Ever known for rear hub to warp on a 997?

[Gibbo205]

Hi there

No before anyone says I've not wacked a curb.

When my car was on ceramics there was a marginal squeak squeak from low speeds at rear but very quite, offset was measured and it had some minor runout. Moving disc on hub helped a little.

Changed to brand new Porsche steels and still runout on the same rear side, which means all that is left is it could be the rear hub. Porsche have quoted me and its about £250 so not end of world price wise, but I just wondered if anyone else has experienced this, done a lot of track work, a few slides and like roundabouts, don't we all, but never hit anything in my ownership.

But now on the steel disc the squeak is much louder, simply because of steel one piece disc making noise louder, but at same time when braking from very high there is a slight vibration when initially braking from high speed, not really felt from pedal just through cabin from rear, no doubt caused by this hub.

Questions:-
1. Anyone ever had this?
2. If I change hub, guess I best change rear disc as well because disc will no doubt also be warped, otherwise it would just warp another hub?
3. Need to change rear pads again as well?

[Trev450]

I can't help with Q1 but if the problem is with the hub there is no reason why the disc cannot be re-used and the same applies to the pads, assuming of course that they are still servicable.

[Gibbo205]

Trev450 said:

I can't help with Q1 but if the problem is with the hub there is no reason why the disc cannot be re-used and the same applies to the pads, assuming of course that they are still servicable.

So the hub would also not warp disc?

I did think spacers but they'd not cause it, they'd cause wheel in balance but not warped/squeaking brakes. Gonna get it all properly cleaned and swap disc either side first before spending money. Just wondered if anyone else experience this as I know it could happen on M3's but not heard it on a Porsche before.

[Slippydiff]

Gibbo205 said:

Trev450 said:

I can't help with Q1 but if the problem is with the hub there is no reason why the disc cannot be re-used and the same applies to the pads, assuming of course that they are still servicable.

So the hub would also not warp disc?

I did think spacers but they'd not cause it, they'd cause wheel in balance but not warped/squeaking brakes. Gonna get it all properly cleaned and swap disc either side first before spending money. Just wondered if anyone else experience this as I know it could happen on M3's but not heard it on a Porsche before.

If the hub is warped, there's a chance the disc mounting face may have warped in tandem with it, especially if the warped disc and hub assembly have been heat cycled a few times.
I'd use some washers as spacers and clamp the disc to the hub and then use a dti gauge to measure the outer disc mounting to wheel face for runout.

[Gibbo205]

Slippydiff said:

If the hub is warped, there's a chance the disc mounting face may have warped in tandem with it, especially if the warped disc and hub assembly have been heat cycled a few times.
I'd use some washers as spacers and clamp the disc to the hub and then use a dti gauge to measure the outer disc mounting to wheel face for runout.

Well hub was heat cycled a lot with PCCB's and same side PCCB had run out. Changed to steels and had run out that side, hence I think hub.

Would you agree that spacer can't cause such issue?

[Rockster]

Gibbo205 said:

Well hub was heat cycled a lot with PCCB's and same side PCCB had run out. Changed to steels and had run out that side, hence I think hub.

Would you agree that spacer can't cause such issue?

No. I would argue the spacer is the 1st thing to suspect, that is it not parallel or possibly there is a burr or something that is preventing the spacer from being flat against the hub face.

Briefly, the hub face wants to be true with no (or within acceptable) radial and axial run out. What these are I have no idea but they are I'm sure given in the factory manual.

Next the matching the mating surface of the rotor wants to be true as well so the rotor runs true. A good hub surface with a bad rotor surface means the rotor will run out and that's not right.

A burr, ding, knick, piece of metal or dirt/grit, can prevent the rotor face from seating flat against the hub face.

Whenever rotors are replaced the hub and rotor mating surfaces should be checked for any burr/ding, anything that would result in run out.

When possible after mounting the new rotor the hub/rotor assembly should be spun by hand and excessive run out checked. This can be done by "eye" by an experienced tech.

A road test should be done and at this time the tech should detect any pulsing or other issues arising from a poorly fitting rotor (or any other assembly faults with the brake hardware).

If the rotor runs out there can be pulsing as the rotor pushes first against the pads on one side then the other.

