Shear pin in front jacks?

[Diamondjim]

Headed North to Ohio for the summer months, as snowbirds, and fortunately the trip was great, sort of.
Weather was OK, 3rd day quite a bit of rain into WV and OH.
2nd night in Wyethville, VA could not put down my front power levelers..................did not worry too much, as we were in and out for the night.
Arrived at Woodside Lake RV Park in Streetsboro, OH in unbelievable torrential rain, doing 20 MPH on Ohio Pike, but for only 4 miles to exit.

The owner/handyman showed up at our site with a container of every bolt know to man. I had jury rigged the only screw I had (1/4") and made sure the motor still worked. We put in a 1/4X5/8 threaded bolt and got it unhooked from the truck.

Any ideas 1) why this bolt sheared off 2) is it a common thing 3) should I carry a supply of these bolts (maybe a higher grade than factory) 4) what did I do wrong?

At the dealership - the tech showed me a goodly supply of 30 amp fuses, as they blow often, I was told. He walked me through all the procedures, both he and I used the jacks to load/unload without a problem. Final hookup, the shop manager jumped in and blew 2 fuses......
I have not blown a fuse. Thus I'm luck or cautious.

 

[jnbhobe]

Are you sure the bolt broke ?? did you find pieces ?? It more than likely fell out I never seen one break, use a 1/4 X 20 X 1 1/2 with a nyloc nut It will last forever.

 

[Grey Ghost]

I've broken four or five bolts, finally went and got a supply of stainless steel bolts and them along with me now. As for the fuzzes, I was also doing the same thing, found out the motor was drawing way to many amps, had to replace the motor, no more problems. Hope this helps!!

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Oh, also by the way, when they replaced the motor they also put in a circuit breaker instead of the old fuzz set up. Now if it does trip I just reset it and carry on. As for the bolts, don't have a good answer just carry a number of spares just in case it happens again, I'm sure it will.

 

[mlpeloquin]

1/4" 316 or 304 Stainless Steel bolts have a maximum of 100000 lbf/in[SUP]2[/SUP] with a minimum yiled strength of of 20000 to 65000 lbf/in[SUP]2[/SUP] and 1/4" 316 or 304 Stainless Steel bolts have a proof load of 85000 lbf/in[SUP]2[/SUP]. 1/4" grade 8 medium carbon bolts have a minimum tensile strength of 150000 lbf/in[SUP]2[/SUP] with a proof load of 120000 lbf/in[SUP]2[/SUP]. Which bolt would you choose for shear strength survivability? Grade 8 bolts have six lines on their hex heads.

 

[Diamondjim]

Grade 8 was what I was thinking as well. And yes, I did find the pieces. Part of the bold was still in the motor shaft.
Unable to put in a longer bolt, as it will hit the motor the as it turns. The nut that was on the unit had a crimp in both sides. We looked at a nyloc nut, but the clearances are not there!

 

[Bones]

If you are shearing bolts there is a very good chance the gear box is binding up somehow if you put in a higher grade bolt and it does not shear the system will find the weakest link in the chain next and break it. When that happens you may not be able to repair it. I am just throwing that out there that something else could be going on. JMHO. It is also possible that this was just a fluke too.

 

[mlpeloquin]

Use Loctite and torque to the proper wet torque specifications. 1/4-20 107 inch pounds or 8.9 foot pounds, 1/4-28 123 inch pounds or 10.6 foot pounds. Otherwise the dry torque for 1/4-20 is 143 inch pounds or 11.9 foot pounds and for 1/4-28 is 147inch pounds or 12.25 foot pounds.

If you suspect that the gear box is binding, have someone watch it as it deploys. Then you will know. Bolts are made from steel and a lot of it comes from China. I work for a government contractor and we had bolts shear do to embrittlement. The metal had the proper composition of alloys along with a contaminant that caused the embrittlement. If mil spec bolts with certification specs had a problem, what are the chances commercial/consumer uncertified bolts may have an embrittlement problem?

 

[Gary521]

More than likely, its not the gearbox but is binding inside the landing gear. The jackscrew needs grease that it is not getting. There are posts as to how to drill holes and get grease on the jackscrew.

 

[caissiel]

Your landing gear gears are not meshing. They are not lining up and the gears are working against each other.
If your unit cannot be raised using the manual crank the centering plate of your jacks need to be held on center.
I had to do this to my 3 5th wheels unit.
Most trailer manufacturer places a clamp in line with the centering plate and usually is not a problem.
My Big Country had the clamping plate lower then the centering plate and the plate was allowed to move sideways.
The centering plate can be seen on both side of the square tube at the top, it shows up in 2 slots. put a hose clamp to hold the plate to center and your jacks will run well.
I never add more power, one single drive unit can easily lift 8000lbs.

This setup is a sales gimic for selling much more expensive systolic landing system.

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