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Discussion Starter #1
Yesterday while refitting the rear calipers, one of the nuts on the right side could not be brought up to full torque. The spec in the "AR Alfetta Workshop Manual" calls for 4.7-5.4 kgm (34-39 lb-ft) dry. At about 30+ lb-ft, further tightening did not increase torque. Something is yielding. Not a good feeling. The nut was turned maybe about an eighth turn in this mode. I thought maybe the threads were buggered. However inspection of the nut and threads following the removal of the caliper showed nothing unusual (excellent threads). The thinking was that maybe the spring washer not fully compressed and so a bullish go at 35 lb-ft was attempted. Not sure exactly why, but this attempt was done wet. Same result even with the nut tighten at 30+ over a quater turn.

One other observation. It was noted at the start (before initial torquing) that the studs protruded from the caliper mounting holes 1/8"+ futher on this right side than the left. I thought it odd at the time, "Why weren't they designed the same?".

A BB search found nothing. I'm concerned that the stud is pulling out of the transaxle. Are the studs threaded (best guess) or pressed in (maybe)? Best guess is that at some point in the past, these studs were overtightened and weakened the mount.
Please tell me that's not the case, it's never happened before, they are rock solid, and that I have nothing to worry about.:rolleyes:

Options:
1) Leave well enough alone and leave the caliper as is, torqued at 30 lb-ft.

2) Remove stud from TA to access situation/damage. Repair as needed:
epoxy? helicoil? weld, drill, retap?, other?

The transaxle/ de Dion is presenly out of the car (Yeah, still!:mad:) so repairs now would be easier than later. What is the probability that this apparent weakness will cause a problem later?

Sorry for the long post. I know we are all busy and it is a burden to reply, but your comments are very much appreciated.
Thanks in advance.
Gerry
 

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Gerry,

If the stud is really questionable...

You may want to start with double-nutting the questionable stud to try and remove it, then assess the "cavity" where it resides. You'd rather have the whole thing removed than have it shear off and then have to remove the broken one.

I've seen (but never done myself) JB-weld repairs on applications like this - that is, where most of the load on that stud is not directly outward, but rather a "shear" force. So, if you can get a new stud in there solidly, you may want to. Then, you can assess whether your new stud can handle all of the specified torque, or whether you can get close and then run a second nut on top of it to keep it from backing off at all. I do seem to recall that maybe these studs are an odd pitch, so replacing it with one of another pitch and with more readily available matching nuts might prove to hold more solidly. Just my thoughts.
 

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Discussion Starter #3 (Edited)
. . . If the stud is really questionable . . .
Ah yes, this is indeed the heart of the question. Certainly, something isn't exactly right. If this was the Space Shuttle or something that needed absolute reliablility, well then, it would need to be investigated. However in this case, does the probability of a successful repair greatly exceed the chance that a dubious 30+ lbft torqued caliper will fail. Don't have a feel for that one.


. . . You may want to start with double-nutting the questionable stud to try and remove it, then assess the "cavity" where it resides. . . .
Was thinking that's what you'd say. Not hoping for it though. This de Dion refurb is waaay behind schedule and this car really needs to find storage before the snow begins to fly.

So I don't muck up the transaxle, I think I'll try stud removal on a spare I have. So you think that indeed the stud is threaded into the TA (not pressed in) and the thread is right handed?

Aren't these studs in tension and not shear? I'm not a mechanical engineer but my understanding was that one does not want to put a threaded bolt in shear (except on a shoulder) as the root of the thread form a nice place for crack propagation to begin and that the bolt will fail in such an application, at a much lower shear force than, say a clevis pin of similar diameter. In the case of the caliper, the bolt torque is designed to put sufficient compressive force between the caliper and the TA mount such that the frictional component of that interface is much greater than the side loads. Less bolt torque would result in less compressive force and therefore less frictional force to counter braking loads. Will these loads cause the bolt to loosen over time to a point where the frictional forces are overcome and do then result in the stud being subjected to shear forces . . . and eventual failure? This all seems to strengthen your argument. OK, OK, . . I'm going out right now to investigate further.:p

. . . Just my thoughts. . . .
And just the kind of feedback/sounding board I was looking for. Thanks.
Gerry
 

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Discussion Starter #4
Imagining things?

OK, so I grew a couple and removed the (thought to be) offending stud.

Voila, The right-handed threads look fine on both the stud (different pitch, good call Rob) and the mounting hole. What the hey???
Alfetta Transaxle Caliper Stud - Small.jpg
Alfetta Transaxle Caliper Mounting Hole - Front Right - Small.jpg

So where is it yielding? Or is it just my paranoia? Just didn't seem right - with torque building quickly to about 30 lb-ft and then nothing - holding constant even through an additionaly 1/2 turn+. The torque might have decrease slightly. You know, that uneasy feeling one has right before a bolt strips. And then there was the additional length of protrusion on this stud, consistent with the threads yielding. Oh well.

I will reinstall and give it another go as there doesn't seem to be anything wrong here. But that's not how it felt.:eek:
 

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Discussion Starter #5 (Edited)
Now what?

Why oh why couldn't I have been wrong:mad: Alfetta Transaxle Caliper Mounting Hole - Front Right 2 - Small.jpg
Didn't even have a chance to reinstall the stud. The threads were already gone. At least some of them.

Suggestions for a long term repair?
 

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If you have room to drill and thread, a thread-insert-repair (helicoil is one name brand) will make a repair as strong or stronger than the original threads. Pick the correct size repair kit and you'll have original size threads so no DPO nominations either.
 
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