I Recently purchased 234RC Head, First time use proved to be either too stiff or too slack in operation with a 50-500 zoom. I dismantled the head for a quick look and found a disc of friction material of approximately 25mm outside diameter x 6mm bore. In a similar manner to another review of this item, I fitted P.T.F.E. shims cut out from sheet material and fitted these in place of the original friction disc. When dismantled, friction disc originally fits in a recess. I used 1 off 1mm shim at opposite end to recess to avoid metal to metal contact, and 2 pieces 1mm shim with a 6mm I/D-25mm O/D washer sandwiched between to make a shim-pack to fill recess. While you are at it, replace the 6mm x 65mm bolt with a stainless steel item. Similarly with Manfrotto 680 or other model monopod where all 5mm mild steel screws and nuts were replaced with stainless 5mm hex capscrews,washers and nyloc nuts. Smooth operation and no rusted or seized up pins in the event of a stripdown
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