Ubolts under torqued

You cannot " check " the torque. The only way to verify the torque is to completely loosen then torque the bolts in the specified pattern with a known good torque wrench. In other words start over from a completely loose condition.

 

This is true, I was wondering when somebody would point this out.

However, if you can turn a nut to tighten it up, then it means the bolt is free and clear to be gauged by a torque wrench.

If all you can do is loosen a nut, can't tighten it, then you can't get a good torque reading, you have to start from square one. If you can tighten a nut or bolt, then you know you have a good basis, you can get an accurate torque reading.

 

haha , like hell you can't check torque, take your "known good torque wrench". pre set it to desired spec. & just start slowly pulling back with even pressure until the "click" or the shunt "gives" some..

 

Why is this in 2nd gen? J/K Doug! Rep for you old man for shining light on this issue.

 

I don't really know iif it's an issue ( personally it is for me) I just know theres nothing out there I put a wrench to that 37 lbs is enough for any Ubolt on an axle....

 

The only change I noticed was that it became MUCH easier to shift. In stock form I had to put into neutral, count at least 4 shakes (oscillations of that rear axle), and then try to put it into gear; otherwise it locked me out of the next gear, sure as shootin'. Now I just shift the truck more normally. I thought it was just the crappy yota springs at first giving all that axle wrap, but it wasn't entirely the case.

On that badly mistimed shift I somehow had it into 2nd gear fast enough that it unloaded the springs against the driveshaft, essentially slowing the rear axle for a split second and putting the two of us hard into our seatbelts and the pizza onto the dash even though the truck was under throttle. It was bad enough for a momentary chirp from the tires as they were dragged down the road (it was during the harsh deceleration). For a split second I expected to see my axle driving away in my rear view mirror. Scared the crap out of me. I've mack truck shifted ever since.

From now on u-bolt torque will be one of the first things I check after buying a truck.

 

Nope. That is incorrect.

You cannot " Check " the torque this way due to the " breakaway " torque needed will give you a false indication that it is up to the torque you have the wrench set to and it could actually be too low. You could also over stretch the bolt and cause a failure.

You also cannot back it off and get an idea of what the torque was set to as the loosening force is not an indicator either.

The Only acceptable and accurate way is to loosen the bolts. Then torque the bolts back to the specified torque in the correct pattern. If the bolts are properly torqued to begin with there is no reason to go back and check it again later.

This is all basic mechanic stuff. Sorry if you disagree.

 

I'm sorry you don't understand what i said, I didn't suggest backing ANY nut off to recheck a torque (?????? ) .. And where the hell did I say backing it off would give any indication of torque ??? don't you pre set your wrenches ??? that wrench responds to pressure my friend & your statement of :

If the bolts are properly torqued to begin with there is no reason to go back and check it again later.

is total BS



This IS basic mechanical stuff.......

Most professionals ALWAYS recheck what they've done, are you going to tell me that if you rebuild a motor & you plasti gauge a journal, you're not re checking or retorquing ?? Oh thats right, you hit it once & walk away never to return ....

Dude, I'm not a professional, but I'm not an idiot ... so don't try to talk down to me like I am...

my whole point to this thread was to have people check their U bolts for the ridiculously low sum of 37 lbs which by all accounts would seem to be a typo, regardless anyone who really thinks that amount is kosher for holding a 400lb + axle assembly together thru the on road/offroad twisting & pull etc: doesn't have any business with a wrench in their hands, tell ya what , you take that "theory" of yours & go lay it on some of the dez mobbers in some other forum & come back & give us a report......

sorry if you disagree.....

 

Hey don't get your panties in a twist. I never called anyone an idiot nor am I talking down to you.

I'm also not saying that 37 Ft lbs is the correct torque either.

If you would stop being so defensive and read what I am saying. The accepted torque method in general terms is to torque at 30% in a crisscross. Then torque at 70% in the same crisscross then 100% in the same crisscross. Then again at 100% in a circular. In some applications they will recommend that you allow the joint to set for 24 hours then torque at 100% again in a circular pattern ( this is usually in the case where a gasket is involved ). After that it should not back off as it is properly loaded.

There are better methods available for torquing fasteners, but they are well beyond the equipment available to most mechanics.

When you attempt to check the torque by turning in a tightening direction it could and often does over stress the bolt and stretches it beyond its safe limit and the bolt strength is compromised. This will and does cause a bolt failure and breakage. When you use this method it is not an indication of a proper torque. You are just seeing the breakaway torque value which is going to be a much higher value than the running torque that you want to measure.

If you feel that the U-Bolts are under torqued you should check them. I agree 100%. However if you are going to check them at least do it correctly. This is not ( contrary to your belief ) a theory. These are the facts.

I don't even know what a " dez mobber " is. I don't think I want to know.

 

Oh no worries, no panty bunching here, i read that brochure too ...

if I took your analogy as condesending thats my problem not yours, so no big....

