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Thread: Broken Spring Hanger Data
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11-24-2018, 08:39 PM #11
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No doubt this stuff is rubbish compared to a leaf spring truck chassis. I have taken video that shows the turning results in each axle with apposing forces so they cancel out. I did not see any hanger motion. When I induced sway, they lit up. Another thought is that heavy braking with perhaps an undercut weld or other defect begins to pull the hanger from the frame. We know the rear axle is under the heaviest load under heavy braking so it makes sense the rear hanger will typically be the one to fail. . This thread may prove this out with data.
So Pats panhard setup and/or a minimum of a center hanger cross member will handle the lateral loads, and the V clips on the rear hangers at a minimum will handle the longitudinal loads from braking.MidwestCamper
Jim & Dawn
Near Milford, Michigan
2017 Imagine 2600RB
2015 GMC Sierra 1500 Double Cab 4x4
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11-26-2018, 01:30 PM #12
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To add a little more. When I was designing the Panhard Bar, I did some research on friction coefficients of tires on Asphalt and Cement.
BTW, the following coefficients of friction could be used for forces under heavy braking also.
The following is a speculation of forces if everything acted equally to the axles.
Reflection 303RLS (11995 lbs. - 2399 tongue weight = 9596 lbs) fully loaded.
- Rotating the trailer 90 degrees to the direction of travel, worst case move. Effectively rotating the trailer in one place (Static coefficient of friction).
- Static coefficient of friction would be about .72 on asphalt and cement (maybe as high as .9) and about .55 rolling.
- Using .72 for friction coefficient each axle gets about 3450 lbs. of lateral force on each axle in opposite directions.
- The center hangers in the scenario basically nullifies the lateral force because the forces are applied from each axle in opposite directions. So basically no side load on the center hanger. (Anyone ever have a center hanger break?)
- The front and rear hangers would receive 3450/2= 1875 lbs force in opposite directions
- Each front and rear hanger would receive 1875/2= 938 lbs force
- Each leg of a spring hanger would receive 938/2= 469 lbs force.
- Now to try to interpret how much torque is being applied to each leg of the spring hanger at the weld
- Correct track spring hanger is 5" high and 4.3" to center of spring bolt hole. (Thanks Rob)
- 469 lbf * 4.3" = 2017 in. lbs. torque applied to the weld of a each leg of the spring hangers.
- 2017 in. lbs. / 12 = 168 ft. lbs. torque basically applied to the weld of each leg of the front and rear hangers. 336 ft. lbs. / hanger
- Now the ME's should be able to calc. the bending moment of Cantilever Point Load, to see how much one of these hanger legs can handle or how close are we to breaking the hangers???
This is not perfect, just giving an idea for the forces applied and where.
This gives an idea of how much side force can be applied to the spring hangers. Coefficient of friction number came from engineering sites and accident reconstruction info. Looked at a few different places so I just wasn’t believing the first numbers I found.
If I totally got stupid somewhere in my interpretation, please let me know.
A lot of speculation, but with engineering behind it .
PatPat&Marlene Gyrogearloose - 2010 Itasca Meridian 34y - 6.7 w/Allison 6spd - Jeep Wrangler Rubicon - previous Reflection 303RLS
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11-26-2018, 04:02 PM #13
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So being as we are off topic I'll add this question. comment.
This is our 4th rv for me to own personally. Started with a 1978 Prowler bunk house , 1998 four winds with bunks, 2011 Kz rv bunk house. After all the miles traveled with these first 3 no suspension problems , or with our current hardly used yet 29RS. Add to that we belong to a camping group that was started in the late 60's. About 12 campers regularly for all these years and none have ever had a suspension problem like spring hangers or springs. We currently have the newest in the group, the oldest being less than 10 years old.
I am not sure but I would guess Lippert has been building frames and suspensions for rv's for quite a while.
So the question , comment, with all these factors and all the 1000's of miles traveled with all these different brands of campers and all these years, what happened?
Brian
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11-26-2018, 06:17 PM #14
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Thanks Rob on the hanger length correction.
This is certainly a cyclic fatigue issue, where there is significant lateral and longitudinal motion to aid in this failure. Just a theory....once a crack is formed from this loading, the hanger will separate. With the loss in traction on the front axle on heavy braking, I believe if only momentarily, additional torque is applied to the rear hanger. Does LCI typically only re-enforce the rear hangers or just those that fail?MidwestCamper
Jim & Dawn
Near Milford, Michigan
2017 Imagine 2600RB
2015 GMC Sierra 1500 Double Cab 4x4
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11-26-2018, 06:24 PM #15
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Pat,
Very nice on the calculations. I'm curious how the forces increase on the rear hangers as the front axle loses traction on heavy braking? A theory is that while the equalizer is in rotation and the front axle is lifted, this force may be much higher on the rear hangers until the system stabilizes.MidwestCamper
Jim & Dawn
Near Milford, Michigan
2017 Imagine 2600RB
2015 GMC Sierra 1500 Double Cab 4x4
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11-26-2018, 10:33 PM #16
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09-24-2019, 04:08 PM #17
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Model--- Reflection 303RLS 2016
GVW----11995
GVW of axels---- 5200 x 2
App. miles traveled----25,000
Disc brakes or drum ----- drum
Suspension upgrades, moryde, correct track, etc-----Lippert 3000 pound rated leaf springs, November 2018
Equalizer type , dexter, equaflex, solide, etc.----Equaflex
Travel weight if known-----11200 approximate, not CAT scale weight
Have you had any hard stops?---- No
Where you on very rough roads when hanger broke?---no
Do you have the 2" spacer tube between the frame and the spring hanger?----no, not that I know of
Spring hanger placement----- left rear (curb side rear)
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09-24-2019, 04:27 PM #18
@Dorwinion,
See this more current discussion. https://www.mygrandrv.com/forum/show...-Hanger-Advice
RobCate & Rob
2015 Reflection 303RLS
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12-23-2019, 06:52 AM #19
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Model--- Reflection 303rls
GVW----11995
GVW of axels---- 5200 x 2
App. miles traveled----9,000
Disc brakes or drum ----- disc
Suspension upgrades, moryde, correct track, etc-----none
Equalizer type , dexter, equaflex, solide, etc.----Equaflex
Travel weight if known-----11,850
Have you had any hard stops?---- no
Where you on very rough roads when hanger broke?---no, on highway at the time, but have traveled through Indiana!
Do you have the 2" spacer tube between the frame and the spring hanger?----yes
Spring hanger placement----- driver rear
Hanger height from centerline of spring bolt to base of hanger (frame contact point)----4 1/2” overall
Hanger had a crack below weld about 50% of the width before it failed.
Watched a video last night on Artic Fox fifth wheels. They build their own chassis and add this steel vertical piece above all hangers to elimate torque. I am no engineer but some of you are, what do you think about that reinforcement?Last edited by Beachcamper; 12-23-2019 at 07:03 AM.
Vivian
2018 Reflection 303rls
2018 Ford F-350 SRW Diesel
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12-23-2019, 11:26 AM #20
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Breakaway Switch Question
Today, 04:10 AM in Axles, Brakes, and Suspension