- Wed Nov 29, 2017 6:00 pm
The 7R gearboxes that are used in most of the newer models are pretty readily available online and sometimes locally (I bought 6 of them from a local repair shp for $20/ea that was getting out of the business). I'm not so certain about 3A and unsure what it takes to switch -- I'd assume that the chassis/frame you are using is probably set up for a 3A box and wouldn't easily take a 7R since it has a different shape and the mounting/retaining is done differently.
The 7Rs have quite a few modification options -- larger motors, steel gears, different pinions, and you can do some amount of upgrading on a small budget if you choose carefully ($50 for 2 new motor-less gearboxes, plus $10 for cheap 775 motors and $10 for pinions). If you can find a craigslist Power Wheels special locally it may be worth trying that route, as that would get you two gearboxes. Note that some of the older Jeeps have original "7" gearboxes which will interchange mechanically with the 7R (eg. you could figure out the mounting, etc.) but aren't as strong.
What diameter are the rear wheels on that, and how fast are you aiming for? That would also influence which 7R flavor to buy if you were buying new ones. You likely will want the 21-22-23T ones from something like a Corvette, unless the tires are >14-15" or you are looking at keeping it pretty slow.
F-150 - 24-36V with homebrew 100A variable-speed motor controller, 4x 775 motors (no, it's NOT all-wheel-drive--look up 'quad damage' in the gearbox section for more info!)
Princess Mustang - 24/36V, 4x 775 motors, awaiting a speed controller....
Hurricane - 24V w/50A step-down controller, 775 motors