[ShoCk_]

I was having some fun keeping up with a 420bhp V8 Ford Mustang in my 330d

But I was highly annoyed how my steering wheel was juddering under heavy braking at high speeds. That's the last thing you want ... to lose confidence in your brakes at those speeds.

What are the reasons for this and how can it be solved ? can some one elaborate.

[maxoutput]

Warped discs usually, could also be bushes but discs would be the first place to look

[adammcf]

Could also be pad deposits on your discs. If you get up to high speed then brake HARD and repeat a few times it should clear them.

[david in germany]

Originally Posted by maxoutput

Warped discs usually, could also be bushes but discs would be the first place to look

Warped disks is the Least likely thing to happen to a modern car.

Originally Posted by adammcf

Could also be pad deposits on your discs. If you get up to high speed then brake HARD and repeat a few times it should clear them.

Spot on.
Deposits on the rotors or what is commonly called "hot spots" are the culprit a week or two of easy braking can some times smooth them out or you can have them resurfaced.
Last option is to replace the rotors.
The heat from the hard braking causes hot spots that build up and can contain/ capture brake pad material causing the pads to bounce over the higher (harder) spots. They are easy to see with a quick glance at the rotor. If there is darker spots on the rotor surface, there is your confirmed problem.

[maxoutput]

Maybe so but my E90 had warped discs due to someone fitting cheap aftermarket ones before my ownership, it's not unheard of

Originally Posted by david in germany

Warped disks is the Least likely thing to happen to a modern car.



Spot on.
Deposits on the rotors or what is commonly called "hot spots" are the culprit a week or two of easy braking can some times smooth them out or you can have them resurfaced.
Last option is to replace the rotors.
The heat from the hard braking causes hot spots that build up and can contain/ capture brake pad material causing the pads to bounce over the higher (harder) spots. They are easy to see with a quick glance at the rotor. If there is darker spots on the rotor surface, there is your confirmed problem.

[david in germany]

Originally Posted by maxoutput

Maybe so but my E90 had warped discs due to someone fitting cheap aftermarket ones before my ownership, it's not unheard of

Who determined that they were warped? Were they placed on a lathe and checked for trueness or were you just told, juttering yep, they are warped. It is very rare for modern vented rotors to ever warp. Single disk rotors could possibly (in a VERY rare case) warp due to over heating an then too rapid of cool down on parts of the rotor. Modern day vented rotors are actually two disks side by side increasing strength immensely.
On the other hand the typical brake shop will sell you what they make money on. Do they make money on 40+ minutes per rotor turning them? NOPE, they make money on putting new rotors on after they tell you your rotors are warped and MUST be changed out. I went back to OEM BMW rotors after running a budget rotor on my 335I for this same reason. They are not warped just have build up and it causes the shaking on braking symptom.

[Len_Beach]

Warped disks are usually the first to be blamed but in reality are the last potential option.

Does the vibration pulse through the pedal or is it just steering?

Try a series of fast to slow heavy braking runs to get some heat into the the discs and pad material and clean off any deposits.

Also check that the disk face that the wheel seats onto into is clean and smooth and that the back of the wheel is also clean.

If that doesn't fix it; have a look at your lower control arms for excessive play.

[david in germany]

Originally Posted by Len_Beach

Warped disks are usually the first to be blamed but in reality are the last potential option.

Does the vibration pulse through the pedal or is it just steering?

Try a series of fast to slow heavy braking runs to get some heat into the the discs and pad material and clean off any deposits.

Also check that the disk face that the wheel seats onto into is clean and smooth and that the back of the wheel is also clean.

If that doesn't fix it; have a look at your lower control arms for excessive play.

And, wheels are properly torqued.

ShoCK_, this is what my 335i rotors looked like after chasing an E60 M5 on the autobahn (and stopping). I am pretty sure your will not be quite this bad unless you are running over 170mph like I was that day. but I know what you are talking about from experience.

[Chappers 71]

My last pair of front discs started to cause severe juddering under hard braking so I had them skimmed by one of those machines that does it whilst the discs are still on the car. That only cost me £80, unfortunately within 1500 miles they had started juddering again.
I ended up putting a new pair of front discs on & all has been fine since.
I did go through a few cycles of braking to try & clean the discs but in my case this didn't work.
Also it was only the right front that was out of balance.
I have now stopped holding the car on the brakes after coming to a stop from high speed or after hard braking, I now pop it into neutral & use the hand brake.
If you have an auto I believe holding it on the brakes after coming to a stop from high speed could cause heat soak, leaving deposits & or distorting the discs

[ShoCk_]

Thanks for the advice guys.

So I made another thread about how I am looking to upgrade my suspension. I was recommended Eibach Springs / Bilstein B8 shocks.

I was told by Avon Tuning (where I had my DPF / Egr delete & Stage 1 map) that my rear, passenger side shock is leaking and that I needed to get all four wheels aligned and steering sensor re-calibrated.

Now when I brake at speeds below 90mph there is no juddering at all. Coming from 140mph down to 90mph and then going back up to 130-140mph and back down to 70mph all of sudden caused violent juddering this weekend on the steering wheel. Not in the pedal.

The discs / pads appear to be fine so I guess the culprit must be the obvious leaking shock / wheel alignment issue ?