If you tightened that set bolt before engaging the WD bars, that's the problem. Engaging the system will pulls up on the head with tremendous force.
When making adjustments, tighten that bolt to contact, just do it doesn't move while you work. Then after engaging the bars, tighten to contact, plus the 1/4-turn.
thebrakeman ('70), DW ('71), DD ('99), DD ('01), DD ('05)
2004 Surveyor SV261T (UltraLite Bunkhouse Hybrid)
2006 Mercury Mountaineer V8 AWD Premier
Equal-i-zer WDH (10k), Prodigy Brake Controller