by Ron Van Ness
Before any attempt is made to remove the bolt, clean the head thoroughly with a toothbrush and solvent. The most common reason for CV bolt removal problems is starting an allen wrench or tri-square bit in a dirty socket and stripping the bolt hex. Start clean and you won't need the Vise Grips or the penetrants. If you still manage to strip the head, you may resort to a pair of Vise Grips brand "locking pliers" or "vise grips". The Vise Grips brand is the best because the jaws are treated and more durable than most other brands. They won't break after a few months of use and the serrated jaws stay sharp longer.
A good penetrating oil like Kroil or GM General Purpose Penetrant and Heat Valve Lubricant (GM Part # 1052627) can also be an invaluable tool for stubborn bolts. The penetrating oil has a better chance of working on the inner CV bolts since the threaded ends are accessible for cleaning and spraying (look behind the flange on the transmission to which the CV bolts attach). Heat and vibration are also good tools. A sharp blow with a small hammer on a stuck bolt head is an appropriate wake up call for frozen threads.
The orginal bolts are an allen head socket but later replacement bolts have a modern tri-square or "triple square" socket head design (improved engineering for more torque). Though they look similar, the "tri-square" is NOT a "Torqx" head, so do not use a Torqx wrench, you will just ruin the bolt head. Good parts stores will sell both an allen bit and tri-square bit for your 3/8" socket wrench--a good investment, and much easier to use and exert torque through than a small allen wrench. After cleaning the head, tap the bit in squarely with a mallet and go to work with the ratchet.
In the case of excessively stubborn bolts, try grinding flats on opposite sides of the head to to get a better grip for a wrench or Vise Grips. In the nastiest worse case scenario you can cut the head off with a Dremel, remove the CV, and work on the headless bolt still in the transmission flange or on the wheel's stub axle flange.
If your problem is with a stuck bolt or bolts on the outer CV, it might be possible to remove the inner CV bolts and swing the shaft down, jack up the wheel and remove the axle nut, and pull or drive the axle shaft with the outer CV off. Then you can bring the assembly to your vise and work a serious attack on the bolts. Similarly, if the problem is only with the inner CV bolts, you can remove the outer CV bolts and swing the axle down and cut off the offending bolt head on the inner CV. Then remove the grease cap on the transmission drive flange and release the flange by removing the circlip. Now you can bring the flange to your work bench and punish it for its obstinance.
Having stuck bolts on CVs on both ends of an axle shaft would be the worst case scenario. In that dreadful instance, if you absolutely were forced to the point of cutting the bolt heads off, you would then need to remove the transmission for clearance to remove the axle shaft. But that's never happened to any VW enthusiast in recorded CV joint repair history. These scenarios are all extreme hypotheticals--do not surrender and try these until the situation is hopeless. Vise Grips and a strong arm (and perhaps some penetrating oil) are usually all that's needed if you find yourself with a stripped socket.