The operators of Greater Manchester's tram network wants the government to help fund new vehicles so it can meet passenger demand.
The bid is separate to plans to extend the network
Metrolink says passengers have suffered delays for months because there are not enough working carriages.
One tram is out of action after an accident in Salford last November, and others have been taken out of service for maintenance, the company says.
The bid is separate from the money already pledged to extend the network.
Transport Secretary Alistair Darling refused a bid for extra funds last year to extend the lines to Oldham and Rochdale, Ashton and south Manchester.
But £520m will be made available for transport improvements that could include Metrolink, it was announced in December.
The cash is dependant on Greater Manchester Public Transport Executive (GMPTE) developing a satisfactory plan to fund the rest of the project.
GMPTE is now asking the Department of Transport for money to buy more vehicles and to carry out upgrade works on the Bury to Altrincham line.
Geoff Inskip, Deputy Director General for GMPTE, said they were putting together a submission to the Department for Transport for more cash to improve current services.
"Quite simply, we need more trams for Serco Metrolink to deliver a thoroughly reliable service - and to meet passenger demand for services," he said.