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 > Hensley Arrow: How does it REALLY work?

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sfdon

Novato CA 94947

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Posted: 02/05/06 02:42pm Link  |  Print  |  Notify Moderator

Hi all. I had followed an earlier topic on "How does a HA work?" I liked the analysis so I shopped for a HA on eBay, but always got outbid in the last seconds. So I went ahead and ordered a new HA. I have it installed on the TT but have yet to take an extended trip. I have not read all 51 pages of this thread but hope that you will find my experience of interest.

As I was installing the HA for the first time I concluded that my driveway was too narrow and at a slope, so I decided to partially install the unit and drive down to a local school parking lot that was open and flat.

I mounted the frame brackets with u-bolts, installed the spring bars and installed the strut assemblies. I did not install the two 5/16" shear bolts into the frame brackets. The trip to the school consisted of driving down our street which is a moderate slope with a 90 degree turn at the end, before getting to an intersection with stop sign.

I approached the 90 degree turn and had no problem, but when I approached the stop sign at the intersection I heard a clunk coming from the hitch. I pulled over and found that the frame brackets had shifted rearward about a 1/2" on both sides.

I concluded the following:

The strut assemblies are in compression. Actually it is a very cleaver design, requiring no external tools.

When I applied the brakes going into the 90 degree turn, the instability of main hitch assembly under braking and turning conditions was enough to overload the struts, causing them to shift on the frame.

The clunking sound was the hitch assembly flopping around because of the loose struts.

My experience seems to substantiate what Ron and others have been saying.

There are a bunch of questions.

Instructions say to tighten u-bolt fasteners to 45 ft. lbs. What force on the struts would cause the brackets to slide on the frame?

What is the shear strength of the (2) shear bolts, resulting in a total resisting force to prevent the sliding to occur?

Finally, what event could occur that would cause the shear bolts to shear and the bracket to slide?

Question: is there any evidence that Hensley-Arrow monitors these treads and responds to them? I would hope they would be actively involved as I believe it would help their sales efforts.

Posting to follow on brake controllers with HA.

Lastly, as I wanted to install the HA myself, I knew that I was not going to lift up the 100# Main Hitch Assembly. I devised a hoist consisting of a collapsible saw horse on which I mounted a small boat winch. Not only did it work well, it is possible to take it with me on trips in case I have to or want to remove the main assembly. If you are interested, I can e[emoticon]ail you photos.


Don


Don and Gail
2005 Forest River Surveyor SV-230
2003 Yukon with Autoride, Honda EU1000i
Hensley Arrow

6MISFITZ

Fort Erie, ON, CANADA

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Posted: 02/05/06 03:07pm Link  |  Print  |  Notify Moderator

Sfdon, congratulations on the hitch.
I thought those strut bars were under tension, not compression.
Once the brackets are shear bolted and U bolted, the strut bars are under tension, right?

Duh! Strut bars compression, weight bars tension.

If you exceed the turn limit of the hitch (forward or reverse) and approach 90 degrees between tow vehicle and trailer, those shear bolts are designed to shear allowing a bit of motion in the brackets, saving the hitch and its components.

My TT's frame is a reinforced C channel, not an I beam or fully boxed frame design. Because of this I am not supposed to use the U bolts as it would cause the open pert of the C channel to deform, so I have to thru bolt those brackets. I did try to use one shear bolt on top of the bracket and can tell you it did shear at bellow 85 ft/lbs. I used the supplied drill bit, went one size bigger and then tried to torque the shear bolt, but it snapped. Several drill bits, easy out and one sledge hammer hit later I scraped the shear bolt and installed the Hensley supplied machine bolts.

With our old Equal-i-zer hitch I could get to a full 90 degree turning angle with the trailer without damage. If I exceed the 82 or 85 degree maximum turning limit of the Hensley, I will most likely need an emergency repair kit.

For now, I make sure the gas stations I enter have an easy exit or I wait for the next station with more room, so I don't test my installation!

Mike.

