Porsche Enthusiasts Club Forum

in reality both work equally as well, the alloying agents used in hight tensile steel also improve the corrosion resistance,
stainless is not generally high Tensile and still contains iron
As aluminium is above iron in the galvanic corrosion table theoretically is should corrode before the steel, using a barrier paint is not a bad idea.
it's a complicated subject with no right answer

I suppose the only way to find out for sure is to try it and see what happens! But I would be worried about the screw head rusting and being a nightmare to remove in the future.

You cant deny that stainless is mostly resistant to rust, whereas any ferrous steel, high tensile or not is susceptible to rusting away! Stainless is high tensile, look at this table for comparisons of tensile strenghs of different metals/grades.

http://www.anzor.com.au/tensile-strengt ... ison-chart


Anyway we are all free to make our own choices and have our own opinions, so just do whatever your happy with!

I am with NicksonMotorsport here.

As I have said before I have on quite a few occasions used high tensile black bolts before. On many occasions in venerable areas they rust and corrode far quicker than the stock (plates and treated that is) items, meaning that a 5 minute job becomes a more lengthy one!

The bolts from the dealers IME tend to come with better treatment. It is a shame that they are so tricky to find in the aftermarket world with a suitable coating (I recently broke a VW Passat for spares with 250k with the original fixings making short work of coming apart.

As I said, your mileage may vary ... The problems I had getting my (soft) stainless steel bolts out were horrendous and could well have been avoided if a harder material had been used. As the hardest (common) stainless has similar material characteristics to mid-grade carbon steels, a higher grade carbon steel bolt will always out-perform a stainless steel item. In the case of the plate bolts they are of course not subject to critical loads so in a primary sense don't need to be too hard, but it is more than a little vexatious when even moderate force applied by a key to remove it results in the disintegration of the hex socket. This simply wouldn't happen with a 12.9 carbon steel bolt. Personally I'll not be leaving them unattended long enough for them to rust so badly that they'll not come out again ...

Don't get me started on leaky caliper bleed nipples either; another brilliant example of galvanic corrosion at work ...

Argh - I forgot to attach THIS LINK just in case anyone's interested in low-level techy geekishness and material specs...

Going slightly OT but what do most find is the easiest way to remove these bolts when the heads have been rounded out?

I'd have thought welding a nut on top of the head would be easiest, heat helping to release the bolt?

I hadn't realised that Stainless was softer than mild, as stainless tends to crack where mild would bend I assumed the oposite!! But even for mild steel high tensile bolts, if corrosion is a worry, why not use zinc passivated ones?

There was a guide which 911 & Porsche World wrote many moons ago detailing how the plates could be removed with dodgy bolts. Welding a nut on top of the existing bolt I seem to recall was cited as one method of tackling the problem. I guess Irwin Bolt grips might come in handy (they have on cars for me on previous occasions).

IME zinc passivated bolts only go so far. On old Triumphs (well, the Slant 4 and Stag engines where both use alloy heads with the Sprint engines to a lesser extent) it is not unheard of for zinc plate studs to seize into the head after only a couple of years causing a manner of problems that they are meant to avoid (where Stainless studs so far have seem to have avoided this issue). That includes individuals who have use copper grease along with that as welll If bolts of a suitable coating could be found I guess it would be a different matter.

My first effort did not go well - after successfully rounding the hexagon on two of four of the bolts I tried grips but couldn't get a purchase on the domed head, so I thought fukkit and separated the caliper halves after cutting the plate in two halves. I used a torx bit that I banged into what was left of the hex and it wound right out. I bent up a new transfer pipe and welded the plate back together then reassembled the caliper halves ... all good.

