Vibration under acceleration only till 70

[Flowgoode]

Ok, my problem consists of my car vibrating/thumping pretty bad under acceleration only until about 70 mph, then it goes away and the car is as smooth as can be.

The car doesn't vibrate (more of thumping feelings) when I left off the gas.

I think it might be the axel or something. The transmission is leaking from the passanger side axel seal and needs a new seal aswell, but I don't think a leak (keep in mind I fill it up constantly to replace the lost fluid when I have to drive that car) will cause the thumping.

Any ideas? I can't figure it out. And I don't want to buy a new axel and not have that fix it.

I have a 93 TSi AWD 23 spline (but the trans is unknown year, but bolted to the transfer case I had stock, so its a 23 spline i know that much).

[Gary 420A RS]

reach under your car and pull on the axel it self. if it has play and you can feel it coming out than all you might have to do is re seed it. check that. also if its your axle then youll feel it as your turning... so make some turns and youll be able to tell which side it is. and if your replacing fluids then you should know that theres a problem and it should be corrected. good luck and let me know if i helped any.

[sonicnofadz]

This sounds like a really strange problem...you might want to also check your driveshaft and rear differential (check its fluid level).

[Flowgoode]

what should i check on the driveshaft?