tekman741 said:
Point is well thought out unfortunetly I am not as knowledgable so I'm trying to take in as much info as possible before sinking another $1000 +/- into the minivan to haul the camper. My goal is to use the local landfill scale for three measurements:
1) tow vehicle weight(sienna)
2) tow vehicle and trailer (both on the scale)
3) tow vehicle and trailer with only the tow vehicle on the scale=tongue weight.
Good, but those scales are not very sensitive so the tongue weight (Sienna with trailer minus Sienna without trailer) will not be very accurate. Also, the WD system must be disconnected for this to work. To really know what's going on, that means three trips across scales which provide individual axle weights:
- Sienna alone for tow vehicle weight and starting axle loads
- Sienna and trailer without WD for trailer weight and trailer starting axle load
- Sienna and trailer with WD connected for final axle loads
The scales which can't be arranged to give a number for each axle will work as planned for tongue weight and total weights.
If you want to get closer, the tongue weight can be measured directly at home with a suitable scale... for trailers with enough tongue weight to need WD, that's a high-capacity bathroom scale, a lever arrangement with a common scale, or a special trailer tongue scale (such as a Sherline).
tekman741 said:
When the dealer adjusted the WD they set it as if the trailer was heavy (3500lbs). There is a set of directions that shows how to do it.
Yes, there are directions... and they do not involve some calculation of over-adjustment for higher loads, and have nothing to do with trailer weight. They could hook up a heavier trailer, with some higher hitch weight which may be different from a heavier trailer that you might tow, and thus get settings which are wrong for you.
More likely they just cranked it up a notch from the setting which they thought would be correct for your actual trailer. They might have some "rule of thumb" which says how much load is transferred per notch or turn of the WD adjustment, so they can guess how much to crank it up, but the result in any case is too much load transfer with the lighter trailer tongue.
tekman741 said:
So the WD works by shifting the weight as evenly as possible based on the measurements
There is no clever design or adjustment of the WD system which can change the proportions of the load redistribution, only the total amount. If the distance between the tow vehicle's axles (the wheelbase, which is 3.0m or 120" for the Sienna) is equal to the distance from rear axle to the trailer axle, then it is like two people on a teeter-totter - the load transferred to each end (tug front axle and trailer axle) is equal. If one dimension is longer (and usually the rear axle to trailer axle will be longer than the wheelbase) then that end gets proportionately less load, like a person sitting further out on the teeter-totter who doesn't need to weigh as much as the person closer in on the other end. The proportions of the load distribution are entirely dependent on the length proportions of the wheelbase and distance to the trailer axle.
So, if the WD system is adjusted to add 150 lb to the front axle, and the trailer axle is 180" from the van's rear axle (1.5 times the wheelbase), then the trailer axle will get 100 lb added to it (150 lb / 1.5), for a total of 250 lb removed from the rear axle.
If by "as evenly as possible" you mean that the person doing the adjustment is trying to even out load on axles, take the vehicle away from them and find someone who knows what he is doing.
Correct adjustment is about counteracting unloading of the front axle and staying within all axle limits, not making anything equal.
tekman741 said:
The airbags would also do this and help with ground clearance. both help with sway along with trailer brakes. correct?
Airbags do
not change axle loads, they only make the suspension stiffer (so that it controls heavy loads better) and higher (to reduce sag). Yes, they would help with ground clearance (by lifting) and sway (with better control).
If the rear suspension height is changed with air bags, then the angle between trailer and van changes, so the WD springs are bent a different amount, so the load re-distribution is changed... so the WD system needs to be readjusted. The same thing goes for loading down the back of the van with cargo so it sits lower... that's another WD adjustment.
Trailer brakes are for stopping shorter and with better control, but they can be manually applied to control sway if it starts. I've never needed to use them that way.
