Finding info about clan before joining it, such as war win/lose ratio

the clan can choose to not let anyone see the war win/lose ratio or they might have not done any wars yet to see their clan just hit view clan and also if a clan says free elder be carfull they could be a failing clan.

There is no chance to get the win/loss ratio

You cannot view their win/loss ratio. You can join the clan, look at recent wars, and make a decision. Related to being elderless, that's primarily opinion based. Elder means different things to different clans.

I'd suggest 1. Joining the clan and taking a look at their past wars 2. Check out the profiles of their leaders, look at their donation rates/clan war stars/any other information you think is important to you.

Unfortunately, Supercell has not provided very meaningful ways to scope out a clan before joining it.

There's no way to determine how good a clan is before you join it unless you are looking for specific things.

You can see where the clan is located. If you are from Australia and the Clan is based in China then it may not be the clan for you unless you can speak Chinese.

You can see how often the clan wars as well.

It terms of telling how well a clan does in war you can look at the players in the clan. A Clan that has a lot of rushed Town Halls don't usually have a great war record.

The best thing you can do is join the Clan and opt out. Watch how they war raid and communicate. The war ratio is not always a good indicator as to how well a clan wars consistently. For example, my clan just had a 5 loss streak because we had 2 Town Hall 10's and the 5 enemy clans all had 4 (why? I'd like to know too). Before that 5 loss streak we hadn't lost a war in 3 months.

Is there a way to know the details of the wars before joining it?

War win ratio is sometimes seen in the clan's description, usually to show off their win streak and how awesome they are. Now even though you can't quite see the exact details of the clan, a very high level clan usually means they win.. a lot.

Clans with high-level players with a serious description and wanting good players for war also a sign that the clan is efficient in war. Clan level at least of 6 usually means a nice history behind them. Matching their number of wars won with their clan creation date (if seen) can also help a lot. Though you can't see all the details yet, with good players, lots of wins, a serious war attitude, and a high clan level usually means a very active, and successful war clan but it's a risk you gotta take.

Joining just to see the history is just a waste of time. Most clans with good histories are also invite only, so watch for those clans. Anyone can join type clans are usually desperate for members, not good war members. And waiting for the invite to be accepted can take a while...

I've seen some clans boast about being Elder free but isn't this a bad thing?

It depends. Elder is a good incentive sometimes if used wisely. If everyone is elder, there isn't much off a difference of all members. Having free elder also helps by letting clanmates invite valuable and/or needed players without lots of begging. Now if you say free co-leader then you got a really big issue here...

War clans isn't operational anymore but that was one way to see win loss record. As for being elder free that all depends on do they get elder for loyalty etc.

You can just check the War Log in order to view War info. (However, you can see it only if it has been set to Public by a Leader/Co-Leader) Also, check if members donate enough. This way you can tell whether a clan is worth joining, or not.

warclans.com can tell you their win/loss ratio