Custom amp pull down shelf

Discussion in 'Tunes!' started by cavero, Feb 10, 2021.

  1. cavero

    cavero forum member

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    I've got a small amp (75Wx4 RMS) sitting around, so I was looking to put it in the trunk. I've seen lots of people mount theirs on the back of the rear seat, on top of the spare tire, or even on a shelf hanging down from the rear deck (saw this one here in the forums):
    amp shelf.jpg


    The thing is, I don't want the amplifier taking up valuable cargo space in the trunk, and fold down my rear seats a lot to put my bike in the back of the car, so the back of the seat isn't going to work (imagine the bike snagging the power wire ).

    A drop-down shelf from the rear deck makes the most sense, since between the speakers probably won't get in the way of loading anything in the trunk. Problem with the shelf idea is the controls are on the top of the amp, so I can't make adjustments with it in place. I could take the amp off the shelf, make adjustments, and put it back on, but where's the fun in that?

    Instead, I got some inspiration from a pull down knife rack we have in our kitchen which uses something called a pull-down rack hinge:

    drop block.jpg

    Here's my mockup (don't mind the Pampers, I've got lots of those boxes right now):
    PXL_20210210_194945409.MP.jpg

    PXL_20210210_195621185.MP.jpg
    PXL_20210210_195720351.MP.jpg




    I've got two issue's i've got to solve.

    1 is what to make it out of. I bought a bunch of aluminum L-bracket from Home Despot, which will work for the arms, but for the shelf and the top mount, I'm going to need something that comes in sheets, which they don't carry in any kind of thickness that's going to have some strength. Anyone an experienced metalworker out there that might have a good idea for what sort of gauge aluminum I'd need for this and where a good supplier might be?

    2. How to make it latch closed. The springs will do a lot to take the weight, but they're not going to work over bumps. The kitchen version uses magnets, but that's not a good idea near a piece of audio electronics.
     
  2. MrBhp

    MrBhp Member

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    What if you didn't use plate. Just put in L bracket where the amp mounts. It would look like a tic tac toe board.
     
  3. cavero

    cavero forum member

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    I need the top bracket to be pretty large (~ 3") to allow everything to fold up like on the mockup. I could try to build it as a cage (that was my original plan), but I'm worried it'd be too flimsy. The kitchen version of that pull down rack has a lot of tension on it w/ the springs.

    Someone on another forum was asking why not just go with steel since it's a lot easier to work with, can be thinner, cheaper, and for the size of the part probably not much heavier, if any heavier at all.


    As far as latching it in the stowed position, the same guy suggested these,
    https://www.ebay.com/itm/264487074947?mkevt=1&mkcid=28&chn=ps
    [​IMG]

    but I also found these:
    https://www.pegasusautoracing.com/p...E4_LkYD0rWevxR1SIQs4TpoQ58YPV3I8aApKcEALw_wcB

    [​IMG]
     
  4. MrBhp

    MrBhp Member

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    Oh yeah I get it. There's bound to be some kitchen storage gadget you could Frankenstein. Lol
     
  5. DieHarder

    DieHarder Member

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    Ditto... Can you still get the undershelf unit you have in the kitchen? Probably expensive for what it is but may be worth it and likely super easy to adapt.
     
  6. cavero

    cavero forum member

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    I ended up buying 22 gauge steel from Home Depot which seems like it's going to do the trick. below is what I've got so far. I'd like it to have some kind of stamping to make it a little more rigid but if it's bolted at all 4 corners, it'll be fine.

    So the top box is steel, the arms are aluminum (I could probably redo in steel if I had to), and the tray is...an Ikea cutting board (see, not done w/ this kitchen stuff yet). The ikea cutting board is polyethylene which is pretty rigid, durable, and easy to work with, and cheap! only $3. I have a stack of these on the shelf for this sort of thing (wouldn't be the first time I used one to mount an amp)

    Rattling is going to be a problem, so I'm going to need some nylon bushings, and will probably use a layer of dynamat between the top bracket and the underside of the car's rear shelf.

