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Author Topic: Check those lower caliper locating pins too!
Juan Pineda Verified Driver Made Donation to Website
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I saw the topic on upper caliper bolts last weekend. Coincidentally, I had a lower caliper locating pin fail yesterday. The driver reported that he had long pedal a few times, but then it came back WITHOUT pumping on the subsequent turn. Inspection of the calipers revealed that the threads in the caliper for the lower locating pin were stripped. Presumably that would have cause strange knock back like behavior with the pin allowed to wobble.

The thing I'm really curious about this is that the 65 ft-lbs torque spec for this pin seems really high for the thread size. I religiously torque to this spec. I'm wondering if for racing purposes, where we are pulling this pin out frequently to change pads, whether that spec is perhaps too high. Probably many people torque by hand anyway and don't realize that the spec is actually higher than would be typical for that size bolt.

-Juan

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www.ArtOfRoadRacing.com Race Craft Clinic - Thunderhill - 30 Jan 2011

fishguyaz
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Year : 99
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sounds like its time to drill some holes for safety wire on my car
thanks juan

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Josh Pitt
AZ Region

wheel Verified Driver Made Donation to Website
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Safety wire is the answer. You can never go wrong with safety wire. Safety wire has saved my life. Safety wire has save my race cars. Safety wire is way better than lock tight, and I love lock tight. I have never not tightened a bolt that requires safety wire.

wheel

Glenn Verified Driver
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How would you safety wire the caliper slide pins? Just asking......

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Glenn
Crew chief Meathead Racing, NE Region Sales Division Race Engineering, The GOLD standard in SM engines, Occasional race slave for OPM Autosports

Keith in WA Verified Driver Made Donation to Website
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I don't have the bolt in front of me to see the size but here's a chart of recommended torque values...

http://www.portlandbolt.com/technicalinformation/bolt-torque-chart.html

If the bolt is lubricated and you torque to 65, you could definately overtorque it. Those values are half the dry torque. If you don't return your torque wrench to zero after use, you could wind up with a bad wrench and overtorque it that way too.

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Keith Novak
(Will work for tires)

Gibscreen Verified Driver Series Champ
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Year : 1995
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I've encountered this issue on my 1.8L. That caliper has a 17mm bottom bolt and a 14mm for the top bolt (I believe it's reversed for the 1.6L). The torque spec in the factory workshop manual for both is around 62 ft-lb. This seemed high for the 14mm, and after stripping it, this thought was confirmed.

So now I torque the 14mm bolt to 43 ft-lb (with loctite), and I torque the 17mm bolt to 62 ft-lb per the spec.

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Rob Gibson
RJ Racing
2010 NASA Nationals TTE Champion
2008/2009 WERC Champion
2007 NASA SoCal SM Champion
rjracing.net
Weekend-Racer.com

Juan Pineda Verified Driver Made Donation to Website
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Rob,

Are the threads same size/pitch top and bottom?

-Juan

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www.ArtOfRoadRacing.com Race Craft Clinic - Thunderhill - 30 Jan 2011

B Wilson Verified Driver Series Champ
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Bruce Wilson
2010 Oregon Region Champ
2010 Monte Shelton Driver of the Year
2010 25 Hours of Thunderhill E3 and Under 2 liter Overall Champion
Oregon Region SM Class Advisor

Juan Pineda Verified Driver Made Donation to Website
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Actually, the 1990 shop manual (PDF distributed through sm.com) shows 33-40 ft-lbs for top bolt and 58-65 for the bottom. But the drawings look strange, and the bottom bolt is shown with a head smaller than the shank, like the bottom pin on the rear caliper. So there would appear to be some confusion in the manual about which bolts are used where.

-Juan

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www.ArtOfRoadRacing.com Race Craft Clinic - Thunderhill - 30 Jan 2011

Gibscreen Verified Driver Series Champ
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quote:
Originally posted by Juan Pineda:
Rob,

Are the threads same size/pitch top and bottom?

-Juan

No. The size of threads is smaller on the 14mm bolt. Without putting calipers on it, I'm guessing it's an M8 thread which would make the 17mm an M10.

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Rob Gibson
RJ Racing
2010 NASA Nationals TTE Champion
2008/2009 WERC Champion
2007 NASA SoCal SM Champion
rjracing.net
Weekend-Racer.com

Gibscreen Verified Driver Series Champ
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Car #: 23
Year : 1995
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quote:
Originally posted by Juan Pineda:
Rob,

Are the threads same size/pitch top and bottom?

