Shaking steering when braking

[Fanatic]

My 04' Z has 83.000km

I have new rotors and brake pads (3000km) and overhauled calipers because I upgraded everything to 3,0si specs front and back. I bedded the brakes according to instructions.

When I am driving at high speeds >130-140km/hour and slow down by braking I can feel a tremble in the steering wheel. I cannot feel it when braking hard to a stand still or at slower speeds when braking for example at a traffic light. Recent MOT did not show any braking inconsistency but of course their tests are at lower speeds.

Any ideas??

 

[pvr]

Generally, I would look at warped disks but as they are new perhaps less likely.

When were the wheels last balanced?

 

[buzyg]

Have you changed any tyres recently. Could be a wheel imbalance, at it's as particular speeds.

 

[Smartbear]

Mine exhibited the same behaviour & it was worn lollipop bushes
Rob

 

[Anonymous]

Wishbone wear/joints

 

[Fanatic]

Generally, I would look at warped disks but as they are new perhaps less likely.

When were the wheels last balanced?

I cannot think how 325mm discs could get warped without any track day use. I have not even put much pressure on them since replaced.


Tires were balanced and alignment was done about three months ago.

 

[Fanatic]

Mine exhibited the same behaviour & it was worn lollipop bushes
Rob

This sounds worth checking. Did they visually look worn?

 

[Smartbear]

Mine exhibited the same behaviour & it was worn lollipop bushes
Rob

This sounds worth checking. Did they visually look worn?

Still looked ok but had developed some slop, I replaced with mehley hd replacement bushes which were not oil damped but have a good reputation for lasting well
Rob

 

[Fanatic]

Mine exhibited the same behaviour & it was worn lollipop bushes
Rob

This sounds worth checking. Did they visually look worn?

Still looked ok but had developed some slop, I replaced with mehley hd replacement bushes which were not oil damped but have a good reputation for lasting well
Rob

Just remembered I had one of them changed a few months ago. :/ Maybe the other one needs replacing also.

Or do they go in pairs? Not sure.

 

[mattyp]

Mine exhibited the same behaviour & it was worn lollipop bushes
Rob

Same for me also. I would be looking at suspension bushes.

 

[Scooba_Steve]

Most likely the lollipops - proper name brake reaction bushings. You could consider poly for these.

Brake discs really don't warp, but I'm not going to get into that.

 

[Fanatic]

Most likely the lollipops - proper name brake reaction bushings. You could consider poly for these.

Brake discs really don't warp, but I'm not going to get into that.

Number 8??

These are a few months old on mine. Original BMW

http://bmwfans.info/parts-catalog/E85/Europe/Z4_2.5i-M54/L-N/jul2004/browse/front_axle/front_axle_support_wishbone/

I would also appreciate reading why rotors don't warp?

 

[Scooba_Steve]

Yes, so if both of those are new you could have worn arms (at 6 and/or 7) which you can check by trying to rock the wheel.

Next could be what would normally be termed warped discs. They won't actually be warped but the usual cure when paying is to replace due to labour costs. You could have them skimmed if you remove them yourself but deposits can return if not enough is removed and/or if there is any runout.

 

[Fanatic]

Yes, so if both of those are new you could have worn arms (at 6 and/or 7) which you can check by trying to rock the wheel.

Next could be what would normally be termed warped discs. They won't actually be warped but the usual cure when paying is to replace due to labour costs. You could have them skimmed if you remove them yourself but deposits can return if not enough is removed and/or if there is any runout.

But my discs are new. Is it possible that new discs can have this problem?

 

[Scooba_Steve]

If they were installed with runout yes, but given the age of the cars I'd expect bushings to be failing - check the front control arms or get someone to do it as the first step.

 

[Smartbear]

If they were installed with runout yes, but given the age of the cars I'd expect bushings to be failing - check the front control arms or get someone to do it as the first step.

Engage the steering lock & try to rock the wheel whilst holding it at 3oclock & 9oclock
Rob

 

[GuidoK]

But my discs are new. Is it possible that new discs can have this problem?

Yes they can.

I suspect warped discs or that the mounting hub wasnt properly cleaned when the discs were installed.
You should use a dial indicator (you know, on a magnetic base) to measure any offset wobble (I think a swivel style dial indicator might be the easiest to use here). If there isnt any offset wobble, front control arm bushings or control arm ball joints could be a problem

 

[Fanatic]

If they were installed with runout yes, but given the age of the cars I'd expect bushings to be failing - check the front control arms or get someone to do it as the first step.

The new rotors were coated when new. Is it possible that the coating has not completely been removed and has a runout? It has been 2000-3000km since though.

 

[Paulwirral]

Bed them in aggressively , blue hot and drive home the long way round .

 

[Fanatic]

Bed them in aggressively , blue hot and drive home the long way round .

How many km do they need to bed in? I have done about 2000km