How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Matt Your Own Question
Matt
Matt, Mechanical Engineer
Category: BMW
Satisfied Customers: 21601
Experience:  BEng hons Mech engineering, in auto industry 22 years
12772297
Type Your BMW Question Here...
Matt is online now

I have a new series 420d and when I drive over 80mph the car

Resolved Question:

I have a new series 420d and when I drive over 80mph the car starts to become unstable with the rear of the car starts to wobble. I was driving along a dual carriageway with a slight bend and I lost control of the car.
Submitted: 3 years ago.
Category: BMW
Expert:  Matt replied 3 years ago.
Hello

hopefully you didn't crash the car and hurt yourself so can check a few things to see what happened

1st check that the tyre pressures are correct and inflated to the maximum as stated on the sticker on the door sill

also check the tyres for any cracks or bulges on the side-wall of the tyre (inside and outside) these will throw the tyre out of shape and produce vibration - take a good look over the tyre sidewalls and bear in mind that anything that looks suspect when static will probably be ballooning out and far worse at speed so if any doubt then replace the tyre. Also check if the tyres have been fitted the right way round as some types are directional

then check for worn suspension joints - jack the car up so the wheel is off the ground (you’ll need to do this for all 4 corners) and shake the tyre from top to bottom and from side to side (with someone holding the steering wheel on the front) there should be no play in either direction. Any play in 1 direction will usually require a joint to be replaced, if there’s play in both directions then the wheel bearing may be at fault. If theres play only up and down its the strut top mount - to find this one you have to shake the suspension strut it self up and down with the wheel off the ground - so you may need to remove the wheel to check this one.
Now with the car jacked up on that side with the wheel about 2 inches off the ground use a steel bar under the wheel and lever the wheel up and down slightly, you should be able to look at the end of the axle and see if the suspension arm is moving up and down separately to the axle.If so replace the bush

To feel if there's a worn strut top bearing then lightly hold the spring by hand and have your assistant move the steering from left to right with the wheel on the ground - a worn bearing will feel 'notchy' through the spring. The wheel needs to be on the ground for the test to load up the bearing

Matt and other BMW Specialists are ready to help you

Related BMW Questions