Member Since: 20 Jul 2015
Location: Here
Posts: 575
Disc runout is always a symptom, never the root cause - I'd want to check the runout of the hubs, and that there is no excessive corrosion on them. Delphi pads should be OK, just a common-sense check that they were not 'bargain basement' pads...
What is your usage cycle like? if the drive distance and brake usage isn't high enough to self-clean the working face, especially on the inner face, this can lead to rust growth that can cause your issue...
7th Jan 2023 7:48 pm
tintenter
Member Since: 29 Sep 2006
Location: Oldham
Posts: 1109
Flatlander, if i get around to checking for runout I would check the hubs as a matter of course, duty cycle is reasonable although a lot of motorway and towing, I do find that if I have to brake hard the vibration can fade, also braking when turning the vibration sometimes doesn't appear. thanks for the input.Tintenter
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7th Jan 2023 10:06 pm
Flatlander
Member Since: 20 Jul 2015
Location: Here
Posts: 575
When you say it fades, is that during heavy braking or subsequent brake applications? also, when cornering, is it turning one way or both that has a positive effect?
7th Jan 2023 10:31 pm
tintenter
Member Since: 29 Sep 2006
Location: Oldham
Posts: 1109
Flatlander, the vibration fade is only under heavy braking and comes back on the next braking, it appears that it is in both directions when turning that it can disappear. I am wondering if it is a track rod end that has a small amount of movement. all food for thought. i have ordered a DTI Gauge so I can try to check the run out on both wheels and hubs. but I am considering just putting a new complete hub and bearings on both sides if I can't prove where the issue is.Tintenter
Corris Grey Discovery 4 HSE
Bigger permagrin now installed
Semper in excretum, sole profundum moveat.
8th Jan 2023 11:56 am
Flatlander
Member Since: 20 Jul 2015
Location: Here
Posts: 575
You'll need to clamp the disc to the hub to get meaningful test values, at least put some oversize hex nuts over the wheel studs then torque the wheel nuts down onto them. If both discs have runout then you need to look at hydraulics (it'd be unusual for both front hubs to have play in them), you say you've changed the calipers so they should be working fine and not have a build-up of brake dust causing the pads to bind.
Next would be the front flexi's having a twist or collapsing internally causing fluid pressure to leak back slower than it should - which would cause hot spots on the discs when parked, that's when discs will become warped, due to unequal cooling.
I think if there was an issue with the inner or outer steering ball joints, then wandering steering and odd tyre wear would be a concern.
It's an odd one, the larger discs will magnify any runout or play in the hubs of course...
8th Jan 2023 2:59 pm
Flatlander
Member Since: 20 Jul 2015
Location: Here
Posts: 575
Whilst I was looking for a photo to illustrate the setup I use...
I came across this - essentially the wheel was not in equal contact with the hub due to being 'refurbished' and powder coated, there was powder coating on parts of the mating face which meant that the brake disc was not equally clamped to the hub, replacing the discs and wheels cured the issue.
It may be worth checking the wheels are contacting the disc equally on both sides.
8th Jan 2023 3:15 pm
tintenter
Member Since: 29 Sep 2006
Location: Oldham
Posts: 1109
Flatlander, thanks for all of that , as soon as the weather and time allow I will have a play and report back. Tintenter
Corris Grey Discovery 4 HSE
Bigger permagrin now installed
Semper in excretum, sole profundum moveat.
8th Jan 2023 4:27 pm
Bicycle repairman
Member Since: 18 Sep 2019
Location: Cumbria
Posts: 158
Just in case you haven't check the mating face between the hub and discD4 GS let the retro fit begin
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, as soon as the weather and time allow I will have a play and report back. 
