300TD vacuum lock troubleshooting proceedure?

they just aren't working??

Check that the vacuum line isn't disconnected from the engine - very common.

then look for cracked lines, accumulators and then check for perished vacuum actuators

its also possible that the 1 way valve has failed in the engine compartment - easy to test that one with your mouth :)

Try this link. It has a section that covers the pneumatic system. It gives you a good test procedure and a schematic.

Bill