924Board.org

morghen · Joined: 21 Jan 2005 Posts: 9105 Location: Romania

what can cause brand new brakedisks to develop complete wall offset on certain areas?

i've noticed that at higher speeds the steering wheel wobbles a bit (over 170-180) kept driving it and now it has become worse and i checked into the problem.

i checked the rims and they are spotless. rubber is not new nor perfect....but think that bad tires alone cannot make the brake disks offset areas...or would they?
_________________
Supercharger and EFI kits
https://www.the924.com

Rich H · Posted: Wed Apr 08, 2009 6:24 am Post subject:

What is wall offset?
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

Typically, incorrect brake pad bedding procedures. Rarely to rotors "warp" Brake material was not distributed evenly on the rotor faces, this leads to pulsation under braking or just coasting. Following proper brake pad bedding procedures will help.

If you are seeing a lot of wear on the rotors, change the rotors and change the pads to a less aggressive compound. Some of the "racing" brake pads are fairly abusive to brake rotors and if you run "cheap" rotors they may wear even faster.

Read these:

http://www.ffcobra.com/FAQ/brakes3.html

http://www.scirocco.org/faq/brakes/pulpfriction/pfpage1.html

http://grassrootsmotorsports.com/forum/grm/bedding-in-new-brakes/4099/page1/

http://www.afcoracing.com/tech_pages/brake_prob.shtml

http://grassrootsmotorsports.com/forum/grm/brake-question/8989/page1/

Good Luck!
_________________
Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

morghen · Joined: 21 Jan 2005 Posts: 9105 Location: Romania

offset means this:

perhaps a better drawing is this:

Pads are not race but normal road use units...disks are not worn at all...just bended.
I never overheated the disks and then went trough wather with them or forced them to cool down in any way.
i bled the system using the right procedure..brake works very good...well except in wobbles the steering wheel.

i'm thinking this could be caused by some mechanical wear in the spindle..bearing..? tho there is no play at all...the car i have swapped the spindles from had the same problem...bended disks..i also took the disks and then realised they are bended..had them changed with new zimmermans and now these got bended.
the donor car had different wheels and tires so i think i can rule out the fact that the tires caused this.
_________________
Supercharger and EFI kits
https://www.the924.com

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Bad/misadjusted wheel bearings?
_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Fifty50Plus · Posted: Wed Apr 08, 2009 7:19 am Post subject:

Several hard stops that heat the rotors and then keeping your foot on the brake pedal (e.g. at a long stoplight) may cause warpage.
Regards,
Chuck

Smoothie · Posted: Wed Apr 08, 2009 7:31 am Post subject:

+1
Wobbling only while braking means warped rotors.
Resurfacing might be an option if they can be made straight again without exceeding the minimum thickness spec. (Going thinner than the min. thickness will leave you with too-skinny rotors that will re-warp very quickly.)
Mine had developed quite a wobble on high speed braking about a year ago. I put on new front discs made by Zimmerman in Germany (pretty good pricing). As predicted that fixed that problem right up.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Smoothie · Posted: Wed Apr 08, 2009 10:14 am Post subject:

Do you torque your lugnuts to spec with a torque wrench? I do.
-But I also do not often (never) find myself braking hard from 180kph..
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Scorpio · Posted: Wed Apr 08, 2009 10:38 am Post subject:

The mitsubishi magna (front wheel drive) had the same problem...no wobble/shaking till about 100km up..then very bad but only every so often....when brakes were hit once wobbling started it would shake the whole car violently

new rotors (turned out cheaper for me to buy new ones then to have them machined..go figure)...new pads....no more problem...still some squeeking though
_________________
1979 NA
MS1..EFI..
GARRETT T25 TURBO
BILSTEIN SHOCKS
GT BASED CUSTOM BODYKIT

Brisbane , Australia
Think mean think fast
all youll see is
my Porsches Arse!!!

morghen · Joined: 21 Jan 2005 Posts: 9105 Location: Romania

guys....the bended rotors are NEW zimmermans...i've mounted them last year in autumn and did max 1000Kms since then. Log nuts are tight no prob. I've replaced the old rotors because they were bended too..
rims are tight,rubber is bad...but rubber alone cannot make the rotors bend/wrap.

the steering wheel shakes when i go over 40mph and it shakes the whole car when i brake...the rotors are causing this...i've had this before...replaced the rotors and that fixed the problem...now it's back !
_________________
Supercharger and EFI kits
https://www.the924.com

Lizard · Posted: Wed Apr 08, 2009 5:05 pm Post subject:

have you rebuilt the calipers?
It is possible that the calipers are dragging some and not allowing proper disappation of heat. As well you need to brake hard and fast, dragging the brakes builds up far more heat far faster.
_________________
3 928s,

Smoothie · Posted: Wed Apr 08, 2009 6:37 pm Post subject:

morghen · Joined: 21 Jan 2005 Posts: 9105 Location: Romania

yea...thanks for the ideeas....the thing is that everything seems perfect...rims are perfectly straight, balanged and all that...bearings have no play and make no noise...alignment is spot on...disks were new..pads in very good condition(almost new)
_________________
Supercharger and EFI kits
https://www.the924.com

Nobbi · Joined: 24 Aug 2006 Posts: 1398 Location: Germany

Do you clean the contact-surface`s? Before installing your rim, clean it and the counterpart at the disc/drum.

It makes a diffrence, especially when going fast.I also would suspect the calipers, because the problem remains whether you changed all other parts.( You get new brakepads as you installed the new discs....?) And you installed the correct wheel (Tire-rotation) in the right place??

just what comes to my mind.
Nobbi

_________________
NA 924 - april/1977- 4-speed-audi gearbox.
500.000 km with fun.....and new toy:Porsche 944 S2 Cabriolet.Other car Daimler c-class cabby,brandnew..Plus : DEUTZ 4005 tractor Built 1967

morghen · Joined: 21 Jan 2005 Posts: 9105 Location: Romania

Thanks Nobbi !!!, i just realised i never cleaned the surfaces and that i have BIG spacers up front. 35mm heavy steel ones...i never tought about it until now...always suspected wear in the bearing housing but that would be much more noticeable.

i'm going to have the spacers removed, disks and tires replaced and pads cleaned and have another try...i doubt that there is anything wrong with the calipers...they just push the pads towards the disk...the disk is only wrapped in one area like in the picture below...so if the calipers would be faulty or the pads would bed in an uneven way there would be wear or wrapage allover the disk.

_________________
Supercharger and EFI kits
https://www.the924.com