It comes after the Caterpillar dealer cut 375 jobs earlier this year in New South Wales and the Australian Capital Territory.
The company said the restructuring would be implemented in the next month at a cost of about $A13 million.
The job cuts will be achieved through a combination of natural attrition, a reduction in contractors and redundancies.
“WesTrac has implemented a series of efficiency and productivity initiatives over the past 12 months in an effort to streamline its cost base, but these measures alone have not been sufficient in view of continuing challenging market conditions,” SGH said.
The company previously said it had seen the biggest slowdown in NSW coal, while Western Australian iron ore has picked up since a price slump last year.
WesTrac said that after the restructuring it would have 3350 employees across WA, NSW and the ACT.
SGH also warned that full-year earnings before interest and tax to be at the lower end of the previous guidance of 30-40% below the 2013 financial year, with a more marked reduction in the first half given the record comparative period.
EBIT for FY13 was $634.6 million, up 9% on FY12.
The company previously said it expected its “exponential growth” to ease with FY14 earnings to settle back at FY11 levels.