how and/or when do you know coil springs need to be replaced?
i have purchased a 1977 ford f-100 and am currently ordering front end bushings (radius control arm, radiator support, axle pivot arm) and will be replacing shocks. don,t know how i should know if i should replace coil springs also.

 

For the average person, just walk around, look for leaning, etc. Take a measuring tape, and do some spot checks here and there on the front end, and see if the 2 sides are similar in height

When you have the springs down doing the repairs, check for stress cracks, or excessive rust.
A machine shop could check by seeing how much compression the spring will still take, they can also magnaflux it, and see if it has any stress cracks.

If you have any doubts, new springs aren't that expensive

 

the 77 I beam arm is similar to this project I did here

https://www.fordtruckzone.com/threads/1980-1996-f-150-shock-mount-replacement.655256/
Spring comes out without compressor, but you do need a jack, and a jack stand
You won't have to remove the spring tower like I did for that repair

Like Ken said, be very careful under there, make sure the truck is well supported

 

Right front spring different from left front spring.

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I've replaced the springs on all my F100s when I rebuilt the front end. They don't cost much & I can feel the difference.

 

I would say yes, replace the springs.

 

Polly bushings are great. I have them on my Ram. I like the Energy orange ones.