Vibrations starting at about 70mph

[renae91988]

Hey I'm new to this forum and I was hoping I could get some help regarding my explorer. I have a 1994 Limited Edition Exploder and I love it to bits but I can't stand the vibrations that I get on the highway.
First of all sometimes when I start my truck I have to let it sit for like 30 seconds for some shakes to stop before I put it in gear, otherwise it shakes like crazy.
Second of all when I'm accelerating on the highway and reach 70mph my truck starts vibrating. Usually if I keep accelerating to about 74-75 the vibrations subside, for the most part at least. Also the other day when I was on the highway, I took my truck off cruise control and the rpm's shot up to 3K and my truck started shaking pretty violently for a few seconds. The vibrations are usually the worst when I'm accelerating, however they continue as I maintain the speed.
Anyway, a little background info, spark plugs were replaced about a year ago by my dad who was a certified mechanic for a really long time. Also, my boyfriend's dad owns a Ronda Tire, and I don't know how many times I've had my tires balanced there. My tires are balanced at least once every month or two, in efforts to try and get rid of the vibrations, however it never really helps. I have GoodYear Wrangler tires, and they still have plenty of treatdon them, however two of them have some weathering cracks. My truck is well maintained and I'm always bringing it into their shop, thankfully I hardly ever have to pay for any labor and I get all the parts at cost. Also, I should mention my truck was involved in a rear end collision, a guy hit me going about 60mph when I was at a dead stop waiting to turn, so the frame had to be straightened, and the truck after the accident set up about 4 inches higher on one side in the back, however now you couldn't even tell that the frame was ever bent!
I'm hoping to figure out what is wrong with my truck soon because in a couple of weeks I'm moving away to college, which is about an hour and a half away from home, and I plan on coming home to visit every other weekend due to my father's illness. So it's very important to me with all the highway driving I'm going to be doing, that my truck is in good shape. Thank you so much to anyone that can offer some advice to me about my vibration problem!

Renae

 

[colecifer]

When the frame is bent that much most of the time the car is never quite the same. I wouldn't be surprised if the frame is still a little messed up somewhere and at high speeds causes problems.

 

[Anime]

With the frame having been straightened, I'd say it's likely that the suspension isn't straight, and the vibrations might be at least partly due to the rear axle or one or both front beams not tracking straight ahead. Has it ever had a front end alignment? If the tire place can do an alignment, get that done, and have them check that the rear axle is tracking correctly, too.

It's actually common on some Explorers to have the ~70 mph "death wobble", sometimes it can be from simple causes like unbalanced tires, or more involved things like worn driveshaft u-joints, or even a bent driveshaft.

As for the starting issue, do the vibrations happen from the engine RPMs dropping, or does the engine idle at 2000-2200 RPM but still vibrates? If the RPMs go down to 1500 or below when it's first started, it might be a part called the Idle Air Control (IAC) valve, which isn't inexpensive, but is easy to replace. Also, be sure to allow a few seconds for the fuel pump to turn on when you turn the key before cranking.

 

[vrytired]

mine had the 68 MPH death wobble. i replaced the two outer TREs and the drivers side balljoints(needed to be done to pass inspection anyway) and took it to a good alignment shop and the problem went away.