* This post was edited 02/09/06 06:49pm by 6MISFITZ *


Mom, Dad, 4 kids, 2 Camping Dogs
Express 2500 LS (135"WB) 6.0L, 4.10, G80, PYO wheels, HENSLEY & McKesh
--------------------
MISFITZ RACING
MFCC Member
Rallies Attended 4, 7 Un-Rallies


Stressor

Whitefish Bay, Wisconsin

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Posted: 02/05/06 04:15pm Link  |  Print  |  Notify Moderator

Garfie|d wrote:

6MISFITZ wrote:

Ron, On my thread, there was a story from what happened to Garfield in a corner with his trailer, so I do agree that the hitch won't save me from every law of physics or that of a ham fisted maneuver by the driver and that towing requires more attention - no matter what hitch.


Gee, I think I was just insulted!!! LOL! [emoticon][emoticon][emoticon] (Kidding Mike!) [emoticon]

Anyway, this thread extension appears to be focusing around an incident that I experienced last summer, so I thought I should clarify things, expecially because it underscores the need to ensure there's proper braking pressure to the trailer to control the Hensley even in situations where it may not be thought necessary.

I experienced a situation last summer where I was slowly coasting into an intersection to make a 90 degree left turn. I was in a small town and there was no traffic around and I had the whole intersection to myself. I rolled into the intersection doing 10-15 kph and quickly cranked on the wheel without applying the brakes. After pulling a long trailer for a while you get into the habit of pulling well into the intersection and turn sharply, and that's what I did.

What happend next I didn't foresee, although I should have. The short wheelbase Yukon turned very quickly as usual, but of course the trailer wanted to keep moving forward in a straight line, so it did. With no brakes to slow it down, it pushed against the Hensley which pivoted to the right and slammed against the stops with enough force to cause the rear wheels of my Yukon to lose traction and skid several feet towards the curb. As soon as I started sliding I instinctively hit the brakes which allowed the trailer to pull back on the Hensley and immediately halted the spin. If we were going much faster we easily could have jacknifed the whole rig.

As I see it there were three major factors that attibuted to this incident:

1. I didn't apply (even lightly) the brakes to help control the trailer in a decelerating change-in-direction manouver.

2. The intersection was wet as it had recently started to rain. It had also been very recently paved and was covered in a mixture of oily water.

3. The short wheelbase of my Yukon worked against me as it turns VERY quickly. A longer WB vehicle wouldn't have been able to turn as quickly and might have prevented this incident.

I consider myself a conservative driver (expecially when it comes to towing) but this incident really caught me by surprise because of the low speed involved. What I've learned from this is the need to apply the brakes in pretty well any decelerating speed manouver in order to ensure the Hensley is well behaved. It also convinced me that there is no way I will ever tow the trailer on snow or ice.

I hope this helps to clarify things.


This I believe. [emoticon]


Milton Findley (and Kerene)

A small piece of my mind...

Stressor

Whitefish Bay, Wisconsin

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Posted: 02/05/06 04:19pm Link  |  Print  |  Notify Moderator

The strut bars are under compression.

6MISFITZ

Fort Erie, ON, CANADA

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Posted: 02/05/06 05:43pm Link  |  Print  |  Notify Moderator

Thanks Stressor, I sit corrected!

Mike.

bettered

UpCountry SC

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Posted: 02/05/06 05:53pm Link  |  Print  |  Notify Moderator

sfdon wrote:

I mounted the frame brackets with u-bolts, installed the spring bars and installed the strut assemblies. I did not install the two 5/16" shear bolts into the frame brackets.


The shear bolts are little more than an indication that the frame brackets have shifted (thus shearing the bolts). They are purposely made of low grade steel for this reason. It's not a good idea to replace them with higher grade bolts because you're preventing the safety feature from working as designed.

sfdon wrote:

I approached the 90 degree turn and had no problem, but when I approached the stop sign at the intersection I heard a clunk coming from the hitch. I pulled over and found that the frame brackets had shifted rearward about a 1/2" on both sides.

I concluded the following:

The strut assemblies are in compression. Actually it is a very cleaver design, requiring no external tools.

When I applied the brakes going into the 90 degree turn, the instability of main hitch assembly under braking and turning conditions was enough to overload the struts, causing them to shift on the frame.


Nope. You may have overstressed the installation when you turned more than 85 degrees. That's one situation in which the frame brackets will shift.

sfdon wrote:

The clunking sound was the hitch assembly flopping around because of the loose struts.

My experience seems to substantiate what Ron and others have been saying.

There are a bunch of questions.

