What will it take to subordinate a second mortgage? Does it require a certain LTV?

The subordination will be approved or denied by the mortgage company who is holding the second mortgage. The higher the LTV the harder it gets to get a subordination. If you are at 95% CLTV (combined LTV) the second mortgage company will carry a higher risk of foreclosure.

this is determined by the bank subordinating thier position. Banks dont have to agree to subordinate if they feel there is any reason for non payment.

You will need to contact your second mortgage lender. Typically, second mortgage lenders usually agree to subordinate since they are already in second position as long as your financial position (credit, income) has not changed drastically. The subordinating lender will need to see the approval by the first mortgage lender, an underwriting transmittal form, appraisal and may require income documents. Some lienholders charge a subordination fee up to a couple hundred dollars.

Good answers below. Here's a word to the wise. Be very careful about locking your rate so you can allow enough time for your existing lender to approve the resubordination request. It could take up to 30 days - and you will need to get the appraisal done first.