raz Posted March 19, 2009 Share Posted March 19, 2009 Is it OK to replace my front brake rotor bolts with stainless A2 grade ones? Or what should I pick? I recall reading somewhere stainless may be a bad idea due to lower tensile strength. I can tell the old ones were damn soft, half of them were totally ruined when removing them regardless of heat added. Anyway I'm thinking of using cap screws w/ 6 mm socket instead of the original button head 5 mm socket. Should be easier to remove next time. Besides, they are cheaper, look better and I don't think the added height (+3,7 mm) is an issue. Link to comment Share on other sites More sharing options...
Paul Minnaert Posted March 19, 2009 Share Posted March 19, 2009 don't use va for brakes. I got ducati bolts, they have a bigger socket size, and are low. And if it works on a duc... Link to comment Share on other sites More sharing options...
Guest ratchethack Posted March 19, 2009 Share Posted March 19, 2009 This came up a few years back on the topic of caliper bolts, but the same fastener grade applies for rotor carriers, that is, yield strength. From my post in that thread: Stainless fasteners should NEVER be used on rotor carriers or calipers! Wot you're looking for here is not tensile strength, but yield strength. Metric class A2-70 is the typical Stainless Steel known as 302. It's rated at 65K PSI yield strength. Metric class A4-80 Stainless Steel is rated at 87K PSI yield strength. Metric class 10.9 grade is hardened steel, rated at 136 K PSI yield strength. . . . . . . . . . . NOTE: The significant measurement here is half for A2-70 wot it is for 10.9! You should always go a minimum of 10.9 grade here. For greater yield strength yet: Metric class 12.9 grade is rated at 160 K PSI yield strength. 12.9 grade is overkill, but there's no downside to higher yield strength than needed, and wot d'you figure a few buck$ worth o' insurance is worth here? Link to comment Share on other sites More sharing options...
felix42o Posted March 19, 2009 Share Posted March 19, 2009 Doesn't stainless have a tendancy to work harden under load? That's what I have always (maybe incorrectly) thought. Link to comment Share on other sites More sharing options...
Dan M Posted March 19, 2009 Share Posted March 19, 2009 Is it OK to replace my front brake rotor bolts with stainless A2 grade ones? Or what should I pick? I recall reading somewhere stainless may be a bad idea due to lower tensile strength. I can tell the old ones were damn soft, half of them were totally ruined when removing them regardless of heat added. Anyway I'm thinking of using cap screws w/ 6 mm socket instead of the original button head 5 mm socket. Should be easier to remove next time. Besides, they are cheaper, look better and I don't think the added height (+3,7 mm) is an issue. Do not use stainless for anything under stress. I replaced mine with 6mm (steel) socket head as you mentioned and there is no clearance issue. I do like Paul's solution though. Link to comment Share on other sites More sharing options...
Fritz Posted March 19, 2009 Share Posted March 19, 2009 Hello, I am new here and thought this would be a good place to jump in to learn if everything is working as it should. I also am desirous of stainless steel rotor/caliper bolts to eliminate corrosion and believe stainless steel bolts may be adequate. To test this I am currently using 304 SS bolts to retain the rear drive sprocket on my 650cc dual sport bike. Just to clarify, the yield strength is not the shear strength. The yield strength is the limit the material can be stressed and retain its original shape. Additional stress applied above the yield strength permanently deforms the material until the tensile strength is reached and at this point the material fails ( breaks ). The shear strength would be the force needed to shear or cut the material with a force applied perpendicular to the long axis. Exactly how the bolt is affected by the rotor. The shear strength may be higher than even the tensile strength of the component as design is a big factor. The tensile and yield strengths can be increased in alloy and some stainless steels by heat treatment. Higher tensile and yield strengths would produce higher shear strength. You are certainly correct recommending stronger, higher yield strength, bolt for brakes. With a given stress level applied to the bolt, higher yield strength increases the fatigue life, or the number of stress cycles to failure, of the component. Another thing to consider is that aluminum wheels, even if forged of 6061 aluminum and heat treated to the T6 condition, would only have yield strength of 40KSI. 7075 aluminum, used for aircraft, heat treated to T6 can achieve 70KSI yield. The yield strength of a cast wheel would be, - pretty low, I think you say" rubbish". Thanks for your time. Regards Fritz Huss Specialty Heat Treat http://www.specialtyheattreat.com/ Link to comment Share on other sites More sharing options...
