trans problems,help please

[94lightning]

so a couple of friends and i took our trucks out over the weekend,a savage .25 and a t-maxx both came up with the same problem,they both are running front wheel drive now,i checked all the shafts and dog bones and both are complete nothing broken or missing,i even took the rear wheels off and made sure the hexes and drive pins were good,....if you pick up either of the trucks and hit the gas all 4 wheels will spin,..but if i just hold the front up it wont move and just spins the front wheels? ....anybody out there have this problem and can steer me in the right direction i would be greatful

 

[Hoppedup Savage]

differential

 

[94lightning]

the rear diff? i was thinking that but it doesnt make any noise and it spins nice with no clunking or grinding

 

[Hoppedup Savage]

check it anyways, ill put money on it that your rear diff is your problem

 

[Jeremy]

Make sure u didn't loos any grub screws it your cup joints KEEP US POSTED !!

 

[matchan420]

Rear diff, had the same problem...