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G&G MP5 cracked gearbox

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  • G&G MP5 cracked gearbox

    My G&G MP5 blowback has cracked it's gearbox casing for the second time.
    I got it used two years back and it's been brilliant. Easily as good range/accuracy as my 416 Recoil so would like to fix if poss.
    It worked great every week for a year and happened for first time. Replaced gbox shell. That lasted about three/four games and now it's done it again.
    Don't want to just replace gbox shell again as clearly something is causing this other than the 'usual' gbox shell weakness.
    Can/should I replace with a non-blowback gbox?
    Would a new blowback spring help?
    Any ideas/ suggestions welcome!

  • #2
    Re: G&G MP5 cracked gearbox

    Cracked after 3 or 4 games ???

    what type of shell was used, coz they are radius'd at front to reduce cracking
    so I wonder if you got a bad or lesser quality shell in there or next to no sorbo

    No way should a box have cracked so quickly or you running a high powered DSG setup in there
    but still shouldn't of cracked so damn quickly - was shell new or s/hand with a hairline fracture starting to appear ???


    • #3
      Re: G&G MP5 cracked gearbox

      It was a new G&G shell. And I mean three/four full game days but even so...
      And it had piston and sorbo replaced at same time on first gbox install plus all new internals and a MOSFET. Regular motor, not high speed. Run 7.4 lipo.
      That's why I'm thinking something else is contributing... (Like the blowback mech)
      Last edited by fatdad; 31st May, 2015, 12:59.


      • #4
        Re: G&G MP5 cracked gearbox

        Jeez that sucks - not a cheap shell either

        yeah I guess disable the blowback - one less thing to eliminate possible cause
        but I will be honest don't really own any blowback stuff myself so not best person to advise

        Did it crack around or on that side, I'd consider just getting a non-blowback box
        (think it is just a gimmick myself but to each their own - soz any blowback peeps no offense meant)


        • #5
          Re: G&G MP5 cracked gearbox

          The g+g uses a pnewmatic blowback doesen't it? Unless it cracked around the port for the pnewmatic blow aback the it won't make any difference at all , did it brake in the normal v2 place at the bottom behind the cylinder head ? With fresh sorbo and a modest setup as described I'd say it was bad luck .


          • #6
            Re: G&G MP5 cracked gearbox

            Unfortunately, G&G shells both standard V2 and the pneumatic type shell are actually very poor for higher rate springs. Their attempt at adding the radius to the corners of the cylinder window in the cast is sub par, in addition to the rest of the front end design and material. In fairness they aren't designed to be upgraded, however stock boxes failing is indication of poor QC, or serious design flaws or the latter.


            • #7
              Re: G&G MP5 cracked gearbox

              Hi mate

              I may be able to help you here on a few counts as i
              a: own a G&G MP5 (namely the one with the front handguard RAS rails and retractable stock)
              b: I tech my own guns; and
              c: I have had the Version 2 blowback gearbox crack on me too.

              So a bit of history on mine, i bought in Nov 2014, I used it once personally but it was used in other skirmishes as a loan gun to friends, on one occasion it stopped working entirely and i had to disassemble it at the Airsoft sites workbench in order to get it up and running again which i did. Fast forwards to May 2015 and i decided to clean and regrease it after it had been to 5 or 6 skirmishes seeing about 1000 to 1500 rounds per skirmish and i noticed that the FPS had dropped from a stable 345FPS to 310FPS. I opened it up to discover that the gearbox case had cracked on the lower shell only near the front end, seeing this i like you purchased another shell to replace the broken one.

              On speaking to my local airsoft shops they gave me a slightly different reason as to why the gearbox cracked, the first stated that as there was an extra port at the bottom of the cylinder, airpressure from the piston was going into the gearbox and cracking it, frankly i did not buy this reason.

              The second shop told me that G&G originally added a M105 like spring in order to compensate for the blowback but when they needed to lower to joule power rather than changing the spring they simply drilled a hole in the bottom of the cylinder, furthermore they stated that the V2 gearbox frame had been modified by G&G to accompany the blowback and this had weakened the frame and that they had experienced a lot of G&G guns specifically the MP5 having this issue, not so much on the TR4-18 series as that has a reinforcement block added with the hop up unit. With that the shop staff gave me 2 free G&G cylinders for blowback but without the port hole at the bottom.

              I believe the second shop was more accurate, that the spring is indeed slightly stronger probably a M105, this alone would not crack a normal V2 gearbox but a modified one that has been weakened, probably, maybe, who knows? G&G uses cast metal (read pot metal) to make its gearboxes, and whilst they are one of the stronger ones it has nothing on CNC Milled gearboxes. I have provided pictures below of what i mean in all this.

              Lastly you ask if you can use a normal V2 gearbox in the MP5 and the answer is both No and Yes but only with some mods to the gearbox, see pictures below.

              Did you gearbox crack like this one, in or around the same place?

              Normally V2 gearboxes have a spine running along the top of the gearbox to reinforce it, here because G&G implemented the blowback system they have left very little material on the top causing an inherent weakpoint.

              See what i mean

              Original and new cylinder both with the blowback hole, notice that this hole has been cleanly cut and filled to remove any burring, one has the additional port hole, the other doesn't but which one :0

              The one on the left had the additional hole, not noticeable in this photo is how poorly cut this one is compared to the other, this indicates that they were both manufactured the same with the hole being done as an after thought.

              Here we have G&G blowback gearbox shells for an M4 type AEG on the right and an MP5 AEG on the left, from what i have been told the MP5 has had certain parts of the shell grounded flat (see photo and compare gearboxes where the red circles are) so that it fits in the upper and lower reciever, if you want to use a V2 gearbox you going to have to grind those bits down.

              Hope this answers some of your questions or at the very least puts you in the right direction.
              Attached Files


              • #8
                Re: G&G MP5 cracked gearbox

                Wow a lot of info. Thanks for taking the time. I'll have a read thru a few times!


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