warped discs.

[norsa]

So, this dude rocks up to the workshop on Saturday and asked if I would have a drive of his BMW 5 ser as there was something wrong with the brakes. Off I went, 65 mph touch the brakes and all hell breaks loose on the steering wheel. Back to the workshop. No play anywhere on the front end that I can find. Put the dial gauge on the outer edge of the discs which looked fairly new to me, no discernable lip, expecting a mill or two of warp in probably both. If anything 0.10mm deflection. I told him that is within tolerance but I cant think what else would make the steering judder. I was out of ideas. I told him I did not want to replace expensive discs and pads to have the same effect but had no other advice. He asked if he should take it to quick fit!!!! Anyroad up, he accepted the gamble and I fitted new. Brakes were perfect. Discuss.
Nick

 

[grim_d]

I know from experience that a tenth of a millimetre can cause vibration depending on setup, wether in spec or not.

However I would be looking at the surface of the discs for pad deposits, this is probably the cause of most wheel judder, discs rarely warp imo, deposits can really cause considerable judder. Every 6 months or so I need to buzz over the discs on the fiesta with a scotch disc in the grinder or the judder is unbearable.

Some cars are more prone than others, often but not always it's also down to driving style, sitting on the brakes at standstill or parking up with hot discs are some causes but we all do it!

 

[slim_boy_fat]

My 5 series suffered the same. New discs & pads and all was well. Examination of the old discs showed virtually no lip so a pal spun them on his Colchester to true them up.

I now have a spare pair of front discs which are still well within width tolerances......

 

[AndersK]

One silly little detail I've seen before that can cause judder is the holes for the countersunk screws. Usually there is only one screw used but two holes in the disc. Rust builds up under the open hole. If a new disc or an old one gets back covering this little bump it's enough to cause judder.

 

[Matrixx]

I know from experience that a tenth of a millimetre can cause vibration depending on setup, wether in spec or not.

However I would be looking at the surface of the discs for pad deposits, this is probably the cause of most wheel judder, discs rarely warp imo, deposits can really cause considerable judder. Every 6 months or so I need to buzz over the discs on the fiesta with a scotch disc in the grinder or the judder is unbearable.

Some cars are more prone than others, often but not always it's also down to driving style, sitting on the brakes at standstill or parking up with hot discs are some causes but we all do it!

Pad transfer is more likely the cause, you should be able to see an image of the pad on the disk, they can usually be sanded off (whole disk)

 

[waldershelf]

One silly little detail I've seen before that can cause judder is the holes for the countersunk screws. Usually there is only one screw used but two holes in the disc. Rust builds up under the open hole. If a new disc or an old one gets back covering this little bump it's enough to cause judder.

This a very good point, I always make sure the disc/hub mating faces are scrupulously clean when doing brakes. Getting it wrong can lead to serious judder or wheel wobble.

 

[norsa]

I follow what you say but if it was a contaminant between the faces it would surely show up on the dial gauge. Anyway, its all sorted with the new discs and hes as happy as a sandboy but im thinking of future reference when checking for distortion, or is this scenario just unique to 5 Series???

 

[zeppelin builder]

So, this dude rocks up to the workshop on Saturday and asked if I would have a drive of his BMW 5 ser as there was something wrong with the brakes. Off I went, 65 mph touch the brakes and all hell breaks loose on the steering wheel. Back to the workshop. No play anywhere on the front end that I can find. Put the dial gauge on the outer edge of the discs which looked fairly new to me, no discernable lip, expecting a mill or two of warp in probably both. If anything 0.10mm deflection. I told him that is within tolerance but I cant think what else would make the steering judder. I was out of ideas. I told him I did not want to replace expensive discs and pads to have the same effect but had no other advice. He asked if he should take it to quick fit!!!! Anyroad up, he accepted the gamble and I fitted new. Brakes were perfect. Discuss.
Nick

i had the same problem with an e39 5series
new discs twice but still an annoying judder from speeds below 50 mph turned out there was a coarseness on turning rhe hub no perceptable play .race must have had a little pitting new bearing no judder

 

[reb78]

It’s often the thrust arm bushes in the e39 that causes this. Change these and the judder will go. I faffed around with discs and brakes for ages on mine then changed the bushes and all was well again.

 

[steviec_lj]

I know the E34 5er can have major vibration under braking.

You don’t say what year it is..

 

[gordon stephenson]

I think that 0.10mm run-out is a tad too much. Have you checked the disc thickness to see if its parallel and not pumping th calipers in and out?

 

[norsa]

I think that 0.10mm run-out is a tad too much. Have you checked the disc thickness to see if its parallel and not pumping th calipers in and out?

Like I said, the discs appeared almost new so checking thickness never entered the occasion.

 

[graffian]

My first car was a mustang and the brakes kicked the pedal pretty badly. There was a lump something like 20 thou high
on one disc. It was where the disc had hard hard spots. I clamped a bench grinder in the toolpost of the lathe and ground the
disc, the lump kicked a carbide tool out; those were the days discs were not cheap.

 

[norsa]

I go back to my original question. What can I learn from this when I cant find a substantial run out in any place on the discs?

 

[grim_d]

You said yourself in your opening post that you checked only the outer edge.

If there are no inconsistencies on either face or difference in thickness then the problem is unlikely the disc, especially if they are old. New discs with judder can often be attributed to debris on mating face

What to take away from this is that the whole disc, including the inboard face needs assessment before a problem can be diagnosed.

Since new discs solved the problem, the problem IMO was more than likely due to pad deposits or runout. As I said, a tenth of a millimetre runout can easily cause vibration.

 

[norsa]

ok. see your point. So can you actually see these deposits or has one to assume because after I had taken them off there were absolutely no visible marks

 

[grim_d]

Yes you can see them, a lot of the time you can actually see the shape of the pad on the disc.

Could be only on the non visible face