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[Diamond Black Geezer]

Looking at replacing several of the bolts on Pissy (the V6) found the main caliper bolts are M12 x 40mm and the smaller 13mms that join the two halves of the Caliper together are M8 x 22mm

My question is - does anyone have specs of what these were, as fitted in the factory? Pondering Stainless Steel for the M8s (not standard SS, but A4-80 grade - which is within a few % the same strength as 'normal' 8.8 High Tensile Steel)
Also need to know, when it comes to getting replacements for the Caliper-to-knuckle bolts - should these be in 'normal' 8.8 High Tensile, 10.9, 12.9 or just 'standard' low/medium carbon BZP?

If at the lower end, the Stainless equivalents may in facts be stronger than OEM which is great.

Sorry to have gone all technical on you - hope this makes sense to some!

[tigers_gonads]

I don't think they are anything other then standard bolts made to fit the hole.
Can't see any reason to make anything special in this case 

[GastronomicKleptomaniac]

Interested in this one - since my quick rebuild is getting ever more involved as I find things to clean, polish, grease or replace...

[Nick W]

For things like wishbone and other large suspension bolts I'd need to carefully examine any replacements for exact sizes before actually using anything different. Just because they use standard metric threads does not necessarily mean that the shanks are going to be common diameters or lengths, and those are important. Considering that these cars use much better quality bolts than the old crap I'm used to, I probably wouldn't both replacing them. Especially as big nuts and bolts tend not to get mangled as much as small ones.I would treat the old bolts to a good wire-brushing though.


Smaller, less critical fasteners are fair game though, they tend to be simpler and easier to find exact replacements for. I would suggest a stock of M6 and M8 bolts is a good thing to have; it makes any difference in flange thickness for V6 waterpumps or thermostats irrelevant.

[Diamond Black Geezer]

Thanks all

This is my reason for asking - before posting I looked around on various other forums, as I can't be the first person in history to look at their corroded caliper bolts and think 'hang on, they make these things in stainless steel - and I'd probably get them cheaper than the OEM replacements from the Stealer, too' - but there are issues to be considered when you're dealing with brakes.

I've tried to do my research as best I can, but now I'm trying to just discover what was fitted originally. What is called A4-80 grade Stainless Steel can effectively replace High Tensile steel bolts - they're used in Marine applications, for instance, due to corrosion resistance. That's if Vauxhall used

I think that every auto maker would use 8.8 or equivalent as it's a good compromise between price and strength, but looking for some hard evidence to support this. I just don't want to be caught using belts 50% weaker than spec, that's all. They are the brakes!