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[omega2018]

i'm getting the same judder from steering wheel when braking that i had when the inside of the disks were rusted up.  this time though the disks are new and on a quick feel, clean of rust.  the car passed its MOT like this.  seems not to happen in the wet and if the brakes are very gradually applied.  before i jack it up any ideas of what to look for?  i wonder if a wheel bearing is worn but thought the mot would have picked that up. 

[Nick W]

In order:

Wishbone bushes
Wishbone bushes
Steering joint
Wishbone bushes
Worn struts
Wishbone bushes
Warped wheel or tyre

[TheBoy]

Or wishbone bushes.  But could be wishbone bushes.

Worth checking for play in steering (idler, TRE, tie rod). And wishbone bushes.

[terry paget]

If it occurred on fitting new discs, a disc may be running out of true. Might be a bit of grit between disc and hub, or a dodgy disc. In the 1960s we had to check disc run out with a dial gauge on new discs it was so common, max was .004".

[omega2018]

i was wondering if it might be the wishbones?

i had a look at the guide on replacing them but what can i do to confirm they are the problem?

i think the disks are ok as they were fine when i put them on and for some time after.

[TheBoy]

If it was a cheap disc, and you drove enthusiastically, its quite easy to warp. Done a fair few on Omegas, hence always using GM discs now, as not knackered on yet.

[Tony H]

Had same problem fitted poly bushes sorted, job done 

[robson]

My other half had her front discs replaced and within 3 months the vibration was bad. They were replaced under warranty and now OK again We will see how long they last this time.I must say that she tends to drive too fast most of the time.

[omega2018]

discs were (are) TRW

[johnnydog]

i was wondering if it might be the wishbones?

i had a look at the guide on replacing them but what can i do to confirm they are the problem?

i think the disks are ok as they were fine when i put them on and for some time after.

I would try to establish first whether it is the discs or the wishbones.  If the wishbones are excessively worn on the rear bush, I would get a friend to walk alongside the car as you drive along slowly, and get him to watch the front wheel when you apply the brakes. If there is excessive wear, you may see the front wheel move backwards slightly on the affected side, and then return to the former position when the brakes are released. You are in effect getting hold of the wishbone checking for any side to side movement which will reveal if one or both bushes are worn.
Or if you have a friendly MOT man, especially with the 'jiggle' plates who may check them for you!

On the subject of so called warped front discs - I do recall referring to this subject in the past? Officially, there is no such thing as warped discs (it's not me that makes this statement, but specialist brake manufactures) - invariably it is a build up of friction pad material that that transfers from pad to disc when hot, especially when the pads are 'clamped' to a hot disc i.e. when sitting at traffic lights with an auto with your foot on the foot brake, which results in high spots around the disc. As the brakes are used, any individual high spots get bigger and eventually cause a kicking through the pedal, more noticeable under gentler braking. People immediately confuse this with warped discs. It can also be caused by contamination behind the hub face and rear of the disc, especially if they have had a smear of copperslip when fitted - they should be fitted clean / dry.  The kicking can sometimes be resolved by a systematic process if firm brake applications - the process is quite detailed, and is also a process for bedding in brakes for more 'spirited' driving.
You may wonder why I say all this. If you google Audi RS4 brake judder, there is a wealth of information on the RS246 forum, from owners (and from myself) about the issues encountered and the technicalities from racing / brake manufacturers.
I know Omegas are a different kettle of fish from an RS4, but the basic principle is the same.
If nothing else, may provide interesting reading before you start giving the supplier of your discs both barrels.....

[omega2018]

thanks that's very helpful.  i had wondered how a disc could warp even a small amount, they are pretty solid and rigid things. 

i need to get under the car and have a look, i will put it on axle stands, and get a crow bar in (i'm not sure I could detect backwards movement while the car is moving).

it is puzzling me that the one time i noticed the judder had gone was when driving in rain, this had made me assume it was rust patches on the inner disc being lubricated by the rain, maybe there are some i didn't spot. 

