CAUTION! - Dexter Axles - Developing Trend?

[Cate&Rob]

About 28 seconds into this LCI video is a quick look at the automated nut runner and digital torque check that LCI uses to assemble the spring to the axle. https://www.youtube.com/watch?v=7k-jikB0S9w GDRV receives the axle with the springs already installed as shown in the video. I didn't go looking for a Dexter assembly video, but their process is likely the same. Just FYI.

Rob

[howson]

About 28 seconds into this LCI video is a quick look at the automated nut runner and digital torque check that LCI uses to assemble the spring to the axle. https://www.youtube.com/watch?v=7k-jikB0S9w GDRV receives the axle with the springs already installed as shown in the video. I didn't go looking for a Dexter assembly video, but their process is likely the same. Just FYI.

Rob

So is the issue the nuts are backing off the bolts from their original torque settings or through break-in of the running gear the bolts and nuts require retorque? I'm well short of being a shadetree mechanic, but if it's the first problem there's multiple ways to set a nut in place. If it's a break-in or wear-induced issue, then we must concede the previous advice to "check your nuts often" is the only remedy.

[Cate&Rob]

So is the issue the nuts are backing off the bolts from their original torque settings or through break-in of the running gear the bolts and nuts require retorque? I'm well short of being a shadetree mechanic, but if it's the first problem there's multiple ways to set a nut in place. If it's a break-in or wear-induced issue, then we must concede the previous advice to "check your nuts often" is the only remedy.

A U bolt is different than a regular bolt. It is a long hoop with a nut on each end that may or may not nest tightly to the axle tube all the way around when first installed. In my case, I installed and torqued new U bolts. A thousand miles later I checked the torque and several nuts needed up to half a turn to regain the original torque setting. Another thousand miles and another recheck found that all nuts stayed very close to their original torque. This is the same concept as checking wheel lug torque 50 miles after installing a wheel. Sometimes, assembled things shift a little in first use. Now, I will check them once a year when I grease the wet bolts, but I don't expect to find any loosened torques on the U bolts.

Rob

[MidwestCamper]

Lots of good information in this discussion! I think the message to GDRV is that checking U bolt torque must be on the dealer PDI. The rig probably left GDRV with the U bolts torqued correctly. The suspension attachments working through the paint on the axle during the delivery trip to the dealer could be enough to reduce the U bolt tension as much as discussed in this thread. Given everything we know about the dealers, every RV owner should own a torque wrench and use it on suspension attachments and lug nuts.

Rob

Rob,

This looks like the best solution since in BigGuys situation his U bolts were excessively loose and I have to believe they left the plant properly torqued as well. Once the RV is delivered, the U bolts and other components could shift where the PDI check would catch this issue. After this, the U bolts are still part of the maintenance schedule that the customer is responsible for. I would not have found the 6K miles U bolt check that Lippert has in their manual if this thread was not started.
A week and a half ago, I checked my newly installed U bolts the next day and found some to be slightly below the 65 lb-ft I torqued them at. And this was with no road miles, so there must be some stretch involved in this process as well. This is OK if the original specified torque is taking this into account. I towed my Imagine about 150 miles since that time and will check the torque again this evening when I get home. Playing near the lake Erie islands.

[BigGuy82]

Guys,

This thing did not leave the factory with the correct torque on the U-Bolts. U-bolts on leaf springs are used in millions of vehicles and they don't normally have this problem - how often do you check the U-bolts on your truck springs? Are your truck springs basically the same or are they somehow different so that they keep their torque? Do you think that your truck dealer does a PDI and checks the U-Bolt torque? This more or less invalidates the stretch or paint theories. When there is a discrepancy of 30 to 40 ft.lbs. from specified torque, that's not due to paint rubbing off, U-bolts flexing or <2,000 miles of travel (or any combination of those). Also, the machine you showed in the video can of course be mis-calibrated (I remember a while back when there was a rash of Heartland hydraulic leaks due to an improperly calibrated crimper). Also, the interesting part is that you would think a machine could bring them down evenly. Oh well.

End of the day is simple - in a past life I was an actual working mechanic (although many years ago). I have been working on my own rigs forever, I know about what affects torque, I use a calibrated torque wrench and I have never heard of properly torqued U-Bolts loosing this massive percentage of torque in only 2,000 miles of operation. I have also never heard of a dealer checking U-Bolt torque as part of the PDI but I've already left an email asking that of my dealer.

