Van has 77K miles. Feeling bumpiness through steering wheel at low speeds. Smooths out somewhat at higher speeds. Are bushings wearing? What would be the best method to diagnose?

Go to alignment shop.possible bad idler arm,ball joints,or even control arm bushings.with loose front end parts you loose your toe in settings that will give you that "floating"feeling shop around for best shop & price.

check your wheel bearings

Wheel bearing going bad I would check that first jack up vehical try wiggling tire from side to side to see if there is slop.If there is change wheel bearing and check for Tie rod wear.

Check engine mounts. If it is a rear wheel drive or 4 wheel drive- inspect driveshaft(s) for damage or missing weights. Also check universal joints for wear, and the rear driveshaft slipyoke for leaks and wear. If there is a leak, the rear seal and bushing should be replaced.

If front wheel drive, inspect drive axles for damage, and inspect the steering components for damage or wear.

Dear Sir,
As you said you have problem with steering wheel drugging while brake, i think it may happen at time when your car abut to stop or got slow may speed between 30 to 20 km/h, if this is case then first replace fr tyre with rear both and then Tyre if problem solve then it is a problem with tyre, it got uneven wear due to imbalance actually tyre shakes and that feeling we feel in steering wheel. and if problem not solve then replace fr both low arm bush and joints. there is only to cause that can make steeing vibrate. i hop after trying this you have soled your problem if any issue please let me know. Thanks.

Yogesh

Have your tire pressures checked, look for any bulges, bubbles, uneven wear. It may be a matter of having the tires balanced too, almost any tire shop will check pressures and inspect your tires for free, balancing runs about $7 USD on average. I hope this helps, and good luck.

its in the suspension some were,, it could be any thing and with out checking it out, nobody can say for certain,,, ball joints shockers wheel bearings rubber bushes steering rack/box road wheel/tires anything can cause it to woble
i would have it checked out as it will wear out lots of other parts if you dont get it fixed

With the information given this is not a sure solution. Questions that need to be asked is when does this happen, turning at slow speedm high speed, when hitting a pot hole etc? Since you have replaced a lot of things already, assuming you have NEW good quality parts so you did not replace bad parts with new bad parts i would definitelu check the pitman arm. This runs from the stering gear to the tierod. It can give you some good clunks while steering, especially at low speed when there is a lot of resistance. Check it by having someone turning the steering wheel when watchin/feeling it.

Rim may have a dent or a weel balance weight may have fallen off.

Have the balance checked before your tires develop abnormal wear.

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I had the same problem with my 2002 Town and Country Limited. I took it to the mechanic and had the sway bar links and ball joints replaced and still had the same clunking noise when going over bumps at low speeds. The van sounded great on the highway, but country roads were horrible. I was about to replace the struts and pay another 700 dollars when i read somewhere that the sway bar bushings could wear and cause the noise. I took it to the mechanic and he said absolutely not it would be a waste of money. Being the stubborn guy I am, I went to NAPA and bought the two bushings for 12 dollars and replaced them myself in an hour. I took the van for a test ride and the noise is completely gone. Please ignore your mechanic and replace the bushings ASAP! Pretty cheap try even if it doesn't work.