Disco 2 Stainless Brake Caliper bolts - Big No-No?

Jamiegreen · May 25, 2018

I, myself like to put stainless steel bolts in whatever hole they fit, nothing worse than a rusty old bolt. Never put them near my brakes though, as to my understanding they don't have the same sort of strength as the steel ones. I just use standard A2 Stainless on my other bolts, although I've been through a few forums and seen mixed thoughts on using them on the brake caliper holder and the brake calipers themselves. Would have been nice once I get my new calipers painted red and clean up the holders, Thoughts?

jamesmartin · May 25, 2018

Jamiegreen said:
I, myself like to put stainless steel bolts in whatever hole they fit, nothing worse than a rusty old bolt. Never put them near my brakes though, as to my understanding they don't have the same sort of strength as the steel ones. I just use standard A2 Stainless on my other bolts, although I've been through a few forums and seen mixed thoughts on using them on the brake caliper holder and the brake calipers themselves. Would have been nice once I get my new calipers painted red and clean up the holders, Thoughts?

not just tensile strength but caliper bolts like many others on your vehicle are special bolts ie specific non std shank length as well as tensile strength,changing such bolts from non standard would invalidate insurance,apart from been stupid

Jamiegreen · May 25, 2018

jamesmartin said:
not just tensile strength but caliper bolts like many others on your vehicle are special bolts ie specific non std shank length as well as tensile strength,changing such bolts from non standard would invalidate insurance,apart from been stupid

Didn't even think of that, with the smooth shank part. Well that just about sums that up since I doubt anyone actually makes stainless versions of them. More regular changes it is, maybe a touch of grease on the head to keep them nice.

jamesmartin · May 25, 2018

Jamiegreen said:
Didn't even think of that, with the smooth shank part. Well that just about sums that up since I doubt anyone actually makes stainless versions of them. More regular changes it is, maybe a touch of grease on the head to keep them nice.

i regularly undo 20 year old unprotected bolts,can be a pain at times if you fitted new every 10 years you be ok,

Nige4927 · May 26, 2018

big no to stainless bolts from me... they just don't have the tensile strength and on something like brakes your risking your safety for a few shiny bits.. they are alo more prone to seizing up..

Stainless steel is the overall name for many steel alloys and they are all have different properties.. the 4 main types are Austenitic, Ferritic, Duplex and Martensitic..

75% of all stainless is Austenitic which has a low carbon content, it is highly corrosion resistant and non magnetic but has poor tensile strength..

Martensitic stainless has a high carbon content and high tensile strength and could be used for you bolts, but here's the kicker.. it has poor anti corrosion properties so you just lost the whole reason to use it in the first place..

you might find this chart interesting

Nige

iansoady · May 26, 2018

Useful little table. Is there a cross reference to grades, eg 303 is austenitic as far as I know?

Nige4927 · May 26, 2018

This video explains all the different stainless steel alloys

Gazbo · May 26, 2018

Jamiegreen said:
I, myself like to put stainless steel bolts in whatever hole they fit, nothing worse than a rusty old bolt. Never put them near my brakes though, as to my understanding they don't have the same sort of strength as the steel ones. I just use standard A2 Stainless on my other bolts, although I've been through a few forums and seen mixed thoughts on using them on the brake caliper holder and the brake calipers themselves. Would have been nice once I get my new calipers painted red and clean up the holders, Thoughts?

20 years back when I worked for a centrifuge manufacturing company, we used stainless socket head cap screws on the bowl and headwall flanges of some machines, particularly in coal washing plants where high sulphur coals increase corrosion rates. The grade bolts we used were A4-80, sourced from Europe, they were pretty suited to the job but strengthwise, (tensile), not up to the standard of an "Unbrako HT", which, if I recall were about 13.9, (standard HT bolts were 8.8), number refers to a tensile strength grade. But as others who know have already said brake caliper bolts are special fit, not only hi tensile, the fit gives maximum shear strength if installed to the right tension, very important in the hard stop situation.

Turboman · May 26, 2018

Gazbo said:
20 years back when I worked for a centrifuge manufacturing company, we used stainless socket head cap screws on the bowl and headwall flanges of some machines, particularly in coal washing plants where high sulphur coals increase corrosion rates. The grade bolts we used were A4-80, sourced from Europe, they were pretty suited to the job but strengthwise, (tensile), not up to the standard of an "Unbrako HT", which, if I recall were about 13.9, (standard HT bolts were 8.8), number refers to a tensile strength grade. But as others who know have already said brake caliper bolts are special fit, not only hi tensile, the fit gives maximum shear strength if installed to the right tension, very important in the hard stop situation.

See it a lot on boats. Everyone thinks it is essential to use stainless, for corrosion resistance.
In practice, stainless often proves to be a weak material, and it can actually cause galvanic corrosion, especially if it comes into contact with zinc, or several other materials.

