Lotus Elan

Rear Caliper

PostPost by: BullAndrew » Sun Jun 11, 2017 10:13 pm

Hi Guys a couple of questions

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

Thanks
Andrew
Lotus Elan+2S 1969
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PostPost by: tedtaylor » Mon Jun 12, 2017 2:41 am

I used the same bolts over again... :oops:
TED
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PostPost by: shaun » Mon Jun 12, 2017 4:52 am

So did i
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PostPost by: Craven » Mon Jun 12, 2017 10:33 am

Hi,
A well-known UK caliper reconditioner replace with cap/socket head bolts IMHO the best are
http://www.unbrako.com/images/downloads/engguide.pdf
Fixing bolts must be the correct length with correct shoulder and they are also drilled for lock wire.
Ron.
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PostPost by: ceejay » Mon Jun 19, 2017 2:01 am

Have owned S2 elan for 35 years, have pulled apart/reconditioned both front and rear calipers three or four times in that period and have never replaced caliper bolts... close inspection is required though, check threads are OK, check that there is NO corrosion along the shank, clean bolt threads with rotary wire buff, degrease and carefully check items again.
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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