My uncle gave me a set of old roof racks:

Unfortunately they are about 30mm too long to fit. He was pretty sure that the two halves of the pipe just slid over each other; there wasn't a locking mechanism.

I have tried the obvious to get them to shift:

- Gentle taps

- Moderate taps

- Absoluting whaling on them

- Heating the outside

- Trying to get CRC in the join

- Trying to ratchet them closed with a tie down strop

- Using a two tonne trolley jack and a bar to try and prise them apart

Nothing has worked as yet. Given the trolley jack was bending the supports before the pipe budged, I think it's fair to say the two halves are firmly attached to each other.

Open to any other ideas, but decided I should also see whether anyone else has a similar style roof rack and can confirm whether or not there is a locking mechanism or other trick to getting them apart.