993 Front brakes

[tony webb]

Any help with front brake problem on a 993.
Car purchased in March needing new discs, pads and sensors. These were replaced with original Porsche parts, after 6 weeks the new ones developed a shake on the steering under light pedal pressure. These were replaced under warranty with more new parts.

After a further three months the latest discs have developed the same problem with quite a violent shake when light braking from around 70mph. This means the car is now on its third set and the problem has returned.

I have been informed by a Porsche specialist that after measurement with a dial indicator that the right front disc is showing heavy distortion over an area covering half its radius. The left front shows distortion but not anywhere as bad as the right.

They have also found that the right hand suspension strut is very weak and needs replacing.

Does anyone know what may be causing the problem and did I recall correctly that Porsche have had problems with the front hubs on these cars.

Any help appreciated befor I invest in more discs etc.
Tony

[Jim Richards]

Hi Tony, I've never heard of this happening before. I'd recommend checking the 993 forum on www.rennlist.com. They have more participation from the 993 owners than Pelican (of course that may change over time).

Regards,

[Britwrench]

I would check the hub run-out first before replacing the discs.
Remove the discs and run a dial gauge on the hubs, if there is only slight run-out then you can re-postion a good disc on the hub and re-check run-out. If out of spec then you will need a new front hub (or two). This entails replacing the front hub bearing as well as the hub. There is a Porsche technical bulletin about this and the necessary repairs. Note that you should renew the brake caliper bolts every time they are removed.

BTW, did you ever sort out the PS2 tester.

[tony webb]

Thanks for the reply, long time no speak!
This is a real weird problem and the guy is not too happy, I just got acopy of the Tech Bulletin on this and can see that porsche look as though they beefed up the hub.

We shall be looking at the run out as we did on the disc, but any other thoughts would be welcome.

The PST has not been put to rest yet, but to keep you up to speed there is a lobby of specialists here who have threatened to take Porsche to the European Courts if they continue to atke their current stance of not allowing access to the data and software.

I have kept in mind our chat but am waiting to see how Porsche respond.

Keep in touch

[Bill Verburg]

Defective suspension pieces can cause the bakes to judder, If left long enough there is permanant damage to the rotors.

I would be sure that all of the suspension pieces are up to snuff. As previously mentioned spec ALL of the rotating components from the bearings out.

[tony webb]

Thanks to all who replied, at last we found the answer which mat be worth checking if you get similar problem.

After checking all components for tolerance and having the latest set of discs checked by an independent test house and found to be within spec we were baffled.

We decided to put the parts back and checked at every stage. The left side no problem, but as we put the right side together we tightened down the caliper holding bolts with the ratchet and everything felt fine. However when we came to torque the bolts the top bolt even though tight with the ratchet kept moving with the torque wrench. We decided to take the bolt out and found that the hole was completely corroded and the bolt was struggling to get through it.

It seems the bolt had probably never been all the way through from the factory as we had to tap the threads to clear them. Once done the bolt went all the way down and seems fine.

Because these calipers bolt on from the front rather than the side as is usual with most calipers, the bottom bolt and loctite had done a good job of holding the caliper in place. I guess over a period of time however the strain being put on the caliper bolt by the braking forces had allowed the bottom bolt to loose just enough grip to make the caliper move so causing the judder under light braking.

Just goes to show that even though the car had been in for two sets of disc change, nobody picked up the problem, probably because no one followed the instruction to torque the bolts, which would have instantly picked up the problem.

I will put something on the site in the future to let you know if I get further problems

[Jim Richards]

Wow, Tony, that's truly amazing. Assembled wrong and (somewhat) improperly maintained by qualified mechanics. Who would have expected it?

[tony webb]

Hi Jim
Yes it takes some believing but that's what we found.