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 Posted: Apr 3, 2017 07:15PM
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I find that i can feel run out the most on rotors while driving the car slowly 5 to 10 mph and gently applying a small amount of pressure with the brake pedal, if they are out of wack you can feel the pulsating through the brake pedal.

If in doubt, flat out. Colin Mc Rae MBE 1968-2007.

Give a car more power and it goes faster on the straights,
make a car lighter and it's faster everywhere. Colin Chapman.

 Posted: Apr 3, 2017 05:23PM
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Quote:
Originally Posted by CooperTune
Now just for a while lets think this though as not a brake problem. But maybe a problem that only shows under high speed braking. Perhaps tie rod bushings or sub frame mounts. Spoke with a guy who said his was a bad shock and another who had a bad axle. Is there any feed back here from that direction. Steve (CTR)
Steve. when the problem first started, it was the "warped rotor" - pulsatile braking only on hard stops at 60 mph. It still is only at higher speeds, but even the lightest touch on the pedal produces the symptoms.  I suppose one could say that
(A) the rotors are getting more warped, or
(B) a loose suspension part is getting looser - either an old part or one of the newer pieces installed preventatively 2 years ago. 
I doubt that. Steering back or forth is tight, same for bumps. No noticeable play in system. I even jacked it up and checked again for worn front roller bearings and ball joints with shaking the tires up/down/sideways/diagonal/in/out.  Besides, it "feel" like rotors/flanges.  Statistically, that is what it is.

A set of higher grade rotors and set of flanges just ordered. Want to be done with this. Get back to everyone in a few weeks. Harvey

 Posted: Mar 30, 2017 12:01PM
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US
Now just for a while lets think this though as not a brake problem. But maybe a problem that only shows under high speed braking. Perhaps tie rod bushings or sub frame mounts. Spoke with a guy who said his was a bad shock and another who had a bad axle. Is there any feed back here from that direction. Steve (CTR)

 Posted: Mar 30, 2017 02:45AM
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CA
Now this is the type of thread we need more of:

Fully informative, no hype just telling it as it is to help others

Big AL

[email protected]

Niagara Ontario Canada

 Posted: Mar 30, 2017 02:25AM
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Quote:
Originally Posted by Alex
 I can certainly attest to brake judder and an uncanny feeling of wheels being out of balance due to flat spots on the tyres (they are a heavy car) after being parked up for a few months.
tire flat spots are , in  my experience, noticeable right out of the garage, ie, even at very low speeds. My car does not go thump thump thump at any speed. It only judders ( a different sensation that flat tires that I have felt before) when brakes are applied at 60 mph. It is not noticeable at lower speeds .You could drive around town and never know there was a problem.

I have never felt flat tires from radial tires sitting long, only in past with bias ply years ago. For what it is worth, I will rotate my tires front to back and see what happens but I really do not think this is the issue. This car never sat more than 3 months. Thanks

 Posted: Mar 29, 2017 07:11PM
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GB
Even if rust isn't present, the pads can still stick to the discs and leave deposits which then cause brake judder.  Sometimes it goes away, sometimes it doesn't.

My MG ZT-T 260 is a bugger for it, and the owners group recommend leaving the car for a while to cool down and then rotate the wheels half a turn when you get back after a spirited drive.  I can certainly attest to brake judder and an uncanny feeling of wheels being out of balance due to flat spots on the tyres (they are a heavy car) after being parked up for a few months.

 Posted: Mar 29, 2017 02:53PM
 Edited:  Mar 29, 2017 02:54PM
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Quote:
Originally Posted by Dan Moffet
You mention it has been sitting for awhile and/or gets used lightly. That suggests to me either a rust patch (or an unrusted patch where the pad was sitting) or uneven caliper pressure. Check for a stuck caliper piston. If one is seized, the other would try to distort the rotor to press against it. You should be able to pry the pads back with a flat screw driver or similar prybar. They should move slowly with hydraulic resistance. The press the brake pedal lightly to see if they move back equally.
Nope again

Stainless steel caliper pistons . Moved easily when I replaced the pads one week ago as an experiment.

