Prusa i2 bulldog extruder jumping back

Hi,

i've been running this Bulldog XL extruder on my prusa i2 fine for a while but now it's acting up.
Whenever i try to extrude any filament , the motor seems to 'jump back'...
There is a fan on the stepper drivers , with heatsink attached to those. the jumping happens straight when i boot up the machine , so i don't think it is related to anything overheating...
the heatsink is cool enough to hold your hand on and the motor itself is feeling warm.
I've also tried changing the temperature of the hotend to a higher temperature so it has less friction to extract the filament , and i've also tried 'helping' the motor with pushing the filament in when it tries to extrude, but to no avail...

Video of the problem here

Does anyone have an idea on what could be wrong / what i can check ?

thank you,

Stef

Perhaps you are extruding too fast? Or there is a "cliff" inside. The filament gets curved and stucked?

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hmh.. i have to say that the extruder is quite old .... and the problem started happening after i didn't use the printer for a couple of months...
The speed hasn't changed with how it used to work in the past so maybe i'll order another hotend and see if that improves the case

thanks for your reply