Axle U-Bolt/check torque often

[MTPockets]

I read on this and other forums, many issues related to tire and axle problems and have to wonder if proper maintenance isn't a major cause. I check all my torques fairly often and one of the surprising (to me) is my axle U-bolts are always (so far) under torque spec. Mine calls for 90 ft. lbs and I've checked them now (this morning) 7 times in the last 14 months. We're getting ready to head out next week to the Williston, FL Rally then to Texas, New Mexico, Colorado before we head back to FL in October. This morning I found 14 out of 16 nuts on my U-bolts to be quite a bit under torque spec. My last check was in September and have only trailered since then about 500 miles, so I find this under/torque surprising. Just suggesting for all to keep an eye on yours to avoid problems...... I think I'll put some loctite on the threads next time and the factory should do this the first time.

 

[TeJay]

Here are some thoughts concerning bolt torque and torque wrenches. You may or may not know this information. If you do then great if you don't others will learn. Torque wrenches are sensitive precision instruments. They should be returned to zero when done. They should be calibrated once in awhile. Usually you get what you pay for. A good Snap-On wrench is between $200-400 or more. Torque wrenches are most accurate in their mid-range. If you have a 0-100 Ft. Lb. its most accurate range would be from about 25-75. Even when you have a good wrench there are many variables that effect the final torque. your wrench, your technique, the friction on the bolt threads, the lube on those threads, the quality of the bolt and nut. I was told numerous times over my career that even under the best of circumstances with good equipment a final torque could be off as much as plus or minus 20-30%. When the auto industry began using aluminum everywhere in the engines they had to do something so they would stay together longer. Aluminum has a greater expansion and compression rate than cast iron and it must be clamped together more precisely. Standard bolts would not work so they switched to, Torque to yield" bolts. A T/Y bolt is stretched beyond its elastic limit which will assure correct clamping force but it can not be reused. By switching to T/Y bolts all the usual variables were taken out of the equation and the engines were staying together.
So why am I telling you this??? I remember torquing a few bolts years ago. I wanted to make sure they were correct so I re-torqued them. A few of them seemed loose so I did it again using the same settings. Eventually I stretched a few of them until they broke. I, without realizing it had reached the bolts elastic limit and they had to be replaced. I did not have good control over all the variables. I'm not saying that you are doing this but it is entirely possible. Here's what I do when putting any fasteners together. I clean the threads with a wire brush, place a small amount of lubricating oil on all threads and I mean a very small amount. The amount of oil will change the friction for that thread and you are using some of that torque to overcome the friction on those threads. If you can determine the class of the bold/U-bolt etc make sure that the nuts are of the same class it will matter. In paces like suspensions I will also use lock-tight as you said. However I would use the red instead of the blue. Red may require some heat to remove but blue won't. I don't want my suspension coming apart unless I'm doing repairs.
JMTCW
TeJay

 

[Gary521]

When you are tightening the U bolts, is there a load on the springs or not? This will afffect the final results.

 

[TandT]

If this is factual, this is a bit of a concern. I have pulled my rig 20,000 miles and never checked mine.

When I had my bearings and brakes redone, I believe they checked all the running gear also.

Now on the to-do soon list. (Even though my alignment and tires seem fine.) Trace

 

[TeJay]

Gary521,
I'm always open to learning. How does the load on the spring shackles effect the final torque??? The torque is supposed to stretch a bolt into but not beyond its elastic limit. The tinsel strength of the steel in the bolt provides a clamping force sufficient to keep it from coming apart. If it is stretched beyond its elastic limit then the bolt might eventually break. If it's not stretched close to its elastic limits then it won't provide the clamping force necessary to keep it together. I'm not saying you're incorrect I'd just like to know what you heard about this.
TeJay

 

[westxsrt10]

A u-bolt should only be torqued once, after that go ahead and double nut it if you are worried about the nut backing off. If you keep re-torquing your axel U-bolts get ready for one to break. Bolts/nuts with a gasket being compressed may need re-torquing.

 

[MTPockets]

A u-bolt should only be torqued once, after that go ahead and double nut it if you are worried about the nut backing off. If you keep re-torquing your axel U-bolts get ready for one to break. Bolts/nuts with a gasket being compressed may need re-torquing.

This I don't understand. May be correct, but the Lippert manual says to periodically check the torque. I would think that a U-bolt that stretches to the point of breaking would be a bad design... If I don't re-torque, then I'm running with U-bolts out of spec... I guess I need to know more about this.

 

[MTPockets]

This I don't understand. May be correct, but the Lippert manual says to periodically check the torque. I would think that a U-bolt that stretches to the point of breaking would be a bad design... If I don't re-torque, then I'm running with U-bolts out of spec... I guess I need to know more about this.

