U bolt nut torque

[Tom S.]

Grayghost, we used to have stamping presses in our plant that were held together with threaded rods that anywhere from 8" to 12" in diameter. It was impossible to torque them tight enough to stretch them the required amount with any kind of equipment we had, so per manufacturer's orders, they were heated with a torch until red hot, then a wrench hooked up to either a truck or a crane would tighten them down. When they cooled, they contracted, creating the needed torque. That was some serious torque stretch!

[Irlpguy]

quote:

Grandpachet wrote:

If there are torque specs of 45-70 i am not going to worry about the recommendation of weight on or off the ground. Checking the torque is important but with the variable numbers recommended it leaves a lot of room for discussion. How could weight on or weight off vary as much as the reommendated specs? Just my .02.

Definitely worth more than .02 Grandpachet, hopefully the vast majority would view this as you have. For those that were originally concerned about damage they might have caused and those that might not think about how illogical this is, then it would be nice to get a definitive answer from Dexter.

There is no need to be an engineer or see this from an engineering point of view, all that is important is those that for whatever reason might ask the question, we can say it either "makes insignificant difference" or "you would see xx lbs difference in doing it one way as opposed to the other".

If indeed there is "any" difference then for sure it will not be sufficient to put you outside the recommended range, especially if you set your torque at approximately the center of the range.

Although it is a PITA, my having to replace both my axles will give me the opportunity to check all this and to recheck the torque at a later date to see if there is any change. I will know what the torque was before my unit moves even one mile, and whether it makes any difference with wheels on or off the ground. Oh yes and I will be starting with all new U bolts.

Can't wait for everyone to arrive for work Monday morning at the Dexter Plant.

[richfaa]

I just made this post "I was a bit confused about the torque on the U bolt so I called Dexter and spoke to Glen who is the rep who is always at the Fall rally'

The 7 K axle uses a 1/2 U bolt and the nut size is 3/4.That is what confused me. Glen said The torque should be between 45 and 70 preferably toward the higher end .I mentioned I thought he said 60/65 at the rally and he said that was a good number.

NOW this is what I do NOT remember him saying..THE TORQUE READING SHOULD BE WITH THE WEIGHT OFF THE AXLE.WE SHOULD JACK THE RV OFF THE GROUND BY THE FRAME FOR THE READING TO BE ACCURATE. I did not have that note in my book from the seminar.

Now I am looking for sound engineering data on the subject. We have many post but no sound engineering data.If I had sound engineering data or could offer it I would never have done the post.

we will get the answer and we will have gained knowledge.
Found this today http://www.suspensionspecialists.com/tech0004.html#2

Note there is NOT a mention of tightening the U bolts with the wheels off the ground...You would think these folks would know HUMMMMMM

[Irlpguy]

Since I am just a layman, I cannot offer any "sound engineering data" but I can offer the following quotes from email responses I have received from Dexter, and to advise that the answer to the "BIG" question will officially be forthcoming.

1) Email from my contact at Dexter.

quote:
Good Morning Ed,

Our Engineering department is working on your questions.

Thank you,

2) Email from Product Engineer to whom my questions were referred.

quote:

Ed,
At this point in time Dexter doesn't have an approved published procedure.
Because of your inquiry Engineering will write a procedure and get it
approved for distribution. Not sure of the timing for completion.

Thank You

3)Second email from Product Engineer in response to my request for an answer to my question at this time.

quote:

Ed,
Unofficially I would recommend that over slung axles be torqued loaded and
under slung axles be torqued unloaded. The reason the under slug is torqued
unloaded is that the vehicle weight is directly working on the tie plates.

I hope this answers your question

It appears Dexter will publish an approved procedure for torquing the U bolts on their axles sometime in the future. I have thanked them for doing this.

I would say it is herein confirmed as I and others have said, there is no weight on the U bolts on an over slung axle but there is on an under slung axle. Although our concern involves only the over slung axle with our Montana's, and not the under slung, therein may lie the possibility of engineering reasons for removing the weight from the U bolts and tie plates, ie: lifting the wheels off the ground.

I think we can all go to bed from now on with the knowledge that checking and re-torquing our U bolts does not require lifting the wheels off the ground.

Now that my new replacement axles have arrived, c/w new U bolts I am looking forward to being able to use my dream home again.

[steelpony5555]

Anybody ever wonder what happens to the hundreds if not thousands of trailers sold to folks who know nothing or don't bother to check forums like this and are happily cruising the highways with their U-bolts straight from the factory.....hmmmmmmmm.... remember we are just a very minor group of owners compared to the number of rigs they have sold over the years.

[simonsrf]

quote:Originally posted by steelpony5555

Anybody ever wonder what happens to the hundreds if not thousands of trailers sold to folks who know nothing or don't bother to check forums like this and are happily cruising the highways with their U-bolts straight from the factory.....hmmmmmmmm.... remember we are just a very minor group of owners compared to the number of rigs they have sold over the years.

