Vibration when braking

stairhopper

hi all
I have a 2009 7 series BMW f01 model 730d.. Just recently it's developed a judder upon braking. It does matter whether it's hard or gentle pressure the vibration is quite severe. The discs themselves look pretty new so although I am certain it could be warped discs I'm not 100% convinced.
Any insight would be much appreciated

burnt_toast_2

If vibration is only apparent when braking then the discs are warped.

Iceweasel

It is perhaps possible to cure the judder at minimal cost - it's worth a try as new discs and pads ain't cheap.

I'm not hard on the brakes of my cars at all, and I've had judder on a couple of BMWs in the past.

Of course the dealers (and many indies) will immediately diagnose warped discs (often without even a test drive or inspection) and will suggest new discs - and pads of course - and sure enough the problem goes away - for a time.

I found that it can quite likely just be down to glazed pads - possibly caused by light use.

There is perhaps no need to replace them - unless they are well worn of course.

Just get a sheet of glass-paper - lay it on a flat surface and rub the face of the pad on it.

NB - Do not rub the pad with the glass paper - as that makes it very difficult to obtain a truly flat surface.

All you need to do is to take the shine off.

You could also use a fine flat file to take a tiny bevel off the edge of the pads all the way round.

Be sure to clean the edges of the pad backing plate and also clean the pad-contact surfaces in the caliper, giving the surfaces a touch of copper grease.

Then and only then if the judder is not cured do you get the run-out of the discs checked.

Good luck.

Richard53

Agree with all of that ^^^


You could also give the discs a thorough clean with brake cleaner. Residue from the pads can build up over time and cause a bit of stickiness, which you can feel as judder. It's good practice to clean the discs off every time you change the pads. ('It's good practice' doesn't mean I always do it, of course.)

colino

Don't jump to conclusions with brake judder on a 5/7 series. Could well be excessive disc run out that you can visually check without the need for a dial indicator, but just as likely that one of the many bushes in the system need to be eliminated first.

pendragon_arther

Or you could try our old-style method of cutting a groove into centre of the pad with a hacksaw a couple of millimetres deep and see if that cures it. But make sure you don't cut too deep.

Babbawah

Warped disks are a myth. {1}

You have a high spot on one or more disks, this is usually caused by holding it on the brakes when the disks are hot.

Are you using the handbrake correctly?

It's possible to sometimes cure this by a few sessions of heavy braking from high speed but NOT allowing the vehicle to stop. Say from 70mph to 30mph but the braking needs to be as hard as an emergency stop.

Best way is to find a garage who will not rob you and simply re-skim or sometimes lightly bead blast the disk surface.

This is becoming more common now that fake branded pads are readily available. Pads off eBay or generic websites should be avoided.

{1} Many people are charged for replacement disks only for the problem to reappear a few 1000mls later. It is caused by the driving style of the motorist and NOT by the quality of the disks.

A genuinely 'warped' disk would spread the pads in the caliper so far that you would need to pump the pedal before the pads contacted.

In many years of garage ownership and many, many years involved in motorsports both 2 and 4 wheel, I have NEVER come across any incidence of a genuinely 'warped' brake disk !

I've seen cracked ones {common} and I've seen shattered ones. The only ones I have ever seen with a measurable 'warp' are the ones fitted incorrectly by grossly incompetant, cack handed monkees who need their spanners confiscating.

NWOIHTS

Check tie rod ends and bush play on front axles.

Mrs_Imp

Our car juddered when braking due to a fault with the ABS. Our friendly garage diagnosed it and fixed it very quickly for us.