V70 Brakes: Warped discs. Urban myth?

[GMad]

I think "warped discs" is a term that has just caught on!
I have had similar issues with discs that have got hot as a result of caliper issues in the past, but fortunately have access to lathes at a lot of the places I, or one of my employees work.
The expression I would prefer to use is, slight distortion. because every time I have faced a brake disc in a lathe, the deflection in said disc has always been very small.
I reckon it's always worth having a go (whatever method you use) at dressing up suspect discs.
So well done that man

[fungus]

I had judder and vibration when braking from high speed.
I stripped the brakes cleaned the mating surfaces and re-lubricated the guide pins.
All good now. The discs and pads had done 40,000 miles, I'll will use mintex again.

[kebab10]

Had my rear disks skimmed today and it worked a treat. £18 a corner so not bad. No juddering, good job done.

[rickmethven]

I'm on my second set of discs in 2 years...still wobbling.
Mechanic thinks it may be warped hubs??
Has anyone heard of this?
11 years old and 212k so not a young car by any stretch.

[AndyV7o]

Yes hubs can get distorted.
You need to thoroughly clean up the hub and check for run-out on the face. If there is no run-out or well within tolerance then the problem lies elsewhere. If you get excessive run-out, fit new hubs.
If the hubs are true check the next two things;
You may have a slightly binding caliper overheating one side.
You might be causing it yourself by holding the car on the footbrake after a long/hard stop.
Also, use quality discs, cheaper ones arent always the purest or uniform of material which can mean you get uneven expansion and contraction leading to distortion.
(Btw avoid mintex, I have had bad experiences of their discs and drums. It was the discs, nothing else. They were fitted correctly, checked for run-out, and to begin with were fine. Judder started, discs were out of true, removed discs, hub face true. Switched to Apec instead, no more problems. Others on here have had similar experience. They used to be quality but now are budget trading on past reputation, thats why they're cheap)

[oragex]

Try looking at this video at 2:45 https://www.youtube.com/watch?v=cH-f0Q1K5H8

Originally Posted by AndyV7o

hubs can get distorted.

I had a hub distorted after hammering the wheel bearing. One way to see if the hub is distorted, is the wheel lugs would loosen by themselves within a few minutes of driving

[davebb]

use a Dial gauge ,
I have had Delphi discs on the front of my D5 for about 3 years I have found them very good and a very good price,
Dave

[canis]

This thread makes absolutely no sense. Unless I've misunderstood, the claim being made here is that warped discs is a myth, and the proof is that grinding my discs smooth cured the problem. So ... that means they were warped, now aren't, and therefore warped discs is CONFIRMED. Otherwise the fault would still be evident after re-grinding.

The reality is that the movement of pads during braking is microscopic. Indeed, it's so tiny there's nothing pulling them off again! So what forces the pads apart when you release the brake - it's warpage, since nothing is ever perfectly flat, it's not technically possible to achieve perfection. The question is; how warped is warped?

Because the movement of the pads on the disc is so tiny, it only takes a tiny amount of warp to produce the effect being described. So in terms of measurement, it's tiny. In terms of brake effect, it's enormous. It's relative.

Let's put it in perspective - pads only move a quarter of an inch in their entire lifetime. The physical action of arresting a disc is so fantastically small it's almost unmeasurable, it's certainly not visible to the eye. Therefore, it's not suprising the warpage is small, it couldn't be anything other than small, but they can be outside of tolerance and that's where the pulsing comes from. Half way around, the pad takes up the slack due to the extreme hydraulic pressure, half way around again it meets massive resistance.

[AndyV7o]

Except that some cases of 'warping' arent warping but spots of pad residue from holding hot brakes on (which can often be got rid of by a few hard braking sequences), cementite forming from excessively hot brakes being held on (usually a binding caliper, or very irresponsible speeds) which cannot be got rid of at all, lumps formed by corrosion, varying disc thickness due to varying density of material (cheap discs), disc and/or pad contamination, etc etc.....

I didnt take too much notice of the original posts as they are 6 years old, but basically, the 'technique' originally posted will have simply removed pad residue and high spots, its not accurate or stable enough to skim a disc in the correct sense.

Most 'warping' isnt warping, but it does happen, regardless, its become a term for disc defects causing judder, as people understand the term readily without any technical stuff getting in the way...

[davebb]

Hi also if you have the 286mm front discs, I would change them to the 305mm
you only need to change the carries and the discs, The 305mm discs have much better cooling, not just the size they have outlet vents near the centre hub that the 286 do not, you can get 2 305 Delphi discs for about £50-£55
Dave