Transverse arm connecting bolt 987186 torque spec mystery

[johnnyfd]

I always liked Skandix ; Hardly ever use them though . As this post has discussed , I have seen a few different terminologies for this, but " bearing bracket " is a new one for me. The found spec of 80 Nm converts to 59 ft lb. Most of these bolts when supplied in the new transverse arm mount kits come with thread locker already installed on them so I don't think those ones would be "self-locking" minus the thread locker and I'm going to assume no compensation is needed for the thread locker especially since it's already dried. I have decided to make a torque compensation for the pinless universal socket I need to access the bolt head though. I'm going to increase the torque spec by 15% for this and also another 5% for an additional attachment to get the socket on the bolt. That will come out to about plus 12 foot pounds for a final approximate torque wrench setting of about 72 ft lb. or 97 Nm . That's pretty close to the 93 Nm you came up with from figuring very different calculation factors than I did. Your post stated 93 Nm is equal to about 60 ft lb, but it's actually equal to 68.6 ft lb. I may be opening up a little can of worms here, but does anyone have opinions on my calculations, particularly the ones which compensate for the swivel socket and additional adapter if needed ? I understand I may be getting into this detail a bit more than is really necessary, but like I stated before, this is making it more of a learning experience for me which I will find very useful in future applications. I'm not an engineer, but I think their knowledge is pertinent in situations like this and I would like to learn how to use that knowledge.

[johnnyfd]

I might even do a mock up with a digital torque adapter in line in order to give me some idea if my calculations are on track or completely off base and full of erroneous assumptions. Once again, all this rigmaro is also to benefit my use in future applications, because I'm tired of hemming and hawing with guessing that often leaves me with nagging thoughts of whether I over or under tightened a fastener.

[abscate]

Ok, a bit of a tome , but here goes.

“ Why torque values often aren’t important “

Fasteners broadly serve three functions.

1, Non critical holding parts on….plastic trim, steering wheel nut,

B. Critical parts holding …wheels, brake calipers.

(iii) critical clamping force …cylinder head bolts, rod bolts, bearing cap bolts


All three don’t care what torque you apply to the fastener , you are given a torque value(s) and procedure to try and generate the design clamping force for the application

This force is a function of three things , friction on the fastener head, friction in the threads, and tension or stretch in the fastener itself, and they roughly equally contribute at the “ design torque” , say 90 Nm for a grade 8,8 M12

When we go to work on an old car, the bolt threads are aged, the part threads are aged, the head might be rough, all of these things work to change the design clamping force at a given torque

Even good torque wrenches have errors of +-5% after calibration , and a rough estimate of torque accuracy as a function of operator technique is even worse, more like 25%.

It’s noteworthy that you never get a torque spec of , for example, 90 +- 10 Nm given in literature. Every engineer would look at a spec and what an error or spec range Analysis.

So let’s cover the scenarios

1, if your too loose your trim rattles, if too tight your plastic breaks and you end up meeting bitter Scots i junkyards in Calgary trying to find parts

B. Too loose, calipers come loose. Bad day. Too tight , stripped metal parts, also expensive bad day. A caliper will stay on at about half indicated torque but who wants to be close to that edge?

iii) cylinder bolts too loose, bad engine. Too tight, up to the point before the head strips , nor problem. Volvo cylinder head bolts are tightened into the plastic regime where the bolts are stretching a few percent under load. That’s why you only use then once, or maybe twice.


Upshot? You can assemble a car without a torque wrench 99% of the time using as a rough guide

Wrist pull on 12 inch handle 10 - 20 ftlb
Elbow pull. ……"…………………..50 ft lb
Shoulder pull…"…………………..100 ft lb

Stand on breaker …your weight x breaker bar length


Back to your rear suspension bolt. I would roll underneath with a 24 inch bar and pull about elbow strength on that one. In a week or two those steel threads are going to meld with the aluminum casting and those parts will mate for life. The actual clamping force isn’t critical, you just need those parts to stay together to avoid embarrassing rear end drags

Your post stated 93 Nm is equal to about 60 ft lb, but it's actually equal to 68.6 ft lb.

My accountant gave me that number, I had nothing to do with it….

[scot850]

So you are saying that there is room for user error on torque wrenches........

So my 35 year old torque wrench is not accurate then........

Good news is that I can now get rid of those pesky bulky tools and go back to shearing bolts like in the good old days..........!

Neil.

[johnnyfd]

I hope this doesn't sound like an obtuse commentary, but if it does I can only plead ignorance with no intention of malice. My objective is to be able to obtain recommended specifications given for fasteners and any possible modifications of those original specifications based on factors that can at least to some degree be calculated for and still come up with an actual number after it all. The reason I want this number so intently is because I know there are so many factors that go into causing inaccuracy of the amount of stretch force actually being put on the fastener. I'm referring to factors like the ones you mentioned ; corrosion on fastener ends, corrosion on threads, any materials / chemicals that would affect lubricity, fastener coatings and torque wrench inaccuracies and variations of user technique. The way I figure it if I have an accurate starting point calculation number it will allow more room for all the inevitable factors arising that I just mentioned. If I start off in the wrong place calculation wise and then throw in a bunch of variability creating factors which are difficult to calculate for then I'm much more likely to end up in the bad zones of truly too tight or truly too loose for the fastener to do its job and not have complete failure. I understand engineers factor in leeway for inaccuracies when using fasteners, but I'm pretty certain that leeway is based on using the correct starting point. I would like to be able to go completely by feel, but I don't think I have worked at this methodology long enough to be able to rely on it. Obviously there are circumstances where I have to use it, but if I can obtain the recommended starting point I will do what I can to acquire it. I know my by feel skills will improve over time because I have to exercise them every time I encounter a fastener which a torque wrench cannot be applied to or is not even required at all.

[johnnyfd]

I forgot to mention that I'm a world-class powerlifter and that's part of the reason why I have a hard time operating without a torque wrench.............. Just kidding of course.

[scot850]

There is a lot of funny guys on this forum! johnnyfd, those of us that like exactitude will always be mocked! Heathens!!

Neil.

[johnnyfd]

Hear hear!

[abscate]

I’ve driven beaters most of my life, and was used to fixing them on the road. Out there, no torque wrenches.

Spend some time with a lugnut torquing it to 10, 25, 50, and 75 ft lbs. see if you can duplicate a torque setting with a 12 or 24 inch breaker bar.

[johnnyfd]

Thanks for the suggestion. I'll try that.