I posted this up on one of the E46 forums.....thought it might be of interest here as lots of similarities between the cars. Its not definitive - please feel free to add/suggest other areas - just thought i might help a few people.............
There seem to be lots of posts about vibrations/wheel wobble etc so thought iÔÇÖd post some info which might be useful as a sticky in the Tech section?. Loads of it is really simple/free to check stuff. Even some of the fixes are ok for the capable diyer.
Just to add, if you do DIY and donÔÇÖt jack the car up properly with axle stands, take proper safety precautions etc etc and it falls on your head/toe/neighbours cat, itÔÇÖs your fault.....so stop reading now and go to a garage.I take no responsibility. All the DIY tasks/replacement procedures are either here or on the web somewhere. All this is for the E46, but from past experience it pretty much applies to E30s and E36s too.
As a general rule 30 ÔÇô 50/55mph vibration is usually front wheels/suspension, 50/55mph+ is usually rears.
Work through these steps:
Check your tyre pressures....eg low pressure on the front nearside tyre will cause the car to pull towards the kerb. Simple really. DonÔÇÖt just pump them up to what you ÔÇ£thinkÔÇØ is right ÔÇô get the exact psi from the book/manual/etc and use a digital gauge.
Check condition of tyre. Is the tread wear even ÔÇô uneven tread often points to poor alignment. Simple tracking fix at a garage ÔÇô but you might want to find out why you have poor alignment.
Take the tyre off ÔÇô look for bulges, nicks and damage to sidewall (the inside sidewall too....so donÔÇÖt be lazy ÔÇô take it off the car!) these can all affect the wheel balance.
Make of tyre. If you/the previous owner have spent ┬ú50 a corner on some ÔÇ£linglong ditchfindersÔÇØ that is not a good sign. Michelins, Pirelli, Goodyear etc charge ┬ú200 a corner for a reason. The quality of the rubber, the tread pattern and how the rubber treads react under speed and load all affect the handing. Most BMWs were ┬ú30k+ cars when new, putting a ┬ú50 tyre on it is just dumb. Go and do your own research ÔÇô and change your tyres while you are at it.
Tread pattern. For some reason I have never found that BMWs like directional tread tyres on the front ÔÇô theyÔÇÖre fine on the back. But on the front they often promote tramlining (especially on the inside lane of motorways where HGVs wear grooves into the tarmac). Try non directionals on the front ÔÇô it might help.
Condition of the alloy. Alloys are easily damaged on our potholed roads ÔÇô often a flatspot is not visible ÔÇô best to get a garage to spin them up and see if they are true. Lots of weights on a wheel is not a great sign either ÔÇô itÔÇÖs probably already damaged and also some of the weights can then get knocked off whilst driving without you noticing, so upsetting the balance again.
Make of the alloys. Replica alloys are cheap for a reason ÔÇô they are made of s**t quality metal. They deform/crack more easily ÔÇô some cracks arenÔÇÖt visible. You get what you pay for. Change them.
Size of the alloy If you like running around on your 18ÔÇØ or 19ÔÇØ alloys expect any imperfections in your front suspension to be magnified as there is less give through lower profile tyres.
Swap all 4. All of the above can be assessed through swapping tyres around (fronts for rears) borrowing a friends set, going to a tyre place to get them checked etc ÔÇô all fairly easy stuff.
Still got problems?.....Get a knocking sound when you go over potholes/bumps?......read on, it could be any of these
Front control arm rear bushes. Look under the car, are they all perished and cracked, do they crumble when you lever them with a screwdriver? A competent garage can change these in half an hour. OEM replacements are usually fine and you might not want to get extra hard poly bush ones as they just push the problems to the next weakest component on the front suspension. Make sure you get tracking/alignment done afterwards.
