Volvo 850 Shake Rattle and Roll

[thomas]

Hello All,

New to the site and looking for expert advice. I have owned a 1996 850 wagon for about 18 months. Bought it from a "trustworthy" used car lot - it had been in one accident but had my mechanic give it a thorough inspection and gave it his seal of approval and could not find any evidence of structural or frame damage. Having had it inspected, I obviously did not do a very diligent test drive, as it was only until later that I noticed a rather pronounced "shimmy" (felt primarily throught the steering column) that shows itself around 105-115 kph (65mph+/-) and eases of a bit at higher speeds than that.

My first assumption was tire balance or wheel alignment - both have been done to no improvement. My mechanic suggested it could be due to the cheap tires that came with the vehicle, so I switched them with some new "h-rated" tires per his recommendation. Still no better. My mechanic is a bit stumped and his only suggestions entail rather costly 'experiments' with no guarantee of improvement (upgrade wheels to machined alum. rims, or replace something to do with the steering column if I remember?)

Anyway, wondering if any of the experts here could offer some suggestions. Or is there likely some invisible accident damage the inspection missed causing this problem?

Thanks in advance for any help!
Cheers, Craig[/code]

[Kmaniac in California USA]

You were on the right track to think you had a tire out-of-balance. The shimmy you describe is indicative of an out-of-balance rotating element. Just remember, however, that your tire and rim are not the only rotating elements in the front end of your car. Your tires and rims bolt up to the hub and brake rotor assembly. The hubs and brake rotors are balanced during the manufacturing process and don't generally lose there balance during there service life. Over the years I have seen what appear to be balance weights of some form welded to these units.

Since your car is a 1996, I would suspect it has had at least one brake job, especially if it has over 75,000 miles. It is possible with either resurfacing or rough handling that one or more of your brake rotors may have lost a factory installed balance weight or lost enough surface to throw off the factory balance.

I have a few suggestions to test this theory. Years ago, I remember some auto shops having a dynamic tire balancing machine that rotated the tire while mounted to the car. If you can find someone with this type of unit, it will be easy to check the balance of each wheel mounted to the car. However, I have not seen such a device in at least 40 years. Next, you could pull all four of your brake rotors and take them to a machine shop that has balance equipment. However, the labor involved to pay both a mechanic (if you don't do this yourself) and the machine shop for this service may exceed the cost of four new brake rotors. My next suggestion would be to replace all four brake rotors. If you are able to verify the balance of all four rotors by whatever method and still have the shimmy, then you will need to look at your wheel hubs.

Personnaly, I have never tested this theory. However, my wife has a domestic mini-van with four wheel disc brakes. In late 2001, we had both rear brake rotors replaced with a rear brake job. At a point after this work, I began to notice what felt like an out of balance tire on the rear of the van, especially when I would ride in the back. Once when following the van in another car, I swore I saw the right rear wheel shimmying on the freeway. I had the tires balanced and rotated more than once since then, but still feel the same out-of-balance feeling when riding in the back. When I can pry this vehicle away from my wife long enough, I am going to remove the rotors and have the balance checked at a machine shop. I suspect at least one of the replacement rotors is the culprit.

Good luck with your Volvo. I have had nothing but good luck with mine, after exorsising the Gremlins that short-sited Volvo mechanics couldn't see.

[thomas]

Thanks for the hints. I'll be sure to post any (hopefully positive) results!

[Kmaniac in California USA]

I now realize that you have an 850, a front wheel drive car. Another thing you may want to check is the balance of your half shafts and the condition of your CV joints. Out of balance assemblies and degraded CV joints could cause your shimmy, too.