I have a 1997 f150 4.6l auto ext. cab 4x4 with around 94000 miles. When i am in 2-OD(usually 35-75) my truck shakes bad. It shakes hte worst when i am in overdrive and i hit the gas just enough to gain a MPH or 2 but not shift out of OD. And when i slow down from highway speeds my truck like sounds like it has a exhaust brake on it when it goes from 60-50 on the decel from highway speeds. I do have a flowmaster muffler on my exhaust but i have had it there for 10,000 miles before this... Could it be my harmonic balancer? Or what do yall think? Thanks for the help!

 

Howdy! Check the tires. No really, check them. I had an '86 that started shakin like the dickens on the way up to Albuqurque one day. Come to find out one of the bands had busted. Same thing on the '77 I just picked up. Except it was after throwing over $1,200 in the front end. The fellers at the garage asked if I wanted to put new tires on it. Didn't think I needed them since the tread was still good for a while. Come to find out, busted bands. May be worth a look. You'll definitely see it. Have a nice lump where it's broke. Also had my front brakes hanging up on me due to a bad booster. Caused it to shake betwixt 40-45. Never mind warming up the rotors a tad. Hope this helps.

Rich

 

check the lower ball joints also.

 

I'd check all the rotating parts. Get a buddy and put all four corners on jackstands. Have the buddy in the truck (for safety and to operate the truck) and look for a wobble in a driveshaft (u-joints, bearings) or the tires (balance, broken chords) as the truck accelerates and decelerates. Listen to noises and track them down. Sloppy ball joints will tend to make the truck wander as well.

-Kerry

 

I had a very similar problem with my 97 4.6L this last summer and it turned out to be the U-Joints. On my previous truck a few years ago I had a serious vibration when accelerating between 50-60 and also when I let off the throttle, it turned out that I had lost a weight on the wheel that was messing up the balance. but with the sound yours is making sounds real similar to the problem I had this last summer with the U-joints..

Good luck