* ZF placement price at 50 SEK, 16% discount
* ZF had announced intention to sell
* Haldex shares drop 6.9%
* Haldex calls on 2nd largest owner Knorr-Bremse to also sell (Adds Haldex comments, adds background, details, updates shares)
By Christoph Steitz and Johannes Hellstrom
FRANKFURT/STOCKHOLM, Sept 20 (Reuters) - Swedish brake systems firm Haldex welcomed the sale of a 20% stake in the company by German car parts maker ZF Friedrichshafen and urged its second-largest investor Knorr-Bremse to do the same.
ZF held the Haldex stake as the result of a heated takeover battle with Knorr-Bremse that flared in 2106, resulting in an ownership deadlock with the two companies ending up holding roughly a third of Haldex.
Haldex has loudly complained that its ownership structure, with two competitors as main owners, has hurt its appeal with investors and deterred current and potential customers.
"I might go so far as to call it an early Christmas present to both Haldex and our customers," Haldex Chairman Jorgen Durban said in a statement.
"If I could wish for another, it would be that Knorr-Bremse should now be inspired by the message and begin the process of selling its stake as well".
Knorr-Bremse, which owns a 10% stake in Haldex, said there was no immediate change on its part.
"We are regularly reviewing our strategic investments. This includes Haldex. There is currently no decision to change our participation," a Knorr-Bremse spokeswoman said.
ZF said it sold its stake for 50 SEK per share, or about 445 million Swedish crowns ($46 million), a major discount to the 59.30 crown Haldex closing price on Thursday.
Haldex shares fell 8.6% to 54.20 crowns by 0940 GMT.
ZF, which had bid 120 crowns per share for Haldex in 2016, said it had sold the stake to institutional investors.
ZF this year agreed to buy Haldex's peer Wabco for over $7 billion. Haldex ranks third in the brake systems market for commercial vehicles, behind its far larger rivals Wabco and Knorr-Bremse.
"We have gotten very clear feedback from big players in the market that they don't like our two biggest rivals also being owners," Haldex's Durban told Reuters.
"But I think this will help things loosen up. Everything is possible now, it's just up to us to manage it". ($1 = 9.6640 Swedish crowns) (Additional reporting by Tassilo Hummel in Berlin; Editing by Riham Alkousaa and Keith Weir)