-Juan

No. The size of threads is smaller on the 14mm bolt. Without putting calipers on it, I'm guessing it's an M8 thread which would make the 17mm an M10.

--------------------
Rob Gibson
RJ Racing
2010 NASA Nationals TTE Champion
2008/2009 WERC Champion
2007 NASA SoCal SM Champion
rjracing.net
Weekend-Racer.com

Randy Thieme
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quote:
Originally posted by Juan Pineda:
The thing I'm really curious about this is that the 65 ft-lbs torque spec for this pin seems really high for the thread size.

Not sure the exact origin of those high numbers but a few years ago there was a popular book on street performance tuning Miata's (book title and author withheld). That book cites 62-ft lbs for the lower pin on the rears. (I still have the book.) A few years back I unwittingly used that number and eventually stripped a bracket.

The 1993 Workshop Manual lists 25-29 ft-lbs for the lower pin on the rears (page P-28, paperback version). Nothing for the upper pin. But the illustration does not completely match the merchandise. The drawing shows what appears to be a flange bolt instead of a pin.

Keith in WA Verified Driver Made Donation to Website
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Interesting. I just looked at the torque specs for grade 8 bolts, metric vs. SAE and was suprised to find that metric bolt torque specs are MUCH lower than SAE of roughly the same size. M8x1.25 is less than 20 ft lbs dry.

The threads in the bracket are longer than a normal bolt...which could account for higher torque allowables but still seems fishy.

--------------------
Keith Novak
(Will work for tires)

Juan Pineda Verified Driver Made Donation to Website
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The torque also depends on the bolt grade (also thread pitch.) I'm guessing that locating pin is 12 grade because it is side loaded vs the typical fastener that doesn't experience significant side loading and can be grade 8.

-Juan

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www.ArtOfRoadRacing.com Race Craft Clinic - Thunderhill - 30 Jan 2011

Randy Thieme
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quote:
Originally posted by Keith in WA:
Interesting. I just looked at the torque specs for grade 8 bolts, metric vs. SAE and was suprised to find that metric bolt torque specs are MUCH lower than SAE of roughly the same size. M8x1.25 is less than 20 ft lbs dry.

The threads in the bracket are longer than a normal bolt...which could account for higher torque allowables but still seems fishy.

Keith - looking at 8.8 or 10.9? M10.9 is the metric equivalent to Grade 8. The rear-brake lower slider pins on the are one of the few odd-ducks in the NA Miata's. They're M9x1.25.

Keith in WA Verified Driver Made Donation to Website
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Freakin metric system!

--------------------
Keith Novak
(Will work for tires)

Randy Thieme
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[laughing] Don't get me started on JIS vs. DIN! (Or why the heck do I have to starting packing a 13mm wrench in my toolkit just cause I went to the hardware store?)

Keith in WA Verified Driver Made Donation to Website
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quote:
Originally posted by Juan Pineda:
The torque also depends on the bolt grade (also thread pitch.) I'm guessing that locating pin is 12 grade because it is side loaded vs the typical fastener that doesn't experience significant side loading and can be grade 8.

-Juan

I don't know that I'd agree with the side loading and bolt grade part. I think the ability to slide and rotate freely on one end takes a lot of stress out of the whole system but not a discussion I'm going to get into in any depth in tonight. I'm pooped and if I'm not getting paid for it or a ride, find your own stress guy. [Smile]

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Keith Novak
(Will work for tires)

B Wilson Verified Driver Series Champ
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I love it when engineers get pooped! [Smile]

-b

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Bruce Wilson
2010 Oregon Region Champ
2010 Monte Shelton Driver of the Year
2010 25 Hours of Thunderhill E3 and Under 2 liter Overall Champion
Oregon Region SM Class Advisor

Kyle Burkhardt
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Is the above poster correct that this is not a problem on 99's? I'm running Road America next year and want to be prepared.

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Kyle Burkhardt
NASA Midwest
#12 SM

B Wilson Verified Driver Series Champ
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Who me? in the other thread? I was just being sarcastic/busting balls. Since the 99 guys keep saying our NA cars are old -- becuase 12 year old cars a WAY newer than 17 year old cars [Smile]

Be prepared! have some spares on hand, not a real big deal, but something to check at least once in a while.

-bw

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Bruce Wilson
2010 Oregon Region Champ
2010 Monte Shelton Driver of the Year
2010 25 Hours of Thunderhill E3 and Under 2 liter Overall Champion
Oregon Region SM Class Advisor

Kyle Burkhardt
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Thanks.

--------------------
Kyle Burkhardt
NASA Midwest
#12 SM

   

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