New Caliper Bolts
12-17-2003, 02:17 PM
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New Caliper Bolts
Is everyone using the new Grade 8 caliper bolts everytime they take off the front calipers? I recall there was discussion that the original bolts are Grade 5 and have a shoulder, the new bolts are threaded all the way to the head and are more brittle. What to do?
Greg H.
Greg H.
12-17-2003, 05:27 PM
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yes thats true to a point. The original front caliper bolts were shouldered, or shanked and 8.8 hardness. New bolts are a bit shorter, threaded the entire length and harder at 10.8 hardness. 10.8 seems too brittle for me to call this a stretch bolt. I reused the originals....
12-18-2003, 02:58 AM
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I am so used to getting my car information here and at P-car.com that I forget about Google. Here is the first hit I got regarding the difference between Grade 5 (the old bolt) and Grade 8 (the new bolt).
Grade 5 vs. Grade 8 Article
One paragraph from that article pretty much sums it up (He is using a .250 inch bolt as an example):
(Quote)
....Again, you can see that the grade 8 will support over 1000 lbs more or a 1/2-ton more. But there’s something more important to note. The grade 5 fastener has already reached its ultimate load and FAILED BEFORE the grade 8 starts to yield or stretch. Therefore, the argument that you should not use grade 8’s because they are more brittle than grade 5’s is not a true statement in most applications.
(Unquote)
He goes on to say that manufacturers generally use grade 5 for cost saving reasons, not because it is better. By the way, I don't know what it is measuring, but 8.8 is the metric equivalent to a Grade 5 and 10.9 (not 10.8) is the grade 8 equivalent.
I don't have the engineering ability to analyze this much further. But it seems to me that Porsche must have had a reason to trade thickness in the shank area for an overall stronger bolt. Also, when would they try to save money, before they sell you the car, or after you own it? I see no reason for them to cut corners on replacement parts.
Greg H.
Grade 5 vs. Grade 8 Article
One paragraph from that article pretty much sums it up (He is using a .250 inch bolt as an example):
(Quote)
....Again, you can see that the grade 8 will support over 1000 lbs more or a 1/2-ton more. But there’s something more important to note. The grade 5 fastener has already reached its ultimate load and FAILED BEFORE the grade 8 starts to yield or stretch. Therefore, the argument that you should not use grade 8’s because they are more brittle than grade 5’s is not a true statement in most applications.
(Unquote)
He goes on to say that manufacturers generally use grade 5 for cost saving reasons, not because it is better. By the way, I don't know what it is measuring, but 8.8 is the metric equivalent to a Grade 5 and 10.9 (not 10.8) is the grade 8 equivalent.
I don't have the engineering ability to analyze this much further. But it seems to me that Porsche must have had a reason to trade thickness in the shank area for an overall stronger bolt. Also, when would they try to save money, before they sell you the car, or after you own it? I see no reason for them to cut corners on replacement parts.
Greg H.
12-18-2003, 02:22 PM
#5
Great article Greg...
I also like this quote:
I also like this quote:
Therefore, you want to make sure you torque your fasteners to the appropriate level using a torque wrench and make sure to torque dry, clean threads. Lubricated threads significantly change the actual preload on the fastener and you risk over torquing it.
12-18-2003, 03:37 PM
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Sometimes fastener torque is specified with a lubricant or anti-seize.
If it is not, then torque with clean, dry threads. Type and quality of plating also affects how a bolt torques.
Chip
If it is not, then torque with clean, dry threads. Type and quality of plating also affects how a bolt torques.
Chip
12-18-2003, 06:26 PM
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Originally posted by chris walrod
yes thats true to a point. The original front caliper bolts were shouldered, or shanked and 8.8 hardness. New bolts are a bit shorter, threaded the entire length and harder at 10.8 hardness. 10.8 seems too brittle for me to call this a stretch bolt. I reused the originals....
yes thats true to a point. The original front caliper bolts were shouldered, or shanked and 8.8 hardness. New bolts are a bit shorter, threaded the entire length and harder at 10.8 hardness. 10.8 seems too brittle for me to call this a stretch bolt. I reused the originals....
Chip
Last edited by 914und993; 12-19-2003 at 01:20 AM.
