I've just bought a new(other) Rockshox Reba but it's 120mm travel and I need to change it to 100mm. They have two service manuals that I've found so far. One is the 2017 rev B and the other 2017-2019 rev D. In the rev B there is no difference between the 120mm and the 100mm air shaft components but in the rev D manual the 100mm has a different jounce bottom out damper, well at least it looks that way because they have highlighted that they are showing the 100mm bottom out damper. If they were all the same I can't see them highlighting the one they are showing is for the 100mm. I wouldn't mind if it was a case of just buying one but I can't find a single kit that has one and the most up to date parts guide doesn't list it. My forks serial number is 18T73493080. I don't know if that makes it a 2017 but they class it as a 2018. I read that they bring out new forks around May/June and class them as the following years model, either way I can't find one.

Can anyone advise me
Thanks in advance.

As far as I can tell, you don't have to change any shaft components to change from 120mm to 100mm only add a spacer. Not sure why you would need to go back to 100mm?

Thanks for getting back to me. I bought the forks because they were new and pretty cheap even with the cost of an air shaft damper. My bike can only take 100mm travel forks.

What's your bike?

It may be all that is recommended, but that does not mean it is all it can take. people over fork bikes with no problem quite often.

The bike is an Alpkit Sonder Frontier with 29" wheels.

Looking at the specs unless it makes it feel funny to you I would say, 120mm should be fine.