On 04/06/2021 21:01, Murmansk wrote:
I have a Witter bike rack that attaches to the towbar.

You put it on and at first its all loose and of course will lift off, then you tighten a big bolt which at first is really easy as it goes round for quite a few turns without much resistance, then as it grips the towball you give it a couple of really firm turns with the spanner to make it fully grip the ball.

Removing the rack is the reverse of the above where you apply big force for a couple of turns to loosen it, then lots of relatively easy turns to make it loose enough to actually come off the towball.

The problem is that once Ive loosened it enough to make the rack sag but not actually come off, the bolt starts to feel really tight again €“ almost as tight as it normally does at the last stage of attaching it €“ so much so that I feel as though I need to apply so much force as to damage the thing.

Im now left with the bike rack attached and sagging but cant remove it and Im wondering if anyone has any experience of this?

Sounds very like a bolt with a damaged thread (possibly a bent bolt).
Can it be economically replaced?
Alternatively you could take it all the way out and 'hand chase' the
threads. This may involve mounting in a lathe (local light engineering
firm for the cost of a couple of pints) and running a chase along it.

Just realised you 'say' you can't move it out at all. Maybe try oiling
and working the bolt in and out eventually freeing it (be prepared to
cobble up a hole new looking system as if the bolt is harder than the
threaded part it may well cut its own thread thus knackering any holding
function).