i have a 1977 chev 1 ton 4x4 tow truck and would like to know if i can put add a leaf in the front springs.  

Not a problem. I have done it a few times in past. What do you have now 2 leafs or 3?  

A 1 ton should have 3 leafs origonally from GM.  Add leaves as you desire, but you will most likely need longer u-bolts and the 2 cap screws (bolts).  

As I recall, 3 leafs were not standard then even on that model.  

Every 1970's and 80's GM 1 ton 4X4 that I have looked at has 3 leafs on the front packs; standard cab or crew cab.  My 1982 1 ton had 3 leaf standard.  My 1976 3/4 ton has origonal 3 leaf that had to have been special order.  On what basis to make that clam snoman, there are more variations on different models and different years than any of us on here know about.  

GM1tonOfFun:
Every 1970's and 80's GM 1 ton 4X4 that I have looked at has 3 leafs on the front packs; standard cab or crew cab.  My 1982 1 ton had 3 leaf standard.  My 1976 3/4 ton has origonal 3 leaf that had to have been special order.  On what basis to make that clam snoman, there are more variations on different models and different years than any of us on here know about.

My first 4x4 was a 67 Chevy and it was but a few years old when I got it. I have owned many over the years and I have seen 1 ton SRW 4x4 both ways (2 and 3 leaf) but the dual models I have seen did have 3 leafs. My 72 3/4 ton GMC had option F60 HD suspension(as I recall) which was a 3 leaf front spring set. ALso there was two different kinds of 2 leaf setups back then. The standard one and one with a little thicker (less taper) and wider leafs. I know they existed too because I seen them. The heavier one were standard on 3500 SRW and 3/4 tons with 6.2. I was driving when all this stuff was new.  

Thank you for the information SnoMan.  The 70's trucks I was refering to is 73 and up.  I also have a 71 3/4 ton Chevy, but it is 2 wheel drive.  I have not yet seen a 73 and newer 1 ton with only 2 leaves, but I will take your word on that.  

As I recall the stock two leaf setup had a "rated" spring capacity of about 1800 lb ea, the HD 2 leaf was like 1950 or so and the 3 leaf was "rated" at 2250 each. Once I made a 3 leaf setup buy taking a 2nd leaf out of a HD 2 leaf setup and adding it to a 2 leaf setup. These leafs were arched a bit higher than extra leaf in a stock 3 leaf so the net result was it raise front end of truck about 2 inches or so and leafs were close to flat rather than reverse curved. I still have those leafs around here somewhere as I used them on my burb for many years when I had bigger rubber on it but I lowered it back to stock with stock type tires many years ago as I need more vertical clearance overhead and I wanted to soften the ride back up a bit too.  

I have also made a 3 leaf set up, but I started with the 1/2 ton springs.  I took the stock springs out of my 82 Blazer and rearched them (I don't recomend rearching but it worked) and took another set of 1/2 ton springs and rearched them the same, cut the ends of the main leaves from the second set to the desired length and taper.  I initially put it together as a 4 leaf but it made the front of the Blazer sit up like a 6" lift, so I took the 4th leaf out so it sat like a 4" lift.  I knew it would settle down a bit and it did exactly as I was hoping.  It settled down to a 2 1/2" lift and never settled any more. I used urethane bushings (greased) and it rode better than any stock front leaf spring truck I have been in yet; and that was with or without the snow plow on it.  I did space the anti-sway bar mounting point down about 1/2" to make sure there was no binding during suspension travel.  I still have this Blazer.  I plan on doing a similar set up on a 1986 pick-up that I have.  Both the 82 Blazer and 86 pick-up have the 6.2 Diesel; so if you know the spring rate of those I would be interested in hearing.  

If those 6.2 vehicles have a two leaf setup, they have the HD two leaf design I was telling you about. Man with a 4 leaf setup like you mentioned, it had to ride ruff at times.  

I never drove it with the 4 leaf set up.  Once I set it down and saw the hight, I jacked it back up and took the 4th leaf out.  Thank you for the info on the spring rates.  

re-arching a leaf spring is fine... as long as it isn't a tapered leaf... they tend to crack more often then not...
some truck supply stores can order leaf springs to specific lenghts for you and then arch them (they come completely flat) to whatever height you desire... same basic thing they do for a pre-packaged lift kit... only much cheaper... me personally i like the older "military wrap" style leaf springs...