Aaaaand were back! 
Have oyu tried hi impact ABS?
I ordered strong black ABS from Formfutura and should do some testing with that when recieving it. If you are interested I could give some feedback in my findings.
But my focus now is to make something about the heating from motor that soften the interface. I made mine in PLA and the first thing i should try is to make the diffcase in ABS and see if the higher glass transition point and some isolation(gasket) in the interface could do any good. Otherwise i think I go for a aluminum flange that screws into diffcase.
If you’re having problems with heat from the motor… why not use a heatsink for the motor and/or a fan? Looks like you might need to cut (or just not print!) some of the top deck so that a heatsink would fit.
I have considered that to and I have actually ordered one from Conrad
http://www.conrad.se/KYLELEMENT-TILL-MOTORER-TYP-540-MED-VENTILATOR-TITANIUM.htm?websale7=conrad-swe&pi=235439&ci=SHOP_AREA_19779_1230020
Depending on what motor you have… you can use thermal paste to get a good seal between motor and heatsink. Use the same stuff you use to get a good seal between cpu and heatsink.
Other suggestions - infrared digital thermometers are pretty cheap now. £10 ish for one off ebay. You can use that to check temps of the motor after sustained running (temp after load). 160F / 70C should be a guideline max temp for the motor. I don’t know what temp causes you a problem - but if you’re seeing higher than 70C then you likely need to look at your gearing.
Lastly are you running brushed or brushless? brushless systems are pretty cheap now, and have good power /weight. i’d guess a cheap brushless system will run a lot cooler than a cheap brushed system - a basic EZRun system will give you 300W.
What temperature causes the problem?
The glass transition temperature is around 50C for PLA. So I think that is the main problem here.
Maybe you can also use ptfe plastica, as used in reprap hotends, could act as thermal jam
It seems that the motor goes too hot. I don’t know if the lipo battery are are the cause or the motor is defect. When I look at the brush cables it looks like they have been around the melting point. Thinking of buying a brushless motor. Any sugestions for a cheap good brushless? The brushed motor is a standard 19T 540.
Good cheap brushless? You will need a brushless ESC and motor. You can use existing nimh batteries, you don’t have to use lipo.
Suggested - for a 1/10th truggy 35 or 60 amp ESC and 9, 10 or 12T EZRun brushless motor. turns don’t really apply for brushless motors - the thing to pay attention to is the kv rating - something between 3 and 4000kv would be good.
Anything more and I’m guessing the diffs aren’t going to take the power. They are printed plastic gears aren’t they?.
I buy from the UK warehouse of hobbyking.
from the international warehouse something like:
slightly more power
ESC choices only:
http://www.hobbyking.com/hobbyking/store/_17228__Hobby_King_35A_Sensored_Sensorless_Car_ESC_1_10_1_12.html
http://www.hobbyking.com/hobbyking/store/_7188__Turnigy_Brushless_ESC_60A_w_Reverse_prog_v2_2.html
Or buy direct from Hong Kong via ebay. E.g. a motor/esc combo by Hobbywing.
Compassho (compass house) have a good rep. There are others. Many in the uk buy direct from them - and typically get the stuff within a week.
Of course the third option - look for a cheap(ish) brushless rtr car locally, strip out the electrics/rx/tx, servo etc and sell the rolling chassis on ebay.
hope that helps!
That battery would be fine. Probably complete overkill for the 80A combo though.
You need enough from the battery to provide the current when needed. That battery will do 200A continous (40C x 5Ah size == 200A). You’ll not draw that in the open RC car, not with that combo. I wouldn’t go lower than 120A discharge for that combo e.g.4000mAh and 30C (which will give you 4 X 30C = 120Amps). Multiply the C rating by the size in Amp hours to get discharge rate. (you could go lower but for the prices why bother? play safe)
You want something 30 or 40C and 4000 - 5000 mAh. Hard case is only needed for racing - soft case is fine if you take care of it.
These would be ok:
http://www.hobbyking.com/hobbyking/store/__9509__Turnigy_4000mAh_2S_30C_Lipo_Pack.html
http://www.hobbyking.com/hobbyking/store/__10301__Turnigy_4000mAh_2S_40C_Lipo_Pack.html
Lastly, I don’t know the level of RC/lipo knowledge of people reading this - so please, please, if you have not used Lipo before get advice, read up, and/or find someone who has had them. (search for lipo fire if you want to see what can happen).
That’s the same lipo charger I have 
Be aware it does not come with a power supply though. You can either buy one with power supply, buy a separate power supply or make one off a server PSU (I’ve not tried the latter).
If you build your PSU see:
http://www.rcgroups.com/forums/showthread.php?t=1292514
or
http://traxxas.com/forums/showthread.php?8949481-Server-Power-Supply-Conversion
Small batteries are ok, but for larger ones or faster you’ll want something that can do a high W output. e.g. 100, 200W or more. Check the specs on your printer psu. I think you need 12V output to that charger.