Caliper rebuild with Stainless bolts....

[catso]

In tidying up my brakes on my project Monster I have dismantled the rear caliper and one of the bolts is badly corroded - looks like brake fluid has got onto it, also they are both shabby looking and cleaning/polishing removes the plating so they will subsequently rust, fortunately the threads in the caliper are fine.

Now I've got some Stainless bolts of the correct size (M8 x 40) and they would look much better and of course not rust and I know that stainless steel is not as strong and therefore not recommended for high-tensile use, so what's the consensus on using stainless bolts to hold a caliper together?

I mean what's the worst that can happen?....

[Vidal Baboon]

Ooooh, i'm interested in this too as I was pondering that very same thought.

My calipers are also sat on he bench ready for some luvvin.

[sjtscott]

You asking advise on here for a safety critical item?
Personally replace them with brand new identical calliper manufacturer recommended items or at least ask someone technical if the bolts you have would be ok. I wouldn't want to guess.

[jp-speed-triple]

catso said:

not as strong and therefore not recommended for high-tensile use, so what's the consensus on using stainless bolts to hold a caliper together?

[catso]

jp-speed-triple said:

catso said:

not as strong and therefore not recommended for high-tensile use, so what's the consensus on using stainless bolts to hold a caliper together?

Well I agree to some extent, however they are big bolts and it is a rear caliper (a Ducati one at that) so doesn't do an awful lot of braking and a stainless bolt has got to be stronger than the manky, corroded bolt that was in there.

I'm certain the original bolts are many times stronger than neccessary, I wonder what 'safety margin' Brembo allow on the spec?

[Fleegle]

I could fix my rear caliper on with cable ties for the use it gets

[catso]

Fleegle said:

I could fix my rear caliper on with cable ties for the use it gets

Well that's also the case for me, almost never use it.

The rear brake on my 916 is used for holding the wheel whilst torquing up the wheelnut and for the MOT test, the 12 year old (original) pads still have plenty of meat on them...

[Vidal Baboon]

They do them for my bike, so they must do something for the Brembo 4 pots...

http://www.tastynuts.com/Products/ZX7R_P1P7_95_Nin...

[catso]

Vidal Baboon said:

They do them for my bike, so they must do something for the Brembo 4 pots...

http://www.tastynuts.com/Products/ZX7R_P1P7_95_Nin...

Interesting, they also do them in Titanium which is less strong than Stainless (I think).

And the caliper I'm fixing is a 2-pot rear caliper, yet the bolts appear to be the same (size and quantity) as used in a 4-pot front which must put much more pressure on them.

[Hooli]

I know a lot of people who have changed front & rear calliper bolts for stainless without the calliper exploding in use.
It might not be as strong but it sure seems to be strong enough. I expect a lot of the reason such a big bolt is used is just so it's harder to strip the thread in the alloy rather than the strength of the bolt.

[catso]

Hooli said:

I expect a lot of the reason such a big bolt is used is just so it's harder to strip the thread in the alloy rather than the strength of the bolt.

Indeed, it really would take something to break the bolt and there must be some corroded ones around, I've never heard of one breaking.

Interstingly the radial front calipers on my 916 use smaller (but more) bolts holding them together

[Condi]

Is there not a rating on them? 8.8, 10.9 or 12.9 are common strengths. If your stainless ones are the same as what came off they will be fine, if they are less then they might also be fine, but it wont be recommended by the manufacturer.

[catso]

Stainless bolts are a standard A2-70, there's no visible markings on the old bolts.

Found this chart online re. strength compared to steel;



From; http://www.volksbolts.com/faq/basics.htm

So not as strong as 8.8 steel, although stronger than 5.8 but my point was how strong do they actually need to be? I'm sure there's some serious over-engineering going on here.

[bimsb6]

i would change them in an instant and never give it another thought ,harrison billet calipers have always used stainless bolts in their calipers .

[Vidal Baboon]

Surely someone that's bored & geeky enough could work this out.


Size of M/C cylinder & Size of Caliper Pistons

Max pressure exerted on the M/C = Max pressure exerted on the Caliper Pistons

Distance of bolts from the applied force- centre of pistons

=Force applied to the body of the caliper.


If it falls within the chart then you know it won't shouldn't fail
There's probably alot more to it than that- but then, i'm no engineer!

Edited by Vidal Baboon on Tuesday 19th October 15:22

[Grommit]

Fit them, jump up and down on the brake pedal, if they snap bin them, if they don't then they should () cope with normal braking.

[Threeracers]

Fleegle said:

I could fix my rear caliper on with cable ties for the use it gets

Coincidentally mine was until I had to get it sorted for a recent MOT!

A thread was u/s and the bolt fell out so a cable tie held the brake lever in place until I had helicoil and a new bolt fitted for the MOT.

[catso]

Grommit said:

Fit them, jump up and down on the brake pedal, if they snap bin them, if they don't then they should () cope with normal braking.

I'm pretty sure the threads would pull out of the (alloy) caliper before the bolt snapped, besides it's a Ducati rear brake so there's probably not enough pressure to squash a piece of Parmesan cheese...

[catso]

bimsb6 said:

i would change them in an instant and never give it another thought ,harrison billet calipers have always used stainless bolts in their calipers .

That's what I'm going to do. So the next question, since stainless will bind in alloy - do I use threadlock or anti-seize grease on the bolts?

[Hooli]

catso said:

bimsb6 said:

i would change them in an instant and never give it another thought ,harrison billet calipers have always used stainless bolts in their calipers .

That's what I'm going to do. So the next question, since stainless will bind in alloy - do I use threadlock or anti-seize grease on the bolts?

I ALWAYS copper-slip them.