Violent Shaking at Highway Speeds

[ConfederateTyrant]

Car is a 1995 Mercury Grand Marquis, and today I took it out on the highway and as I got up to about 55+ mph, the car began to shake very violently. Last time I had taken it on the highway, it rode hella-smooth, so I am a little unsure of what could have happened in that time frame. None of the tires are exposing belts nor do they have any buldges in them.

I am suspecting U-joints, as there is a slight vibration while driving regardless (along with a slight ticking that seems to sound everytime the wheel makes one full turn). A friend of mine suggested it could be the U-joint or unbalanced tires (front ones may be out of balance, but rear tires are new and I watched the installers balance both).

Any ideas?

How could I tell if the U-joints are shot?

 

[brianl703]

A weight could have fallen off one of the wheels. That happened to my brother.

 

[simple_gifts]

Tread separation? I'm not sure you can always tell by a visual inspection.

 

[55Test]

I had a 93 Crown Vic a little while ago and the front U-joint was shot. One of the bearing caps was missing and the little needle bearings were gone. It shook at highway speeds and make a loud squeak-squeak sound while the car was moving that increased in speed directly with the speed of the car. I had my dad replace the bad U-joint, and the shaking and squeaking noise went away. I'd suggest doing both the front and rear U-joints. They're cheap so why not? Just watch when you haul the driveshaft out of the transmission, some fluid will leak out, although not much. It also might be a good time to change the differential fluid since you'll be down there unbolting the driveshaft from it.

 

[ConfederateTyrant]

55, I do plan on replacing both U-joints if those are the case. Could you hear the squeaks at higher speeds over the road noise? I have to really pay attention, or have the windows down, but after 25-30 mph I no longer hear it. It's very noticeable when coasting as well.

 

[55Test]

The squeaks went away at about 30 mph, just as you're experiencing. Mine were also loud on coasting, and even louder on hard acceleration away from a stop light.

 

[JTK]

What type of steering does this type of CV have? recirculating ball or R&P? I've seen sloppy pitman arms cause VIOLENT front end shimmy on big'ol RWD recirc ball steering cars @ hywy speeds.

G/luck
Joel

 

[carock]

Ummmm... posting this question on the board is a good idea, but you really need to get a pro to investigate also. There are a lot of potential sources or major vidrations. I used to sort some of these out on a chassis dyno. Other shops have wheel balancers that spin the wheel on the car, these can be helpful. A shop that has one is commited to solving problems.

 

[stogiedude]

Get yourself to a mechanic or tire shop ASAP. Could be tierod(s), wheel balancing, alignment, a bushing(s) or a bunch of other things. Put it off and you'll likely be replacing a tire or both of them in the front. Worse case you could have a high speed blowout or some other dangerous calamity.

 

[ConfederateTyrant]

It has been less than a month/300 miles since I last checked the suspension. None of the tires had any abnormal amounts of give in them, so I am not suspecting a tie-rod end, and when I changed my oil I checked all of the suspension parts up front and none were worn or loose, though that can change.

I have an idea to check and see if it's a front end issue. I jack up the rear end and support it on 4 jackstands (two on the axle, two on the frame) and slowly accelerate the car up to speed. If it shakes badly, would that be enough to knock out any front-end issues and blame the u-joints?

 

[labman]

Leave plenty of clearance between the tires and floor. Centrifugal force will increase the diameter as you build speed.

Also, check wheel bearings.

 

[ConfederateTyrant]

The wheel bearings on my car are a sealed system, what could I do to check them?

 

[mechtech]

You may have loose suspension/steering components also, but the shaking is initialized by the tire/wheel assemblies.

 

[ConfederateTyrant]

mechtech, would you recommend that I note the wheels and see if they are shaking or bouncing up and down while I do my "no load" test?

Would there be anything in particular that I should look for while doing that to see if it is the U-joints at fault?

 

[labman]

Check wheel bearings by seeing if you can wobble the wheel with it off the ground. Check vertically, not horizonally. If you support the weight on the A-frame in the front, the wobble could be a ball joint.

 

[dickwells]

Aside from what has already been posted, Drive through any deep mud lately? A chunck of mud stuck in the wheel can do this. Good Luck

 

[Papa Bear]

I used to slide under my buddies car and stick a 3oz wheel weight on the inside of a front tire. His reaction was very similar to yours.

P.B.

 

[bdcardinal]

definately check for a wheel imbalance. the idler arms are a very common problem on panther chassis cars liek yours. enough that a lot of dealers carry them in stock. if it is the u-joints, check to see how much that would cost, then compare that to a new driveshaft, especially a Police Interceptor one. the CVPI driveshafts are aluminum.

 

[alreadygone]

Check Ujoints by visual inspection, looking for rust streaks coming out of caps and obvious out of center trunions. Manual inspection by gripping front or rear yoke in one hand, driveshaft in other and twist back and forth like you were trying to twist it intwo by hand (you can't but you can often feel slop/looseness). Often when causing vibration you cannot tell bad Ujoint without pulling shaft and working joint back and forth feeling for stiffness. (Really bad shakers are almost allways front joint).

If these terms or procedures confuse you hire a professional. You're not to this level of DIY yet.

Sounds more like a tire though. No load spin doesn't usually show you much, should allways be done in LOW RANGE shift position AT IDLE SPEEDS (yes I am yelling)Unless you can resist reving engine don't do it! If you do it get in visual line with tires and watch for lumps/humps in tread area WITH SAFETY GLASSES.

Bob

 

[stogiedude]

One other thing to look into, when the transmission on our '94 Chrysler Concorde was dying I confused a shaking of the front of the car for a suspension problem. I had the front struts replaced only to find out later that the problem was in the transmission.