New to this, but I'm looking at buying a used boat. It has a lowrance X85 in console and a lowrance X75 on the bow. If i would upgrade the console X85 to a new lowrance with GPS would the current transducer work or would it have to be changed also.
Thanks for any information....

If the electronics are nearing, or have met obsolesence, you can rest assured the transducer has also. But, while you're in the investigative stages of buying a grand older boat, ask the nice owner if he would object if you pointed the bow to the sky and removed the transducer(assuming it's transom mounted). "Upgrading" electronics may quickly become less important should you find a hull full of water...and no better way to assure that it does or might not have, would be to back out a couple of those screws and observe.
Safe boating...

The transducer is glassed into the boat. i would have to have the new one mounted on the exterior I think.

Nope, I have X85 & X65 and now I also have a HDS 7. They are noway anywheres near the same. Some glassed ducers in the hull will pop out with a tap of a hammer. That being said I have one I can't get out even by whacking with a hammer and chisel.

The statement is correct that the ducers won't work on today's units. The kHz is way off the current 200 though I don't remember what my 75 and 85 units were.

The way I remove glassed in ducers is with a piece of 2x4 and a hammer. I put the 2x2 on an angle against the top of the ducer and hit the board with a hammer. You probably will kill the ducer but that is not the concern.

Once you get it out be sure to sand off all the old epoxy to get a good clean place to glue the new one down. On the new one it does not matter if it is a puck or skimmer type. They both will glue down in the hull.

Thanks. My only concern is pulling the new feed thru to the console for the rear hull. The one on the bow is mounted to the trolling motor, a no brainer there, its easy. i didnt think that they work work being there age and the new electronics.

Running a new transducer cable to replace an old one is easy.
Just tie a heavy duty string to the old transducer plug, tape up the connection so it won't get hung up in the boat wiring harness and pull the cable out. Tie another string to the new cable. Use the string to pull the new transducer cable and new string to the console, do the same taping up of the joint so it won't get hung up in the wiring. That will leave you the extra string to pull another wire or cable later if you need to. Always add a pull string as a spare when you do that kind of operation.

There are 2 ways to do this: 1. tie a stout nylon cord to the old transducer cable and pull it through as you take the cable out. 2. Get yourself a fish tape and either pull it through like the nylon cord or run it by itself.

Either way tape the new on to your pulling device and get someone to be on the other end while you pull it through.

A second person is usually necessary as they get hung and have to be pulled back and forth to clear the blockage.

Good luck

Thanks...sounds like good advice.