Brake discs

M

mantona

Member
So the front brake discs on my 2008 Z4MR are warped. Any suggestions on repair or replacement please? My inclination is the simple (but expensive) option and get them replaced at the main dealer on a like for like basis. Whilst I am an enthusiastic driver 😊 I don’t do track days. I’m based in the West Midlands.
 
Get them to a machine shop and get a few thou skimmed off them. I've heard it said that discs don't even actually warp but just get pad material transferred to them giving high spots.
 
Really? I’ve heard this done across the pond frequently. Not seen it here in the UK? Or have I been going to the wrong places/searching for the wrong thing? If you know of any places in and around London please do give your recommendations!
 
It's the province of little engineering firms with a manual lathe. Few quid and 20 minutes would get it done. My one regret with my little large is that it's too small to take brake discs!
 
Years ago I asked about disk skimming and was told that it is really only recommended for cars with expensive brakes as its almost just as cheap to replace the disks on normal everyday cars
 
Nictrix said:
Years ago I asked about disk skimming and was told that it is really only recommended for cars with expensive brakes as its almost just as cheap to replace the disks on normal everyday cars
Click to expand...
This!

Also modern brake discs have a minimum thickness tolerance (only a few mm below new). If you skim 2mm off they will be knackered anyway and cost you to knacker them! Don't see it being a viable option anymore TBH; and potentially a dangerous one. :?
 
I only suggested this as it was in reference to an M car which on 3s and 5s always seem to command extortionate prices for things like discs. Dunno how the Z4M stacks up.

A minor wobble ought to require no more than a tiny amount off the disc, say 0.05 to 0.1mm (2 to 4 thou in old money) which would leave loads of metal. One has to assume the disc is fairly new or, yes, just throwing new ones on early is the easier option.
 
Great advice - many thanks. The car has done 28K miles so there should be some life in the discs. There are some specialist machine shops so I’ll try one of them and see what they say
 
See if there is a significant wear lip around the edge of the disk. Its fairly common to swap disks at the same time as pads these days as modern asbestos free pads are far more abrasive than they used to be! Wear limits are surprisingly low, as said about 1mm per face, once lots of material has gone then they overheat even more.
 
I’m getting wheel wobble at higher speeds too. They have been checked at Kwik Fit (convenient for an assessment if nothing else) and they confirmed they were warped - the driver’s side more so than on the passenger side. The steering wheel also wobbles under braking.
 
Not sure I'd trust a KF assessment tbh - do they have the equipment to properly assess or was it an opinion based on symptoms?

Before splashing out on new discs, try rebuilding your calipers. Disc warp is extremely uncommon and sticky calipers very common. It could also be your wishbone bushes.
 
In fairness KF did a proper on the ramp assessment. A friend of mine (a classic car expert - dismantles and rebuilds engines so knows his stuff) suggested it as a possible cause. I thought the KF assessment and the fact that it was so uneven under braking confirmed it. It’s good to know about the other possible causes too. I’ll need to get it properly looked at and assessed. Thanks everyone for your input.
 
I fitted new oem discs to my x5 and a few months in had a vibration under braking ( all front suspension had been refreshed) I put a dial gauge on them and there was fluctuations in the readings , found a local tyre and brake centre that machine the discs whilst still bolted on the hubs . No problems for the last 3 years . Apparently the guy said that they do a lot for Bmw main dealers ( in my case Ocean Bmw Falmouth.
 
I replaced the discs on my Z4M due to the NSF being clearly warped, no more issues.

Discs can cause brake vibration due to either deposits or being warped. Some will say they don't warp and it's always deposits that cause the issue, in my experience that's not true. I've seen may warped discs, it's an easy thing to measure.

A few years back I had an issue with brake vibration on an E39 M5. Changed a lot of components including the discs, issue came back after a few hundred miles. It was finally fixed by getting the discs skimmed on the car, problem solved. That model has a reputation for brake vibration mind.

That was using fairly new discs though, if your discs are already quite worn, I'd just replace them.

Mine came from Autodoc but it was pointed out on here that BMW are sometimes close to the same price, it's worth phoning around and always ask for discount.
 
Excellent advice. In fact I was giving this some thought and I remember I had warped discs on my Z3MR and just replaced them. That might be the easiest option.
 
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