Front End Shimmy and Rattle

dwkerch · 11-08-2011, 10:01 PM

We recently purchased a 1999 Monaco Diplomat and in October we made a 4,300 mile trek to/from New England. When we test drove the coach it had a hard pull to the right so front end alignment was checked before we picked the coach up from the dealer, and was said to be okay. On our trip we had a terrible shimmy at 45 to 50 mph, and the shimmy dimished toward 50 and went away above 50 mph. Along with the shimmy we had a loud rattle at 45 mph, again diminishing towrd 50 mph and going away above 50 mpg. After our trip I found the outside edge of the right front tire heavily cupped, indicating mis-alignment. The rattle is a solid rattle, unlike that of loose or worn shocks. Had the alignment checked again today and had the front end checked for loose and/or worn parts and the shop (who regularly deals with buses and heavy trucks) said the alignment was within spec. and there were no loose or worn steering or suspension parts, and that the front end had no provisions for alignment adjustments. Has anyone else experienced this phenomenon? If so, what did you do to correct the problem?

sc3283 · 11-08-2011, 10:32 PM

Possible broken/shifting belt(s) in tire....broken belts can cause vibration/shake to come and go...can cause noises due to the vibration and make the tire produce noise as it rotates on the pavement.
Not all tires with a broken belt can visibly seen but a shifted belt is almost always visible.

if you can jack each frt corner up to get tire off the ground....spin tire and look directly at tread....your looking for a side to side wobble...and an up and down hop in the tire....if any are seen...replace that tire immediately!

Mike Canter · 11-09-2011, 06:27 AM

That rattle/shake is at the characteristic MPH for tire unbalance for those large tires. Cupping on the tire is not from miss alignment. It is caused by either an unbalanced tire or a bad shock. It could be that the shock is blown and the tire is bouncing up and down or a defective tire or a bent wheel or just needs balancing. Shake is NOT caused by front end alignment and they should have told you that rather than take your money but at least they checked it all for wear. The big problem is that now the tire is cupped you can never get it to ride smooth again unless you buy a new tire.

What is the DOT date on the side of those tires?.

Do you know what brand shocks are on the MH. What color top dust cover and bottom cylinder do they have?

dwkerch · 11-09-2011, 07:00 AM

Good, usable info from both of you - thanks. 1) I can lift the front, spin, and check for broken/shifting belt. That's a problem I've not heard of, and I am getting a loud "singing" type road noise that seems to come from that tire. 2) I have suspected worn shocks from the start, since the coach has 62,000 miles and probably has the original shocks, but the rattle just doesn't sound like the classis "shock rattle" it is more like a solid, thick metal to metal rattle. I also considered worn King Pins, but the shop said they are good. Is there any way to check for a worn shock other than remove it? I know that a vibration/vertical shake is from out of balance tires but thought a true shimmy, felt through and visible in the steering wheel, was more of a mis-alignment issue?

Mike Canter · 11-09-2011, 07:15 AM

Unless a tie rod end is worn or something else is worn then the shake is not caused by alignment. Since they checked the front for mechanical wear and there was none then it is the shock or the tire. One problem with shocks is that Monaco elected to use Monroe shocks and these are bad bad shocks that wear out at 17,000 miles. These shocks are yellow on the bottom tube and yellow on the metal top dust cover. Bilsteins which are great shocks are yellow on the bottom and have a blue rubber top dust cover. But any brand shock can fail. One thing you can do is to see if any of the shocks are soaked in oil. Bilsteins used on some earlier Monacos had a custom large top rubber bushing that gets cracked and fails and just the bushing can be replaced. You can use a flashlight to check the upper busings and make sure they are all there and not cracked. Try grabbing the shocks at mid point and shake them. The other option is to drive the MH down the road and have somebody in a car on a cellphone drive up either side of the MH when it is happening and see if there is visible bouncing. Like I said once the tire is cupped it is going to always shake and make noise even if the problem has been fixed. This can make you chase your tail.

Openroad3310 · 11-09-2011, 07:29 AM

While you have the front end up, check for bad wheel bearings. If you do not find anything wrong with the front tires, swap them side to side and you will probably find your pull is due to the tires. It sounds like you have bad tires. Either old or a cheap brand. You had the front end alignment checked, but did you have the rear end checked also? if the rear end is off alignment, your chassis will not be running true down the road. You will have to compensate with the front end. Your metal to metal sound from that one wheel might be a bad wheel bearing or a tire telling you it is about to go.

Openroad3310 · 11-09-2011, 07:36 AM

You very well might have worn shocks, but that is not your problem. Your problem in the tires or a wheel bearing causing the tire to go prematurely. Once you get a bad wear pattern in the tire, you will never correct that tire.

tomwalt · 11-09-2011, 08:02 AM

Good info from the previous posters. On the rattle, I'd bet the imballance (sounds like a bad tiire to me) is causing some un-related item to rattle - Something else is lose and the shaking is rattling it.
If it is heavy metal sound, check the wheel wells - there are welded plates that don't always fit tight (not a problem and will go away when the tire is fixed). Other than that - do chassis inspection and look for the cause.

Openroad3310 · 11-09-2011, 09:22 AM

When I worked in a shop, the guy I learned everything from was very old school. Everything was done by hand. My suggestion is to find a shop that will spin balance the tires while they are on the vehicle. They are out there, you just have to look for them. We worked on motorhomes quite a bit and your problem was almost always in the tires and or balance and alignment. If you can find someone to spin balance on your coach, you will be very pleased with the results. Do not do just the front tires. Do them all. The shop I worked at is Milo Johnsons Automotive in Escondido California. That is the north side of San Diego. They do spin balance on the vehicle.

Openroad3310 · 11-09-2011, 09:32 AM

And one more thing. Never settle for an answer that says it is within specs! That is a cop out for I dont have a clue! It is either right or its not! It sounds like that shop you went to is clueless! With in specs does not mean it is right. Even if the front end can not be aligned, which I highly doubt, there are still adjustments that you can make. Like toe end settings and different shims to correct camber and caster settings. I hate that saying that it is within specs! That is about the most vague and misleading statement a shop can make! Ok, I think I am off my soap box now.

sc3283 · 11-09-2011, 10:53 PM

Your frt end will have adjustable tie rod ends....those allow for "toe in/toe out" changes

Camber and Caster while not having a simple adjuster...can be adjusted but its done by bending the axle...a very specialized service, requiring a very specialized repair shop....and a very good chunk of change to have a "bend" performed if needed.

For a repair shop to tell you....no adjustments ...that is just absurd....find another shop.

REMEMBER SAFETY............if you jack up the RV to check frt tire runout....BE SAFE....it is HEAVY!

I have no idea if your RV is included in this situation...but do a search about trailing arms....some Monaco models and years had defective suspension parts that can fail....