 Posted: Mar 29, 2017 02:52PM
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Quote:
Originally Posted by nkerr
ahh!!

key information late in the thread:  was fine for a long time, but had been sitting a lot and on its own it developed this pulsing, which occurs only under braking, and rotors confirmed not warped.  Plus it has been sitting.

My money is on rust causing the issue.  Normally, on a regularly used car the rust is continuously removed by pads dragging while driving.  A car which sits develops rust on the exposed rotor but the portion under the pads does not = uneven braking, and pulsing.

Either drive it enough so the rust is completely worn off, or have them turned to clean up the faces.

Nope. Not that neglected. In garage. Absolutely no rust on rotors.

 Posted: Mar 29, 2017 07:11AM
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CA
You mention it has been sitting for awhile and/or gets used lightly. That suggests to me either a rust patch (or an unrusted patch where the pad was sitting) or uneven caliper pressure. Check for a stuck caliper piston. If one is seized, the other would try to distort the rotor to press against it. You should be able to pry the pads back with a flat screw driver or similar prybar. They should move slowly with hydraulic resistance. The press the brake pedal lightly to see if they move back equally.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Mar 29, 2017 07:10AM
 Edited:  Mar 29, 2017 07:11AM
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ahh!!

key information late in the thread:  was fine for a long time, but had been sitting a lot and on its own it developed this pulsing, which occurs only under braking, and rotors confirmed not warped.  Plus it has been sitting.



My money is on rust causing the issue.  Normally, on a regularly used car the rust is continuously removed by pads dragging while driving.  A car which sits develops rust on the exposed rotor but the portion under the pads does not = uneven braking, and pulsing.

Either drive it enough so the rust is completely worn off, or have them turned to clean up the faces.


N

 Posted: Mar 28, 2017 04:50PM
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Quote:
Originally Posted by DRMINI
Measure rotor thickness in 8 places with a micrometer. Thickness variation causes this problem more than disc runout.
More than 1/2 a thou variation, machine rotors or replace.
Thanks, however.......

the problem was NOT there after installation 2 years ago. Smooth as silk then. Surely if it were a factory defect (that thickness variation suggests) then the shuddering would have been there all along.

No, the symptoms have developed after 2 years, and with the car sitting a lot, and no wheel/tire changes or lug nut overtightening.  To me, that sounds like warped rotors/rotor runout, although why it developed is what does not make sense considering the light duty the car has had. 

When I get all the parts and time, we can measure all that as suggested.

 Posted: Mar 28, 2017 03:02PM
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Measure rotor thickness in 8 places with a micrometer. Thickness variation causes this problem more than disc runout.
More than 1/2 a thou variation, machine rotors or replace.

Kevin G

1360 power- Morris 1300 auto block, S crank & rods, Russell Engineering RE282 sprint cam, over 125HP at crank, 86.6HP at the wheels @7000+.

 Posted: Mar 25, 2017 02:39PM
 Edited:  Mar 25, 2017 02:46PM
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The problem developed on new rotors and new EBC green pads installed 1500 miles ago and were smooth as silk until recently. The break-in method of my new EBC black pad experiment had nothing to do with it. It neither caused nor alleviated the problem. Thanks

 nkerr - I tried some long hard stops (with the EBC green pads before I replaced them). This just made the shuddering worse. While doing this, the car pulled to the left, but oddly the R rotor was 500F and the L rotor was 360F. Stump the stars. 

 Posted: Mar 25, 2017 11:28AM
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Just make sure you bed them in per the instructions!! I note you said the instructions said medium hot for brake in, not red hot. but then you said you did them somewhere in between.........Oh and make sure you use new pads with the new rotors not ones previously used. When we had problems with Rolls-Royce brakes the factory supplied pads with a nice coating of abrasive material that we bedded the brakes in with before handing off to the customer and noise and vibration complaints dropped away to almost nothing...................

Mini's are like buses they come along in a bunch

 Posted: Mar 25, 2017 11:05AM
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Thanks for all the help.

