I've had it twice now.

This time I was sure it was the front stay rod bushings again, a problem when I got this car 11 years ago, replacing them with IPD's blue poly version. Problem solved. But could those polys be bad now? They looked OK, so I went at the front rotors (based on feel). There I saw pad deposition marks, which I tried to erase with a rotary wheel sander, but the wheel-speed vibration persisted.

Then, when my son suggested the Rear rotors, I had a 15-year flashback to a friend's 240 with the same shaky symptom. That one had voids in the 1/2" wide rust band that circled a rear rotor near the hub. The pad would catch a void every time it came around. Chipping the thick rust band off helped some, but new rotors finally fixed it.

Now recalling that occasion, I pulled the 940's left rear rotor to find what's shown in the photo below – a flaked off chunk of rust (on the inside) leaving a tell-tale void/gap only about .010" deep.

Two days later I had a pair of Meyle rotors (China) and Volvo OE pads (India) from eEuro, one of set of which went immediately on the Left Rear. That test drive was fine, but both sides were replaced.

Braking shudder caused by rust flake "void" - LR Rotor, inside surface.







--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

I have replaced 100s of rear rotors and never seen such a thing. but, that's why I replace rears and don't turn them. not enough meat. btw, did you buy those or were they on the car already? whose?

the shake-in the steering wheel or just the car? thanks, chuck.

Hi Chuck,

The rears were Brembos with about 12,000 miles on them since August 2011. I mostly drive short trips anymore and sometimes the car doesn't get used for days at a time. Beats me how those rust "bands" get built up, 1 down by the hub and 1 at the outer rim - and how come the pad wear conforms to the rust, instead of the keeping the rust worn down?

I saw the same on a 240 maybe 10 years ago. Tackled the fronts first and saw this big chunk missing on one. Spent hours chipping them away, filing smooth, etc. on both sides, both wheels. But still got shaky braking. Found it was a rear rotor like this one, much to my surprise.

No the wheel didn't really shake, but I thought I felt it in the pedal, as the car slowed down. I like Spook's comparison to a wheel dropping into a pothole
I suspect maybe the same thing on a front rotor would be felt at the wheel.

Bruce
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

wow. brembo's been using Chinese rotors for a while, I wonder if that's what those were. I always read the box or get zimmermans since I found a Chinese brembo. I still see Italian brembos, also.

it looks like it delaminated. again, wow. thanks, chuck.

Bruce,

What a find! Have also never seen anything resembling that. Are those on yours?

The pic belongs on the BB's front page, so thumb it up folks!
--
Art Benstein near Baltimore

You may be only one person in the world, but you may also be the world to one person.

Wow, never seen anything like this on any cars I have had.
Dan

Dear lucid,

Hope you're well. That photo is worth a few thousand words!!

I wonder if the "flake" was caused by a hair-fine (or finer) casting flaw, into which water entered, allowing rust to form and eventually causing a section of rotor to separate.

Surface rust is not likely to cause a failure in so limited an area. Is the flake's depth only 0.01"? The photo suggests a depth closer to 1/8"(0.125").

In any case, your report should go into the FAQs, as it will save much aggravation by those, who are presented with similar symptoms.

Yours faithfully,

Spook

"Surface rust is not likely to cause a failure in so limited an area. Is the flake's depth only 0.01"? The photo suggests a depth closer to 1/8"(0.125")."

Hi Spook,

I know it's hard to accept, but the effect is akin to a 1-tooth ratchet, with the pad being like the pawl. Every time the gripping pad encounters that low spot (or more likely when it exits) the repeated shudder makes itself known.

And yes, .010" was read with a depth mike as accurately as possible in that rough area, say ±.002".

Thanks for the compliment, and how would I get this to Steve for his consideration?


--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Dear lucid,

Hope you're well. Thank you for the further explanation: at the speed the rotor spins - and given the length of the "divot" and the "narrow" pad - it's akin to what happens when a tire goes into a pothole at highway speed.

I'm sure Steve - site secretary - will read and add to the FAQs.

Given enough time, anything that can happen, will happen.

Thanks again for the post: it will surely save frustration.

Yours faithfully,

Spook

Wow, very interesting Bruce, I'd not have thought of that.