Jamiegreen · May 26, 2018

Great info there, thanks.
And since on the bolts topic, I fekin snapped this bolt and then while drilling it out, snapped the damn drill bit inside there too, any idea if it will be a problem leaving it out?
just say no.. please

Gazbo · May 26, 2018

Jamiegreen said:
Great info there, thanks.
And since on the bolts topic, I fekin snapped this bolt and then while drilling it out, snapped the damn drill bit inside there too, any idea if it will be a problem leaving it out?
just say no.. please

Those bolts are A2 stainless,no,no,no, do not use A2 stainless bolts for holding a head down, only the original type carbon steel high tensile bolts for that job, and that is a 100% definite.
Definitely yes, it will be a problem leaving it out, you are going to have a head gasket failure without it, and using A2 low strength SS bolts, the bolts will stretch and or fail (fatigue and fracture), giving the same result.
Have you tried gripping the broken drill flutes with a set of long nose pliers and trying to undo the broken bit of the bolt or twisting the drill out?
I'd suggest if your attempts to remove that broken bolt fail you should remove the head and properly remove the bolt end, then replace all those SS A2-70's with the correct HT bolts

Jamiegreen · May 26, 2018

Gazbo said:
Those bolts are A2 stainless,no,no,no, do not use A2 stainless bolts for holding a head down, only the original type carbon steel high tensile bolts for that job, and that is a 100% definite.
Definitely yes, it will be a problem leaving it out, you are going to have a head gasket failure without it, and using A2 low strength SS bolts, the bolts will stretch and or fail (fatigue and fracture), giving the same result.
Have you tried gripping the broken drill flutes with a set of long nose pliers and trying to undo the broken bit of the bolt or twisting the drill out?
I'd suggest if your attempts to remove that broken bolt fail you should remove the head and properly remove the bolt end, then replace all those SS A2-70's with the correct HT bolts

Looks like I really fooked that up then, thanks for saving me on that mess. I'll have to get to the fixings place Monday and see if they have these carbon high strength bolts, or is the part number just for them? Did get the drill bit out and made it to a 8.5mm, so will have to get a new tap and find one of those bolts in M10 1.25.
I really gotta stop removing bolts

Turboman · May 26, 2018

Jamiegreen said:
Looks like I really fooked that up then, thanks for saving me on that mess. I'll have to get to the fixings place Monday and see if they have these carbon high strength bolts, or is the part number just for them? Did get the drill bit out and made it to a 8.5mm, so will have to get a new tap and find one of those bolts in M10 1.25.
I really gotta stop removing bolts

You might be able to fit an insert to size it down again. If you snap bolts, try drilling out and an easy out, instead of drilling to oversize.

Probably not a good idea to fit an oversize bolt, it will be difficult to get the torques even with the others.

Jamiegreen · May 26, 2018

Turboman said:
You might be able to fit an insert to size it down again. If you snap bolts, try drilling out and an easy out, instead of drilling to oversize.

Probably not a good idea to fit an oversize bolt, it will be difficult to get the torques even with the others.

Will see what the fixings place has, would be nice to get the same size bolt in there.
Just curious though, the bolts I took out say "AA 8.8" on them, and look just zinc coated, isn't that a pretty standard bolt strength?

Turboman · May 26, 2018

Jamiegreen said:
Will see what the fixings place has, would be nice to get the same size bolt in there.
Just curious though, the bolts I took out say "AA 8.8" on them, and look just zinc coated, isn't that a pretty standard bolt strength?

Yes. But head bolts shouldn't be 8.8.

Jamiegreen · May 26, 2018

Turboman said:
Yes. But head bolts shouldn't be 8.8.

From what I can tell my other td5 has the same bolts, bolt
heads very worn and rusty but think I can make out the aa 8.8.
These are definitely head bolts right?

Turboman · May 26, 2018

Jamiegreen said:
From what I can tell my other td5 has the same bolts, heads very worn and rusty but think I can make out the aa 8.8.
These are definitely head bolts right?

I am not very familiar with Td5, but most engines have higher tensile bolts than that.

As I cannot see your engine, I do not know where the bolts came from, but you should. I was going from Gazbo's post^^^.

Jamiegreen · May 26, 2018

Turboman said:
I am not very familiar with Td5, but most engines have higher tensile bolts than that.

As I cannot see your engine, I do not know where the bolts came from, but you should. I was going from Gazbo's post^^^.

Sorry pic was a bit further up, here's a better one

Turboman · May 26, 2018

Jamiegreen said:
Sorry pic was a bit further up, here's a better one

I would say those are head bolts. As I said, it is not an engine I know well, although I have serviced them. But the location of those would only suggest head bolts, I imagine the others will be under the rocker cover.

Jamiegreen · May 26, 2018

Turboman said:
I would say those are head bolts. As I said, it is not an engine I know well, although I have serviced them. But the location of those would only suggest head bolts, I imagine the others will be under the rocker cover.

Was just looking at a cylinder head and don't really see how these bolt it down, looks more like they are just sort of holding a top section on or something

Disco 2 Stainless Brake Caliper bolts - Big No-No?

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