98 Rodeo front vibration

[coolscheid]

I have a 98 Rodeo that has major vibration starting around 60 mph. The car only has about 49000 miles on it and has been well taken care of my by mother-in-law. I had all 4 tires replaced and spin balanced, but it had no effect on the vibration. I had a friend put it up on a lift one day and discovered that the front wheels were in 4wd, without the transaxle engaged. It was like I had a car with manual hub locks and I forgot to unlock the hubs. After pushing the 4wd button a few times, it disengaged. But shortly thereafter, it seemed to go back into 4wd mode. I notice that the gas mileage on the highway is really bad. My father-in-law said that once he took it on a long trip and managed to get about 28 mpg. I got about 18.

I notice that when I am coming to the end of a braking maneuver, the car lurches forward. I don't know what is going on, can anyone help?

[amigo-2k]

New shocks could help the vibs.

28mpg is unheard of, 22 is the best I've done.

Check out my FAQ link below for some help on MPG and a couple of other things.
-Ryan

[coolscheid]

I was thinking more along the lines that the vibration was coming from the transfer case since the hubs were locked in. I guess I am looking for some trouble shooting tips on the vacuum assisted shifter used on the front axle to put the car into 4wd.

Shocks may be a small problem. When I did manage to unlock to hubs, the car rode very smooth at high speed. I think that the vacuum system may be slipping the car into and out of locked and unlocked hubs. Is this a problem anyone else has experienced?