Juggular

That's how it's supposed to be, if you build it vanilla (without doing anything special). I try hard to make the diffs like what @Superluminal said. That's called "Limited Slip Differential." I like mine to turn the same way, but when I put it on the ground and pivot on the center axis, they turn the opposite way. To achieve that, I use differential clay, a million weight silicone grease, etc. But if you didn't use any of those special grease or clay in your diff? It should turn just like the Grasshopper. If it doesn't, you should pop the rear and check the diff.

Ooh, a mystery! 4WD, but I didn't spot a motor sticking out. Longitudinally mounted (like Avante)? Where are the front springs? Are they laid low (like Avante)? Hmm... maybe it is a simplified version? (a plastic tub chassis, lower A-arms, etc) I'm interested only if it costs 40-50% less.

Either Deans style or XT60 should work fine. They are both good up to 60A. That's about 30 times better than Tamiya connectors. I occasionally get a 10 pair of XT60 from Amazon for $9. https://www.amazon.com/gp/product/B01ETROGP4/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 They fit tightly and securely; tight enough to hold the weight of a battery, but still easy enough to disconnect. It's simpler to solder than Deans because you stick the wires into tubes and solder, instead of soldering on a flat surface. It's easier to grab. (But if you can get sheathed Deans-style connectors for more surface to grab)

It does not matter either way. If you remove the dog bones only, then the front gears would just rotate doing nothing. That's fine. Just take out the drive cups from the gearbox and store them safely. If you haven't already, they will pop out. Also you can tape up the holes with masking tape or something. No need to let dust in when it's so easy to block them. If you remove the driveshaft connecting the two gearboxes, only the rear gearbox would be engaged. That's also fine. Less energy wasted, so that much more power goes to the rear wheels.

I thought it was 1:1 for a second there. Well done!

I use ebay. Many of them are in Hong Kong also. Or there are companies like Amain or Towerhobbies. They don't have large Tamiya selections. But Tower gives you $20-40 coupon every week. If they have what you are looking for, it could be faster, cheaper and more reliable than many ebay sellers. If what you need are parts, ebay has several reliable kit breakers. They buy re-released kits and sell parts one by one. I restored many that way.

I'm thinking a photo might help? I have cut old battery boxes out (where I could) and soldered 2 pin connectors. So I could use modern 11.1v LiPo battery in all my old Futabas. I always hated rummaging through 8 AA batteries. At least in those 20 year old Futaba radios, red was + and black was -, like all DC circuits. I never had to touch the switch. I simply used the wires connected to the battery contacts.

That is surprising. Usually that's because of high-load on the motor. 1) Are you using 3S? 2) Is the gear ratio excessively high? 3) Have you mounted heavy or large diameter tires? 4) Are the gears and wheels freely rotating?

It could be that the thermal protection had kicked in. When the ESC gets hot (especially if he used anything more than the stock 540 motor), it shuts down to protect the circuits. After cooling down a bit, it would run again until it heats up again. If he's using a faster motor he'll need a better ESC. I doubt that BEC would be a problem. BEC is 'Battery Elimination Circuit.' It just means that the ESC gives power to the servo from the main battery pack. Nearly every ESC has BEC. It simply lets the battery's power run through the receiver. Sometimes BEC could cause a problem when the servo is digital and cannot handle the voltage. Most servos like 6v. 7.2v was fine when servos were analog. But digital servos doesn't like higher voltages (but they like higher current as you have discovered yourself). LiPos can get well over 8v when fully charged and digital servos designed for 6v doesn't work well (that's why they sell 'high voltage' servos and ESCs which down-regulates the voltage to 6v = 105BK is one of them, but it adds heat if the battery has higher voltage). 1) I'm sure he checked to see if the battery hasn't run out after 10-20 minutes? 2) Check to see if the motor isn't anything better than the stock 540 motor (Tamiya 25t might be fine, but even Sport Tuned might be too fast). 3) Check to see if the servo isn't digital. I hope these would be a good starting point.