Yep, I see at least one every day and wonder how they ever survived.

[richfaa]

Seven pages and we apparently have the correct answer and all I did was ask a question.. You know someone may have asked T.Edison " how come it is so dark in here.

[Irlpguy]

Absolutely nothing wrong with asking the question, however sometimes any of us will question the answer we have been given. I suspect that Thomas would have said "I am working on it, someday darkness will become light". Until then everyone carried on lighting their candles and kerosene lanterns, and the wheels did not fall off.

Steelpony5555, I suspect the vast majority of U bolts are fine from the factory with most being within the specs... We need to strike a balance in reporting things of possible concern to the MOC, otherwise we can cause unnecessary anxiety for some who rely on what is posted here. I hope Dexter will come through with a published procedure which will provide a ready reference to questions we might have regarding U bolts and other parts of their axle assembly.

Not performing regular maintenance and service keeps the repair people in business and we see it every day as was mentioned. I will be going with a young friend to retrieve his tent trailer because he did not check the wheel nuts and lost a wheel and subsequently broke off all 4 wheel studs. Hard to get those broken studs out on the side of the road so he is forced to replace the hub assy. Sometimes we have to learn from experience.

[Art-n-Marge]

Richfaa, two things. First, remember there is nothing wrong with questions since there is NO such thing as a stupid question. I have said in the past and will restate, there are sometimes some stupid answers and I think that dude gave you one that started these 7 pages of discussion.

The second thing is from what everyone has posted, I feel confident that with the range of torque specified for the nuts being from 45 to 70 (that's quite a swing), that achieving this torque with the wheels on the ground is suitable. I have been sleeping just fine several pages back and with a few more pages of posts, I can still enjoy a great night's sleep.

Richfaa, there was NOTHING wrong with your question and it sounds like some overzealous Dexter person talked too much without a good reason (gee, I've never done that). It happens and you can be congratulated on helping us realize that sometimes you should ask several people before deciding on the overall answer. It's kinda like the MOC, where I've posted a question and gotten a range of answers, and collectively I've arrived at THE answer and its conditions. Sometimes it's done in 1 page, sometimes it's 7. It has saved me hundreds of dollars.

[richfaa]

Looking at my first post on the subject I was questioning the off the ground statement as I had not heard that in ANY of the Dexter seminars at the fall rally and we have been to 7 of them. Apparently it was the over slung and under slung issue that was miss communicated and many here suspected that.I myself was clueless. I will now go out and torque my lug nuts to 60lbs.

[robert285rld]

New tires installed - I requested the torgue on the u-bolts be checked and corrected. The results were what others have reported. All were found to be between 20 and 30 ft. pds. Manufacturers spec is 90 ft. Lbs. I feel much safer NOW !!!

[8.1al]

quote:Originally posted by robert285rld

New tires installed - I requested the torgue on the u-bolts be checked and corrected. The results were what others have reported. All were found to be between 20 and 30 ft. pds. Manufacturers spec is 90 ft. Lbs. I feel much safer NOW !!!

Where did you find a spec for 90 ft. lbs., I believed it to be 45-70

[bncinwv]

Beat me to it Charlie, overtorqued can actually be just as problematic as undertorqued since it can lead to u-bolt failure by shearing or twisting the bolt!
Bingo

[robert285rld]

Down loaded lippert components - trailer axle operation and service manual.

[BB_TX]

Sprung Axle Torque Specifications

Axle size Axle Capacity Maximum ft.-lb.
U-Bolts 2k 25 ft. lb.
3.5k w/1/2" 50 ft. lb.
5.2k 65 ft. lb.
6-8k 90 ft. lb.

From page 13 of Lippert Trailer Axle Operation and Service Manual

Oops! Info all runs together. Can't figure out how to space the info into columns. But you can see it on the link.

[8.1al]

Do you have Lippert axles with 9/16" u bolts? Dexter uses 1/2" and specifies 45-70 ft. lbs. Before using that 90 ft. lb number I would make sure I had 9/16 u bolts.

[DQDick]

I agree with Charlie and bingo. For Monty's, up till now, 70# has been the max.

[robert285rld]

I have dexter axles and lippert frame. Are the springs normally attached by the axle manufacturer or by the frame supplier or by a third party? I will have to check the u-bolts diameter next week. Leaving on a 6 month trip in a week. Adjustment can be made very easily if required. Thanks for identfying the potential problem. This forum is great place to gain knowledge.

[BB_TX]

OK, then. From the Dexter axle manual page 66.

1/2" U bolt 45 min - 70 max ft-lbs
9/16" U bolt 65 min - 95 max ft-lbs

[8.1al]

It also says 5/8 100-120, what size are your bolts?