This Focus is bloody strange...

[Gary406]

when did you replace disc and pads ?

i would put it down to faulty discs maybe.

its a strange one this.

[CountryPug]

Its been suggested already but I would have put money on a warped disc. I had a warped disc on my 406 and it made the same racket that your describing

[steve_earwig]

But he seems to be saying he gets the wobble without touching the brakes

[highlander]

He wouldn't need to - the brake disks spin at the same speed as the wheels themselves, don't they? Therefore, a warped disc might have the same effect on the car as an imbalanced wheel - it's to do with weight distribution around the circumference of the disc.




Note: I don't know if that's technically correct but holy sh*t that actually sounded like I knew what I was talking about!

[Gary406]

also the pad could be touching the disc constant . it is possible .

[sirwiggum]

You mentioned you put new discs and pads on all round, so that can be discounted.

The first post of braking from 70+mph on your private test track made me think of the rear wheels.
On the 406 at least, the rear brakes were really only used at these kind of speeds (hence the 110s issues with binding rears).

Only other constructive suggestion I can throw into the pot is that my dad has this on his BMW (German reliability.... ) and after changing wheels, discs and hubs, turns out it could be components of the suspension subframe causing a vibration at a certain resonant frequency. Though this is only at around 50mph.

[steve_earwig]

He wouldn't need to - the brake disks spin at the same speed as the wheels themselves, don't they? Therefore, a warped disc might have the same effect on the car as an imbalanced wheel - it's to do with weight distribution around the circumference of the disc.




Note: I don't know if that's technically correct but holy sh*t that actually sounded like I knew what I was talking about!

The brakes aren't actually on all the time, even if they're very warped the first time the warp hits the pad it'll shove it back into the calliper.

[sirwiggum]

He wouldn't need to - the brake disks spin at the same speed as the wheels themselves, don't they? Therefore, a warped disc might have the same effect on the car as an imbalanced wheel - it's to do with weight distribution around the circumference of the disc.




Note: I don't know if that's technically correct but holy sh*t that actually sounded like I knew what I was talking about!

The brakes aren't actually on all the time, even if they're very warped the first time the warp hits the pad it'll shove it back into the calliper.

Even if the pads are sitting back against the caliper, nowhere near the disc surface, I think what highlander is getting at is the centrifugal force of a warped disc spinning might cause a vibration (similar to a wobbling spinning plate), regardless of whether brakes are applied or not.

But Bailes has already said he changed all the discs?

[steve_earwig]

Yep, all new disks apparently. I'm pretty sure he's had one or two of the wheels straightened too.

Is this one of those reverse logic things where the closer the imbalance is to the centre the more effect it has? In days of old you could balance the wheel, hub and disk together but that's impossible now

I'm getting the resonant frequency thing but I think applying the brakes should stop it. Duff tyre? Change fronts to back? Send for a witch doctor?

[waue1978]

Yep, all new disks apparently. I'm pretty sure he's had one or two of the wheels straightened too.

Is this one of those reverse logic things where the closer the imbalance is to the centre the more effect it has? In days of old you could balance the wheel, hub and disk together but that's impossible now

I'm getting the resonant frequency thing but I think applying the brakes should stop it. Duff tyre? Change fronts to back? Send for a witch doctor?

Don't write off the warped discs until they've been checked. Back when I had my 325tds I had new brake discs put on that (bought from Ebay) & got similar symptoms. Eventually got it properly checked & one of my new discs was warped.

Moral: just because they're new, it doesn't mean that they aren't warped.

[Bailes1992]

It ain't the discs.
The old discs were warped and when I hit the brakes I would get very bad wheel wobble.
But theres no steering shake when hitting the breaks bar the usual vibration I'm getting.

[lozz]

Have you checked the "Strut top mounts,
the Wishbone bushes are like choclate on Fords too

[jasper5]

There is a clue perhaps in what Steve said about having had wheels straightened? How could they be straightened?

Were there damaged wheels on the car? If so, it's more than likely that a hub has got damaged and is running out of true.

My advice is to get a dial gauge and check the hubs (all of them) to see if they are running out of true.

If you can't get a dial gauge rig up something where the tip is just touching the hub and gently turn the hub and look for any gaps or any sign of wobble....a small wobble here will be a large wobble at 100 mph.

You say you put Bernard's wheels on the Focus? You mean the 406 wheels? How can you check a fault with the wrong wheels on, if that was the case?

When fitting the discs did you clean the face of the hub correctly? Dirty hubs will cause warped discs.

[sirwiggum]

Had wishbone bushes go in an Orion.

Symptom of it though was that it pulled to the right when racing people off the lights. Near caused a crash.

Vibrations would have been unnoticable with the other issues.

[Bailes1992]

Bushes are fine. No play.
Not sure how they straighten the wheel but there a reputable company and the wheels have been balenced twice since.
Maybe it could be a hub? Although wouldnt they have picked this up when doing the wheel alignment as they spin the wheels?
And the front of the hub was clean.

You can see why I'm pulling my hair out