I have a 1988 Ranger stx 5spd manual 2.9l engine 4x4 with manual locking hubs.

I have developed a vibration. It consistently starts around 58 mph and it's at it's peak about 63-65 and then fades away above 70. Usually this is in 4th gear when it starts at the lower speed and it starts at about 2500 rpm. If I shift up into 5th as I speed through it the vibration will still be there at about 2000 rpm. However at those rpm ranges in other gears there's no vibration. In 4th gear it sounds like a muffled rumble strip or how a bearing with a flat spot would. I thought it was coming from under the front end or under me. I can feel a little of the vibration in my foot on the gas pedal. In 5th gear the vibration has a deeper tone and quieter sound then 4th gear.

The 1st thing I did was rotate my tires. No change.

Then I had the tire place put on my snow tires. Same rims. However with the wheels balanced and different tires....no change.

While they were under there I asked them to check out the front end. They tell me my shocks and ball joints needed replaced.

So I took the truck home and replaced the ball joints(1 was bad), front wheel bearings(inner/outer), front/back shocks, front rotors/brake pad, and rear brake pads. I greased everything I could find. The tie rod ends look like they'll need replaced eventually but they didn't have play in them. My axle shaft u-joints weren't loose. Still no change.

While driving it yesterday trying to feel the vibration I notice at those speeds and rpm I feel it when my foot is on the gas. If I accelerate hard the vibration is harder but it almost goes away when I coast at that speed.

I also noticed that at any speed at any rpm, when I let off the gas there's a clunk felt under me and I can feel it in my hand on the stick shift. Same thing when I press on the gas quickly.

Doing some reading online and in the manual, I'm leaning towards u-joint bearings on driveshaft or possible motor or transmission mounts. Though I think I'd feel the mounts at different rpm/speed ranges.

Any ideas on where to start looking?

Thanks in advance.

 

sounds like the u joints need to be checked

 

I inspected them today. Just by grabbing on to them and wiggling. Both the front and the rear have equal amount of play. It's very small side to side play.

I'm just not convinced that that's the vibration. Wouldn't I feel it at more then 1 speed? There's a lot of stuff on this old truck that's worn out. I'm trying to avoid throwing tons of $$ fixing random things.

 

Vehicle Vibration Analysis Flow Chart http://www.tirerack.com/images/tires/vibechart.pdf
You've already done some of them, so were you using this helper?
EDIT: Did the problem come about slowly over time, or suddenly after some event?

 

It was't a specific event. I just started noticing it. I haven't seen that flow chart before. Thanks

 

years ago i had a 88 ranger and the vibration i had you could feel it thru the stick shift and it turned out to be the u joints the one near the tranny had a bad bearing replaced and vubration went away,,,,