Balljoints/bushes on the front control arms. Jack the car up. Grab the wheel at 9 and 3 oÔÇÖclock give it a waggle and try again at 12 and 6 oÔÇÖclock. Any movement is usually (but not always) the balljoints. Sometimes you can get a screwdriver at the outer balljoints and push them up and down ÔÇô not a good sign. A small bit of movement when stationary translates to a lot of movement with 1.5 ton of car on them at speed. You can get a new balljoint pressed in, but I usually take the view that if the outer one is shot ÔÇô the inner one wonÔÇÖt be far behind so prefer to replace the whole control arm ÔÇô not too hard a job ÔÇô plenty of info on here.
Still no better.....? Ok ÔÇô now itÔÇÖs getting harder to source the problem ÔÇô remember, fixing one component can just push the problems to the next weakest component on the front suspension so donÔÇÖt just go replacing components piecemeal ÔÇô check all the front suspension or get someone to check it all first before you start.
Droplinks and Anti roll bar bushes. You could replace the front droplinks and arbs while you are under there ÔÇô it probably wonÔÇÖt solve the problem of vibration on its own but might tighten things up and help your handling if you are fixing other components at the same time. Worn anti roll bar bushes can give rise to a clonking sound - especially if you go over a bump/mount a kerb etc.
Tie rod ends. Not an expensive part ÔÇô it can just be one side, but play in the steering, vibration and at worst being able to grab and wobble them with your hand is a sure sign that they need replacing. Once again, itÔÇÖs best to make sure you get tracking/alignment done afterwards.
Steering rack. A reasonably robust component and unlikely to be the cause but donÔÇÖt rule it out, but get a professional assessment from an indy before thinking of changing this. Much more likely are the various joins/knuckles from the steering wheel to the rack. These joins all get nicely cooked as they pass the exhaust/manifold over time and replacement of the joins can help. A visual inspection will tell you if they are brittle and disintegrating. Or get someone to twist the wheel whilst you see how much play there is in the various joins.
Brakes. Warped discs (not going to going into discussion of whether they warp or if itÔÇÖs a build up of break deposits) but fairly easy to check. Jack the car, spin the wheel, does it spin totally freely or seem to grab halfway round ÔÇô if so, it could be damaged discs.
Thin disc/cracked discs/or old discs with a big lip on them can all cause the brake pads to wear unevenly upsetting the front end although this is usually only likely to show up on braking
As is a sticking calliper ÔÇô Go for a spin, brake a couple of times then hop out and check the temp of all the discs (if you use your finger you will burn yourself ÔÇô but up to you) If one is much hotter than the others it could be a sticking brake calliper.
If none of these have resolved your problems, you are fast running out of options, so donÔÇÖt rule out crash damage (youÔÇÖll need a full jig/geo set up to determine if that is the root cause)
Vibration over 50/55mph
If you are unsure, but donÔÇÖt feel much/any vibration through the steering wheel at this speed, take a look at the passenger headrest ÔÇô is it vibrating/wobbling around, can you feel vibration through your seat? If so, itÔÇÖs probably caused by something other than the front wheels/suspension ÔÇô usually the rears!
Rear ball joints. Clonking or knocking over bumps/potholes ÔÇô could be the rear wheel balljoints. Jack the rears, grab the wheels and do the wheel wobble test as stated above. Movement usually means the rear ball joints are suspect. Usually a garage job unless you have a balljoint puller and a magical ability to remove badly rusted and seized mounting nuts.
Rear bushes. As long as itÔÇÖs not the much feared rear subframe crack, your rear bushes could all be getting worn so check to see if they are the culprits by the condition (or ask a garage) and donÔÇÖt rule out the diff mounting bush either.
Propshaft The propshaft guibo is often a cause of vibration, get your hand underneath and try and turn it sharply....is there a clonk? ÔÇô if so ÔÇô that could be your problem as the joins/guibo does wear.
This is not definitive but working through a lot of these could help save you time and money ÔÇô hope it helps.
Questions and answers on steering, suspension, bush replacement, wheels, tyres and much more
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