Intermittent vibration at 70-75 MPH? - SOLVED!

[terr5178]

Similar issue for me turned out to be bad u joint in front drive shaft

 

[whtbronco]

I would have gotten into even more trouble back then if we had the communication we do now. Yikes.

Yeah, my 79 Bronco had a manual with 6.32:1 first gear, granny gear. At a stop, push the clutch and throttle to the floor and slide your foot off the clutch to the left. Either rear pinion broke, the driveshaft exploded or the front end went straight up. I even busted the rear window once when the spare tire got pressed into the pavement a bit. Seemed like forever I was looking at the clouds. I destroyed a lot of rear driveshafts.

 

[kep5niner]

SOLVED!

Replaced the front drive shaft U-joints, and sure enough, the U-joint at the transfer case was smoked. Test drive up to cruising speed was without incident - smooth as glass.

Thanks fellas for all of your input!

Pete

 

[whtbronco]

Great news.

That was same u-joint responsible for most of my vibration as well.

 

[SafariGoneWrong]

Nice work and thanks for sharing! I didn’t know until a few days ago our front driveshafts are spinning in 2H. I don’t like it…. My Bronco’s front driveshaft hasn’t rotated in years…the way it should be.

 

[kep5niner]

Surprising to me as well. Seems having the front driveshaft rotating 100% of the time would create excessive wear and tear. It would be interesting to figure out if my ‘14 Super Duty does the same thing.

 

[whtbronco]

Surprising to me as well. Seems having the front driveshaft rotating 100% of the time would create excessive wear and tear. It would be interesting to figure out if my ‘14 Super Duty does the same thing.

If you can't look at the driveshaft while someone else drives it. Put a camera under there and record while you move the truck like 1'. You'll know if the driveshaft turns.

I bet if it doesn't have this AWD crap the front driveshaft won't turn.