Brake Judder from a Pot-Hole

[pcarmour]

My AM DB9 has been slightly juddering whenever I braked between 50-60 MPH, below and above this speed range all was normal.
My research, and a comment by a mechanic, all pointed to warped discs, something I found hard to reason with so I had a very experienced engineer test drive the car. He could not feel it, he did however say that as well as the discs it could be a hub. This reminded me that I had hit a pot-hole some time ago - which was before I became aware of the judder, I then connected the pot-hole with the issue.
The engineer offered to check both the disc and hub run outs for £140.
Knowing that two discs are only £210, I decided to check the run outs myself.
I found a new Katsu Dial Indicator Test Gauge on eBay for £8 and made up a flexible but sturdy support from pieces in my garage, see photo

Aston Martin's workshop manual guidance states that the run-out should be <70 ?m measured @ 2 mm in from
the brake disc edge, i.e. no more than 0.07mm. From my setup I was able to measure the offside disc at 0.04mm and the nearside at 0.10mm, so here was my problem, 3 hundredths of a mm over the max! Swapping discs around i was surprised to find that not only was the NS disc warped so was the hub, quite a pot-hole! I guess that a warped hub will then warp the disc too.
One new hub (£210) and two new discs fitted and both disc run outs now measure well inside max - and NO MORE JUDDER!
Peter.

Edited by pcarmour on Tuesday 1st November 08:46

[R129 300SL]

Good work.

Main dealer would have charged you for the 2 discs and then further labour when that alone didn't work.

Probably would have changed both hubs as well when the 2 new discs didn't work.

[pcarmour]

Thank you for your reply.
Yes, and at AM prices, the 2 discs are 155.80 each +VAT=£373.92 and hubs are £251.06 +VAT = £301.27 each which means I saved £255 on parts alone

Edited by pcarmour on Tuesday 1st November 08:48

[BGB autosport]

Good work, pleased you sorted it.

You may want to consider next time putting a couple of wheel nuts on and torque them up. This ensures the disc is pulled back to the hub

Edited by BGB autosport on Tuesday 1st November 06:48

[Astontony]

I would also check the wheel for true roundness as a big pot hole can easily bend a rim. I know from experience.

[pcarmour]

Thank you. Yes, I did check for a buckled wheel prior to this whole exercise, quite easy with a screwdriver mounted on a block of wood. Inside and outside of all rims checked and were OK. I also had them balanced.

Edited by pcarmour on Tuesday 1st November 08:41

Edited by pcarmour on Tuesday 1st November 08:43

Edited by pcarmour on Tuesday 1st November 08:43

[Astontony]

Thats a simple device I must try it.