Its a fairly easy thing to fix, I,ve done it to a few Synta style focusers, in step eleven of the link below just put a little more pressure on the reduction asjusting nut. Depending on how much you tighten it (within limits of course so that the reduction assembly still rotates) you will then be able to adjust the tension knob quite tight for heavy loads.
http://www.agenaastro.com/Articles.asp?ID=179