Caliper Halves Holding Screws/Bolts

[Pawel66]

I have come across the issue while having my calipers plated. One of the bolts holding halves of the caliper (one of the ones in the rear) just broke. This is the black one, one of the four keeping the halves together. I see it is a low head 6x60mm torx screw. I guess the steel is 10,9 as it is black (here this is the colour coding - if it is black it is usually 10,9 or 12,9 steel).

I found similar imbus (allen) screw, 6x60mm, 12,9 steel. But it is not a low head torx...

Is there a source for these screws? Other than aftermarket, of course.

Pawel

[rgafitanu@gmail.com]

Pawel a quick look in McMaster Carr didn’t show anything. Belmetric.com has button head torx 70 mm. I think that you have better chances of finding them in Europe. Any reason for the low profile head? Worst case you can use threaded rod with nuts on both sides which is a common method for fastening very thick parts (electrical motors armature and end caps). Depends how original you want to be.

[wwheeler]

When I cleaned up my calipers, I searched for the torque value of these bolts as I wanted to take the calipers apart. I never found anything and I remember reading something, somewhere cautioning you NOT to these bolts off. Not sure if it was a scare tactic or if there really is some trick to these?

[Pawel66]

Thank you both for your kind attention!

15 bolts/screws we did ok, this one just broke. Material fault? Corrosion? No idea.

All of them had low torx head and nut on the other side. The replacement I found is not bad - at least for a while. But I will be looking for the original screw. The caliper rebuilders did not have one at hand, they said they would look for one. They said the similar screws are in W123 calipers, which is increasing the chances.

As these screws are 10,9 I suppose, my mechanic said he used the standard 6mm 10,9 value (do not remember what he said it was). So nothing special.

Here splitting the calipers for their rebuilding is quite common (very value oriented country).

anyway, I had to buy 10 of those allen 6x60mm screws, 12,9, so if any of is in need - let me know .

[Shvegel]

If it is a read pretty much any Mercedes of the era should work.  If it is a front it has to be from a non vented rotor car as the vented ones are too long.

[Pawel66]

ok, thank you for the tip!

[doitwright]

PMB Performance is my go to source for caliper parts and questions.

[Pawel66]

Good tip. I have already been in touch with them. See if I can find anything closer and go to them if need be. Thank you!

[wwheeler]

I assume PMB also will rebuild Mercedes calipers? Mine are ATE, so I would think so. I will keep that in mind for down the road.

Thanks.

[Shvegel]

Wallace,  Indeed they will. I was in contact with them before I ended up replating my own and then ordering new ones instead.

[mdsalemi]

Hmmm...

I had to do a search for what Pawel is meaning by 12,9. Well, for those Americans here, we would say 12.9, as the Europeans seem to mix up the comma and decimal on a regular basis 

But seriously, it's all about the grade and besides "Grade 8" bolts which are stronger than normal but still commonly available in the USA, we don't normally here about such thing except in extraordinary circumstances.

I found a nice chart that explains it all in both USA and ISO standards.

https://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx

BTW, a grade 8 bolt equates in strength to just under a class 10.9. The 12.9 is a bit stronger. There are grade 9 bolts that are 20% stronger than a grade 8 but I've never seen them advertised anywhere--they are probably in the specialty category.

[wjsvb ✝︎]

Pawel:  I have several used calipers at my shop.  If a used bolt will do for you, I can pop a couple of and send them.  Pay only the postage.  Jon

[66andBlue]

Hmmm...

I found a nice chart that explains it all in both USA and ISO standards.
...

We have had one right here for a long time already. In PSI and MPa 

http://www.sl113.org/wiki/uploads/Restricted/Bolt_Grades.pdf

[mdsalemi]

We have had one right here for a long time already. In PSI and MPa 

http://www.sl113.org/wiki/uploads/Restricted/Bolt_Grades.pdf

That's great, and thanks for the link.

However, let's say you had no idea something like this existed somewhere on our website. How would you go about finding it? I did a brief look at the Tech Manual, a couple of searches in various places, and came up empty. Of course, your link works, but if the information isn't readily available or indexed, it isn't useful.
By contrast, all I did was type in "steel grade 12,9" in my browser search bar, and the link to the BoltDepot.com page was in the top hits.

[Pawel66]

Yes, indeed we are mixing comas with dots in front of decimal places in some parts of Europe... Drives lots of emotions when looking at bank account statements...

Yes 12.9 is a grade of steel. I could not find information what should be the grade for caliper bolts. As they come black, I assumed they may be 10.9 (black here often means higher grade steel than 8.. This assumption is safe, I think, even if it is not true. I could not find 10.9 bolts that would fit, I found 12.9. A bit different than original, but would do for now.

[Pawel66]

Pawel:  I have several used calipers at my shop.  If a used bolt will do for you, I can pop a couple of and send them.  Pay only the postage.  Jon

Jon, thank you, this is very kind of you. I just checked the usual sources here, but I cannot find it. So, as much as it feels a bit odd to send a piece of screw over the ocean, I would appreciate it. I will PM you for payment details.

I am also attaching the picture: torx, low head, 6x60mm caliper halves holding screw, rear ATE caliper.

[Shvegel]

For future generations who might search here I wanted to point out that those bolts should never be plated.  Unless proper steps are taken the plating process can make them very brittle through what is called hydrogen embrittlement.  I had some large thin hardened washers plated by mistake once.  they came back so brittle I cold snap them with my fingers.  Black Oxide is OK.

[wwheeler]

For future generations who might search here I wanted to point out that those bolts should never be plated.  Unless proper steps are taken the plating process can make them very brittle through what is called hydrogen embrittlement.  I had some large thin hardened washers plated by mistake once.  they came back so brittle I cold snap them with my fingers.  Black Oxide is OK.

Absolutely correct. Same for split lock washers. Pretty much anything that is spring steel, acts like a spring or is hardened, should use caution when plating. There is a process to treat for embrittlement, but is expensive and is another step.

[Pawel66]

Ok, calipers are in place now. They look kind of funny - gold calipers...

One more question if I may: why does the EPC say you need 4 lock plates  for caliper to wheel hub holding screws? I have 2, one holding two screws on each side. What am I missing?

[wwheeler]

Maybe left and right?

[Pawel66]

But then it is two.... 4 would be if one lockplate was for one screw, but those are one lock plate for two screws, like in the front...

I am attaching a picture. Maybe the earlier locks were one for each screw and the number stayed by mistake?

[Shvegel]

They may be including the front and rear calipers?  I thought the fronts had a different bend but maybe as a replacement now they are the same part.

I normally don't point out things that may be incorrect but since you just went through the process of replating the calipers so they are the original finish it is obvious that you care a lot about originality.  I am fairly certain the center section of the rear brake rotor is supposed to be painted black right up to the machined braking surface. The front rotors are left natural while the hubs and bearing caps are painted black. 

Assembly line photo from the era for reference:

[Pawel66]

It does not seem to be the case... I am attaching the picture of the front.

If you are using just the two lockplates, then I htink it is just a mistake.

[Shvegel]

I had just ordered 2 fronts and 2 rears from Mercedes and they were a different  part number and a different part but I thought perhaps that had changed.  It just must be a miss-print in the EPC.

[Pawel66]

I also think it is a miss-print.

Thank you for pointing the black rotors centre - I will see to it, it is a relatively easy job.

Yes, I am trying to have as many pieces look or be original as possible. Some of it will stay incorrect, I am afraid, but what I can fix, I will. Long winter evenings are good for it  .