    Still looking for ideas on how to latch it closed. Someone on another site suggested this
    https://www.amazon.com/TCH-Hardware-Small-Padlockable-Keeper/dp/B07F1RWTT1
    [​IMG]
     
  7. cavero

    cavero forum member

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    48
    PXL_20210215_234635993.MP.jpg PXL_20210215_234602851.MP.jpg
     
    MrBhp likes this.
  8. jewc75

    jewc75 S197 Junkie S197 Team Member

    19,569
    765
    My amp is bolted to the rear speaker tray. Im curious to see what you come up with.
     
  9. tabstang

    tabstang Junior Member

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    nice work! kinda overkill IMO, not sure why the amp needs to come down that way but I like it.
     
  10. cavero

    cavero forum member

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    Mostly because I wanna be able to make adjustments after installing it without dropping the amp shelf, partly because just doing a hanging shelf is too easy and I'm running out of mods to do :D
     
    MrBhp likes this.
  11. cavero

    cavero forum member

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    I had the week off from work so I decided to press on the install and iron out any kinks later. There were some things that were awesome (like how Ford left a nub on the firewall grommet perfect for a 4 gauge or bigger power cable) and some things that ROYALLY SUCKED (like feeding the speaker cables into the doors -- my hands are still killing me 3 days later).

    For the rack itself, I used the spring pins, and tried to make everything as tight as possible. Problem is the rack is great in theory, so-so in execution (my tolerances are pretty spotty despite my best efforts). Getting the spring pins to engage is a pain in the *** but once I get them lined up they lock tight and there's no rattling.

    One fitment issue I have is even though I offset the shorter arms so they could stack with the long ones, I didn't space them out enough, so there's still some interference there. They can be forced, but when I take this back apart for painting, I'm going to add some more spacers.

    PXL_20210309_170354783.MP.jpg

    You can see in this one how it sticks through a hole in the bracket to lock it. I ended up beveling the pins a little bit to make them easer to end up in the hole (jokes). I had to make adjustments to the depth of the whole spring pin assembly and slotted the mounting holes so I could tweak the exact engagement.



    PXL_20210309_170401547.MP.jpg

    PXL_20210309_170350371.MP.jpg
     
  12. cavero

    cavero forum member

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    Mounts for the car. I have heavier duty bolts in the center, and because the steel for the top bracket is so thin, there's enough flex that I had to add two more on each side. I epoxied the bolts in from the top, so hopefully whenever I have to remove the rack, I won't have to pull the whole rear shelf panel out again.
    PXL_20210312_210318620.MP.jpg

    PXL_20210312_210242063.MP.jpg
     
  13. cavero

    cavero forum member

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    And here it is installed. This isn't the finished product, but I'm going to enjoy my amp for a bit [​IMG]
    Still on my to-do list is:
    1. Paint
    2. Offset the arms so they stack nicer
    3. Add some rubber edging like this:
      [​IMG] Amazon
    4. Tweak some of the tolerances


    Folded up:

    PXL_20210313_202445370.jpg



    Folded down. It'll actually fold down 90 degrees, which is perfect for making the connections in back and tweaking the settings

    PXL_20210313_201615546.jpg




    Here's a look at the back of it. I left a lot of slack on the power/ground cables to let it fold down all the way, now I'm second guessing that. They're pretty flexible cables but they're REALLY flexing when the thing's folder up. I tried tucking them up into the car's frame but it didn't help a whole lot. Copper work hardens too, so if I folded this up and down enough (or maybe just road vibrations), the cables could get pretty stiff.

    I purposely set the arms back in the top bracket so keep the amp as out of the way in the trunk as possible (which I did, it's hard to see when it's folded up unless you crouch down), but if I ever make a V2, I'm going to revisit that.


    PXL_20210314_023457661.jpg PXL_20210314_023617037.jpg
     
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