First post - Brake Judder
Discussion
Thanks for the replies. I'll get my mechanic to check the other possibilities bought up in this thread to check its all right 
I've had this juddering before and its been sorting with new pads (and i think discs). I don't get to drive it that much as i'm at uni, so i'll get it sorted when i'm home for the summer
>> Edited by rico on Tuesday 20th April 22:48
I've had this juddering before and its been sorting with new pads (and i think discs). I don't get to drive it that much as i'm at uni, so i'll get it sorted when i'm home for the summer
>> Edited by rico on Tuesday 20th April 22:48
on a 306... 
Most brake judder is caused by having incorrectly tightened wheels cause the discs to have a degree of run out. This results in having flats worn onto the discs and then you get judder. It's solved by fitting new discs and pads and torquing the wheels accurately with a torque wrench, then repeating the process after 100 miles of running.
GavinPearson said:
Most brake judder is caused by having incorrectly tightened wheels cause the discs to have a degree of run out. This results in having flats worn onto the discs and then you get judder. It's solved by fitting new discs and pads and torquing the wheels accurately with a torque wrench, then repeating the process after 100 miles of running.
Don't quite understand this. On mine the disc (well, the bell anyway) is trapped between the hub and the rim. Assuming a clean surface on both sides, the only way I can see for it to distort under the clamping loads is it the material of the bell deflects under pure compression, causing it to expand by the Poisson's ratio effect. It seems unlikely that a quarter of an inch of cast iron would deflect far enough to matter under the relatively low clamping loads that are applied. Or am I missing the point, wouldn't be the first time!
greenv8s said:
Most brake judder is caused by having incorrectly tightened wheels cause the discs to have a degree of run out. This results in having flats worn onto the discs and then you get judder. It's solved by fitting new discs and pads and torquing the wheels accurately with a torque wrench, then repeating the process after 100 miles of running.
Don't quite understand this. On mine the disc (well, the bell anyway) is trapped between the hub and the rim. Assuming a clean surface on both sides, the only way I can see for it to distort under the clamping loads is it the material of the bell deflects under pure compression, causing it to expand by the Poisson's ratio effect. It seems unlikely that a quarter of an inch of cast iron would deflect far enough to matter under the relatively low clamping loads that are applied. Or am I missing the point, wouldn't be the first time!
I work at Ford as an Engineer. A friend lead a study team on brake judder warranty and went through all possible reasons that there might be variability in the shape of the disc after running.
Disc profiles of vehicles under warranty that had problems were measured. They had 'flats' on them coincident with the location of the wheel studs.
Using a turned down wheel disc runout was measured with wheel studs torqued to extremities of tolerance. When you have two adjacent studs at bottom limit and three at top or vice versa there is varing conformity to the wheel mount face and run out changes. It doesn't by much, but enough that if you do a lot of motorway miles the constant brushing of the disc on the pitched out parts of the disc gets worn. Under braking torque the spot on the discs that is low cannot generate the uniform braking torque to remain shudder free, and if there is high ground wheel offset there with be steering wheel pitching.
ADDITIONALLY if the rotational frequency of the reduced braking corresponds with the natural frequency of the bushings in the suspension it will feel worse at that speed and even worse still if it is the same frequency as the steering column.
What makes it even worse is when people replace the steering wheel with a light one. BMW steering wheels have steel rims rather than magnesium which is commonly used - the reason being that it proveds inertia that damps out pitch of imbalanced wheels and shuddery brakes.
So now you know.....
Okay, so I fiited a second hand set of Wilwood racing 4 pots and 300mm disks onto my Griffith, and under hard braking (say from over 100mph) allowing a good bit of heat to build up, they start to judder. Subsequent gentle braking at lowish speed has no juddering.
If I look at the disks immediately after judder, I can see the unevenness of the braking on the disk.
The previous owner of the brakes reports no problem.
Any ideas what it's likely to be? could it be that since they've been refitted onto different hubs, any wearing due to unevenness is showing up?
If I look at the disks immediately after judder, I can see the unevenness of the braking on the disk.
The previous owner of the brakes reports no problem.
Any ideas what it's likely to be? could it be that since they've been refitted onto different hubs, any wearing due to unevenness is showing up?
GavinPearson said:
Most brake judder is caused by having incorrectly tightened wheels cause the discs to have a degree of run out. This results in having flats worn onto the discs and then you get judder. It's solved by fitting new discs and pads and torquing the wheels accurately with a torque wrench, then repeating the process after 100 miles of running.
