The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Cano on January 26, 2011, 03:02:03 PM
-
Hi guys. First post. I bought an 81 r65ls that has been sitting for 20+ years. It's got the two piston Brembos on the front, which I'm in the process of rebuilding. Neither Clymers nor Haynes have a torque value for the two bolts that hold the caliper halves together, which seems unusual with the dangers of leakage and warpage. Does anyone have a factory manual they could check to see if any torque values are listed? Thanks in advance for any help.
-
I posed the same question some time back when I overhauled my caliper and I don't think I ever found a published torque value. That was for an ATE caliper though.
I rationalised it this way. The issue is not leakage as even a low torque value would compress the sealing ring between the two halves of the caliper. It more about structural integrity of the caliper under braking forces which are trying to force the two halves apart so I reckoned that meant getting on for as tight as the safety of the threads would allow. That's not going to be much ... maybe only 15 ftlb. Heres a link to my previous thread. http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1270141341/4#0
If you don't find a recommended figure I would look for general guidance on torque values for the size of thread being used in an alloy casting.
-
It does not appear that the microfiche lists that fastener (http://www.realoem.com/bmw/showparts.do?model=0365&mospid=51899&btnr=34_0600&hg=34&fg=05), so I can't get the dimensions. You will have to measure it with a caliper.
Here is a chart for some fasteners. If you don't find it here, just do what I did - Google "fastener torque chart".
http://www.imperialinc.com/pdf/A_FastenerTorqueCharts.pdf
These fasteners are probably cadmium-plated, so you will need to take that into account, as it may change the numbers.
-
Looking at my previous post ATE fasteners were 8mm so maybe Brembos are the same.
Also bear in mind that torque charts are generally listing figures for the various grades of steel fasteners. Truth is I don't know what your caliper material is but I assumed mine was a high grade alloy of some sort which is why I arrived (guessed) at 15 ftlb for the 8mm fasteners approx. 20 - 25% less than the typical figures for steel and I've had no problems.
If in doubt you might want to follow Duane Aushermans advice on torque values and err on the low side. He often quotes his experience as a dealer saying they got quite a bit of work as a result of home mechanics over torquing fasteners but very rarely got work from those who under torqued them. Perhaps do them by feel and then test with a torque wrench very very carefully to see what youv'e got.
-
Thanks for the responses guys. The rebuild kit contains new bolts, and they do appear to be plated. 15 ft/lbs sounds about right with the alloy calipers.
Very happy to have found this site -- hopefully I won't ask to many dumb questions over the next couple of months while I get the bike road worthy.
-
I've always taken the opportunity to replace the OEM plated bolts with stainless whenever I've had Brembos in two pieces. Also the sealing between the two halves depends upon the O ring rather than tightening torque and I've never had a leak from a caliper having tightened the bolts by feel alone.
-
And the Brembos are copies of the ATEs. I'd bet $5 that the fasteners are the same dimension.
The alloy of the caliper may be different, however.
-
I think I piut a light "grunt" on them so 15 ft-lbs is probably OK.