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-ollie-
Newbie


Joined: 26 Sep 2018
Posts: 27



PostPosted: Sun Jan 20, 2019 4:33 pm    Post subject: 997 GT3 brake change Reply with quote

Hi guys,

I'm a reasonably competent driveway mechanic and am about to refresh discs & pads on my 997 GT3.

I've heard that the 2 x 10mm hex head bolts that secure the caliper are one use only on these cars - is this true? If it is I'll replace them naturally, just sounded unusual to me having never come across this previously whilst messing around with other cars (on calipers, at least).

Any thoughts? Can anyone confirm or deny?

Cheers

Ollie
 
  
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NXI20
Paul Ricard


Joined: 02 Feb 2008
Posts: 3342
Location: South Bucks

2004 Porsche 996 GT3 Mk2

PostPosted: Sun Jan 20, 2019 5:04 pm    Post subject: Reply with quote

Unnccessary caution on Porsche's part ime. My car is tracked extensively & I don't change these bolts even though the calipers come off at least 3 times a year. What does tend to happen is the threads in the upright wear out until you cannot tighten to 85nm without stripping them. Mine are all TimeSerted now and have been no trouble since.

Using a good amount of aluminium grease (Wurth AL1100 is perfect) on the bolts when you put it all back together & you'll extend the life of the original threads but they will go in the end.
_________________
Nick

2004 GT3 CS in Atlas Grey with too many mods to list!
1995 993 GT2 recreation in Polar Silver
2010 GT3 CS in Riviera Blue Smile
1978 Carrera SC Barn Find in Red (restoration project)
 
  
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-ollie-
Newbie


Joined: 26 Sep 2018
Posts: 27



PostPosted: Sun Jan 20, 2019 8:45 pm    Post subject: Reply with quote

NXI20 wrote:
Unnccessary caution on Porsche's part ime. My car is tracked extensively & I don't change these bolts even though the calipers come off at least 3 times a year. What does tend to happen is the threads in the upright wear out until you cannot tighten to 85nm without stripping them. Mine are all TimeSerted now and have been no trouble since.

Using a good amount of aluminium grease (Wurth AL1100 is perfect) on the bolts when you put it all back together & you'll extend the life of the original threads but they will go in the end.


Thanks Nick, useful info there.

Will get some ally grease, we talking just a slither on the thread?

So the uprights are ally, the bolts are steel - is that correct? Is it galvanic corrosion that damages the thread over time?
 
  
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NXI20
Paul Ricard


Joined: 02 Feb 2008
Posts: 3342
Location: South Bucks

2004 Porsche 996 GT3 Mk2

PostPosted: Sun Jan 20, 2019 9:43 pm    Post subject: Reply with quote

-ollie- wrote:

Thanks Nick, useful info there.

Will get some ally grease, we talking just a slither on the thread?

So the uprights are ally, the bolts are steel - is that correct? Is it galvanic corrosion that damages the thread over time?


Yes, just grease the bolt threads, it doesn't take much.

The uprights are cast ally & the bolts are steel. It's not corrosion so much as the combination of heating & cooling plus differential material expansion rates & a relatively soft metal under a fair bit of load. A thin layer of the ally threads will adhere to the steel bolt and act as an abrasive as the bolt is screwed out.

Lubrication will minimise this but won't completely solve the problem.

It's always good practise to ensure the bolt thread is cleaned off with a wire brush before reassembly.
_________________
Nick

2004 GT3 CS in Atlas Grey with too many mods to list!
1995 993 GT2 recreation in Polar Silver
2010 GT3 CS in Riviera Blue Smile
1978 Carrera SC Barn Find in Red (restoration project)
 
  
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-ollie-
Newbie


Joined: 26 Sep 2018
Posts: 27



PostPosted: Mon Jan 21, 2019 8:55 am    Post subject: Reply with quote

NXI20 wrote:
-ollie- wrote:

Thanks Nick, useful info there.

Will get some ally grease, we talking just a slither on the thread?

So the uprights are ally, the bolts are steel - is that correct? Is it galvanic corrosion that damages the thread over time?


Yes, just grease the bolt threads, it doesn't take much.

The uprights are cast ally & the bolts are steel. It's not corrosion so much as the combination of heating & cooling plus differential material expansion rates & a relatively soft metal under a fair bit of load. A thin layer of the ally threads will adhere to the steel bolt and act as an abrasive as the bolt is screwed out.

Lubrication will minimise this but won't completely solve the problem.

It's always good practise to ensure the bolt thread is cleaned off with a wire brush before reassembly.


Thanks Nick, it's interesting to learn about the little quirks on these cars as I play with it a bit more.
 
