Right, my 740 has a totally different pump so that blew that idea out, anyway, I decided to go ahead on the 940 and see what happens. I'll give a full run through of the procedure for anyone else wanting to try this. Before attempting this, make sure your pump and rack seals are good, if there is any sign of leaks it would be a good idea to get them done now as increasing the pump pressure could very well blow the seals out.
Ok, first place a clean container under the pump, clean the pump and run a wire brush around the fittings to remove any crap and muck. The fittings are very tight so use a spanner (or wrench as you yanks like to call them) to hold the high pressure fitting as you undo the feed line fitting otherwise the whole lot will turn and you wont be able to remove the feed line from the fitting
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Once the feed pipe is removed, remove the high pressure fitting then use a magnet to draw out the pressure piston and then a pair of long nose pliers to remove the piston spring. This is what you'll have
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and this is the part that you'll be working on, the pressure relief piston
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the article that I gave a link to says to hold the piston in a vice,,, DONT, you'll fuck it up, instead use a pair of vice grips to hold it like this so that you dont damage the machined surfaces
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also be aware that in the end of the retaining cap there is a very fine gauze filter so dont go poking around at it
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remove the retaining cap, be very carefull as the cap is VERY tight so make sure you've got a good grip of everything. When the cap is loose undo it with your fingers and be prepared for it to fly off as there is quite a bit of spring pressure behind it.
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