Instructions say to tighten u-bolt fasteners to 45 ft. lbs. What force on the struts would cause the brackets to slide on the frame?

You will find that the lug nuts on your wheels are in the same neighborhood. 45 ft # is a LOT of torque. You will probably get some localized deformation of the tongue - mine are rectangular and I've noted a little. The brackets sliding on the tongue are a last resort outcome. I've never experienced my brackets sliding, although I've heard the system clank from time to time. I'm not familiar with the special requirements of non-rectangular structural tongues.
sfdon wrote:

What is the shear strength of the (2) shear bolts, resulting in a total resisting force to prevent the sliding to occur?

It's very low - probably 35,000 psi or less.

sfdon wrote:

Finally, what event could occur that would cause the shear bolts to shear and the bracket to slide?


You've experienced (or caused) one such situation. Another might be the link collapse / hitting the stop phenomenon described on the previous pages.

sfdon wrote:

Question: is there any evidence that Hensley-Arrow monitors these treads and responds to them? I would hope they would be actively involved as I believe it would help their sales efforts.


You should call the Hensley service folks and discuss with them. What you experienced is not something I would expect. It sounds to me as though you may not have reached the 45 ' # of torque specified. Near the limit when the brackets were breaking loose at the specified torque, you might have noted some groaning or popping that would have alerted you to something being amiss. The fact that both brackets moved adds some logic to my suspicion about the installation.

From what we can tell, Hensley is selling all the Arrows they can make, so I wouldn't worry about it on that side. What you've experienced is out of the ordinary.



sfdon wrote:

Posting to follow on brake controllers with HA.

Lastly, as I wanted to install the HA myself, I knew that I was not going to lift up the 100# Main Hitch Assembly. I devised a hoist consisting of a collapsible saw horse on which I mounted a small boat winch. Not only did it work well, it is possible to take it with me on trips in case I have to or want to remove the main assembly. If you are interested, I can e[emoticon]ail you photos.


Don


You might find it easier to use a floor jack. I jacked my hitch up, secured it with some blocks, lowered the coupler down onto the ball in the hitch with the TT tongue jack, locked the coupler on the hitch on and then raised the trailer to clear my blocking. As you know, the hitch normally "hangs" on the ball.

Overall, my hunch is that you're experiencing problems of an unsatisfactory installation. Under normal circumstances, the frame brackets will not move and generally, they shouldn't.


BetterEd

DW + 2 grandkids + Mini Schnauzer
2005 Chev 3500 Crew D/A 6.6L LLY, 6 x 6 DRW, 3.73
Tru-Flow + Banks, 2005 Flagstaff 831FKSS
Hensley + Prodigy

"Genius may have its limitations...." E. Hubbard 1856 - 1915

Ron Gratz

full time RVer

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Posted: 02/05/06 06:15pm Link  |  Print  |  Notify Moderator

sfdon wrote:

There are a bunch of questions.

Instructions say to tighten u-bolt fasteners to 45 ft. lbs. What force on the struts would cause the brackets to slide on the frame?
To answer this, one needs to know the U-bolt diameter and thread pitch.

Quote:

What is the shear strength of the (2) shear bolts, resulting in a total resisting force to prevent the sliding to occur?
Assuming the bolts are Grade-5 and 5/16" diameter, the ultimate shear capacity per bolt is about 5700 lbs.

Quote:

Finally, what event could occur that would cause the shear bolts to shear and the bracket to slide?
Let's assume the TV is turning to the right and the TT is pushing on the hitch. The thrust from the TT will tend to rotate both of the HA's side links CW about their front pins. The TT must apply a CW torque to the HA's rear unit to prevent the HA's linkage from "collapsing".

The only way for the TT to apply the torque is via the struts. If a frame bracket slips, the torque will not be sufficient to prevent the collapse. Once a frame bracket slips rearward, there is no way for the strut to apply a tension to pull the bracket forward. That probably explains why both brackets were moved rearward.

Quote:

Question: is there any evidence that Hensley-Arrow monitors these treads and responds to them? I would hope they would be actively involved as I believe it would help their sales efforts.
I once was told that, if a manufacturer tries to explain the workings of a complex device to a customer, the customer will only be confused, and a confused customer will not buy a $3,000 device.

