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© Copyright 2006, Sargent & Greenleaf, Inc.
Model 6730, 6735, 6738, 6741 Mechanical Combination Lock
Troubleshooting/Dialing Diagnostics
Even though a wheel is unlocked, it will seldom slip if you dial
smoothly and slowly. The critical time occurs when a drive pin
first contacts the fly on the unlocked wheel. Slow, smooth dialing
gives the friction, which exists between the wheel center and
the case time to overcome the inertia (tendency to stay in
place) of the wheel case.
Our original combination was set to 20 • 60 • 40. For our
example, we’ll assume only the #3 wheel is unlocked. This
means our first two numbers are 20 and 60, and the third num-
ber could be anything. Moving slowly and smoothly, we dial
four times left to 20, then three times right to 60. Although
slow dialing is not critical at this time, we don’t want to
encourage any unnecessary slippage in the #3 wheel, because
the more times it slips, the greater its tendency to slip during
upcoming dialing operations.
The dial is now set on our second number, 60. Dial left two times
to 62, then right to the contact area. It’s okay to oscillate the dial
in the contact area, because only the drive cam is moving, and it
is not contacting the #3 wheel. If the lock does not open, dial left
directly to 64, then right to the contact area. Keep adding 2 to
your previous 3rd wheel number until the lock opens.
If the opening doesn’t take place, chances are very good the
#2 wheel is also unlocked. To remedy this, dial four times left
to 20, then three times right to 18. Now dial two times left to
20, then directly right to the contact area and oscillate. Dial
directly left to 22, then back to the contact area, and so on.
After you’ve worked the #3 wheel all the way around the dial,
you can drop another two numbers down on the #2 wheel by
dialing four times left to 20, then three times right to 16.
Begin checking the #3 wheel with number 18, and again
work the #3 wheel all the way around the dial.
Yes, this can be a time consuming process, but remember that
the most likely situation is for only the #3 wheel to be unlocked.
In any event, dialing open a safe is almost always preferable to
drilling it open.
concLusion
These diagnostics and opening techniques have been compiled
for Group 2 locks, although most will work on Group 1 locks
as well. I encourage anyone who has additional techniques or
improvement on the ones given here to jot them down and send
them to me. I’ll make sure they are tested and added to the list.
Remember, we’re looking for non-destructive diagnostic and
opening procedures. Send your comments and suggestions to:
Brian Costley, CML, CMST
Sargent & Greenleaf
One Security Drive
Nicholasville, KY 40356
bcostley@wheelpost.com
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