Very Weird Radio (AM/FM)

[Subzero]

My truck has the am/cm radio option on it. It lights up and plays fairly well for a 45 year old radio. Occasionally it will change stations by itself or go off the station. It's hard to explain so I'll use an example: say a station is on 100 FM , sometimes the radio will "slide" the stations down. The station that is on 100 FM now will play when the dial bar is close to the 96 mark on the face and if set to the 100 mark it will be static.

All the stations do this, I can't seem to figure out why but it gets frustrating when you have to keep searching around when they slide like that. What could be wrong with the radio?

[Mancar1]

Sounds like a reception problem. May be the antenna causing it. Check for a bad or corroded male/female end where the antenna plugs in. You may need a new antenna. Or could be the Gemlins that the people over at Bow Tie country like to plant in our Fords.
Or are you saying that the dial actually moves on it's own? That would be a worn out internal part. A well tuned radio expert member will chime in I am sure.

[Nitekruizer]

Sometimes the mechanical tuning in old radios gets sloppy over time just from wear and tear. Could also be an internal electronic part going bad or may even be dirt, dust or corrosion in the mechanical tuner (variable capacitor).

Does it only do this on FM or does it do it on AM too?

[tac]

You might try taking the top off and see if there is a buildup of dust and blow it off with air. Don't bend any of the little wire coils (inductors). Does it change when hitting a bump (mechanical tuner) or does it start changing after it warms up (probably leaky caps). You can clean the tuner but the caps will need to be replaced.

[Subzero]

It does shift when going over a bump but it also could be the caps. How do I take the top of the radio out?

[tac]

Straining my memory on that one. These were new when I was in high school. I think unplug antenna and power, then pull the knobs and remove 2 nuts under them and then I think there is a bracket on the back of the radio. Somebody correct me if I'm wrong. I think there are screws that hold the covers on but I'm not too sure. Only original radios I have here is a 66 mustang AM only and 66 thunderbird AM/8 track.

[tac]

Going over a bump sounds mechanical. You may want to look at this to see what the insides of it will look like:
http://www.mustangcountry.com/articles- ... /home.html
If you want to have it fixed:
Guy in Aurora IL http://www.unitedradioserviceinc.com
Or expensive complete restoration
http://classicradio.com
or,
http://www.fredsclassicradios.com/

[68RGR]

If the tuning knob is connected to a variable capacitor, it might be that the capacitor's tuning shaft is too free to turn. If so, there should be a way to add tension to the shaft. Look for a jamb nut and a screw on the back side.

Various other things could cause this behavior but, obviously, something in the tuning circuitry is being affected by vibration or movement. If you can get it out of the truck (it's not easy if it has to come out from the underside of the dash), remove the cover and connect a speaker, antenna and power to it. Then, use a wooden or plastic rod (pencil, dowel, etc) to apply slight pressure to any coils, etc in the tuning circuitry. Doing so could reveal the problem. To me, something is loose and, when it moves, the resonant frequency changes. I suspect you will find a mechanical problem. Of course, it could be an intermittent connection from a poor solder joint but that's still "mechanical" even though it is an electrical connection. It might even be a stray piece of metal affecting the tuning capacitor. I'm betting you can find it and fix it yourself.

[FORDification]

Funny you should bring this up, since the factory AM/FM radio in my '75 does the exact same thing....and it makes the radio virtually unusable. In fact, I just picked up another AM/FM from the junkyard but haven't had a chance to install it yet. I'm going to pull this one apart and clean/lube it first, because I think I know what's going on.

If this radio is like virtually every other older stereo/radio I've ever torn apart, the tuner control has essentially what is a piece of string which is wrapped around it, and the station indicator/marker is attached to this string. When you turn the dial, the string wraps around the shaft and moves the indicator. Now...to keep the string tight, there is a small inline spring. If the tuner controls are binding at all, then it's slightly stretching this spring out, so that when you drive and go over the bumps, the spring is slowly retracting....and changing the station!

My 'new' radio is sitting on the workbench out in the garage, and I'm thinking that sometime within the next couple days I'm going to pop the covers off this thing and take a look...and see if I'm right.

[Subzero]

Thanks for the info, I'll try cleaning it out first, then if that fails I can move on to more serious work. I plan to put in a hidden aftermarket radio when the funding shows up, won't be anytime soon so I want to fix this radio. Mine is able to be listened to, some drives it does fine no matter what I run over . Other times it will drop out just on it's own.

[oldyeller69]

have you ever thought of an exersist