While Toronto's fleet of 35-year old streetcars struggle to stay running in freezing weather, TTC CEO Andy Byford says he's not happy with Bombardier, the company building the new cars, over delays in delivering their replacement vehicles.

"I'm banging my head on the desk," Byford said Wednesday in an interview on CBC radio's Metro Morning show. "Bombardier knows that I'm not happy with this."

Not happy because as has often happened in recent winters, the cold weather is causing the TTC to pull many of its old streetcars out of service. When temperatures dip to about -10 C or colder, the pneumatic systems that operate the doors and brake lines seize up. A total of 25 streetcars were pulled from service on Wednesday. They were replaced by buses on the 511 Bathurst, 503 Kingston and 504 King routes.

Byford said the old streetcars are "worn out" and require maintenance crews to work "through the night" to keep them running.

The new streetcars operate using hydraulic systems that are not affected by frigid temperatures. Two of the new cars entered service on the Spadina route in September. The sleek new low-floor vehicles have higher capacity and so far, have performed well in cold weather.

Byford said the new cars have been "superb" and popular with passengers. The only problem is, there aren't enough of them in service. The TTC has a plan to replace all off its old streetcars by 2019 but Byford said production problems with Bombardier is delaying their delivery. The TTC was supposed to by now have more than 40 of the new cars in service as part of its $1.2 billion contract with Bombardier. Instead, only three have been delivered.

The problems include:

Delays caused by a recent strike at Bombardier's plant in Thunder Bay.

Problems with the new streetcars accessibility ramps. The TTC needs them able to deploy at both street level and at raised concrete islands.

"We are pressing Bombardier to fix these production issues," Byford told Metro Morning host Matt Galloway. "We do have a contract with them. There are penalties within that contract and we will apply them. I am not going to let them off the hook. We cannot continue struggling through winters with streetcars that are worn out."