Al-Ko Trailer Tongue failure

On Friday, July 8, 2016 at 6:14:51 PM UTC-4, JS wrote:
On Friday, July 8, 2016 at 2:13:45 PM UTC-7, Casey wrote:
On Friday, July 8, 2016 at 4:08:38 PM UTC-4, wrote:
Rather than drifting this thread on into principles of bolt engineering, instead lets focus the on the real problem. The new Al-Ko tongue design again leads to concerns of possible tongue failure. The old style Cobra round tongue also has a history of failures and also generated the same concerns. As Cobra trailer owners, we should be campaigning Spindelberger to provide better engineered tongue components. A new, well optioned, Cobra trailer can easily cost $20,000 or more. The last thing I expect to do after taking delivery of a new trailer is upgrading tongue bolts.

Right On. I can't believe they are still using steel wheels with hub caps. Nice aluminum rims are not even an option. Not sure if current hubs come with bearing buddy/quick lube fittings. But if not that is amazing as well. A shot of synthetic grease every couple of years and one would never need to replace bearings or have to open bearing cap.

Has anyone checked if their fuel tank is within the range of motion the chains will allow?

To get an idea of what the trailer tongue has to deal with behind an RV, try riding in the back seat of one of those shuttle buses built on a truck chassis, AKA "short bus". Enjoy a glass of something colorful if you dare. After that, the idea of loosening or breaking things shouldn't come as a big surprise.

Casey, you've probably noticed when replacing the steel wheels on your own trailer that AlKo have used sealed bearings for more than a decade.

Jim

Jim,
Wow. I did not realize that. My trailer is a 1975 Pfeiffer but probably does have the Alko axle. The bearings are not sealed of course. I pulled the bearings out, inspected, cleaned and re-greased with synthetic grease. I'm so use to re-greasing trailer bearings that I did not even know/realize that they were using sealed bearings. I never had a trailer with sealed bearings. I guess not common in the US. I just wonder why they are still using steel wheels and hub caps without a upgrade to aluminum wheels.

Casey

On Friday, July 8, 2016 at 1:08:38 PM UTC-7, wrote:
Rather than drifting this thread on into principles of bolt engineering, instead lets focus the on the real problem. The new Al-Ko tongue design again leads to concerns of possible tongue failure. The old style Cobra round tongue also has a history of failures and also generated the same concerns. As Cobra trailer owners, we should be campaigning Spindelberger to provide better engineered tongue components. A new, well optioned, Cobra trailer can easily cost $20,000 or more. The last thing I expect to do after taking delivery of a new trailer is upgrading tongue bolts.

On Thursday, July 7, 2016 at 5:21:21 PM UTC-4, Dave Springford wrote:
On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture he


No intention to get off into the weeds on bolting technology, but there's no evidence at this point indicating a bolt shear failure rather than the bolt working its way out. Dave would have likely found the remainder of the bolt shank in the square section draw bar if the bolt failed in shear. If there was nothing remaining then the probable scenario is the nut coming loose and the bolt working its way out. Dave will have to let us know what the situation really was. If the nut came loose then loctite is a better solution than nylocks and there's no need to upgrade the bolts on your new trailer.

Here's a better picture of the bolt I added to the tongue of the Duo trailer to eliminate the shear loads on the two cross bolts.

http://www.foxonecorp.com/images/tongue%20bolt.jpg

KS

On the subject of trailer tongue issues, I just noticed that the coupler can rotate 360 degrees inside the tongue round tube in my Cobra trailer. It was always relatively loose and could rotate 30 degrees but not 360. Not sure when it happened but it towed just fine before I noticed this today. Nothing looks broken and all bolts seem to be in place. Problem is that I am in the middle of a flying trip. Anyone experienced this or has an idea what is going on and how to fix this? And most importantly, is the trailer still road worthy?

Thanks

Ramy

Got a very quick reply from Alfred that my issue is simple to fix and not a big concern so I am relieved. Excellent customer service.