Greg Field Posted March 20, 2009 Share Posted March 20, 2009 Do not confuse the rabble with facts. It's not cricket, what? Link to comment Share on other sites More sharing options...
Bruce Reader Posted March 20, 2009 Share Posted March 20, 2009 don't use va for brakes. I got ducati bolts, they have a bigger socket size, and are low. And if it works on a duc... I did the same as Paul- Much better. Link to comment Share on other sites More sharing options...
Guest ratchethack Posted March 20, 2009 Share Posted March 20, 2009 Just to clarify, the yield strength is not the shear strength. The yield strength is the limit the material can be stressed and retain its original shape. Additional stress applied above the yield strength permanently deforms the material until the tensile strength is reached and at this point the material fails ( breaks ). The shear strength would be the force needed to shear or cut the material with a force applied perpendicular to the long axis. Exactly how the bolt is affected by the rotor. The shear strength may be higher than even the tensile strength of the component as design is a big factor. The tensile and yield strengths can be increased in alloy and some stainless steels by heat treatment. Higher tensile and yield strengths would produce higher shear strength. Thanks for the correction, and welcome, Fritz. I'll go back and edit my posts now. Any knowledgeable Pro is always MORE than welcome here. Got to keep the looners on the path, you know. . . I note that shear strength of bolts is seldom given for fasteners, where yield strength is much more readily available. I reckon for this reason, though incorrect, as you point out, yield strength is often used, and more correctly relied upon as a preferred indicator of shear strength, as opposed to looking at tensile strength. . . . but o' course, that's just me. Link to comment Share on other sites More sharing options...
raz Posted March 20, 2009 Author Share Posted March 20, 2009 Thanks guys. OK, no stainless. And an ordinary 8.8 bolt is not strong enough? The OEM bolts seemed so soft I thought they were 8.8. Hell, I could swear they were made out of lead <_> I did consider Ducati bolts too, maybe that is the easiest way to know they are the right type. And as noted they are cap head, 6 mm socket but lower height than usual. I'll probably go for that. Unless they cost several bucks a piece. Link to comment Share on other sites More sharing options...
todd haven Posted March 22, 2009 Share Posted March 22, 2009 Hello, I am new here and thought this would be a good place to jump in to learn if everything is working as it should. Well, all that is well and good, but what does it have to do with feral cats, or the best place for dinner on Tuesday night... Link to comment Share on other sites More sharing options...
Paul Minnaert Posted March 22, 2009 Share Posted March 22, 2009 Duc bots, head height 6.7mm, socket 6mm Link to comment Share on other sites More sharing options...
raz Posted March 22, 2009 Author Share Posted March 22, 2009 Duc bots, head height 6.7mm, socket 6mm Maybe it's the picture but it looks too short. Is that 20 mm? Link to comment Share on other sites More sharing options...
Paul Minnaert Posted March 22, 2009 Share Posted March 22, 2009 that is 15.9 mm, should do it. I have these for years, no problem. here they are: http://www.sd-tec.de/catalog/product_info....52a035dee63996e http://www.gothamcycles.com/servlet/the-76...ke-Rotor/Detail But Ducati now uses the same as Guzzi :-( New ducati part, from 749 and on: http://www.gothamcycles.com/servlet/the-77...ke-Rotor/Detail Link to comment Share on other sites More sharing options...
emry Posted March 22, 2009 Share Posted March 22, 2009 Why not buck up for some Ti bolts. Those are also readily available for Duc's. Link to comment Share on other sites More sharing options...
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