I shortened my brand new shimano XTR brake hoses.

The front lever has a very short throw and feels firm.

The rear lever was much much softer and had a longer throw. I pumped it a couple times and now the throw is shorter and feels more firm, but it is not quite the same as the front lever, close, but no the same.

Did I do something wrong? Should I bleed the rear brake?

Sounds like you got a bit of air in there and need a bleed. Luckily XTR brakes are super easy to bleed!

I find generally the rear is never quite as firm as the front (I don't have braided hoses) and it can only be the longer hose that is the culprit.

there is no harm in bleeding the rear - sometimes get away without doing that when cuttring hoses, other time not.

I agree with the consensus here. Just a lever bleed should usually suffice.

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Sur La Plaque!

2012 Ridley Damocles RS
http://weightweenies.starbike.com/forum/viewtopic.php?f=10&t=111632
2012 Dekerf Team SST
http://weightweenies.starbike.com/forum/viewtopic.php?f=10&t=112060&p=957055#p957055

Yep I bled the rear and the front, I found out the front was too stiff, somehow, it may have had too much fluid or something when cutting the hose