8. #8
    Alex Lancaster
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    Also, forget about the 1/4" screws or bolts suggested previously, those would be for mounting the driver to the horn, and 1 1/4 is too long.

    Alex

  9. #9
    Senior Member Guido's Avatar
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    @ alex

    The screws I recommended to Bruno are for the mounting of the 2307 Horn to the baffle.

    It's taken from:

    http://www.jblproservice.com/pdf/Stu...ries/4333B.pdf

    Maybe I didn't get the problem right, Sorry

  10. #10
    Alex Lancaster
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    Guido:

    I see, but originally it said "screws or bolts" ON THE "back", as for the baffle board mounting, it could be just about any thread depending on the cabinet.

    For the driver to horn bolts, I use grade 5, 1/4" NS by 3/4 or 1" long, depending on the horn.

    I had to grow up on a "metric" country, where until a few years ago, the only places to get metric hardware were the VW and Renault dealers.

    Alex

  11. #11
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    Machine Screws ( bolts )

    Hi Bruno

    For a 2410;

    The 3 screws ( machine bolts ) for the diaphragm are #6-32 by 3/4" long ( or @ 19 mm long )

    The 2 screws ( machine bolts ) for the back-cap are #8-32 by 1.5" long ( or @38 mm long )

    For a 2420/1; Don't have one to measure

    For a 2426;

    The 3 screws ( machine bolts ) for the diaphragm are #6-32 by 3/4" long ( or @ 19 mm long )

    The 3 screws ( machine bolts ) for the back-cap are #8-32 by .5" long ( or @ 13 mm long )

    The bolts that hold in the diaphragm should be nonmagnetic ( brass ) - if you can find them .

    regards <> Earl K
    Last edited by Earl K; 08-11-2003 at 10:19 AM.

  12. #12
    Bruno GINARD
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    Thanks all

    Metrical screw is of course very “ dangerous” for threading of the drivers, that’s why I need US screws. Many years ago, I bought a JBL cabinet with internal nuts totally destroyed with metrical bolts!

    Actually, I spoke about the rear chamber of the driver, as indicated on the (blurred) picture at the bottom.

    Does anybody knows were these bolts are available in Europe ( Germany, UK,..) or so in US on a commercial Web site, even if it’s only for US residents?

    I’ve found US big sized nuts and screw in France, but not so little models.
    Attached Images Attached Images  

  13. #13
    Senior Member Steve Schell's Avatar
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    I have repaired many used JBL compression drivers, and sometimes these back cover screw holes can be a real mess. Even with the correct screws, sometimes the screws cannot be tightened fully; they freeze in their holes before they secure the back cover. This is due to ferric particles that have found their way into the holes.

    I have had good results by "chasing the threads" with the appropriately sized tap, then running a piece of steel wire attached to a magnet into the hole repeatedly to remove as much metallic junk as possible. After a couple of repetitions of this ream and clean process, the screws will operate as they should.

  14. #14
    Administrator Mr. Widget's Avatar
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    Earl K posted all of the correct sizes, however I would recommend that you order them from JBL since the head size is also important and from my experience it can be problematic to specify the head sizes.

    JBL is pretty reasonable for small items like this. If you can not get JBL to send them to you maybe you could get a Stateside Forum member to order them and then ship them to you.

    If there is a doubt about the condition of the holes I would recommend that you follow Steve's advice and get a tap from here as well.
    Good Luck!

    Widget

  15. #15
    Senior Member Steve's Avatar
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    taps.....

    Aloha
    As mentioned above earlier, clearing the threads with a tap is a great idea, probably the best way to save the threads, if they aren't already too damaged.
    There are basically 2 types of taps, Standard and Bottoming taps.
    The bottoming taps are not as tapered and will allow tapping or clearing threads to the bottom of the hole. The standard tap is a lot more tapered, as they need to be that way to start the cutting of the metal into threads. It would probably be best to use a bottoming tap, if available. I remember at one time using taps made specifically for thread straightening and cleaning. Haven't seen any thing like then for sale in a long long time.

    One trick that is used often to keep the metal cuttings from falling inside is to coat the tap in grease. That way a lot of the cuttings will stick to the grease in the side clearing cut outs on the tap. Back out the tap often after one or two turns or so to clear out the cuttings and keep them from gawling what is left of the threads.

    Another trick I have used is to take a piece of cotton or small piece of cloth, Q-tip end will work great and make it small enough to fit in the hole you are working on. Push it to the bottom. When done cutting or clearing the threads, Use a vacum cleaner with a small hose attached to the end, I haved used a funnel on the end of the hose , and vacum out the hole, then use a small pair of tweezers to pull out the plug ifthe vacum won't pull it out. Be sure you can reach the plug before you clear the threads so you won't push it to a point you can't get it out. Be sure not to push the plug out of the threads too. Measure the distant and mark the tap. If there is more threads to tap just at the point of where the plug was, clear the threads to the plug, pull the plug, then finish the last bit.

    Another trick I use...I apply a very small dab of anti-seize compound to the threads of the screw so they won't seize up later on.

    The screw you install, be sure it is a rating of 3 or above....I prefer a rating of 5...
    That way the screw is tough enough in case it does get stuck, it won't twist the head off and warrant drilling out the old screw.

    If the threads are way too messed up, tap the hole one size bigger.
    Be sure the thread pitch is correct also.

    Hope it works out.
    Steve

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