One of the sources said that bids worth 7.5 billion and 8 billion had been made on Wednesday from private equity houses Nordic Capital, Triton, KKR, EQT, Cinven and PAI Partners, among others.

Both sources, speaking on condition of anonymity since the process was private, said that the sale was expected within the first quarter after German brake manufacturer Knorr Bremse triggered an auction for it by making an offer that prompted its owners to cast the net wider.

Knorr Bremse had submitted a bid in the auction, they said.

Knorr Bremse declined to comment, while the private equity groups declined to comment or were not immediately available for comment.

Dellner serves all of the world's leading train builders and operators by providing couplers, or the link connecting train bogies, and shock absorber as well as rubber connectors for bogies, but does not provide any financial details.

The other source, who also declined to be named, said that Dellner has about a 30 to 40 percent global market share for its couplers.

The company had seen "great growth" over the past five years, and has strong margins, the sources said.

(Reporting by Esha Vaish in Stockholm; Additional reporting by Arno Schuetze in Frankfurt, editing by Louise Heavens)

By Esha Vaish