Brake judder

[Dieselman]

Oh yes they do!

I asked my 40 years in the trade garage owner friend about this the other day and he agrees with you that they can indeed warp and therefore the myth that's it's a myth is definitely a myth

I'd be interested in knowing how these are being measured.

Disks don't warp, but suffer friction material deposition, hence have brake grab and varying thickness measurements.

I've never had warped disks, but have had symptoms like warped disks apparently give. If the trick of driving with the brakes applied hard for a while fixes the problem, the issue is friction material deposition.
I have cleaned this off with a wetstone and had perfect braking.

In the o/p, I suspect the rust look was in fact friction material.

OK picked the car up and did some repeated hard braking and the brakes feel a lot better now so seems that Whitefield Mercedes were spot on.

Almost certainly not so.

-Warped- Brake Disc and Other Myths

 

[ItalianTuneUp]

I'm reading DM's link on the warped disk myth now.

Olly says disks do warp, and DM says they don't, so now I'm confused.

Interestingly, I had the same gritty brake feel and had front discs and pads changed. The feeling is improved but not gone altogether, so I'm assuming either there is a deposition issue like DM talks about, or grittiness is from rear discs...

 

[WG M-B]

Discs do warp

 

[ItalianTuneUp]

The author of the link DM refers to says:
(apologies for long copy and paste)

With one qualifier, presuming that the hub and wheel flange are flat and in good condition and that the wheel bolts or hat mounting hardware is in good condition, installed correctly and tightened uniformly and in the correct order to the recommended torque specification, in more than 40 years of professional racing, including the Shelby/Ford GT 40s – one of the most intense brake development program in history - I have never seen a warped brake disc. I have seen lots of cracked discs, (FIGURE 1) discs that had turned into shallow cones at operating temperature because they were mounted rigidly to their attachment bells or top hats, (FIGURE 2) a few where the friction surface had collapsed in the area between straight radial interior vanes, (FIGURE 3) and an untold number of discs with pad material unevenly deposited on the friction surfaces - sometimes visible and more often not. (FIGURE 4)In fact every case of "warped brake disc" that I have investigated, whether on a racing car or a street car, has turned out to be friction pad material transferred unevenly to the surface of the disc. This uneven deposition results in thickness variation (TV) or run-out due to hot spotting that occurred at elevated temperatures.

 

[markjay]

He he....

'...tightened uniformly and in the correct order to the recommended torque specification..'

So warped disc must be a very common issue then..

About half the tyre fitters I visited don't bother with torque wrenches.

 

[msavill]

hi all I have a new problem I changed discs and pads when I brake hard all is good but when I tap them going about 5 to 10 mph it feels like something is moving I made sure all bolts were not lose can you help please

 

[Dieselman]

He he....

'...tightened uniformly and in the correct order to the recommended torque specification..'

So warped disc must be a very common issue then..

About half the tyre fitters I visited don't bother with torque wrenches.

Are your disks mounted on top hats?

No.

 

[Dieselman]

Discs do warp

Can you qualify that?

I'm asking as I have never had warped disks, but have had uneven friction material deposition more than once.

 

[streethawk]

Can you qualify that?

I'm asking as I have never had warped disks, but have had uneven friction material deposition more than once.

I've definitely seen and had warped discs. Iam a mechanical engineer for 23 years and at weekends I'll do little jobs for friends when needed like service, change brakes etc. When I have someone say I've got judder I take the discs into work and mount them level on inner boss face and clock them on disc face and they can be upto worst I've seen .015". Quick skim if there worth doing of course and alls good. Friend of mine used to have an m3 csl and tracked it a lot so had him skimmed several times. Amazingly only .005" run out can be felt on the car. The only thing I can think is it's down to over heating discs and then maybe quick cooling like water from washing or rain or puddles. Agree with dm also about friction material or rust causeing issues. Just thought id share my experience's.

 

[guydewdney]

Next time you get a "warped" disc, try this, to settle the argument. Mount in a lathe or similar. Rotate with TWO dial gauges, one on the inside face, one on the outside. If its warped, they will move togther, if its deposition, they wont, or are unlikely to, move togther?

 

[streethawk]

Next time you get a "warped" disc, try this, to settle the argument. Mount in a lathe or similar. Rotate with TWO dial gauges, one on the inside face, one on the outside. If its warped, they will move togther, if its deposition, they wont, or are unlikely to, move togther?

How do you think I know if there warped? Obviously I do check them like and also put them on boss mating face after a clean on a ground riser on a granite surface table with clock and stand to verify what iam getting on machine. Done at least a dozen sets.

 

[guydewdney]

Yrs, but the point is to see if it looks like a wave washer, as in warped, where the disc thickness will be even(ish) around its surface or if the deposition theory holds true, in which case the high spot on the clock will result in an increased thickness at this point. So, did you check, by marking the high spot and using a micrometer either side of that spot, or use two clocks, on opposite sides? I can see you know what you are doing, and have the kit to do it, and this isnt an accusation, its interest.

Im ex aerospace mech design, so have some knowledge of precision engineering.

 

[streethawk]

Yrs, but the point is to see if it looks like a wave washer, as in warped, where the disc thickness will be even(ish) around its surface or if the deposition theory holds true, in which case the high spot on the clock will result in an increased thickness at this point. So, did you check, by marking the high spot and using a micrometer either side of that spot, or use two clocks, on opposite sides? I can see you know what you are doing, and have the kit to do it, and this isnt an accusation, its interest.

Im ex aerospace mech design, so have some knowledge of precision engineering.

Your right in the wave washer! Clock one side marking high spot and then other you will get low spot then Mic disc and thickness is uniform which indicates a warp. I've done anything from fiesta to top end bmw's but only bother with high end as cars like fiestas are cheep as chips for discs. I think because they try to make them as light as possible now days maybe that's why it's more common. Iam also a aerospace engineer! Manual milling is my thing but can do it all but prefer real engineering

 

[guydewdney]

Iam also a aerospace engineer

Wroted like a proper engineer... :fail

LOL

 

[st13phil]

Wroted like a proper engineer... :fail LOL

Reminds me of some graffiti in the Students Union bar at Brunel 30+ years ago when I was an undergraduate:

"This time last year I couldn't even spell the word engneer, now I are one"