I recently bought a 2001 Dodge Ram Van and did all the usual post-sale maintenance to it. Changed the air filter, oil and filter, spark plugs and even changed the transmission filter and oil (ATF +4).
It drives great around town and at lower speeds, but I tested it on the interstate the other day and it would violently shake at speeds above 50mph. It was most noticeable on the two side doors and the rear end, which sounded like I had a helicopter in my back seat. When I slowed down, the shake would go away, but if I sped up again above 50mph, the shake returned like clock work.
In all fairness, the tires on this are in pretty bad shape and should be changed out - but I don’t want to invest in that until I know how much this problem could possibly further set me back. Though I don’t know if that’s a contributing factor, I do hear that these vans tend to eat up front suspension parts, and if the front shakes, I’m sure it travels down to the rear and multiplies itself. After all, it is pretty much a rectangle on wheels!
Any input for what I should be looking at for possible repairs would be appreciated. Thanks!
(Bonus: the cruise control doesn’t set a speed but appears to otherwise turn on. Would that be due a speed sensor on the transmission?)
The shaking is caused by your tires. I had a very similar issue above 60 mph. It was caused by the tires needing to be balanced.
I am not a specialist like other commentators, but…
If I were you, I would first check out the wheel balance/alignment.
It may not affect at slow speed but it will do at high speed.
Thanks for the replies, guys.
I think you’re both right about the tires being a problem in this situation. Here’s why. I noticed the driver’s side tires are 225s and the passenger’s side has 245!
Which brings me to my next question. I’ve been looking for tires to replace the above ones with and have encountered different opinions on what to put on. This is a 15 passenger van that will likely never be filled to capacity, but will be used for highway purposes. Will these tires be safe to use?
As the link suggests, I’m looking for an el-cheapo tire.
Those will be fine if they are the recommended size for your van. Whatever is listed on the door jamb sticker or your owner’s manual is what size you should use. Just all the same size! 
A standard, non aggressive tread on an all season tire will ride quietly on the highway.
“I think you’re both right about the tires being a problem in this situation. Here’s why. I noticed the driver’s side tires are 225s and the passenger’s side has 245!”
That’s going to be VERY hard on the rear end!!! The axles are turning at different speeds! Buy a set of the correct tires for this vehicle and have the oil changed in the rear end…
When you were shopping for this van, THAT’s when you should have noticed the tires and walked away…The former owner obviously did ZERO maintenance…