Timm's Curing The BMW E31 50MPH - 60MPH Shimmy
The E31, E32 and the E38 7-Series can suffer from the dreaded 'shimmy'. This is wheel-wobble that usually first shows itself under braking, for instance, when coming off a motorway intersection and braking from high speed. The wobble can be felt through the steering-wheel but it usually disappears as the car speed reduces.
Sometimes this is all you ever get, but more usually you will start to get wobble as the car is accelerated through 50 - 60MPH. The more you drive the car the worse it will get. The wobble is quite often accompanied by tram lining and a general feeling of imprecision from the steering in general.
The shimmies are often an indication of general wear in the steering system and suspension, the BMW E31 has a great deal of weight over the front wheels, especially when braking. It also seems to have a resonant frequency that occurs between 50 and 60 MPH, if there is any weakness it is at this speed where the problems will occur.
Wobbles that aren't shimmies
Let's first get rid of the wheel-wobble that isn't shimmy. If you get a wheel-wobble that really feels as if the wheel is coming loose and gets worse when the brakes are used then the first thing to suspect is a sticky brake calliper. The difference between shimmy and the wobble caused by a sticking brake calliper is that latter causes a massive wobble, the steering wheel is difficult to keep hold of and the wobble keeps going when you slow down, almost to a standstill.
One method of checking if a sticking calliper is the cause of vibration, is to drag the brakes for 30 seconds or so to heat up the brakes - keep off the brakes for a minute or so and then drive through the problem speed. If the vibration has gone you can be sure the calliper is stuck to some extent. The Brembo 4-pot callipers on the 840ci are prone to sticking. The fuzzy picture below shows the brake parts taken from my current 840ci, the inner surface of the disk shows only 1" of wear, the outer 1" or so has delaminated brake pads stuck to it:
Where the calliper is sticking, both pad and disk reaches extremely high temperatures. After a drive the pad sticks to the disk, the next time the car is driven part of the pad can be left behind on the disk. This is often confused with a warped disk as the effect is just the same with tight spots felt as the wheel is rotated.
Vibration that only shows itself when giving the car some welly, especially in 2nd and 3rd gear is quite often due to the propshaft centre bearing. The bearing is held in a rubber-enclosed housing. When the bearing starts to fail the rubber soon deteriorates and this allows the propshaft too much lateral movement. The movement causes a vibration through the car, it will eventually get to a point where the propshaft will start thumping the transmission tunnel. This type of problem always goes away when the throttle is lifted whereas shimmy doesn't.
If you get a wobble that is only noticeable in 5th gear when you have your foot on the throttle it is almost always due to a single-cylinder failure on the engine. The lack of a single cylinder on a V8 is not that easy to spot, the power is a bit down and the tick-over is a bit lumpy but V8's are prone to that anyway. It is most noticeable when on the flat at about 70 MPH when accelerating. The wobble goes immediately the throttle is lifted. A check of the sparkplugs will show 7 white plugs and one oily one! I have had this fault on my E32 and the repair is covered here.
Getting rid of the shimmies - the easy things
The best place to start (and often the cheapest) is with the road wheels. The first thing to check is if the wheels are right for the car. The standard wheels for the E31 are 16", they have an offset of 10 -15 and a centre bore of 72.6mm. Here is a list of offsets of BMW alloys:
If you have fitted an alloy from a model with a different centre bore then you must fit spigot-rings. The only problem is that spigot-rings are not normally high-precision parts, they wear and corrode and when they do they will not hold the wheel central to the hub. If you are using spigot-rings consider getting alloys with the correct offset and bore, or, at the very least get new spigot rings.
Even if you are using standard wheels or are using wheels with the correct bore and offset it is worth cleaning the bore and mating surfaces on both the inside of the wheel and the hub. Where there is corrosion on the hub or wheel the wheel will not mate correctly with the hub.
Replica alloys usually have a 74.1mm bore and require hub-centric rings, if you have fitted replica alloys ensure these are fitted. Without the correct rings you will never get rid of wobbles and shimmies for any length of time. Click here for more information on fitting replica alloys.
Cheap tyres are often a cause of problems, although these balance fine at low speeds, once they are taking the load of the car and are rotating at speed they do not retain their shape or were not round in the first place. There is only so much that sticking lead weights on the rim can compensate for. If you have a lot of lead on your wheels then something is not right in the first place. If you do not have staggered wheels fitted it is well worth rotating the wheels from the back to the front of the car to see if there is any difference. If it makes a big difference it is probably a problem with the tyres.
One of the unusual but easy things to try before going much further is to remove the backlash in the steering column where the it telescopes. There is a large nut as shown here:
Tighten the nut as much as possible, some have adjusted this to the point that the column does not telescope any more (putting the column in the preferred setting beforehand). As I say, this sometimes works but is a bit of a long shot.
Getting rid of the shimmies - the harder bits
Once all the easy options are out of the way we have to move on to the front suspension components. There is a lot of advice given on what to change first but in my experience most problems are either removed entirely or at least made significantly better by replacing the upper arms and rubber bush (item 9 in the diagram below):
While you are at it you might as well replace the lower arms as well (item 13), the cost is not all that high and is worth doing once the car is on the lift. A big difference can be made by just changing the bushes (items 10 but normally if the bushes are damaged then the ball-joints are damaged at the same time. Some like to replace the bushes with polyurethane after-market versions, be aware though that this will significantly affect the quality of the suspension and may well lead to other component failures.
Getting rid of shimmies - it's getting much harder now
We have now covered the possible causes in 95% of the cases I've been involved with. I have heard of miracle fixes where just one component of the front suspension has been replaced before the usual things have been tried but these are really just one-offs. So, in order of the most likely here are the remaining candidates:
Front stabiliser joints (item 6)
Centre tie-rod (item 9) Drag link
bearing (Items 14, 15 and 16) Tie rods (item 3)
Once you have got to this point things have got pretty expensive. You can get complete suspension refurbishment kits from Ebay.de, I have never tried these but have heard good things about them. The last two diagrams only represent 5% of the causes of shimmy so hopefully you will not need to get to this stage. Unfortunately, if you have just bought an E32 that has shimmy you will not be aware of what has been changed already. My best advice is don't buy an E31 with shimmy, it can be simple to fix, but it can also be expensive!