Shimmy.......again UPDATE

clipper47 · Post by **clipper47** » Sun Oct 12, 2014 1:44 pm

I recently took my 635CSi on a 1600mile road trip and discovered that the car had an annoying shimmy at about 100KPH. I have replaced the UCA and LCA with Meyle HD's and the shimmy was still there although somewhat less and more of a minor nuisance since it was pretty mild. In any event about 1/2 way through the trip I had the wheels rebalanced to see if that was the problem. The shimmy disappeared at the 100KPH point but is still there. It now occurs at about the 120KPH point! The speed limit on the roads in my area are all 90KPH and so I rarely ever drive the car much beyond 100KPH so this isn't a serious issue but I am wondering what would likely cause the shimmy to occur at a different speed?

Alpinacsi · Post by **Alpinacsi** » Sun Oct 12, 2014 2:15 pm

What wheels do you have and does the fitment require a hubcentric ring?

clipper47 · Post by **clipper47** » Sun Oct 12, 2014 4:51 pm

Wheels are 15" style 5 from an E 34 and seem to fit the hub pretty snug but I will check the diameters again to be sure.

Checked the wheels to be sure and they are correct hub size. Wheels spin on hubs with no obvious drag on rotors which would, to me , indicate warpage.

GazM3 · Post by **GazM3** » Sun Oct 12, 2014 7:06 pm

Hey there. How old are the tyres
I have often had shimmys caused by tyres themselves when the wheels have balanced up fine.

clipper47 · Post by **clipper47** » Sun Oct 12, 2014 8:15 pm

Tires are two year old Michelin Primacy tires. I could try switching them back to front to see if that would make a difference. I have a new center link that I could install although everything in the front suspension is either new or looks good. I am thinking that perhaps a brake rotor is out of balance?

Ralph in Socal · Post by **Ralph in Socal** » Sun Oct 12, 2014 9:07 pm

Be careful of the torque on the lug bolts. Over torquing can also create shimmy problems.

Ralph

clipper47 · Post by **clipper47** » Sun Oct 12, 2014 10:54 pm

Lug bolts are torqued to Bentley manual spec, so not likely the problem.

Brucey · Post by **Brucey** » Mon Oct 13, 2014 9:37 am

There are many possible causes for this;

Primacys take flat spots very easily. Before balancing the wheels, you need to run the tyres for at least ten miles and then take them off the car inside fifteen minutes of that, else the tyres will have flat spots in them that will make any balancing operation a bit iffy.

Often a 120kph shake is actually the rear wheels. On a long sweeping curve you can often feel the wheels (which are going at different speeds) going in and out of phase. A 60mph shimmy will be felt very strongly through the steering and what you feel will vary a lot as the phase changes. The rear wheels (70-75mph) will also be felt through the steering wheel but the changes in what you feel (with L/R wheel phase on a long sweeper) will not be so much.

The tyres need to be round. Ideally you should see less than 1mm run-out in the tyre tread. NB Until the flat spots are run out of the tyre most tyres won't be this good.

A lot of wheel balancing machines locate on the front of the wheel which may not be concentric with the rear spigot. A 0.1mm concentricity error is a bit like losing a 10g weight off the wheel (or worse).

I keep an old set of wheels/tyres (which are perfectly round and well balanced) so should I have a shimmy issue I will use these for diagnostic purposes, i.e. by driving the car with those fitted to be sure that it is a problem with the current wheels.

cheers

clipper47 · Post by **clipper47** » Mon Oct 13, 2014 11:54 am

Thanks Brucey. What should I look for if the rear wheels are causing the shimmy besides wheel balance? I am still wondering why after balancing the shimmy would occur at a different speed.

Hefeweizen · Post by **Hefeweizen** » Mon Oct 13, 2014 1:24 pm

When I first got my car it had the shimmies real bad. I bought new parts for the front suspension which are still in my parts shed. There are so many different things that can cause the shimmies. The shimmy saga starts here at the bottom of this page:
http://house-calls.us/BMW2.html

clipper47 · Post by **clipper47** » Mon Oct 13, 2014 8:22 pm

Rainer, Interesting read, thank you. I might install new rotors and try those to see if that is the problem. Not a big issue since the vibration/ shimmy doesn't occur until about 75mph and I rarely drive at that speed except when ion a trip to the USA Interstates. Just annoys me that such.an otherwise beautiful car can develop such an annoying problem.

Brucey · Post by **Brucey** » Mon Oct 13, 2014 11:00 pm

clipper47 wrote:Thanks Brucey. What should I look for if the rear wheels are causing the shimmy besides wheel balance? I am still wondering why after balancing the shimmy would occur at a different speed.

If you have a bad front shimmy then it can be so overwhelming that a rear shimmy can go almost unnoticed, until you have removed the front shimmy.

If the rear tyres were balanced with a flat spot in them, they could be worse not better than they were before.

As I said before, a set of 'known good wheels/tyres' is an excellent diagnostic tool.

cheers

clipper47 · Post by **clipper47** » Tue Oct 14, 2014 11:48 am

Brucey, The front shimmy at 100kph point was quite mild and I drove several thousand kilometres with it. More of a minor annoyance. The shimmy at the 120kph point is much more severe and more than annoying and only began after the tires were rebalanced. I don't have a source for a second set of wheels and tires to use as a diagnostic tool so will have to try to solve this problem by other means. Thanks for your input and sharing your incredible knowledge of these cars.

Brucey · Post by **Brucey** » Tue Oct 14, 2014 3:03 pm

if you doubt that the wheels were correctly balanced, have them checked (after running out the flat spots of course). If you doubt the accuracy of the machine, have them rotate the wheel 180 degrees on the spindle and then check it again.

Most of the 6ers I have driven have shaken the front around 100kph and the rears around 120kph, but these speeds can vary with wheel mass and the stiffness of the bushings etc. I suppose it is possible that yours does not follow the usual pattern.

Another reason for trying another set of wheels is that it could be a problem with the propshaft (misassembled, failed joint/mounting, weights dropped off etc.) You can test for this by running the car up when it is on axle stands with the wheels off (refit the wheel bolts with spacers to retain the discs)

BTW on a very long sweeping turn, if the shaking is constant as you go round the turn (rather than varying as the wheels on each axle go in and out of phase) then this is indicative of a single wheel that is causing the trouble.

cheers

cheers

clipper47 · Post by **clipper47** » Sun Oct 19, 2014 9:06 pm

Update: I changed the tires front to back and also checked the driveshaft when the rear wheels were off. Driveshaft spin with no vibration up to 3000!in 5th. I drove the car on the highway today and ran it up to about 145KPH. Very mild vibration at 100kph, slightly more at about 120 then smooths out. Not the best but good enough for the kind of driving that I do. Winters coming and time to put the old gal away until May anyway. Thanks for all the help.

sansouci · Post by **sansouci** » Sun Oct 19, 2014 10:08 pm

I have always had Michi MXV4's on all my BMW and if sitting for a few weeks (common for my 2nd car) 'tis true that they take a few miles to "round out" less though in hot weather (think summer!) I've always gotten great mileage (60K+) and a smooth quiet ride
I also have an E32 which is bigger and heavier than my E24.
--Ken