  
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NXI20
Paul Ricard


Joined: 02 Feb 2008
Posts: 3342
Location: South Bucks

2004 Porsche 996 GT3 Mk2

PostPosted: Mon Jan 21, 2019 8:59 am    Post subject: Reply with quote

My 996 is approaching 170K miles so I've probably encountered most if not every problem possible! That said, they are incredibly well engineered & given the use mine has had, very reliable all things considered.
_________________
Nick

2004 GT3 CS in Atlas Grey with too many mods to list!
1995 993 GT2 recreation in Polar Silver
2010 GT3 CS in Riviera Blue Smile
1978 Carrera SC Barn Find in Red (restoration project)
 
  
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Slippydiff
Monza


Joined: 22 Nov 2007
Posts: 242



PostPosted: Mon Jan 21, 2019 11:31 am    Post subject: Reply with quote

If the threads in the uprights are still good, you could go with a stud kit such as this :

http://www.rennline.com/Brake-Caliper-Stud-Kit-Cup-Car-Style/productinfo/CS-BCSK/

If the threads are questionable, than as Nick says, Timecert them and stick with the bolts, or go the belt and braces route and fit studs into the Timecerts.

As regards replacing the OE caliper securing bolts every time they’re removed, I’d chuck the standard bolts and fit some decent grade replacements from your local fastener supplier, as long as the threads in the upright are Timecerted and/or lubricated with Ali paste, the bolts will last a long time...
 
  
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-ollie-
Newbie


Joined: 26 Sep 2018
Posts: 27



PostPosted: Mon Jan 21, 2019 7:34 pm    Post subject: Reply with quote

Slippydiff wrote:
If the threads in the uprights are still good, you could go with a stud kit such as this :

http://www.rennline.com/Brake-Caliper-Stud-Kit-Cup-Car-Style/productinfo/CS-BCSK/

If the threads are questionable, than as Nick says, Timecert them and stick with the bolts, or go the belt and braces route and fit studs into the Timecerts.

As regards replacing the OE caliper securing bolts every time they’re removed, I’d chuck the standard bolts and fit some decent grade replacements from your local fastener supplier, as long as the threads in the upright are Timecerted and/or lubricated with Ali paste, the bolts will last a long time...


Thanks Slippy.

My bus has only covered 35K and I appear to the first owner who has "sullied" it with track use. Laughing I hope the threads are good, but have bought some ally paste and will have a good look at them upon removal.

I had absolutely no idea these caliper bolts/threads where such a "thing". Upgraded stud & nut kits for calipers - bonkers!

Genuinely makes me quote excited to learn what else is available for these things. Now if only the weather would get a little better, I could use the thing a little more.
 
  
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Slippydiff
Monza


Joined: 22 Nov 2007
Posts: 242



PostPosted: Mon Jan 21, 2019 11:02 pm    Post subject: Reply with quote

Certainly on the 996 GT3, the caliper securing bolts go into open ended holes in the upright/hub carrier. The holes get full of road dirt, water, grit etc, and if the bolts/threads haven’t been protected and lubricated with Coppaslip or Ali paste, the threads corrode and accelerate any galvanic corrosion.
Often the damage is done when you remove the bolts ...
IF the bolt hole ends are open to the elements, it would be a very wise investment of your time to spray the holes/bolt threads with a decent penetrating/maintenance spray (or the perennial PH favoured PAS fluid and acetone) :

https://www.pistonheads.com/gassing/topic.asp?h=0&f=140&t=974663

Spray it on a few nights on the trot before undoing the bolts and you should avoid tearing the threads out of the upright when you remove the bolts.
 
  
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Slippydiff
Monza


Joined: 22 Nov 2007
Posts: 242



PostPosted: Mon Jan 21, 2019 11:11 pm    Post subject: Reply with quote

And a great DIY on hub carrier Timecerting :

https://rennlist.com/forums/996-forum/1069650-time-sert-repair-of-caliper-mounting-hole.html
 
  
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-ollie-
Newbie


Joined: 26 Sep 2018
Posts: 27



PostPosted: Tue Jan 22, 2019 10:46 pm    Post subject: Reply with quote

Thanks for the info Slippy.

In terms of this brake change, I think I will be "winging it" and seeing how I go.

I'll carefully remove the bolts in the hope that the threads are okay, and apply some ally paste upon refitting.

Then I'll either timecert of fit studs at the next change (if I get away with this one!)

What an unusual issue, I'm glad I researched it prior - I'm used to old M power BMW's which are broadly indestructible (unless you crash them).

Cheers
 
  
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