Rear end bounce / wobble at highway speed?

Laurie · Mar 8, 2014

Anyone managed to solve the rear end bouncing / wobbling at highway speeds? Around about 60-70 mph while cruising - sometimes the rear of the truck just starts getting into this oscillating rythm bouncing up and down. If I step on the gas more - it goes away.

Also if I hold the same speed but give it a light application of left foot brake - it also goes away.

I'm thinking it may be caused by the rear leaf springs being so soft that the axle housing is moving around a bit?

Would adding some traction bars to the axle housing to prevent the housing from rotating eliminate this?

Anyone got any experiences?

Red · Mar 8, 2014

could be that the tires are out of balance.

AZEngineer · Mar 8, 2014

There is a cast iron harmonic balancer that is mounted on rubber bushings above the drivers side frame rail just in front of the bumper. I'd check to make sure it's there and the bushings are ok. I posted a question a while back about what the cast iron thing was and I was told it was to eliminate the instability you are experiencing.

Here a couple of pics, crappy iPhone pics, hope they help

Laurie · Mar 9, 2014

AZEngineer said:
There is a cast iron harmonic balancer that is mounted on rubber bushings above the drivers side frame rail just in front of the bumper. I'd check to make sure it's there and the bushings are ok. I posted a question a while back about what the cast iron thing was and I was told it was to eliminate the instability you are experiencing.

Here a couple of pics, crappy iPhone pics, hope they help

Ok - will check on that weight issue. I did notice it on another Raptor that was in a friend's shop being worked on with the bed removed and thought it was a strange thing to be on a truck... The truck is only 2 months old so I'd be surprised if it was that already... but we have had one hard landing so maybe that wrecked the bushings in it.

---------- Post added at 12:17 AM ---------- Previous post was at 12:15 AM ----------

Red said:
could be that the tires are out of balance.

They were balanced just recently... by a reputable shop... but I guess doesn't hurt to have it double checked. It doesn't feel like tire vibrations though - in my experience with the Wrangler with the same diameter tires - they were much higher frequency vibrations. The bounce I'm getting is about 1/2 or 1/3rd the frequency of what I would expect with a tire vibration...

Still... it's cheap to have double checked so will give it a go.

WRCRaptor · Mar 9, 2014

I assume this is you first raptor. Have you modified it in any way? You could Find another raptor owner near you and let them drive it to see if it is truly a problem or nomal.

Sorry just looked at your build thread to see mods. Could the rack and tent set up you have be causing this? Mabe you have a tire that is defective see if you can get them balleced on a road force balancer that would show if one or more of the tire is out of spec.

Laurie · Mar 9, 2014

WRCRaptor said:
I assume this is you first raptor. Have you modified it in any way? You could Find another raptor owner near you and let them drive it to see if it is truly a problem or nomal.

Sorry just looked at your build thread to see mods. Could the rack and tent set up you have be causing this? Mabe you have a tire that is defective see if you can get them balleced on a road force balancer that would show if one or more of the tire is out of spec.

Will try and take a test drive of a new one at the dealer... a friend has one of the first 6.2Ls in the country and says his does it too... so... I think better to try and check on a new one.

Thought about the rack possibly contributing just because I didn't keep the thing stock for very long so don't have much of a "before" reference - but I doubt it would be the cause. It's coming off next week for powdercoating anyway so will do a few test-drives with it removed to be sure. Doing a few shake-down camping trips before powdercoating it

Yukon Joe · Mar 9, 2014

I would have expected this on a SCREW not a SCAB. What highway do you run? Midwest concrete with many joints? I had a problem when living in Omaha. Too many damn joints.

Yukon Joe
www.RUNRAPTORRUN.com

Laurie · Mar 9, 2014

Yukon Joe said:
I would have expected this on a SCREW not a SCAB. What highway do you run? Midwest concrete with many joints? I had a problem when living in Omaha. Too many damn joints.

Yukon Joe
GREAT LAKES RAPTOR EXCURSIONS

Our highways in Dubai area actually very smooth. Compared to highways I've driven in the states and other parts of the world - it's race-track smooth.

Sometimes a few small bumps but no expansion gaps or joins.

Yukon Joe · Mar 9, 2014

Hmmmmm

Yukon Joe
www.RUNRAPTORRUN.com

DEADEYE · Mar 10, 2014

In my experience it is the road ! Have a section of hyw where I live that would have this same effect on almost any vehicle I drove over it.
So just curious , pay attention and see if it is the same sections of road that it occures on ? And yes the speed you are traveling will make a huge differance on recreating.
Good luck !

Rear end bounce / wobble at highway speed?

Laurie

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Red

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AZEngineer

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Laurie

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WRCRaptor

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Laurie

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Yukon Joe

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Laurie

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Yukon Joe

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DEADEYE

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