996 Turbo Front Disc Run Out

[Nobby Diesel]

Does anyone know what the maximum allowable is?

[bo duke]

I've not seen it written down anywhere (so it could be cobblers) but when I took my car into the OPC with a brake judder, they told me the maximum runout was 0.06mm.

[Nobby Diesel]

Thanks Bo,

what was the cause of the vibration?

[Rockster]

Nobby Diesel said:

Does anyone know what the maximum allowable is?

Here is what the factory service manual has on this:

• Lateral runout of the removed brake disc: max. 0.03 mm!
• Wheel hub lateral runout: max. 0.03 mm!
• The permissible lateral runout of the installed brake disc is max. 0.06 mm!

[cd1957]

Hi when checking the run out,make sure the adapter plate is bolted to the wheel flange, as there could be different readings when the disc is not clamped tight to the hub.

Chris

[bo duke]

Nobby Diesel said:

Thanks Bo,

what was the cause of the vibration?

The summary is that I’m not absolutely sure.
When the car first developed a judder, the inside of the discs had corroded and started to delaminate (common problem), so I replaced the discs/pads all round and it was great for a few months. Then, on a spirited drive rounds the Brecons, the judder returned. At this point I figured I shouldn’t be able to warp 996T discs on the road (I wasn’t going nuts).
So I took it to the OPC and asked them to check for sticking calipers, worn bushes etc.
They gave it the all clear and concluded my pagid discs from Design911 were made of cheese, and replaced all 4 discs/pads again.
3 months later on a spirited drive in France, the judder returned. This time I was in convoy with a bunch of other cars inc. a 90s merc SL, none of whom had warped discs.
It went back to the OPC, who ran more tests and concluded the front calipers must be sticking when hot. They replaced the discs free (for not having picked it up initially), I replaced the calipers. The judder was better but not gone. I paid them to replace the rears too and it finally went for good.
My theory is that the front calipers stuck when hot/warped the front discs, and then the rears took up the strain and warped too. Was quite an expensive fix though!

Edited by bo duke on Saturday 12th May 18:32

[Nobby Diesel]

cd1957 said:

Hi when checking the run out,make sure the adapter plate is bolted to the wheel flange, as there could be different readings when the disc is not clamped tight to the hub.

Chris

Thanks.
I'm measuring the disc and then removing that, to measure the hub.
What I have found is that off side is within 0.02mm on both the hub and the disc, but the near side is running out at 0.15mm on the disc and 0.12mm on the hub.
So, leaning toward a bearing issue, I think, unless anyone can offer another likely cause?

There is no glazing of the pads, so I doubt that the calliper is sticking and building heat.

[Nobby Diesel]

bo duke said:

The summary is that I’m not absolutely sure.
When the car first developed a judder, the inside of the discs had corroded and started to delaminate (common problem), so I replaced the discs/pads all round and it was great for a few months. Then, on a spirited drive rounds the Brecons, the judder returned. At this point I figured I shouldn’t be able to warp 996T discs on the road (I wasn’t going nuts).
So I took it to the OPC and asked them to check for sticking calipers, worn bushes etc.
They gave it the all clear and concluded my pagid discs from Design911 were made of cheese, and replaced all 4 discs/pads again.
3 months later on a spirited drive in France, the judder returned. This time I was in convoy with a bunch of other cars inc. a 90s merc SL, none of whom had warped discs.
It went back to the OPC, who ran more tests and concluded the front calipers must be sticking when hot. They replaced the discs free (for not having picked it up initially), I replaced the calipers. The judder was better but not gone. I paid them to replace the rears too and it finally went for good.
My theory is that the front calipers stuck when hot/warped the front discs, and then the rears took up the strain and warped too. Was quite an expensive fix though!

Edited by bo duke on Saturday 12th May 18:32

That does sound expensive!!! I hope that I'm not heading in that direction.
I'm tending to think that there is a bearing issue on one side, as the run out is only evident on the net side.