Well i just finished building my associated t4 and went 2 run it 2day and i noticed alot of the time the pinion and spur would spin together but the wheels would not, just not 2 sure what 2 do 2 fix the prob, any help apreciated
cheers

If your gear mesh is okay it sounds like either your diff or your slipper might not be tight enough. Did you build both to the settings in the manual?

If your slipper is loose, it makes a high pitch noise. If your diff is loose it's a lower pitch.

yer i built all the specs, it is very high pitch noise, and diff was surely tight enough, as when i tightend it a bit more the lockin nut a spring shot across the room

That doesn't sound good. I think you need to pull it apart and make sure it's all there and in accordance with the manual. The spring needs to be there to put the main plates under presure so you have a solid diff (i.e. so it doesn't slip). When you turn one rear wheel, the other should turn in the opposite direction - if it doesn't you have a problem. It should also be smooth with noticeable resistance, but not too much.

A high pitch noise indicates a slipper problem - the manual should tell you how to adjust it. Basically with the diff at the right tension, it should slip for a couple of feet under full power take off on a high grip surface. You will then need to adjust it to the racing surface when you get to the track.

the manual sais 3 turns in, from the slipper nut sitting flush with the slipper bolt, and thats wat i did, but i did not compress the spring on the diff first, so that could be part of it

I think for an Associated you need to tighten the diff all the way up and back it off a fraction. Check that you've done that. It's best done out the truck.

alright mate, will give that a try in the morning and when i get a new diff thrust bolt, cheers 4 the help, will let know how it all goes.
cheers

Just be careful how you do it, you don't want to be breaking diff bolts all the time. Take it easy when tightening up the diff bolt. Do it a little at a time and rotate the diff halves between each time.