After doing that I read that someone had used a centre punch to tap the bolts round - I gave that a go on the other calipers with a degree of success but don't expect to be able to use the bolts again.

you would not want to use any bolt again in brakes, always new anyway

good debate ! my calipers have some plate lift and I'm going to take them all off this winter and tackle it
its a subject thats been debated quite alot recently ,but the more you read the more you know and it makes
the job easier to tackle

the hex will always round off, a high tensile steel screw will suffer the same fate. these are only small screws, and once the galvanic corrosion has taken place between the screw/ally caliper housing in the thread, the torque required to undo the screws will be too much for a small 4mm hex to undo successfully. it is also very likely with a steel item that the hex drive will have corrosion/rust in it which will make the hex piece even harder to insert fully, once again increasing the likelihood of rounding the head off as surface area of contact patch of hex piece is further reduced.

I never even bother using a hex piece to even try and undo the screws, they always round off if they have been in there a few years.

why would you want to re use the screws? they are a couple of quid for 16 new ones lol!

I have never had an issue removing the screws, using a vice, chisel, and an extractor tool that bites into outside of screw and winds it out. chisel breaks the initial torque, and puts some sharp edges into the screw head as shown in your pic, extractor bites into these edges and winds screw out easily.

sometimes the head breaks off if your a bit heavy handed with the chisel, in this case split the calipers and you can drill a small hole and use internal extractor piece to remove the stud. you never need to split the plates, as if you break the bolt heads off with the chisel, then the plates come out anyway as the heads no longer hold plates in place. even if you just get one screw from each plate off you can split the calipers leaving the plates still bolted to one side of the caliper, which then leaves the remaining 2 screws with easier access for removal, and easily drill/extract studs if needed with calipers split, and plates all in one piece.

(plates are £30 odd quid each so you don't really want to cut them in half!)

its easy when you know how! and have the correct tools.

for someone having a go, with limited tools etc, they can be an absolute nightmare! in most cases, its the sort of job you just send to someone else to do who has the specialist tools available to them, and experience of doing the job many times before.

we are happy to help anyone in need of removing these screws and we charge £30 per caliper for removal. looks like marks2ply calipers will be on their way to us soon, and we just removed 16 screws with no issues last week from another forum members set of 4 calipers for an s2 track project.

cheers
nick

Hahaha ... I'm glad my humour about reusing bolts wasn't lost (although in the case of these they are not stressed in the least bit) my comment was made with tongue firmly planted in cheek given the amount of effort required to remove them - as the picture illustrated.

I'm sure I won't have been this first to have tackled this job for the first time and without assistance, working on the car has been a learning process from day one and this was no exception. At the end of the day though my end result was the same - problem resolved and brakes restored, I just took a different route than might be considered conventional. How did you manage to get an extractor onto the boltheads?? I was struggling getting enough of an angle through the top of the caliper with a punch!

One thing I did find though was that the threads in the holes were quite badly compromised by the corrosion - if I was doing it again I think I'd seriously consider drilling them out and going up a bolt size...



G

I think you would find that the next size up pan / button head bolt would foul the pads.

I found that a half blunt small cold chisel worked much better than a centre punch, the punch tended to just plough into the head but with the larger contact area of the chisel it broke the bolt free much easier, just my experience so far I guess method is a bit of personal choice.

I have done 6 calipers so far and no disasters with bolts snapping, got 4 more to do on another 968 soon

received marks2ply calipers this afternoon. all screws out with no issues at all within the hour.

if anyone else needs same job carried out just get in touch.

nick

Just a quick update received my front calipers back from nickson motorsport a few weeks ago after they removed the remaining seized plate bolts fo me. Having just come back from two weeks holiday, I have received new seals from bigg red for £33
today i have removed all the corrosion and cleaned up and taken to my local powder coaters who are soda blasting and powder coating fitting the decals and lacquering for £60.

I used kens idea to block off the piston chambers.

I am awaiting 4 new bleed screws from bigg red along with a 36mm reclaimed piston (one was chipped).

Thanks to Ken and nick for their help so far.

will post up when they come back.

Mark

Totally forgot to send the plates

I guess your sorted post some photo's when they are finished