Does riding with suspension locked do any harm long term I bought a Trek 4300 MTB a few months back as my main intent was to ride off-road on local dis-used railway paths. I've since moved house and my main use of the bike is now for my commute to work. Consequently I've replaced the tyres with slick roadies and ride with the suspension permanently locked.

It hasn't taken long for me to notice a juddering when I brake and it seems to be coming from the front-forks.

I was wondering if the odd pot-hole in the road that I hit now and then has done some damage to the internal workings of the suspension that would have otherwise been absorbed had it been free.

Is there something I can do with the preload to find a happy medium where I can ride with a really stiff suspension or do I need to continue to look on with bike envy at other commuters with road and hybrid bikes.
On Trek 4300 you have RST Gila fork which is cheap and simple. You can't really lock it completely, just pre-load the spring to maximum. I'd say you should not worry about it - the internals are very simple and can't really be damaged easily: this is no oil/air fork. It has a steel spring and some rubbers to work as dumper.

And most likely the juddering you notice is not from the fork, but rather from the breaks themselves.