Ron

bettered

UpCountry SC

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Posted: 02/05/06 06:18pm Link  |  Print  |  Notify Moderator

6MISFITZ wrote:

Sfdon, congratulations on the hitch.
I thought those strut bars were under tension, not compression.
Once the brackets are shear bolted and U bolted, the strut bars are under tension, right?


The brackets merely offer the struts something fairly firm to push against. The purpose of the struts is to keep the hitch from pivoting on the ball. They might have been designed to work in tension and the effect would have been similar, but as you can tell by loosening up on the strut bar bolts, the actual design puts them in compression - as Stressor noted.

When I first installed my hitch, I overtorqued the strut bolts resulting in a "overcenter" condition (like a vice grip) when the hitch would shift from right to left or vice versa. It took me a little while to figure it out, but once I reduced the torque it's been working fine ever since. Even under those conditions though, my brackets have never slipped.

6MISFITZ wrote:

If you exceed the turn limit of the hitch (forward or reverse) and approach 90 degrees between tow vehicle and trailer, those shear bolts are designed to shear allowing a bit of motion in the brackets, saving the hitch and its components.


Exactly correct Mike. The bolts shear with primarily one purpose - to provide a visual indication that the brackets have slipped for one reason or another. The service folks told me that under normal conditions, you might never know you'd experienced a bracket that had slipped without those bolts.


6MISFITZ wrote:

With our old Equal-i-zer hitch I could get to a full 90 degree turning angle with the trailer without damage. If I exceed the 82 or 85 degree maximum turning limit of the Hensley, I will most likely need an emergency repair kit.


Would it be fair to assume you already know that Hensley will be only to happy to fix you up? I bought the kit for about $30. It's got a myriad of pins and clips as well as some extra bolts and a couple of zerk fitting combo gizmos for the spring bars.

6MISFITZ wrote:

For now, I make sure the gas stations I enter have an easy exit or I wait for the next station with more room, so I don't test my installation!

Mike.


That's not something I've been worried about. Maybe because I'm a box frame type.

I really appreciate your commentary about your earlier experiences. Keep up the good work, Mike.

bettered

UpCountry SC

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Posted: 02/05/06 06:23pm Link  |  Print  |  Notify Moderator

Hi Ron. I don't know how he could have made both brackets slip if they were properly installed. Once the compression force was relieved on the one side (by the bracket slipping) there would have been nothing in compression on the slipped side to force the other side bracket rearward.

The actual shear capacity of the bolts is not particularly meaningful because the torque on the U-bolts is what restrains the brackets. The shear bolts have no practical mechanical function. They are extremely mild steel on purpose.

Ed

* This post was edited 02/05/06 06:59pm by bettered *

Ron Gratz

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Posted: 02/05/06 08:06pm Link  |  Print  |  Notify Moderator

bettered wrote:

Hi Ron. I don't know how he could have made both brackets slip if they were properly installed. Once the compression force was relieved on the one side (by the bracket slipping) there would have been nothing in compression on the slipped side to force the other side bracket rearwar.

The actual shear capacity of the bolts is not particularly meaningful because the torque on the U-bolts is what restrains the brackets. The shear bolts have no practical mechanical function. They are extremely mild steel on purpose.

Ed,
The brackets were not properly installed. The shear bolts were not in place. The HA instruction manual states:
"CAUTION
In some cases, damage to the struts can occur if:
Shear bolts are not in place."
and
"---The frame brackets are designed to slide when too much force is put on them from the strut bars. If the brackets don’t slide then it’s possible for the strut bar to be damaged."

This means to me that, in addition to whatever frictional resistance to sliding is developed by the clamping force from the U-bolts, the shear bolts are intended to supply an additional amount of sliding resistance limited to their combined shear capacity.

If the 5/16" shear bolt is Grade-2 rather than Grade-5, it still will have an ultimate shear capacity of about 3000 lbs (or 6000 lbs for two bolts). The bolts do have a practical mechanical function as Don found out when he towed his trailer without them.

If one bracket moves rearward, then the struts are loose and the HA's linkage can "flop" around. If the loose struts allow the linkage to shift to the right, TT thrust can overload the left bracket causing it to move rearward. If the linkage shifts to the left, the right bracket can be overloaded. Both brackets can be pushed rearward.

Ron

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