The shudder or pulsating feels just like other cars with warped rotors coming down a long mountain grade except mine is not in the mts, but hard stops around town from 60 mph, but not at slower speeds. No wobbly feel like a bent rim or imbalanced tire, I know about those from personal experience. No slop in steering and steering wheel does not shake on brake application, only brake pedal and front of car. . With car jacked up and jerking the tire up down left right diagonal there is nothing to suggest bad suspension parts. Steering rack ends, etc are tight. Wheel bearings rotate freely without suggestion of rough needle or race, and there is no play. Castle nut is tight. I changed the barely worn EBC green pads to black just to do a cheap experiment. I had read about the deposits -on-the-rotor discussion. Rotors look clean and pretty. New pads no different. Package insert said medium braking for break-in, not red hot. I sort of did in between. 

The game plan now is to replace the rotors and drive flanges. I am sure that all of you have run out if tests and patience and at some point reached and impasse and decided to just start replacing parts, beginning with those most likely to be the culprit. Stay tuned, it will be a few weeks before I get the parts and work. Harvey

 Posted: Mar 25, 2017 09:54AM
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GB
Quote:
Originally Posted by h_lankford
checked the outside surface all around with dial indicator

figured that the inside surface surely must be parallel to the outside surface as it is a solid rotor.

maybe I should put the old rotors back on - there was nothing wrong with them other than some normal rotational grooves. They were neither noisy nor pulsatile. So this might all be a result of modern crap metal going bad just sitting on the garage?
You'd *hope* that they were parallel, but it isn't always the case. 

We fitted a new set of hubs, balljoints, discs, pads, CVs etc to Tigger before the IJ in 2011 and he warped the generic budget discs in a week.  The much dearer Unipart discs are still on the car and have now done two trips to Italy and back with no problems.

 Posted: Mar 25, 2017 04:53AM
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US
You didn't mention if you are feeling this shudder as a shaking of the car, vibration of the steering wheel, or pulsing of the brake pedal.

I offer a different suggestion unrelated to the new disks and pads.  Take a close look at the condition of the ball joints and the wheel bearings.  Remember one ball joint has the internal spring and may seem OK at first but have play in it that shows when loads are high (like high-speed braking).

Doug L.
 Posted: Mar 25, 2017 04:41AM
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I had this same thing happen to my mini when I fitted all new parts:  my pulsing was caused by improper bedding of the new pads to the new rotors.

Googling on this I found a lot of brake manufacturers have posted guidelines on how to initially bed them in to avoid uneven braking.

The issue is non-asbestus pads work by depositing a layer of material onto the rotor, and the layer on the rotor interacts with the material in the pad to create braking as intended.  If the bedding was done a certain way that layer can be uneven, resulting in bad pulsing.

Either have the new rotors turned (to clean off that layer) and try again, or there are ways to "re-bed" existing rotors on the car (which is what I did, and in my case it was not 100% perfect but it helped a lot).  

Note that re-bedding will result in a LOT of brake dust.


Summary of how to re-bed:  get the rotors very, very hot (by several very hard brakings from speed), then drive until they have completely cooled.  Once the heating procedure is begun do NOT stop and during the cooling use no hard application of the brakes, and no stopping, until the rotors have cooled.  So, find a long, straight, deserted road to do it in.


Above is just a summary, 
N

 Posted: Mar 25, 2017 04:31AM
 Edited:  Mar 25, 2017 04:32AM
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Quote:
Originally Posted by Alex
So you've checked the inside and the outside of both discs in 3-4 places across the wear surface all the way round for warping and bulges ?

Odd, that's usually what it is - remember they can warp in the blink of an eye especially when new if they are not OE discs...

checked the outside surface all around with dial indicator

figured that the inside surface surely must be parallel to the outside surface as it is a solid rotor.

maybe I should put the old rotors back on - there was nothing wrong with them other than some normal rotational grooves. They were neither noisy nor pulsatile. So this might all be a result of modern crap metal going bad just sitting on the garage?

 Posted: Mar 25, 2017 02:41AM
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GB
Quote:
Originally Posted by h_lankford
Quote:
Originally Posted by Alex
Warped discs or rust buildup behind or on the pad.

Pull the front wheels and check for a pad shaped lump of corrosion and use a DTI to check for runout.
Both of these were done

So you've checked the inside and the outside of both discs in 3-4 places across the wear surface all the way round for warping and bulges ?

Odd, that's usually what it is - remember they can warp in the blink of an eye especially when new if they are not OE discs...

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