Technically, there shouldn't be noticeable slop. That is why I finger roll them before I install them. Some of them have too much slop, it might run okay with a lot of grease. (At the expense of rolling efficiency, of course.) Too tight a bearing might loosen up as it wears down (if you run them without any lubrication for even 5-10 minutes). ABEC rating feels counterintuitive to me. ABEC 1 isn't the best, it's the worst of the 'Precision Bearings.' At 0.001-0.002mm deviation allowed, ABEC 9 is the best tolerance. But having 0.001mm deviation allowed doesn't mean that they designed a 0.001mm gap. They could design the gap between ball bearings and the races to have a gap 5 times larger than the tolerance. If the bearing company wants the least rolling resistance without much load, they'll make it looser. If the bearing company expects a lot of load, they might make it tighter. RC cars being light (compared to skateboards, cars or trains), somewhat loose bearings are better. (The only exception to this is motor bearings, because of the speed, motor axle bearings tend to be very tight.) Even for that, I bought the cheapest Chinese bearings (no ABEC ratings). Oddly those motor bearings are very tight. Generally the problem is two folds. 1) Since most Ebay sellers would slap on ABEC on most bearings, you can't tell which is true and which is not. 2) Inconsistency. Cheap bearings might be rejects. But that doesn't mean that some were intended to be ABEC2, but didn't meet the quality control and sold cheaply. I only use 7-8 bearings out of 10. But at about $3 per 10, I don't mind testing them. Better bearings cost about $10-$15 per 10. For stuff like Konghead, they cost about $40-$45. I'd rather spend $18 for 60 and use only 50 of them after a 10 minute finger-rolling test. For the money saved, I could buy 2 Sport Tuned motors. [Above is my toilette paper test (not paper towel, but TP). While holding the inner race, I try to roll the outer race with a folded edge of TP. If it rolls easily, it's good. If it doesn't, it's too tight. This is the cheapest bearings; about $3 for ten. I did replace heavy grease with very light grease. All my gears get these. But for wheel bearings, I leave heavy grease in tact. They fail my TP test, but they need heavy grease because of the weight on them.] If you don't want to bother, RCMart sells Yeah racing bearings. They are not expensive. They should be good quality bearings. https://www.rcmart.com/yeah-racing-rc-ptfe-bearing-5x11x4mm-10pcs-yb6014b-s10-00001611 Even with cheaper ones, I very rarely come across sloppy bearings that I could feel. After washing out all the grease, many of these cheap bearings would spin flawlessly like a fidget spinner. Some would have some minute slop when it's totally free of lubricant. But even a drop of light machine oil would make it very hard to feel the slop. So if you could feel the slop on RC 1150 bearings, I'm afraid that's not a good news.

It sounds more like a thermal shutdown (except it's not shutting down entirely). Maybe you could try another ESC? Cleaning a brushed motor won't hurt. It's easy. Just dunk the whole motor in a cup of water (use a disposable cup) and run it at 5v or so for about 5-10 minutes. It's going to slush around and clean everything. Let it dry and lubricate the bushings.

That would have been my guess too. Though I'm yet to build mine, I think I'll keep to the silver can.

My M07 can take liquid diff oil. The other 3 dozen or won't take liquid. I use Bad Horsie stuff (sparingly) even on completely open diffs from 1980's, like the Grasshopper, Hotshot, etc. (please ignore the gray thing, that's plumber's grease -- for water resist treatment of the gearbox) This much bad horsie stuff won't fling out. Below is Lunchbox gearbox. It's hard to see because the gears are all white. Putties would work only within proper diff housings. 3Racing Ultra High Viscosity thing would benefit from a diff housing too. At the same time, it might even be okay to use on open diffs. Below is what it looks like today, after a year of lying around on its side. I would have thought it would have leaked, or clumped to one side. But didn't. I had a piece of paper wrapped around it to catch any watery substance, but there was none. So I got that wrong. You don't want to pack your diff housing with this stuff anyway, it would be totally locked. If you use it sparingly, it should be okay with most diffs.

When you are using grease, I would make sure to check if it's plastic safe. Automotive stuff could contain petroleum and that could crack plastic.

[1] If you want to almost-lock it, you could use putties. Tamiya sells one, there are other brands too. Too hard for my purposes, I only use this in my Konghead. Dynahead includes this in the kit. [2] If you are in US, "Bad Horsie Diff lock grease" has been my favorite. It's somewhere between putty and grease. It doesn't lock, but it slows things down quite a bit. Very very sticky stuff that doesn't wash off from your fingers for days. I've put this in Wild Willy 2 in 2001. 20 years later, it still maintains the same stickiness (one on the left is 20 year old one). When WW2 catches a tree root and stands on one wheel and the wheelie bar, this gets it out. If putty was available 20 years ago, I'd have used it because WW2 is quite heavy. Most of my buggies get this. It's like chewy toffee or caramel (not that I've eaten it -- don't eat it kids!). [3] Very similar to above, but "grease" would be "3 Racing Ultra High Viscosity Gear Diff Oil." (AW grease is there for size comparison) You can find it easily on ebay. Stickier than AW grease. This should be good for most buggies. After a year in the container, it separated a bit. I found some watery stuff around the edge of the container, as if it's leaking a few drops of water. If you use the solid part, it should be fine. [4] For on-road cars and lighter vehicles, like Dancing Ricer, etc, I use AW grease. It's the go-to limited-slip-differential grease for most people. But it's the weakest stuff I use.