Rebuilding the rear calipers, they have been split, I have read on the forum that I should use new bolts, and I have the following suggested torque settings
7/16 bolts - 55 - 70 ibf -
3/8 - 40 - 50 ibf
5/16 - 20 - 25 ibf
The bolts that I am looking at look like they have a full tread, does that matter the existing bolts are only part threaded and would you use socket head caps?
The bigger question the bolts mounting the calipers through the rear upright, again this is part threaded i would not call it a shoulder bolt but again can I use a full thread bolt of should this be un threaded were it goes through the ally upright. I can not find anyone listing them as spares and the ones I can find for M16 front caliper seem to have an un threaded section that is more than the thickness of the upright, I guess I could use some washers
Any comments on bolts but also on rebuilding rear calipers would be welcome
Lotus Elan+2S 1969
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"Driving a Lotus is a triumph of bravery over intelligence." Stirling Moss
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A well-known UK caliper reconditioner replace with cap/socket head bolts IMHO the best are
Fixing bolts must be the correct length with correct shoulder and they are also drilled for lock wire.
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Very rare to have a caliper bolt/s fail.
And if you read the lotus workshop manual they'll say "DO NOT" split the caliper bodies... why not you might ask? The most likely reason is that some absent minded DIY mechanic just might forget to renew/replace the small O ring seal between the caliper halves.
Most important also to torque the bolts to the correct torque during re-assembly. But alas, the workshop manual does not provide torque figures for the caliper body bolts, but they are just humble HT 7/16" UNF, and to save you the search, the torque loading is 40-45 ft lbs.
Generally, I think people get a bit too pedantic about bolt replacement due to the brainwashing that goes on out there. I built my twin cam engine 35 years ago, and reused the original HT conrod bolts, at the time I had no idea how many re-torquing/stretch cycles the bolts had been through prior to that.... so, have I ever had any trouble, NO, But I will admit that the engine has never been taken beyond the redline, but all the same the engine has been given a good workout over the years.
But the next rebuild will see the old "well cycled" conrod bolts replaced with ARP, because as we all know, it is peace of mind when it comes to an engine rebuild, isn't it.
But getting back to caliper bolts.
The breaking strength of a HT 7/16" UNF bolt ranges from 7850 lbs to 17800 lbs depending on the grade.
How much pressure can one apply to a brake pedal? Not enough to break a caliper bolt, not even one that has been re-used two or three/four times.
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