It's easy to not be able to effectively communicate tone in a post so let me explain - I'm not at all upset by your opposing views. I just very much disagree with them and I think that GD is getting a pass on a potentially dangerous situation. So, whatever the cause of this problem, I'm trying to get them to address it - whether it requires different manufacturing protocols or insuring that their dealers include this in their PDI. I'm not going to add another comment this thread until I hear from Grand Design and my dealer service manager, at which time I'll post their responses. That way we can avoid circular arguments.

Safe travels.

[gbkims]

One thing about the trailer u-bolts I noticed was the type of nut used.
For u-bolts I saw references to "hex nuts" and to "deep nuts".
I see that many u-bolts and tie plates sold for trailers have the "hex nuts", which look like what TTs & 5th wheels are shipped with.
The u-bolts sold with lift blocks and sold for truck springs have the "deep nuts."
I had noticed the difference in the nuts when I bought my lift blocks kit.


https://www.fastenersdirect.com/Category/pSearch/723
U-Bolt Nuts Are Sometimes Known As Deep Nuts. They Are Taller Than Regular Hex Nuts And Used On U-Bolts, Especially In The Automotive Industry.

https://www.autoandtrucksprings.com/...deep-nut-kits/
Leaf Spring U-Bolt Deep Nut Kits - Bolt Deep Nut Kit
Deep Nuts Are Used Primarily On U-Bolts With Leaf Spring Suspension.
Deep Nuts Are Much Higher Than Standard Nuts.
Deep Nuts Have More Threads Than Standard Nuts And Provide Additional Torquing Ability

[MidwestCamper]

Guys,

This thing did not leave the factory with the correct torque on the U-Bolts. U-bolts on leaf springs are used in millions of vehicles and they don't normally have this problem - how often do you check the U-bolts on your truck springs? Are your truck springs basically the same or are they somehow different so that they keep their torque? Do you think that your truck dealer does a PDI and checks the U-Bolt torque? This more or less invalidates the stretch or paint theories. When there is a discrepancy of 30 to 40 ft.lbs. from specified torque, that's not due to paint rubbing off, U-bolts flexing or <2,000 miles of travel (or any combination of those). Also, the machine you showed in the video can of course be mis-calibrated (I remember a while back when there was a rash of Heartland hydraulic leaks due to an improperly calibrated crimper). Also, the interesting part is that you would think a machine could bring them down evenly. Oh well.

End of the day is simple - in a past life I was an actual working mechanic (although many years ago). I have been working on my own rigs forever, I know about what affects torque, I use a calibrated torque wrench and I have never heard of properly torqued U-Bolts loosing this massive percentage of torque in only 2,000 miles of operation. I have also never heard of a dealer checking U-Bolt torque as part of the PDI but I've already left an email asking that of my dealer.

It's easy to not be able to effectively communicate tone in a post so let me explain - I'm not at all upset by your opposing views. I just very much disagree with them and I think that GD is getting a pass on a potentially dangerous situation. So, whatever the cause of this problem, I'm trying to get them to address it - whether it requires different manufacturing protocols or insuring that their dealers include this in their PDI. I'm not going to add another comment this thread until I hear from Grand Design and my dealer service manager, at which time I'll post their responses. That way we can avoid circular arguments.

Safe travels.

When your speaking with Dexter on their manufacturing errors, ask them why your solitude uses 1/2 inch U bolts as you stated in post 69, and my Imagine 2600RB with Lippert 3500lb axles uses 9/16 U bolts.

[klenger]

When your speaking with Dexter on their manufacturing errors, ask them why your solitude uses 1/2 inch U bolts as you stated in post 69, and my Imagine 2600RB with Lippert 3500lb axles uses 9/16 U bolts.

It could be the grade of the steel used, in the same way as Graded bolts. Just guessing.

[BigGuy82]

When your speaking with Dexter on their manufacturing errors, ask them why your solitude uses 1/2 inch U bolts as you stated in post 69, and my Imagine 2600RB with Lippert 3500lb axles uses 9/16 U bolts.

Don't have a clue but that's what's on there. I have no problems with that. Also, these are Dexter axles on a LCI frame, so it's Grand Design I'll be having the discussion with. Thanks.

[klenger]

I wonder if it would help double nut the U-bolts, assuming there is enough thread to add a 2nd nut.

In the aviation industry, the nuts would have small holes in the sides to allow safety wire to be attached and secured to another blot/nut or nearby structure.