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Vibration creeps in and won't go away

3K views 14 replies 4 participants last post by  Shaftcam 
#1 ·
2012 Grand Cherokee Limited with 20" tires.

I'll try and be brief but I suffered through the Fortera vibration issues, did three road force balances and vibrations got worse. I finally ditched them about a month ago with 20" Falkens which immediately made the car more responsive at low and high speed. The ride is a little harsher but not by much but more than offset by the sharper handling. No more vibration at 115 km/hr or 70 MPH.

BUT........after about 40 minutes of sustained highway driving, a vibration will creep into the ride and then never go away for the rest of my drive. It sounds like it comes from the rear of the vehicle and is accompanied by a low grade rumble and a harsher ride. It feels like a tire issue but can that be??? For the first 40 minutes, I can go up and down through the speeds and there are no issues, vibrations, noises.

Braking is still smooth. There are about 1000 kms (600 miles) on the new tires. 21,000 kms on the vehicle. The new tires have not been road force balanced.

I'm at a loss to figure this out. I'd prefer to be able to go to the dealership with something for them to go with otherwise I guarantee they won't feel anything.

Any ideas? Thanks.

Dan
 
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#2 · (Edited)
By any chance is this a Hemi vehicle?

Otherwise, it could be that after that amount of high-speed driving your tire pressure has increased (due to tire heating) enough that a slight out-of-round condition is resulting in more road force variation on each tire rotation. The increase in pressure would also explain the harsher ride, especially with tires that are stiffer to begin with.
 
#7 ·
That's where I'd start. After driving at high speed for a bit, your tire pressure could he 4-5psi higher than your normal cold inflation pressure. I'd have the shop inflate the tires up to that level, then do a full road-force balance (indexing the tires as necessary). Then when all of that is good, lower your pressure back to normal.
 
#6 · (Edited)
Could it possibly be Rear Load leveling Shocks?

I think normally with a trailer load they will stiffen up and try to lift the rear.

But if they are faulty and stiffen up they might transfer normal vibration into the frame so you feel it.

I thought I read there was a problem with load leveling shocks in earlier WK2 years.

Otherwise I agree with tire pressure. If you don't have TPMS display get out and check them manually once it starts vibrating.

Seems weird so many tire/balance issues. I never had tire balance issues on my old jeeps, even with cheapo tires. I have two sets for my 2014 and both are fine to 80 MPH.

Oh and I run my tires at 40 lbs and still no issues.
 
#9 ·
Could it possibly be Rear Load leveling Shocks? I think normally with a trailer load they will stiffen up and try to lift the rear. But if they are faulty and stiffen up they might transfer normal vibration into the frame so you feel it.
Certainly possible...but the timeframe would be random. This would be something to look at next after completely evaluating the tires.

Seems weird so many tire/balance issues. I never had tire balance issues on my old jeeps, even with cheapo tires. I have two sets for my 2014 and both are fine to 80 MPH. Oh and I run my tires at 40 lbs and still no issues.
It's not all that strange when you consider that these vehicles are simply becoming more sensitive by design. Older jeeps also had solid axles...more unsprung weight. As such...more mass under the springs. Mass is the best way to dampen vibration harmonics.
 
#13 · (Edited)
Thanks for the input. I've been chasing one vibration or another since new and I've spent a ridiculous amount if time trying to resolve it. Let me add, the new tires resolved any front end vibrations I was having with the Forteras. The front end is planted and no shimmy at any speed even while the vibration is present. Alignment was done three weeks ago.

Leads me to believe its a problem in the rear? I wondered about warped rotors too. Anything else that can oscillate under there?? Exhaust?? Is it reasonable to just road force the rears? I know one shop I contacted only offered the service for all four wheels which I found odd.

Before the vibration sets in the drive quality is fantastic but once it creeps in, it's there for the duration of the drive.
 
#14 ·
I'd try the road force on the rear tires first. Other things can cause this, but it would be odd for them to only show up after prolonged high-speed driving of that length. On the other hand, your tire pressure will be steadily increasing as the tire warms over that timeframe (up to a point of course).

Any shop can do this on just the rear. Any that refuse to do this are just trying to get more money from you.
 
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