pete01_996

I'm replacing all 4 rotors on my 99. In this aritical:
https://rennlist.com/forums/showthre...eferrerid=6422

It was recomended to replace all the Caliper bolts too. Most of these bolts look like they are in great shape, so I'm hesitating a bit on replacing them.

So ... curious what others have done. If you have replaced your rotors, did you replace these bolts too?

Thanks in advance!

umn

Here is what I wrote on the same subject in another forum:

"In answer to your question, it is not always possible to tell from visual inspection if a bolt needs changing or not.
I am a little surprised to hear that Porsche recommend changing them, because other manufacturers don't.
One reason would be if the bolt was to be tightened into the plastic range. However, the bolt is M12x1.5x72. Under the conservative and most likely assumption of bolt grade 8.8 and a coefficient of friction of mu=0.125, the recommended torque would be 83 Nm, which is pretty much the 63 ft-lb that xxxxx mentioned.
I can therefore only assume that they are concerned about progressive crack growth during cyclic loading, which could occur due to loss of preload (or because someone hasn't tightened them properly in the first place).

Anyway, I don't think there is anybody in this forum who can answer this question. Considering the low price of the bolts and the importance of the part in question, I would probably go with Porsche's recommendation.
"

Incidentally, there are two things that I would question in the posting you quoted:

1) Using a torque wrench to brake loose the old bolts: A torque wrench is a precision instrument and since the required torque to brake loose the bolts is much higher than to tighten them, you risk damanging your torque wrench. Use a breaker bar instead. (Karl probably uses his 400 ft-lb torque wrench, so he's safe. But a less robust wrench could be damaged. )

2) Using copper anti-seeze compound on the new bolts. UNLESS EXPLICITELY STATED IN THE ORIGINAL FACTORY MANUAL, never do this! The idea is of course to make sure that the bolts will come out after a couple of years. The big problem is that you drastically reduce the friction of the bolt. When specifing the required torque, the manufacturer assumes a certain coefficient of friction, typically lightly oiled with a coefficient of mu=0.125. If you put on copper grease, you massively reduce that coefficient of friction to about mu=0.08. The result is that if you apply the same torque, you over-tighten the bolt by almost 50 per cent! It won't break, but it will lose its elasticity and be much more susceptible to stress fatigue.
Incidentally, the same holds true for MOST wheel nuts, some older Porsche wheels being one of the notable exceptions.
In fact, don't use copper anti-seeze at all. It the kind of crap we use in Europe because we can't get anything else. You guys have great products like Never-Seez, which is much superior in terms of contact corrosion.


Cheers,
Uwe

pete01_996

Very helpful!

Thanks Uwe!

Orient Express

The actual reason that Porsche wants to have the caliper bolts replaced is that they come with a little capsule of Loctite retaining compound on each bolt which is crushed on insertion and tightening. Porsche wants to make sure that when the bolts are reinstalled that they have a new application of thread retaining compound on them to lock them in place.

It is perfectly safe to reuse the bolts as long as they have been cleaned of surface corrosion, inspected for obvious damage, had a new application of a retaining thread compound such as Loctite Titen on them, and they are torqued to the correct specification.

While the opinion of UMN certainly has merit, if there was a danger of the bolts cracking, we would probably see a similar remove and replace recommendation for wheel lug bolts as well.

While there is nothing wrong with replacing these caliper bolts, because of the fact that they have a retaining compound capsule on them, they are in excess of $8.00 each to get new ones. In my book that is a little pricey to throw away a perfectly good bolt.

As always a good visual exam for obvious cracks is in order, but if the bolt looks solid, just give it a new drop of Loctite and reuse it. I have done this for years with out any issues.

Lastly: DO NOT APPLY ANTI-SEIZE PASTE TO THESE BOLTS!

mds

Interesting. The caliper bolts I ordered for my car came with no loctite nor did the bolts I removed have any indication of it being used. The workshop manual also make no mention of it.

GMS

Porsche state that the caliper fasteners (and some other bolts) have an anti-corrosion coating which will be damaged when removing the bolt.
There is no mention of stretch or Loctite.

mds

GMS, thanks, I believe you are correct. I just checked the old bolts from my car. They have a very thin gold colored coating that is easily scraped away to bare shiny metal with a file.

mds

I did more hunting on this. Apparently without the coating the steel bolt would tend to bond with the aluminum in the caliper and wheel carrier. If you find the bolt hard to remove, tap its head with a hammer a couple of times and try again.

Orient Express

The gold coating is alodine which is used for corrosion control. The loctitie capsule is on the end of the bolt and is usually completely obliterated when the bolt is installed. This type of fastener is pretty standard in the automotive and aerospace industries, and usually does not have special mention in shop manuals.

Interesting that the replacement bolts you were sold did not have the capsule. How much did you pay for these bolts? If it was less than $5ea., chances are they are standard fasteners, and not the completely correct bolt. Never the less, just put a drop of loctite on them and you will be fine.

mds

The GT3 bolts I bought are expensive, part number 999-067-047-09, description CHEESE-HD. SC lists for $27.26 each. I got a 19% discount from Suncoast. They came with no loctite capsule, just the bolt, sealed in a appropriately labeled bag.

umn

Looks like you are spot on. I just called someone up at the factory and he said they are coated with microcapsules (the bolts that is, not the people at the factory). I haven't been able to check it myself.

New bolts for the standard Carrera are only 2 Euros over here but we pay 25 Euros for a quart of Mobile 1 at the dealer's

Cheers
Uwe

GMS

The coating is the same as used on 964 and 993 cars, all of the coated bolts I have seen have NOT got any micro-encapsulated locking chemical on the threads. We recently replaced most of the right side suspension of a 2001 996, none of the coated bolts were treated with any locking chemical. All bolts were purchased from the local Porsche dealer and were the correct part number.
The coated bolts include 964/993 front lower control arm, brake caliper, rear suspension fasteners etc..

mds

Bolt anti-corrosion coating may have changed at some point, current GT3 bolt coating is a light golden color, some older 996 coatings are a much darker reddish color.

A loctitie capsule at the end of a GT3 bolt would do no good as the wheel carriers both front and rear are drilled completely through, so a capsule at the end would never be crushed.

The GT3 bolts do not have microcapsules either. Just the clean surface of the anti-corrosion coating.

Seeeu911

Bump a ancient thread....for some good info

scorchpa

Sweet... good info here.... so no anti-seize, that's good to know.