Volvo: S40 front end shaking, front end alignment, accurate diagnosis

Question
I have a 2000 S40 and it shakes and vibrates in the front end horribly at about 50 mph.  When you let off the gas the shaking stops.  In October 2008 it was doing the same thing and I took it for a front end alignment.  I was informed that I needed front axles so I had axles replaced.  I also bought all new tires.  When S40 began to shake again, took for front end alignment and was advised an alignment would not cure shaking.  Front end tech said it was the transaxel/transmission.  Took back to mechanic who installed front axles and was advised the axles could be bad again.  How can I get an accurate diagnosis as to whether this is an axle issue or a transmission issue?

Answer
Tammy,
If the shops that you are using have no experience on Volvo's getting an accurate diagnosis is almost impossible. Try a shop that works on Volvo's. Yes it is possible that the axles are bad again, but should be under some sort of warranty. I have also seen the ball joints,the control arm bushings, tie rods go bad.
When the shop fixes your car ask to do a test drive before paying, have a tech or service advisor take a ride with you both before and after the repairs. That way they will know that they need to get all the vibration fixed as you will test drive the car before paying and taking the car home.