Ramy

To answer Ramy's question, I have had two trailers who's hitch would rotate 360 degrees......... Never any problem. It can't rotate off the ball and is limited to about 30 degrees by the hitch sides.
Now, I'd like to ask (and answer) why these hitch bolts are failing. AN bolts are good for 125,000 psi, but these are common hardware bolts, so let's say they are good for 100,000 psi tensil strength. A half inch bolt cross section would have .19635 area X 100,000 = 19,635 t/s. Say 50% for shear strength, no let's say 40% because the shear load in on the threads = 7854 psi shear strength...........we can expect the bolt to shear off when 7854 pounds of force is applied.
Now, let's take a look at what's happening as we exit a gas station in out motor home with a large over-hang.........tow ball 10 feet behing the rear axle. As the rear wheels approach the curb (low point at edge of road) the rear end of our motor home drops and the trailer tung skid starts dragging across the pavement, but the motor home rear wheels are not yet all the way down to the curb. At this point the a good portion of the weight of the MH is pulling down on the tow ball. Our trailer skid is now acting as a sliding fulcrum and trying to lift the trailer. Most MH weigh a good 10,000 pounds, so let's say half of that is pulling down on the tow ball.
The bolts that have sheared off are located 15" behind the skid plate and the ball is about 10" forward of the skid, so we have a one to one and a half ratio. 5000# X 1.5 ratio = 7500# shear force applied to our half inch bolt that should shear off at 7850#.
I'm sure the engineering types in this group will have fun pointing out the errors in my thought process.
;) JJ

On Sunday, July 10, 2016 at 1:20:11 AM UTC-7, wrote:
To answer Ramy's question, I have had two trailers who's hitch would rotate 360 degrees......... Never any problem. It can't rotate off the ball and is limited to about 30 degrees by the hitch sides.
Now, I'd like to ask (and answer) why these hitch bolts are failing. AN bolts are good for 125,000 psi, but these are common hardware bolts, so let's say they are good for 100,000 psi tensil strength. A half inch bolt cross section would have .19635 area X 100,000 = 19,635 t/s. Say 50% for shear strength, no let's say 40% because the shear load in on the threads = 7854 psi shear strength...........we can expect the bolt to shear off when 7854 pounds of force is applied.
Now, let's take a look at what's happening as we exit a gas station in out motor home with a large over-hang.........tow ball 10 feet behing the rear axle. As the rear wheels approach the curb (low point at edge of road) the rear end of our motor home drops and the trailer tung skid starts dragging across the pavement, but the motor home rear wheels are not yet all the way down to the curb. At this point the a good portion of the weight of the MH is pulling down on the tow ball. Our trailer skid is now acting as a sliding fulcrum and trying to lift the trailer. Most MH weigh a good 10,000 pounds, so let's say half of that is pulling down on the tow ball.
The bolts that have sheared off are located 15" behind the skid plate and the ball is about 10" forward of the skid, so we have a one to one and a half ratio. 5000# X 1.5 ratio = 7500# shear force applied to our half inch bolt that should shear off at 7850#.
I'm sure the engineering types in this group will have fun pointing out the errors in my thought process.
;) JJ

Well, one thing is that the bolts are in double shear and so should be good for twice that.

I'd go more with the fatigue argument. With a large overhang, sometimes the trailer gets into some serious pitch oscillations with large reversing stresses. Not amenable to simple analysis.

Trust me, I'm an engineer:
https://youtu.be/rp8hvyjZWHs

So... What was the fix?


On 7/9/2016 11:12 PM, Ramy wrote:
Got a very quick reply from Alfred that my issue is simple to fix and not a big concern so I am relieved. Excellent customer service.

Ramy

--
Dan, 5J

Fix? Best to roll down drivers window and listen for any scraping noise as you exit any parking area. Stop immediately if trailer skid makes contact. Probably best way to proceed is un-hook trailer and move it by hand past the curb problem area.
JJ

To fix the rotating issue I mentioned (not the main issue in this thread) I will need to order a little sliding part to replace the damaged one.

Ramy