Gavin, this is what I was told at school, I think you are absolutly correct! I have also experienced this unequal lug nut torque myself on my truck. It happens all the time when Techs used air guns instead of torque wrenches to fasten the wheels.
rico said:
Is break judder normally caused by pads or discs that are ready to be replaced?
I bow to the professional explanations previously posted and would just add these notes.
I have known dodgy brakes (pulling left or right randomly and severely on a new vehicle) be cured by changing tyres. There is some potential for slightly out of balance tyres to show mild symptoms hardly noticable on a front wheel drive car until the wheels end up at opposing balance tolerances and produce a much more obvious vibration which then can disappear again. Add in the speed factor and it may be an influence.
I once had front disks on a Senator changed when advised the regular but not always existent juddering required disks and pads. When that failed to work the diagnosis was 'must be the rear disks'. That didn't really work either but with new disks and pads all round the problem was masked for a while.
IIRC that was the car that could be juddereing consistently until one pwerformed a reversing manoeuvre with a fairly hard brake to a stop at the end - after which the problem took a while to recur. I was always suspicious of suspension problems.
My Omega had dreadful brake judder but a 4 wheel alignment helped a bit.
Pads and disks changed a few times - including one set of front disks changed under aftermarket warranty due to warping after about 6000 miles. (20k life expectancy only apparently.)
After an interesting forst track day in the thing, where the brakes had been worrying in the morning but by afternoon seemed to have settled down and become consistent at least, I had the pads checked (I estimate they were 50% used prior to the track session) and discovered that on the fornt n/s, one pad had only a thin and crumbling layer of friction material left which could be wiped off. The other pad was about at the point where it would recommended for change during a service. On the O/s the worst pad was in the same condition as the best pad on the n/s and the final pad was about half worn.
So I suspect that some of my braking judder was just down to poor system design (Servicing was main dealer and regular ...)and uneven or irregular pad pressure from the pistons. Or it could have been poor hub/wheel fit, which is why it could come and go. Mind you I suspect the front brakes did more work than intended as the car was an auto and the rear brakes never seemed to have much effect for more than 1000 miles after a decent service.
Now I have a Saab and the brakes are just incredible. IMHO.
BCA said:
Dont worry about it - his 306 died a looooooooong time ago (probably suicide out of the shame of not being able to really out accelerate a standard Smart - which itself wasnt running 100% lol)
Doh!
Didn't spot the original year in the date!
Damn confusing when these posts get resurrected after 12 months - they look like they could be current!
But hey, the comments posted might still offer some resonance with the used brake problem. (!)
I used to have a Mondeo auto and my drive to work was lots of 70mph limit straights and roundabouts. It got to a point where the hubs were apparently warped so fitting new discs or skimming only improved things for a short while. Maybe worth getting checked if the problem keeps coming back.
Fantastic explaination there Gavin
As daft as it sounds, the discs and drums DO distort when clamped up.
Usually this only pops up after tyre fitters have gunned the wheels up, with both the incorrect torque and tightening sequence.
We used to suffer with major judder problems on transit because of this, I tested a few at dealers where breaking at 50mph would shake everything off the dash board
the only solution g/teed to fix it was replace all the rad wheels and drums etc, using the correct torque and sequence on the rebuild.
The wheels on Trasit are still made of chocolate now
I've also seen it happen after heavy breaking when the car hasn't been touched for 10k, i've not got eveidence to back it up, but I suspect that a cast disc which never sees 100% braking and the heat generation that goes with it gets used to it's temperature operating range, then when an out of the blue full on stop occurs the heat build up affects it, causing run out.
As daft as it sounds, the discs and drums DO distort when clamped up.
Usually this only pops up after tyre fitters have gunned the wheels up, with both the incorrect torque and tightening sequence.
We used to suffer with major judder problems on transit because of this, I tested a few at dealers where breaking at 50mph would shake everything off the dash board
the only solution g/teed to fix it was replace all the rad wheels and drums etc, using the correct torque and sequence on the rebuild.
The wheels on Trasit are still made of chocolate now
I've also seen it happen after heavy breaking when the car hasn't been touched for 10k, i've not got eveidence to back it up, but I suspect that a cast disc which never sees 100% braking and the heat generation that goes with it gets used to it's temperature operating range, then when an out of the blue full on stop occurs the heat build up affects it, causing run out.
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