Also the vans age the steering is a little more sensitive beacuse of the extra weight so they exagerate the feel when there is a bad alignment. I would take it to a good alignment shop, not a 39.95 in an out in 30 minutes or it's free shop. One where they have REAL trained ASE certifed techs, not high school kids who dropped out.

 

well here is your brake popping problem. change the pins that hold the calipers to the spindle problem fixed. front end the vans eat radious arm bushings because of the weight. and when the radious arm bushings go bad this puts a bind on the I beam pivot bushings. witch in turn wears them out also. and a second effect or radious arm bushing is it starts wearing the tires on one side (cant remember if it is outside or inside) ford power stearing boxes do not last. this is with f and e trucks. get a repair manual there is an adjustment on the top of the stearing box to tighten it up. also check the tie rods. if you can find them use all moog front end parts. also if you want to save yourself from having to change tie rods and ball joints often because of no grease fittings i drill holes in all mine and add my own grease fittings just like should have been done when they were built.
the crazy shaking you feel when you hit your brakes is a warped rotor. the rotors on the 150 trucks are small and get real hot quick. high speeds and fast stops is the cause of warped rotors. dont forget you are driving a 6000lb truck and trying to stop it like a small car with rotors no bigger then a standard full sized car brake rotor. also check and make sure you have your back brakes adjusted to specs. if they are not this puts even more load on the front brakes. alignment on ford trucks should be done buy a dealer. not some fly buy night repair shop. the dealer does alignments on these vans every day. they know the proper way to set a ford truck with I beam suspension. hope this sheds some light on the problems you are having. i have had all the same problems you are talking about and more. the 350 van has large brake rotors. they will also warp under heavy braking. if your van is extended you are trying to stop that much more. also with extended vans you have like 3ft of van hanging over the rear axel. at high speeds the wind is pushing down on the rear of the van witch in turn is taking weight off the front end making the rear squat and letting air under the front of the van witch gives a lifting effect and could cause a lose feeling in the front end. on the 350 van i cant remember how the calipers are mounted to the spindles. reguardless all brake hardware should be checked replaced cleaned and antisized as required. the pins that hold the 150 calipers to the spindles are made with rubber. rubber does not like heat. and brakes get ultra hot. i replace the pins everytime i change pads. they are cheap to buy and they get weak so replacing them should be a common practice.

 

85K, and I just replaced brake pads, the rotors looked a little scored, but not bad. I do nopt get the 'pulsing' feeling that one gets when their rotors are warped. This is a violent shaking on the wheel, and consequently the entire front end parts when I first hit the brakes at 75-ish mph.

Airborne; I don't know about all of you here, but with 3.73 gears and an OD tranny, 75-80 is where this engine likes to run. Here on the west coast if you're not at least 75 mph you're getting flashed and tail gated to pull into the slow lane.

 

Cool, radius arm bushings, I'll look into this, thanks. Your post has a veritable plethora of knowledge, thank you so much. This is the things I was looking to find, the extra length etc, the replacement of pins. To everyone else who answered, thank you also, to camarokid, thank you again !