Over time it is possible this can cause the rotor to wear out of parallel and thus even if the mating/mounting problem were corrected the rotor would still pulse because it has now assumed abnormal form from the mounting problem.

The only recourse is to resurface the rotor or replace it.

I might add true warping of the rotor is rare. Often what happens is there is uneven pad material deposition with the rotor. The rotor face then has a difference in its friction coefficient and during braking as the pads encounter this you feel this as pulsing.

[Slippydiff]

I concur with Rockster. The 996 Turbo I briefly owned, had spacers all round, removing them cured a horrendous vibration.
I run them on the rear of my daily smoker 335D, they do create additional vibration if the wheel balance isn't spot on.
I also run them on the rear of my Mk1 GT3 with no issues whatsoever.

[Gibbo205]

Hi there

Ok I shall try removing all spacers as an easy thing to try.

[Rockster]

Gibbo205 said:

Hi there

Ok I shall try removing all spacers as an easy thing to try.

Be sure the wheel spacers are not needed for the wheels to clear the body, brake hardware, or suspension/steering hardware.

Also, a co-worker had a problem that was traced to the wheel spacer center hole not being the right size.

[_gez_]

Also consider that the slight run-out issue you measured would lead to the disc wearing a 'thin spot' which would become more pronounced over time(use). This is what most people confuse with a warped disc.

You could always have the disc refinished on the car. This will remove the problem but not the underlying cause. At £35 you could get it done numerous times and still not spend £250 on the hub

[Gibbo205]

An update, removed just the rear spacer, not tested high speed braking yet, so can't comment if fixed, shall test later when roads quieter.

Though I have noticed car seems to turn in marginally better, spacers that were on rear were 7mm per side, front still has 5mm spacers on it and widened front track due to GT3 LCAs.

Is it normal that reducing rear track helps turn in? If so what's negative to it?

Also booked in with a Pro Cut garage tomorrow that will remedy any run out my car has, by skimming disc while on the car, worth a try me thinks instead of spending £400 on hub, bearing and fitting.

[Rockster]

Gibbo205 said:

An update, removed just the rear spacer, not tested high speed braking yet, so can't comment if fixed, shall test later when roads quieter.

Though I have noticed car seems to turn in marginally better, spacers that were on rear were 7mm per side, front still has 5mm spacers on it and widened front track due to GT3 LCAs.

Is it normal that reducing rear track helps turn in? If so what's negative to it?

Also booked in with a Pro Cut garage tomorrow that will remedy any run out my car has, by skimming disc while on the car, worth a try me thinks instead of spending £400 on hub, bearing and fitting.

The hub and rotor all need to be installed correctly. Among other things this means with no unacceptable run out either axially or radially.

If the rotor and hub do not mate up with axial and radial run out within spec, the resurfacing operation machines into the rotor the (radial) run out, cuts the rotor thinner in one area leaving the rotor thicker (less material removed) on the other.

Now there is a weight imbalance. You have traded one source of imbalance for another and the real source of the original symptom is still present. When you install new rotors they may not run true and then you are back where you were.

Next once you are sure the hub and rotor are ok the spacer needs to be checked to ensure it is parallel. As is the case with the hub and rotor the spacer must fit to rotor face with no run out.

When the wheel is then mounted it must center on the spacer so the wheel is centered to the hub even though the spacer resides between the rotor and the wheel.

[DiscoColin]

I've never heard of a warped hub, but I know of 3 997.2 GT3s so far that have warped the rear disks now.

[legend4games]

Gibbo205 said:

An update, removed just the rear spacer, not tested high speed braking yet, so can't comment if fixed, shall test later when roads quieter.

Though I have noticed car seems to turn in marginally better, spacers that were on rear were 7mm per side, front still has 5mm spacers on it and widened front track due to GT3 LCAs.

Is it normal that reducing rear track helps turn in? If so what's negative to it?

Also booked in with a Pro Cut garage tomorrow that will remedy any run out my car has, by skimming disc while on the car, worth a try me thinks instead of spending £400 on hub, bearing and fitting.

My mates Boxter is showing brake disc vibration, just interested to know what was the outcome of this skimming for you? Was it a porsche specialist or a standard garage?? ( www.skimmydiscs.co.uk have 3 levels of service centre listed on their garage finder, standard, premium and specialist - is one better than the other?)
cheers mate.