I found the same when I ran full vehicle durability. In order of most to least tire replacements it was, RR, RF, LR, LF.

 

Rob, On another note. Sorry I didn't have time to meet for lunch but we were on a hectic schedule the few days in town. trip was awesome and aside from our meeting with Dana Spicer, and Jeep we meet with the Ford performance group and the truck group including getting to do some work with the new Bronco that is coming out. Some exciting stuff in the works, hopefully we can catch lunch next time.


spent some quality time in Mecca but this is the only pic I got because they sequester phones/cameras for the cool stuff.

 

^No problem, that week was hectic for me too! Hopefully next time we can meet up!

 

I believe that was the most politically correct statement I've seen on here! You running for office?? You used a 3 syllable word followed by a 5 syllable word making your sentence have "Gravitas" It does take a Village to fix an Excursion

 

I speak with the experience of replacing EVERY piece of suspension on my Excursion. I have ATS V/C springs, Hellwig bars front and back, Rancho shocks, new steering box and every front end part possible. The front end has been aligned to factory specs.


My truck still does not steer perfect and still wonders some. Driving the truck takes more concentration than it should.


The only thing it can be is the CASTER. My next step is to take it to the alignment shop and ask for 5 deg of caster. Don't know what else to do...

 

I took about 3-4" of play out of the center of my steering adjusting the steering box. Huge improvement! I will probably replace with a cardone before long anyway. '04 with 114k on the truck, ball joints and tie rod ends are pretty tight.

 

If you're referring to the V/mod B springs that many have done (including myself), then I disagree that the modification leads to a spring with the same rate but just longer. Are you aware that the mod B part is removing the overload leaf and add two leaves from the Excursion spring pack to the F-250 spring pack? If the Excusion rear springs are rated for 2200 lbs and the F-250 springs are rated for 3000 lbs (both numbers from memory) then I don't see how 3000 + two extra leaves = 2200.

Further, here are a couple pictures of my rig with the rear axle loaded to 7160 lbs according to the cat scale I weighed it at:





You are going to have a hard time convincing me that these springs are the same but longer.

 

The problem with "aligned to factory specs" is that those specs have a wide margin. Caster 3.5* +\- 2* Camber .025* +\- 1* Toe .003* +\- .25*

You can have foul handeling Ex and be within spec.

It could be as simple as a slight toe out adjustment, but it is likely caster.

If you are on stock front springs what is your measurement from the center of the wheel hub to the bottom of your fender arch ? Just curious how much your springs are sagged ? Also what tire pressures are you running front and back ?

 

simple comparison

ford specs the Excursion rear spring rate as 410 pounds per inch. and a rating of 2275. simple math shows that 410 lbs inch x 5.5. inch = 2275 pounds

so there is the Excursion 5.5" of travel

Ford spec on the B code F250 spring is 320/670 rated for 3000 pounds.

the main leaf pack of the B spring is rated at 320 lbs per inch ( compared the the excursions 410) and we can see from looking at the engineering drawings that the overload leaf does not come into play for the first 5" of travel.

That puts the B code at 320 lbs inch x 5" = a "rating" of 1650 pounds. ( graph shown is copied from engineering blueprints )

However the Mod B spring most people build uses the bottom 2 leafs of the Ex spring. here is where you have to take it on faith since I don't have both springs in front of me to measure but since you live close I will be happy to come over to your house and we can measure and calculate together ( ill bring the beer ). The Top 4 leafs from the Excursion (which has a total of 6 leafs ) and the 4 leafs from the B code are both 320 lbs inch springs.

Adding the Bottom 2 leafs from the Excursion pack onto the B code pack increases the B's spring rate from 320 lbs inch to 410 lbs inch the same as the excursion.

Since the B code spring has more travel at 7.1 inches you can take
7.1 travel X 410 lbs per inch = 2911 rating ( what it takes to compress the spring to its design limit, i.e. flat )

Now the overload.

since we know the Stock B has a spring rate of 320/670 we can subtract and come up with the overload leaf has a rate of 350 lbs inch.

This would give the typical B mode spring a rate of 410/760

since we know that the overload spring only adds spring rate for the last 2" of travel we can figure the rating as

410 x 5 = 2050
760 x 2 = 1520
total rating = 3570

fell free to ask question

 

I'm going to have to read that over again tomorrow to get it all. Thank you for going through that, it did make a fair amount of sense the first time. And I need to update my location. I've since relocated somewhat...

 

While I am thinking about it, here is a summary.

Stock G code Excursion

Main pack spring rate 410 lbs per inch
Main pack travel 5.5 inches
Main pack "rating" 2258 lbs

Over load spring rate 0
Over load travel 0
overload rating 0

Rating 2258 lbs


Stock B code F350

Main pack spring rate 320 lbs per inch
Main pack travel 5.1 inches (7.1" total )
Main pack "rating" 1632 lbs

Overload spring rate 670 lbs
Overload travel 2 inches
overload rating lbs 1340

Rating 2971 lbs


Mod B code

Main pack spring rate 410 lbs per inch
Main pack travel 5.1 inches (7.1" total )
Main pack "rating" 2091 lbs

Over load spring rate 760 lbs per inch
Over load travel 2 inches
overload rating 1520 lbs

Rating 3611 lbs

 

Pirate, I agree with your math but for clarification I will say...

Call the overload spring, the "secondary rate" to avoid any confusion for those who use the pick-up overload spring in their main packs.

I agree that one needs some faith with the Ex spring calcs. I know you know this but for clarity sake...Even though the drawing is linear, actually linear for all leaf springs since they are tested at only a few load points. The reality is the rate is progressive and one rate rolls into the next but we don't have any load points in between. If it was linear like the drawing, the passengers would know when the second rate engaged! I will venture to say that the two small Ex leaves do not add much to the rate at light loads/lower deflection...but for the sake of conversation, this is all we can do is to make the "linear" assumption. Nice job with the math!

Lastly, was this a typo?

410 x 5 = 2050
760 x 2 = 1520 should be 670 (avg rate per dwg)x2 or 1340, total load rating of 3390?
total rating = 3570

 

Ha, if you knew how hard it was for me to call the secondary rate leaf an overload. Lmao I used the commonly misused name to try and avoid confusion.

Typo, no.

On the stock B code the secondary rate of 670 is achieved by adding the 350 lb rate of the 5th leaf to the 320 rate of the main pack.

On the mod B the main pack is 410 so add the secondary rate leaf at 350 and you get a 760 secondary rate. Secondary travel is still 2" of travel so 760 x 2 = 1520

As far as the passengers knowing when the secondary engages. I'd beg to differ, it's that hard hit you feel in the seat right before you slam your head into the roof.

 

Ha! Thanks for the clarification of my clarification!

If you keep the ratio of the secondary to the primary rate close to 2, it's very subtle. This is one of the reasons I chose my SRW C codes. I have a column in my spreadsheet that calls this out. From memory one of the worst springs is the F code, ratio of 2.33 IIRC.

 

The x2 secondary rate holds true even in desert racing.

I've wondered if the factory bump stops use the same formula, I use an air bump and the rate can be adjusted by changing the pressure. I've never calculated the rate but it is pretty obvious when it is to high.