I've recently being exploring the issue with juddering through the steering wheel when braking and in turn the front rotors (most the right hand side) rubbing on the brake pads as I manual turn them. Runout or warping would have seemed to be the obvious explanation but having engaged the use of some digital calipers and a dial indicator I found some surprising results.

First of all measuring the thickness of the rotors at various point around the circumferences and from the outer edge to the centre, they range from 31.07 to 31.26mm only. A variable of only 00.19 and the high point not in line with the area of the rotor that touches the brake pads as it rotates. However, using the dial indicator provided a variance of 0.3 mm from the high to the lowest point. The high point being exactly 180 degrees for the low point of the rotor. The variance from the high point to the lower decreased in quite a linear fashion. Addition and when measuring the other side of the rotors, it produces the exact opposite measurements. In that the high point of one side of the rotor produces a low reading on the other side at exactly the same point. This would seem to suggest that the rotor is being turned at a less than true rotation by the wheel hub as opposed to a issue with the rotor itself.

Is this being caused by a worn or damaged wheel bearing or are there a number of other possible explanation that need further investigation?

thanks in advance for an insight into this.

2008 portfolio XKR

 

Probably need to take the rotor off and check the same on the hub. If the hub is even, there could be debris / rust between the hub and rotor, causing it to not sit flat.

 

It is very common for brake pad material to bond to front rotors, especially if you've come to an abrupt stop from high speed, which gets the rotors and pads very hot, and you keep your foot on the brake pedal while waiting for the traffic light to turn green. That hot pad material melts and sticks onto the rotor, which causes one or more high spots on the rotor. You'll feel those high spots when braking, as steering wheel wobble or shimmy or a pulsating brake pedal.

Many brake shops describe this as "warped rotors", but the truth is that it takes a lot more heat and pressure to actually bend an OEM-quality cast iron rotor. The other truth is that brake shops are in the business of selling rotors and pads.

Machining or "turning" the rotors can remove those high spots, provided the rotors have enough thickness left. Because of the cost of labor to do so, most people decide to replace their "warped" rotors with new ones.

 

Just to 'play it again Sam', in your previous thread I gave my experience with the pulsing. The cure was a new set of Brembo Rotors. I chased my tail for 6 months trying and checking everything.
ymmv
Wj

 

Sorry Stuart you are grossly exaggerating the possibility. "That hot pad material melts and sticks onto the rotor, which causes one or more high spots on the rotor. You'll feel those high spots when braking, as steering wheel wobble or shimmy or a pulsating brake pedal."
High spots would be visible. Just switch the faulty rotor (warpage) and clean the mating surface of the hub.

 

If I can't convince you to stop believing that OEM quality brake rotors are easily warped, maybe this will:
Brembo - Debunking Warped Rotors
​

 

Yep, this "warped brake rotors" myth has endured for many decades, long after actual warpage became a relic of the past.
I have posted much the same as Stuart in other threads and linked to several other web pages.
Put simply brake rotors rarely if ever actually "warp" any more, instead they suffer from brake pad material deposition and a build up of cementite.
The problem is that almost all mechanics/shops etc still call this "warped brake rotors" despite it not being that and them knowing that it is not that, well not according to my idea of what "warped" really means.
I reckon "warped" means bent or twisted and not "uneven" but maybe that's just my warped sense of humour!
Also it's much easier for mechanics to say "warped" than to say "uneven pad material deposition".

 

What is the meaning of "warped"?

 

Brembo - Debunking Warped Rotors.. I read it. Its a long winded and basically a lot of verbal diarrhea. The most frequent causes are not that many.
Drive along at 70 mph and slam on the brakes. Well that should help warp a disk. Then there are the garage monkeys that put on your wheel rims using the pneumatic gun at its full strength, not thinking to torque the nuts properly. Right there are other les frequent causes. I don't remember if the dialogue mentioned calipers starting to seize up. Enough heat is generated then to start the warpage.
"believing that OEM rotors are easily warped" is the worst of all that verbal diarrhea, Written by an aftermarket rotor manufacturer, its pure propaganda!

 

@sony2000 You can believe whatever you want, but note that the term "warped rotors" appears nowhere in this scholarly and analytical paper. Overheated cast iron rotors will crack, not warp.
https://www.sae.org/publications/tec.../2015-26-0206/

I'm done .

 

Since I've seen rotors that are no longer on a perfectly flat plane many, many HUNDREDS of times with my own eyeballs, I have my own thoughts on this matter...

 

Not sure that quoting that SAE paper is helping your argument. They say that hot rotors could undergo “thermo-mechanical stresses and associated deformations” - that sounds to me like “warping”.

Either way, if it were me, I’d replace the rotors and properly wire brush the hub surfaces first.

 

Thank you to all who have replied to the my post. Whilst I am still open to the possibility that the rotors are warped or that I have "uneven pad material deposition" the measurements I collected appear to point to something else. I will be taking up some advice offered, and removing the rotors to measure any runout on the hubs in addition to removing any debris and rust that may prevent the rotors from sitting flat.

 

Hi Colt. I had a Volvo that went thru too many rotors. Finally at the dealer they checked the run out of the hub and then checked the run out of the rotor, in the 5 different places they could install it, to get the least error! That's how they must do it. Good luck!

 

If I understand this correctly, I think I would check the hub face and work out from there. If the hub face is true the next thing I'd look at is whether the rotor is mating to the hub perfectly and, if it is, I'd then look at why the friction surface isn't following the same path as the hub face and rotor hat. I can think of three conditions that would give the results you're seeing (excuse this awful MS Paint sketch, I'm not on my usual PC!):

1. All surfaces are true to each other but the whole thing is on a lean (MS Paint wouldn't let me rotate the whole thing!), so the issue is with the hub or something behind it
2. The whole rotor is off from the hub, so the issue is between the hub and the rotor hat
3. The hub and the hat are true, so the issue is with the rotor's surface

#2 seems most likely - it could be something as simple as a metal shaving or a little rock or something caught between the hub and the rotor as it was installed.

Like most here I am #notamechanic, this is just how I would troubleshoot the problem if I got the measurements you posted.

I will not get into the "warp" debate other than to say "warped" is a word people use when the surface of a rotor isn't as flat or true as it's meant to be, and whether it's semantically correct really doesn't matter when you're just trying to explain the feeling you get when you step on the brakes. If the rotor is out due to deposits and you're calling it warped, using a different word doesn't change the fact the rotor surface isn't flat.

Good luck

P.S. please keep updating this post with your findings!

 

DTV is the term you use to avoid this argument

 

All good suggestions from @dangoesfast also consider inspecting the calipers for proper fitment, pistons and no binding of the slide pins. Also have a look at the wheels mating surface to the discs.

 

Deja vu…

We can all agree on this:
That replacing rotors and pads with quality replacements and, performing caliper and fluid maintenance will bring your braking feel and performance back to where it should be.

Like tires, you don’t realize the ***** you are putting up with until you replace them.

Cheers!

 

I have had 3 Jags now and to be honest they all felt lacking in braking performance. My S Type went through disks like tyres! However I just wanted to mention I too had a tremendous judder from braking at 70 mph or more on my XKR, I mean the steering wheel would judder quite violently, my mechanic said he would change the disks at the next brake pad change. Before this happened I had to renew both front tyres, after the fitment of the new tyres lo and behold my juddering had vanished. So my issue seems to have simply a balancing weight had dropped off one of my front wheels, or the wheel had not been torqued correctly. So maybe before you go to the cost of disk replacement, a wheel balance check could provide a solution. Even if this is not the case for you, it’s a cheap check.