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.

 

I kind of had the same scenario with my 1988 Ranger S/C 4x4 XLT with the 2.9 w/5 speed. Don't know of yours is regular or extended cab. If extended, it could be your center support bearing for the rear drive shaft. That was my problem. Or you could have a stiff drive shaft U-Joint.

 

It's only a single cab but I'm leaning towards those u-joints. Now I just need the time to get to it.

 

i had the same thing and after buying all kinds off diffrent parts i finaly hit what it was ,it was the dam u joint the one for the rear starting from the transmission and the center bearing that the drive shaft hooks up too👍