The burden on part of the front axle (3)
I believe the answer is:
tax
'the burden' is the definition.
(I've seen this before)
'part of the front axle' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'TAX' can be found hidden inside 'front axle'.
'on' acts as a link.
(Other definitions for tax that I've seen before include "Make heavy demands on as Revenue Commissioners do" , "Tariff" , "Impost" , "Compulsory contribution towards a country's expenses" , "State levy" .)