Tired of looking this issue up on multiple websites, so here's as much info., in one place, to help the next person.
The original TSB is TSB 99-16-3. The fix as of today, 7/24/2012, is a kit that comes with 8 plastic pieces. The current part number is 1C3Z-5B302-AA. The parts fit a particular front spring style, width, etc.
Squeak in front springs. It appears that this issue began in 1999, and although it is not mentioned in the Ford TSB system, it continued into 2000. At some point in 2000, a change in the front springs occurred. Some owners have purchased this kit and modified the parts, or omitted some of the parts, to fix their squeaky springs for other model years after the 2000 spring change occurred.
Here's what FireMe from Ford-Trucks.com posted:
There's a few things you should know about the isolator kit. First, it is intended for 1999-2000 SD's that have mid-eye front main leafs. That is, the lower spring contacts the upper spring only at the eye and not along its entire length. Ford changed the design on later models to a flat upper leaf and the spring isolators last longer on them because of a larger contact area.
Second, the kit contains a lower spring isolator that is similar to the factory one, except it is made of a much harder plastic. There is also an upper isolator that mounts on the spring eye and provides a contact surface for the lower isolator. The two isolators contact each other so you have a plastic-on-plastic sliding action, instead of plastic on metal. These last a very long time compared to the originals. Sorry, no pics.
I suppose you could buy the kit and just use the lower isolators, but that would mean throwing away half of what you paid for. There is no way to use the upper isolators on a later vehicle with the flat main leafs, and there really isn't any reason to.
If you want isolators similar to what were installed at the factory, just go to the dealership and purchase some. The part numbers for the isolators were made available in a TSB and they should be able to look them up. I can't get on that part of Ford's system from home, so I don't have the TSB number handy, but it is still valid as I just looked it up a couple of weeks ago. I'm sure a spring shop could get you the same thing.
Squeaky Springs - Isolator Kit Questions - Ford Truck Enthusiasts Forums
Squeak in front right leaf spring. - Ford Truck Enthusiasts Forums
This is for the FRONT springs. Of course, the rear springs squeak as well, but that's different TSB's and parts, or maybe some of these parts. It's a bit of a hodgepodge of information when you research it.
Back to the parts in the kit... They are a hard white plastic. Some guys say teflon, but they don't look like my egg skillet, so I'm saying plastic. The plastic pieces fit between the springs so that the metal of the springs don't rub each other and squeak. Supposedly, the original pieces were too soft and wore out quickly. They may be completely missing if yours are worn completely through.
Again, the current part number is 1C3Z-5B302-AA. My Ford dealer looked it up for 1/2 an hour, repeatedly saying it's obsolete, doesn't exist, can't find it, no such thing--the excuse train. But, alas, he found it, ordered, it, and I got it. $50-ish. The part numbers have changed, superseded, etc. The original TSB 99-16-3 states part number F81Z-5586-AA. Note that the TSB is from 1999 and even though it applies to some 2000, I could never find an official source. My truck is a 2000 and it is the correct kit.
SUSPENSION - FRONT LEAF SPRINGS - "SQUEAKING" NOISE HEARD WHILE DRIVING
NOISE - "SQUEAKING" NOISE HEARD FROM FRONT LEAF SPRINGS WHILE DRIVING
Publication Date: JULY 23, 1999
1999 SUPER DUTY F SERIES
A "squeaking" noise may be heard from the front springs as they compress during driving on some vehicles. This may be due to debris imbedding between the front spring tip isolators and the front springs.
Replace front spring tip isolators with revised isolators. Refer to the following Service Procedure for details.
Raise the vehicle so that the front axle is allowed to hang freely suspended (lift vehicle by frame).
Use a prybar to open gap between two (2) leaves.
CAUTION: PRIOR TO STEP 3, IT MAY BE NECESSARY TO REDUCE THE HEIGHT OF THE CENTER BARBED NUB WHICH PROTRUDES THROUGH THE LEAF. CAUTION SHOULD BE TAKEN NOT TO NICK OR GOUGE INTO THE METAL OF THE LEAF.
Pry out worn tip isolator.
Using pliers to hold the replacement spring tip isolator on the locator flange and maintaining force on the prybar to keep two (2) leaves separate, position the isolator so that center barbed nub fits into the hole of the lower leaf and the two (2) locator flanges are oriented outboard of the spring.
Remove prybar and allow leaves to close on each other.
Follow Steps 2-5 for both front and rear front spring tip isolators.
PART NUMBER PART NAME
F81Z-5586-AA Front Spring Tip Isolator (Qty. 4)
OTHER APPLICABLE ARTICLES:
Eligible Under The Provisions Of Bumper To Bumper Warranty Coverage
OPERATION DESCRIPTION TIME
991603A Replace Front Spring Tip Isolators 0.5 Hr.
BASIC PART NO. CONDITION CODE
304000, 390000, 702100, 790000