BAD vibration when towing

[Ironman03R]

I've noticed this before but only towing combined GVW of 30,000 or more.
Today I pulled a trailer with next to nothing on it but trailer weighs a little over 2000lbs. I was driving around 30-45mph and it is best described as a THUD THUD THUD........(pause)........ THUD THUD THUD
Its always had a shake pulling really heavy things, mostly with the G/N hitch.
This was a tag trailer and I pull it alot and have never noticed this. All the front suspension and shocks have been replaced and tires are good.
It allways has a tire vibration but thats at 60 or above.
Could it be a ujoint problem?
I dont think its a trailer issue because this trailer sees regular use between the 3 of us and I'm the only one that has noticed it.
Ant ideas???

 

[MIDNIGHT RIDER]

Without actually driving the truck, here are a few possibilities.

The limited-slip mechanism, in the rear-end, could be grabbing; although, this usually is only noticable when making a turn.

A bad u-joint/s.

U-joints are sometimes hard to diagnose, without actually disassembling them for a visual inspection.

Pull the rear-end cover, with the axle on jack-stands.

Examine all teeth, including pinion, and pay especial attention to the carrier side bearings.

Also, check all engine/transmission mounts.

Another possibility is a cracked bell-housing.

Have fun.

 

[subway]

looks like Midnight Rider has most all of it covered, just one more to add to the list

pinion bearings, see if you can shake the yoke on the axle any play is to much

 

[Ironman03R]

Limited slip problems are out since its and open diff. Trans bell houseing and case are ok. The Ujoints, carrier bearing, and rear pinion were ok at the last oil change.(1000mi ago) I'm gonna double check everything in a few days, I did notice that one of the rear swaybar bushings on the axle has some play in it. I've never worried too much about chasing down vibrations in this truck, but now its gettin bad.
What bothers me is its only when towing something. I drove 40mi today and its fine.

 

[mr_josh]

Couldn't be your trailer brake controller malfunctioning, could it? Seems unlikely but...

 

[sign_man]

U-Joints

Mine started vibrating and after a crawl under the truck, I couldn't see any slack by wiggling the U-joints. I had the tires balanced and rotated with no sucess either. Finally I went to my driveline shop and while putting pressure on the driveline by easing from first to reverse the owner, who I didn't squish, saw the bad joint move. The center support bearing, next to the bad U-joint was starting to come out of the rubber, so it got replaced too.

 

[subway]

i agree with sign man, somthing is happening under load changing your drivetrain goemetry. no offence but unles you are superman you probubly cant put the torque on your driveline to show something like when pulling a trailer like you mentioned.

could you hold the brakes tight and slip the clutch between forward and reverse while someone lays beside (not under) your truck watching everything.

come to think of it i think one of the darwin awards was a guy who got wrapped in the driveshaft while lying under his truck trying to diagnose a drivline problem.........while the truck was driving down the road

 

[MIDNIGHT RIDER]

One way to check U-joints and slip-yokes is to pull the trailer for about twenty miles, at highway speed; then, quickly pull over on level ground, set the brakes, crawl under, and touch each U-joint cup, also the slip-yoke.

Any that are hot enough to fry your finger are either not lubricated enough, or, more likely, going out.

Also, if the carrier-bearing is going bad, you will smell burning rubber, on account of the bearing seizing and turning inside the rubber holder.

Don't run over yourself, while performing this investigation.

 

[Ironman03R]

Thanks guys, I was thinking it could be a u-joint/driveshaft problem but wanted some other input.
I'll check it out this weekend. I've driven it everyday this week unloaded and its ok so I guess as long as I never use it to tow anything it will be fine

 

[96_Bear]

Check the rivets in the frame for cross memebers. I read somewhere people where having the same problems some from just a twist on the frame from turning. They were removing the rivets and replacing them with hardend bolts.