Vibration at 51 mph

[srimes]

Hi guys

Vibrations at 50-60 mph always point to an imbalance in the "rotating mass", ie your tire because of the nature of the suspension

Natural frequencies of suspension systems are usually in the area of 10 Hz, very low because of the relatively low spring rates of your suspension (compared to your unibody). 55MPH on a jeep running a stock 225 tire, (27"ish inches) is a rotating frequency of 11.5 Hz (rotations/sec). You're hitting a resonance frequency because you're right around the natural frequecy of the suspension of the car. Balance the imbalance and your problem is solved. Bearing, out of round tires, improper balance, bent rims, etc

Greg

Hey thanks for the explination.

 

[mfeucht]

It seems as though new tires, tire balancing, or new hubs is the most successful solution to the "vibration at 51 mph" problem. How many others have had success with new hubs? Would'nt runout on a hub also be felt (pulsating) when brakes are applied?

 

[skid_j2x]

had a similar problem.. turns out the spider gears in the front end are worn and dont mesh like they should and kind of shudder/bind when they spin.. seems to transfer out to the wheels

 

[asatxj]

gtpolkus provided an excellent indication of one of the primary causes. Everyone memorize that. However, this is if all components are in good condition. I have well balanced tires, new track bar, new steering components, good brakes and still have it. The cause---worn lower control arm bushings. Moral of the story- it's a system, everything has to be in good shape for it to work well.

 

[lizarralde]

Try to find out were the vibration is coming from (rear / front). Front: take out the front diveshaft and test it. No vibration!!! (change the u joints). Still vibrating, check the rear shaft and u joint (not to expensive).

Also test your trac bar with a freind. With the Jeep turned on, move your wheels side to side "just like a kid trying to drive" and check under the drivers front wheel, the tracbar end is there (see if it's not shaking).

 

[mfeucht]

FYI followup:
The lower control arm bushings appeared worn/degraded. I installed new OEM style control arms and this cured the vibration I was experiencing at ~51mhp. Since the front end seems OK now, I'm going to wait until after I replace the saging rear leaf springs before I get an alignment.

History:
The 2001 Jeep was purchaesd used (96K) recently. The worn out trackbar (ball joint end) was replaced the first week that I owned the vehicle. This improved the feel of the front end but did not stop the vibration. Balanced / rotated tires. No effect. Tie rod ends checked numerous times for looseness. None found. Hubs and ball joints checked for looseness. None found. I had not thought of checking the control arms until seeing it mentioned in this thread. Thanks.

 

[Peter D]

New tires did the trick. 235/75/15 Goodyear Wrangler Radials from Kauffman Tire. I believe it was under 300 dollars.

 

[wicked_xj]

it was my bent and un ballanced and lack of wheel wates