Booster, you probably discussed this at lenght in Photog's thread, but could you give me (us) the reason(s) the Moog 81004 would lift and hopefully smoothe the ride of our rigs, replacing your original Tuftruc 1617 that are no longer available ?
I compared spring rate, free length and installed height between the OEM, 1617 and 81004 and it seems that the 81004 specs are much closer to the OEM than the 1617 which seems to be stiffer.
Just cant seem to get the courage to order before I am certain they will do the job up front.
Thanks
Even if the details were in Photog's thread, and thus very hard to find, some things have changed since then anyway. The idea behind it all is still the same, however.
We likely had the very first set of the 1617 springs that Tufftruck sent to the US, and it appears that ours were not what the specs at the time stated. The spring shop and I did not notice that they were made of smaller wire size than the 1617 spec called out, at 1.03" diameter wire instead of 1.06" diameter wire. Later 1617 springs that others got shortly after ours were of 1.06" and stiffer, with some complaining of too stiff and others not. The current 1617 is different again, so can't compare, it appears.
As it turns out, the 81004 spring is also made with 1.03" diameter wire, is the same free height, and has the same wind angle (so same amount of coils) as our Tufftrucks. They are essentially the same spring that we have, by all accounts, and have been giving folks the same front end height as we got.
The stock springs are mostly in the .94" diameter range, from what I have seen, although we have heard of some that said they had seen some 1.0" ones. Stock springs have a higher wind angle, so less coils and stiffer, but take a set easier and are more progressive in springrate.
The "smoothing out the ride" comments are kind of a catch all term without the details necessary to decide if they are right for you, or not, IMO.
The backstory of it has to do with the design of the GM van front suspension, particularly the springing method. The vans have to be able to ride acceptably when empty, so softer springs would be nice, but they also need to be able to carry the big loads in a 1 ton van, so stiffer springs are needed. The way GM chose to address this paradox is to use softer springs but add a special bumpstop on the control arms to pick up the extra load when the soft spring gets compressed too far. It is a Timbren type urethane spring and very progressive in springrate because of it's limited height and travel. It sort/kinda works OK for a work van that sees varying loads, and is OK for empty vans as it is running on the softer springs then. On a fully loaded all the time van like a Class B, however, the front suspension is constantly bouncing off the very high springrate bump stops, which adds a very progressive spring in the middle of bumps, causing harshness and "pitching" of the front of the van. The shocks can't be tuned for both springrates, so seem to be set to match the softer springs more than the stiffer combination of spring and bumpstop, so the rebound off the bumpstop is much less damped than if it was shock matched, thus the pitching issue.
The net result of all the tech garble above is that the stock springs will likely be softer than an 81004 on small bumps, but harsher or the same on bumps larger than that because the bumpstop is getting hit. This is just for the softness, not the control or stability.
The 81004 is a non progressive spring so constant springrate, and with a lot of coils so more consistent over it's travel. With the 81004 in the van, it will ride nearly 2" higher, so the bumpstops don't get contacted on anything less than a huge bump, so there is no sudden change in springrate in the middle of a bump. The shocks will be damping against the same springrate all the time, so damping won't change over the travel, unless it is designed intentionally into the shocks.
What most of us describe would the with the 81004 springs, small bumps will get a bit harsher and the larger bumps will get less harsh and more controlled.
The 81004 (and our near duplicate Tufftrucks) seem to match very well with the stock replacement Bilstein shocks, as the designs are somewhat complimentary. The Bilsteins use variable damping that is set up to provide less damping on small bumps when you don't have travel control needed much, but want comfort. On the larger bumps, the damping increases to control the higher load and faster wheel motions and gives more control of the vehicle. Most feel the ride quality on big bumps isn't any worse than when on the bump stops all the time, but that the control and consistency is way better than stock.
So as you can see, the "smoother ride" is really an conglomeration of individual experiences, each of which is a very personally subjective item.
It does appear we have had very few, if any, real complaints on those that have used the 81004 springs concerning the ride and handling quality of them. Some wished raised the van more, but that is not what they were meant to do. As it turns out, they put the van just about right at the ride height that GM calls out in the factory service manual, so all the front suspension is right were it should be, geometry wise, for best handling characteristics.
As much as I like to compare factory specs on things, the spring rates that are out there for the different springs mystify me. I have not been able to even come close to duplicating the various rates across manufacturers when I use the spring specs and dimensions to calculate the springrate on a spring calculator program. It is very frustrating to say the least, and in Photog's thread gave us fits trying to guess what would happen with any given spring, based on the supplied spingrate.
While the rates between the OEM and the 81004 springs looks to be fairly close, depending on what place you get the rates, the results would indicate they are not all that close. The springs are the exact same free height, but the 81004 lifts the front end 1.75" on average (depends on how bad the front had sagged-they all end at the same height).
Hopefully, some of the folks that have recently switched to the 81004 springs will chime in with some more detailed impressions of ride quality under different conditions for you. If they also let you know which shocks they are running, that would be a big help also to putting the pieces together. Perhaps if someone lives near you, you might be able convince them to give you a test ride.
Good luck on your quest!
