After crashing my bike

I have now got serious speedo problems. Replaced the speedo cable twice but it still reads silly speeds. (177mph when doing about 75mph i reckon

)
The speedo casing was damaged but I managed to get it plastic welded in work. Everything else works perfect on the clock apart from the MPH reading.
I hope I don't need to replace the clock as I rang Suzuki this afternoon and they told me £305 +VAT for the electronic gubbins alone.
its a 2004 K4
Any ideas as to a possible cure??