I am curious tho' , how many axles have you dropped in the last week, last month.. ?? I'm sorry bro' but when you call me out with this "Thats incorrect" bullshit, all I can do is laugh & I'm not saying you're wrong in the " right out of the big book of torque specs" that you attempt to make your case & I appreciate that, but you really should find out & talk to some of these guys that just haul ass thru the desert all the time & you WILL get an education into what torque & tightness is really all about, I seldom use a torque wrench to re tighten the already used U bolts my clients have on their trucks , I raise & lower axles & R&R springs all the time & you can ask anyone of them about coming back for a tightness determination (dont even feel like saying torque anymore)


What can you tell me about axle shims ??

 

I didn't call anyone out. I just wanted to clear up a Common Misconception about checking the torque of a bolt. Any bolt, not just U Bolts or rear end mounts.

You cannot "Check the torque" of any bolt that has already been torqued. I have been turning wrenches since I turned 15 years old, I am presently 57. I don't need a lesson on torque or tightness. Thanks for the offer anyway. :\

I don't know what this brochure is you are talking about.

If ( as you say ) you are not using a torque wrench to re-check on your clients U Bolts and you say that you check the "tightness" please explain how this is done properly without over stressing or stretching the bolt. I'd really like to know. A calibrated elbow theory method isn't working for me.

What can I tell you about axle shims?

Probably nothing without getting you all fired up again. Take my advice or leave it. That is your call. I say do it correct or don't do it at all.

 

If going from 37# up to 73#, there is no reason to loosen the bolts. To go lower, you always have to loosen past where you want to be and tighten up to the torque you want. It's as simple as that and you both know it. You two need to knock it off or no Luby's for a month.

The opinion of some of the farter smellers on this topic is that the 37# is a typo and it should be 73#, which makes a lot of sense to me, so I tightened mine. Again, if someone has some evidence of why they should be at 37#, post it up. I will then use the proper procedure to loosen first and retighten to 37#.

 

Hahaha, ohhhhhh people ... I give up.....


Just remember to maybe check your bolts , or not... or send your trucks to M.I.T. for a team of technicians to do it for you...

Who even fuckin' cares now anyway....

Disregard this thread, apparently I don't know wtf I'm doing... I'm so ashamed....... jeeezus.....

 

I find it funny how the biggest argument in this thread is irrelevent, and both sides are correct, at least to a point. While it is very true you cannot precisely check torque (fastner tension load to be more specific) without backing a nut off due to breakaway torque, it's really not a factor if the nuts are "backed off" to begin with. The difference between breakaway torque and actual torque is 10-15%, so if the nuts were torqued to 37 originally, they should start to move at a little over 40 ft lbs, barring any corrosion and seizing. Just like torquing in stages.

And anyone who retorques ( to the same spec they were originally torqued to) their ubolts will know from experience that even with the factor of breakaway torque, it's very common to have most if not all of the nuts move a bit. All which means there was even less actual tension on the u-bolts after things settle in. Fastner tension is what keeps things tight, not torque. Torquing is just a way to get the tension in the right range.

 

So the u-bolts are 14mm right? I have not measured mine.

I am a mechanical engineer and consulted one of my torque charts.

For a class 8.8 bolt, which has 92.8 ksi yield strength and a 116 ksi ultimate strength

14mm...........

Torqued dry: 107 ft/lbs
Torqued lubed: 76 ft/lbs

Just to muddy the waters a bit.

 

14mm is correct. I found this link as well that has some thumbnails attached with charts.

http://www.fjcruiserforums.com/foru...2814-nuts-bolts-sizes-wrench-equivalents.html

This refers to standard bolts, not flanged nuts on a u-bolt, but I would think it is pretty close. Even with the lightest grade bolt the torque is much higher than 37#. I'm thinking 90# is probably about right.

 

OK, so now you've all riled up a little paranoia in me.
I'm no mechanic here, so just trying to apply a little common sense.

So, if my 5 month old 2012 was factory torqued to 37# and someone said, "no, it should be 43#" (a 15% increase), I would have figured that it would be difficult to tell with my torque wrench what the actual torque really was given the break-away resistance need be overcome.

However, if you say, "no it should be 73#", I would have guessed that if I set my torque wrench to say 37# and it clicked without turning I would know it was probably more than that. If I incrementally increased by 10-15 # and reapplied the wrench and it kept clicking, I would know that it was still higher. If I got to 75# and it still clicked without turning I would know that I was within 15% of of the desired value and have not risked going over. That would be good enough for me.

If the wrench turned at, say 50#, before clicking I would know to continue to 75#. Does this sound reasonable?

(boy, that's a lot of words for something that seems intuitively simple)

Now Nat brings up another variable: lubricated thread.
I almost always apply anti-seize to most bolts including lug nuts (not including valve covers, head bolts and the like, which I don't usually mess with).
>Would that affect the torque spec in this case?
>Would application of a penetrating oil before "re-torquing" affect the outcome?

 

Lubricated threads do make a big difference in fastener tension, more specifically the torque required to achieve it. Post 79 on the previous page gives an accurate picture of this.

 

Thanks Landphil.
That is exactly the post that prompted that part of my question.

>So, I'm interpreting that to mean you would need less "torque" with a lubricant to achieve the same amount of "fastener tension" . Right?

>OK, how much less?

Is it proportioal to the numbers that Nat posted as an example?:
Torqued dry: 107 ft/lbs
Torqued lubed: 76 ft/lbs

(are these maximum loads for Grade 8 14mm bolts??)