Just found this from a "Hensley" trailer manual - regarding axle U-bolts Note: Re-torque the U-bolt nuts regularly starting within the first 200 miles.

 

[MTPockets]

Here is a link to the Lippert Axle Manual .... In it, maintenance suggested is to check suspension fasteners every 6 months/6000 miles. It also says to check U-bolt torque every time unit is taken out of storage. Link: http://lci1.com/index.php?option=com_content&view=article&id=176&Itemid=106

 

[Willym]

Here's another link with some good info on spring U bolts.

http://www.suspensionspecialists.com/tech0004.html#2

 

[57chevyconvt]

Thanks Bill, good info. Have saved in my maintenance file titled "axles and suspension".

 

[Gary521]

This is in response to the load on the springs question. The springs form an arc when off the trailer or no load on them. The mounting plate for the springs that the U bolt passes thru is flat. Torquing the springs with no load on them would be "slightly" against spring pressure. When the load is applied, the actual nut would have less torque on it than without a load. I have an older Corvette with a tranverse rear spring. The attaching procedure for this spring specifically states to have a load applied before measuring the torque.

 

[TeJay]

Gary521
Thanks for the reply. I do like to learn and for the life of me I couldn't think why it would make a difference but now I understand. Bills information from previous post was also interesting and also covered the compression of the leafs in different situations. I've worked on many Corvette's but not on the rear leaf spring.
Thanks again,
TeJay

 

[lwmcguir]

Of all the different trailers we have and have had including all the ones on the Farm & Ranch we never have checked them more than three times. Never had a problem either and if you ask anyone with a bunch of different trailers for different uses you would find they probably never checked them. This is interesting and if the U bolt is getting loose then there is an issue for sure. Checked the Augusta the third time after a year and it was right where I torqued it the first time.

 

[mobilcastle]

If this is factual, this is a bit of a concern. I have pulled my rig 20,000 miles and never checked mine.

When I had my bearings and brakes redone, I believe they checked all the running gear also.

Now on the to-do soon list. (Even though my alignment and tires seem fine.) Trace

Same here-I best check them.

 

[rick_debbie_gallant]

So does that mean we should also be checking the torque on the suspension of our trucks and cars also?? Once something is torqued to specs why would it need to be re torqued? It seems that over time bolts that are torqued or re torqued too many times would eventually fail. 😶🙀🙀


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[MTPockets]

So does that mean we should also be checking the torque on the suspension of our trucks and cars also?? Once something is torqued to specs why would it need to be re torqued? It seems that over time bolts that are torqued or re torqued too many times would eventually fail. 


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The Lippert manual says to check 'em. I know the automotive industry uses a lot of thread lockers (loctite) in vehicle assembly; liquid, encapsulated, etc.. Whether they do on the U-bolts I wouldn't know. They also use a different class of U-bolt which may make a difference too. In this case, since 'my' manual says to check and re-torque, I'll go with that. I would think if a problem occurs, that would be a direct line to Lippert if I follow their instructions.

 

[JohnDar]

Checking them takes all of 20 minutes (OK, I'm slow). Good time to check the tire inner walls, springs, brake wires and spare while you're down there.

 

[TeJay]

I believe MTPockets hit the nail on the head. Our trucks and cars will have a better class of bolt. That means that they have a higher tinsel strength and will be torqued to a higher torque which means that the clamping force will hold it together better. We have all noticed if there is a way to cut costs the TT industry (may??) do it. The auto industry does but they usually won't compromise when it comes to safety perhaps because of law suits. Also the TT industry knows that probably 80% of TT's that they sell see very little usage. So why built a unit that can go 150,000 miles when it might go 20,000???? Dropping from a class 8 to a class 5 U-Bolt would save them some $$. It's also difficult to determine the class of the U-bolt and nut because I don't believe there are any markings like you see on the head of a bolt. It might be marked on the outside of a box but we can't see the box they came it. Yet the solution, if it is a concern of yours, seems to be very simple. At some point during the life of your TT if you want to or feel you have to torque simply remove the nuts, use red or blue lock-tight and torque to specs. In this situation I prefer red because you should not have to remove these nuts again. OK you're done, nevermore to redo.
TeJay

 

[Igotinertia]

I've read the replies you have recieved and there is some good advise in them, in my experience if somthing has been removed, replaced retorquing is a good idea because of the dirt, dust, paint, grease that gets between the surfaces and prevents proper seating. I would not use locktite in this application because you can't check tightness any more except to look for movement of the fastener (fretting as it wiggles back and forth)., if your fasteners are getting loose mark your nuts/ bolts and see if they are turning or streching, two different problems, double nut to lock, or replace bolt/nut remember that nuts and washers are "graded" also. hope this helps, Ben