Having struck a bargain with General Motors (NYSE:GM), the United Auto Workers must now grapple with Detroit's other giants, Ford (NYSE:F) and Chrysler. At the latter, the UAW says it will strike unless a deal is struck by tomorrow.

Historically, "pattern bargaining" ensured terms struck with one automaker applied across the board. But times have changed.

All three automakers are restructuring and Chrysler is now owned by private equity. That complicates matters.

At the core of the GM-UAW agreement is the transfer of retirees' healthcare obligations from GM's balance sheet to a separate trust, in return for an upfront slug of cash and other assets. Securing this may have been more expensive for GM than originally expected. Factor in the use of part of its overfunded pension scheme and a commitment to pay benefits for another two years, and Goldman Sachs estimates GM funded the trust at an implied 80 cents on the dollar. Investors expected somewhere between 65 and 75.

For Ford, higher upfront funding costs could add to pressure to sell Volvo. And, unlike GM's, Ford's pension plan is in deficit, not surplus. Arranging more debt financing for highly leveraged Chrysler could also be tricky. Issuing any equity-linked securities, like those GM wants to use, would be more problematic in the absence of a liquid stock.

On top of this, Chrysler and Ford may well think healthcare funding is not the top priority. At Ford, for example, the ratio of retirees to active workers was 1.6:1 in 2006, compared with 4:1 at GM, according to Citigroup.

Meanwhile, Harbour Consulting says average capacity utilisation at Ford's North American factories was 77 per cent last year, compared with 93 per cent at GM.

So for Ford, pushing for more flexible working practices and freedom to close down production lines could be more helpful to the bottom line. Persuading union members to open a wide gap in working practices between different companies is another matter.