Mishne: Borrowing from a goy against chametz Jewish collateral, or lending
to a goy against chametz goyish collateral. Is the issue only when the loan was not repaid with cash on time after Pesach, or even if the loan was repaid with cash on time after Pesach ?
These halachos are found in OC 441. Here is a quick summary of the Halachah (v'Lo l'Ma'aseh):
If, when giving the collateral the borrower, he states that if the loan is not reapayed by the agreed date then the lender should take possession of the Chametz from that time (Me'achshav), then the Chametz is considered to be the possession of the lender from that time, in the event that the borrower defaults and does not pay the loan. Of course, if he repays the loan then the collateral never became the property of the lender at all.
Accordingly, if the lender is a Goy and the borrower a Jew, the Chametz
would be Mutar after Pesach as it was in the possession of a Goy. If the
Lender was a Jew and the borrower a Goy then the Chametz would be Asur, not
only after Pesach, but also on Pesach because of Bal Yera'eh and Bal
Yimatzei, as it was in the possession of a Jew.
The Mishnah Berurah (#3) points out that the implication of the Shulchan Aruch is that the Chametz is only permitted b'Di'eved. Since the possibility exists that the Jew could repay the loan before the designated time and thereby the Chametz reverts to the possession of the Jew from before Pesach, many Acharonim hold that the collateral of Chametz should be redeemed before Pesach and this arrangement should not be relied on l'Chatchilah.
Kol Tuv
Ilan Segal