All 4 wheels locked

It's been a long time since I posted to these forums, but I have a weird problem with one of my 2006 Jettas. All 4 wheels are locking up after about 10 minutes of driving. Originally the shop thought it was the manual transmission but that was not it, then they thought it was a break issue and replaced the vacuum break booster and master cylinder and that didn't solve the problem. Now they're telling me all 4 calipers need to be replaced but I find it very hard to believe that all 4 calipers would seize at the same time. Does anyone have any ideas on what to look for here? Thanks.
Shaun

No they wouldn't seize at the same time. Have you even looked at it yourself? Very simple, just jack it up and spin each wheel. See how easy this can be? Shops are not to be trusted. They've already stolen your money and you have nothing to show for it.

When it happens, jack one corner up, take off the wheel and crack open the brake bleeder and see if the caliper frees up. That will tell you if all 4 calipers need replacing (BTW, don't go back to that mechanic - they're guessing) .Sounds like it's building pressure and not releasing to the MC when your foot is off the brake. Don't know about if this is the same on a VW but on other cars I've worked on if the brake pushrod isn't adjusted right (and there is another one between the booster and the MC on some cars) it will cover the port on the MC and do just what you're experiencing.

Could be a faulty abs unit.

Thanks for the replies.

ABS unit would be my suspicion too. Is there an ABS light on the dash? How are you verifying that all 4 wheels are looking and not just the drive wheels?

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You need to first verify that it is indeed all four wheels. If so, I would try and determine if there is hydraulic pressure on the system causing it, which would be easy. While they are in this state, crack a line loose. There are two circuits from the master cylinder to the ABS unit. They are paired LF/RR one one, RF/LR on the other. You can crack one or both loose between the master and the ABS. Neither end of these lines is really "easy" to get at, but at least that will tell you if the problem is in the primary circuit(s) or not. If no pressure exists, and the brakes still remain locked on, I would then start by taking a line loose at the calipers, see if anything changes. Surprised the shop has not already tried this. The braking system on your car is pretty textbook, there isn't really anything strange about it.

All four wheels are locking, after about 10 minutes of driving. No ABS light. Thanks for the replies.