[johnnydog]

By applying the brakes when moving forwards, it tries to stop the rotation of the wheel, but the force exerted by the weight of the car at the same time results in the whole wishbone, front strut and hub with the brake components in effect trying to move backwards. Put another way, when you apply the brakes, the brakes work against the forward momentum of the car, so if any wear in the two bushes on the wishbone (especially the rear one) will become apparant by the wheel appearing to move backwards, and then returning to a more forwards position when the brakes are released.
This is my description of it from a non expert point of view! Maybe it could be explained more scientifically by more the more knowledgable perhaps.
Rust on a disc from normal rainwater etc, would never cause a problem. When you have been on holiday for a coule of weeks for example, a couple of applications of the brakes remove the surface rust that has formed, and a few miles down the road, all the rust has gone. Rust that causes a kicking in the pedal is usually when serious corrosion is evident from long periods of inactivity, which has caused flaking of the disc face when the contact surface has lifted through corrosion.
Whether the discs are cheap or higher quality ones, they will rust at the similar rates with inactivity due to being made out of cast iron.

[TheBoy]

On the subject of so called warped front discs - I do recall referring to this subject in the past? Officially, there is no such thing as warped discs (it's not me that makes this statement, but specialist brake manufactures) - invariably it is a build up of friction pad material that that transfers from pad to disc when hot, especially when the pads are 'clamped' to a hot disc i.e. when sitting at traffic lights with an auto with your foot on the foot brake, which results in high spots around the disc. As the brakes are used, any individual high spots get bigger and eventually cause a kicking through the pedal, more noticeable under gentler braking. People immediately confuse this with warped discs. It can also be caused by contamination behind the hub face and rear of the disc, especially if they have had a smear of copperslip when fitted - they should be fitted clean / dry.  The kicking can sometimes be resolved by a systematic process if firm brake applications - the process is quite detailed, and is also a process for bedding in brakes for more 'spirited' driving.
You may wonder why I say all this. If you google Audi RS4 brake judder, there is a wealth of information on the RS246 forum, from owners (and from myself) about the issues encountered and the technicalities from racing / brake manufacturers.

That is one of the rumours that has been going around the internet for a while, and has elements of truth it in.

However, the disc itself can suffer deformaties due to "abuse" (the wording used by a manufacturer I was talking to a few years back about this very subject).  This is sometimes due to poor materials/process (in which case it can't be overcome, it will happen again) or a cost saving by skipping a process (which generally a skim following this will overcome).


Specifically on the Omega, I can tell you from bitter experience, it ain't worth going down the cheap disc route, I can deform them on a whim within a few minutes. Been there, bought that t-shirt far too often.  Definitely worth buying the £80 axle set via tradeclub, and you get a free set of pads as well.  I've not yet managed to deform/warp the GM ones, which surprises even me.

[omega2018]

Rust on a disc from normal rainwater etc, would never cause a problem. When you have been on holiday for a coule of weeks for example, a couple of applications of the brakes remove the surface rust that has formed, and a few miles down the road, all the rust has gone. Rust that causes a kicking in the pedal is usually when serious corrosion is evident from long periods of inactivity, which has caused flaking of the disc face when the contact surface has lifted through corrosion.
Whether the discs are cheap or higher quality ones, they will rust at the similar rates with inactivity due to being made out of cast iron.

my car doesn't get used daily (and also i don't brake a lot) so rust on the discs has been a problem.  does get used every week though.  last judder was definitely caused by rust on the inner discs, seemingly it is a common mig issue.  new discs fixed it. old discs were badly pitted but only on the insides.

[omega2018]

Specifically on the Omega, I can tell you from bitter experience, it ain't worth going down the cheap disc route, I can deform them on a whim within a few minutes. Been there, bought that t-shirt far too often.  Definitely worth buying the £80 axle set via tradeclub, and you get a free set of pads as well.  I've not yet managed to deform/warp the GM ones, which surprises even me.

the new discs i put on were cheap (£17.50 for a pair, new in box, inc delivery!) but they were genuine TRW, is that not a good make?

actually they sent me two pairs in the end, they were old stock and first pair had a bit of rust on them, gave those free to James when he did my cam belt.