Vibration at high speeds

[jmartinez1228]

I just picked up an 86 MJ with a 2.5l 4banger about less then a month ago. Everytime I get on the high way once I get to about 55-60mph the whole truck starts to vibrate. At these speeds I'm usually in 4th gear and rarely even see 5th unless if i can get it up to 70 which again rarely happens. Anyways when i get up to these speeds the whole truck starts to vibrate like it wants to take off or something. To me it almost feels like its coming from the rear end but this vibration is so hard that its really hard to tell since the previous owner took out alof of the interiour so its mostly metal in the cab. Any ideas on where I should start looking first?

 

Also he took out the lines for the A/C so i was wondering if i take the A/C compressor out can i replace the belt with a non-A/C belt? do they even make one?

[mvusse]

Out of balance tire or drive shaft.

[jmartinez1228]

Out of balance tire or drive shaft.

 

The tires have been replaced and it was making this noise before then. What do I have to do to balance the drive shaft?

[dasbulliwagen]

Could be a bad U joint too, or bent driveshaft. Check the rear driveshaft and the front for that matter for looseness or play at the U joints and replace the joints as necessary. Set parking brake and put trans in nuetral and reach under and wiggle the shafts back and forth, there should be no visible movement between the shaft, joint and pinion.

[mvusse]

The drive shaft has been balanced at the factory, and will stay balanced unless it got bent, twisted, or dented. If it is damaged like that, it can possibly be repaired/rebalanced if not too bad. If the damage is bad it will need to be retubed or replaced.

 

The u joints are a good possibility also.

[jmartinez1228]

thanks for the tips ill check it out and let you guys know what i find. i wouldnt be surprised is something was loose or bent this truck was pretty beat on from what ive heard.

[jmartinez1228]

So i got under the truck today and tugged on the driveshaft both ways and didnt see any kind of play at all it felt pretty solid. One thing I noticed is a leak coming from the cover and from where the driveshaft connect to the rear end. Here is a pic of it and could someone tell me what rearend and tranny i have? the rear end looks like a dana35 but i havent seen a 35 in person to tell. Let me know guys thanks.

[mvusse]

Yup, that's a D35. Pinion seal leaks can be caused by an out of balance (bent) drive shaft. Add to that the vibration and it's a definite possibility.

[Geonovast]

The balancing weight on the DS can also fall off, causing it to vibrate.

[jmartinez1228]

so swap out the DS or take it somewhere to get balanced? Is that pinion seal hard to replace?

[choochoo1996]

which end of the truck shakes the most front or rear....I had a track bar mount go bad on me and the front of the truck had a violent speed wobble up front, like it was going to throw me out of the cab...rebuilt track bar mount at frame and made it adjustable for alignment and problem went away...When I use to go over railroad tracks too fast....60 mph.....it headed for the rubbarb....track bar upgrade fixed that also...

[Oizarod115]

u-joints can also get tight spots so if you pull the shaft be sure to swivel them all directions and check for a tight spot in a cap... this will cause hellacious vibrations

[jmartinez1228]

The vibration honestly comes from the back and the front. I noticed that it would only vibrate under load like if I'm going up a hill. If i get the truck up for like 70 and put it in 5th sometimes it won't vibrate much.

[Pete M]

We had a vibration in the liberty (only happened at around 55 mph) that turned out to be a dry rear U-joint.

[jmartinez1228]

Alright ill check this stuff out. thanks for the info guys i definitely appreciate it.