is the slipper clutch the problem?
 

My sons 22 under full throttle is barely moving, i can hold the car in place with one finger. I tried tightening down the slipper clutch as much as possible and still no luck. Any ideas???

Is the pinion gear on the motor shaft spinning, is the spur gear turning? If both of these gears are turning then I would think it is a stripped gear in the transmission.

I have a feeling the slipper pads are really glazed is what your issue is your having. Which if you dont sand them to clean them it will constantly slip and not being able to set it right .

Could be the slipper slipping way too much. Or it might be the pinion came unscrewed (happened to me the other night, I got worried my motor died lol)

I can literally hold the car in place with one finger with no pressure at all. While i hold the car still the pinion and spur gear are still moving, but the wheels arent turning at all.

You should be able to see the metal pads turning if the spur is slipping that bad.

Ball diff or gear diff?

If it's a ball diff, you need to tighten the diff screw. And by this point, your diff balls and rings are probably knackered from the slipping, so you might want to rebuild it. New diff balls and flip or replace the rings.

If it's a gear diff.. something else is probably the problem

Check the wheel drive pins (in the hexes). One of them might be sheared off.

WeLL, I do remember when I put it together I only tightened the diff until when I spun one side , the other side spun the opposite direction. I didn't have to tighten it down to much for this. So I'm hoping that it just needs to be tightened down.

Yes, but if it has been slipping a while your rings and balls are probably shot. Judging by the fact that the pinion and spur are moving but the car is not, I would say with 95% certainty that the diff is way too loose.

heres a thing i did that was eastyier to do with checking the ball diff and thats holding the right wheel and spur gear, and turning the left wheel if it turns a lot its to loose and slipping if its to hard to turn its to tight . So you want where its inbetween kind of tightest and not causing a bind.

Issue is if it was already slipping bad before odds are the balls are shot . Now you can flip the diff rings around but you need new diff balls.

Personally i get tired of ball diffs i just bought a gear diff for my t4.1 .

The slipper clutch ethier sand the slipper pads and the plates or get new ones . When you adjust it tighten like the manuel says than put the truck on a table hold both wheels and do quick blips of throttle and you want the Front wheels to go up 1 to 2mm high.

However when you go on the track odds are you will need to adjust to the traction on the track.

And you only want the slipper to slip a little.