Tow Bar Attachment

[MotorPro]

Originally Posted by twinboat

Ah, but they do.

Yes but you should never use grade 9 bolts in a situation like this. Grade 9 bolts are very hard and very brittle. They are used in as sheer pins when you want them to break to save more important parts or people.

[johnboy2]

I never knew that about grade 9 bolts that's very interesting, I never knew there was a grade 9 bolt I thought I was being silly. Don't worry bout using gd 9 I think gd 5 bolts are plenty to hold base plates on a toad.

[TonyMac]

BUT WHAT GRADE IS THE HITCH PIN? And there's only one of those...

[johnboy2]

The hitch pin is where this whole thing started.

[twinboat]

Cold*rolled*has a shear strength of around 40,000 psi and your area under load for the pin is about 0.3 square inches for a 5/8" pin so in single shear you are good to around 12,000 lbs. The pin is in double shear so you might expect 24,000lbs...but it is not just the shear strength of the pin it is the compressive strength of the wall of the tube. You have 0.188" by .625" across the diameter of the hole which gives an area of about 0.12 square inches so each side of the tube can take 4700 lbs for a total of just over 9,000 lbs if the tube is standard hollow structural with about the same yield strength as*cold*rolled. Obviously the pin is not really the limiting factor it is the*tube*thickness.

[jmckinley]

Wow Twinboat, now you've gone and done it. Don't you know you're only supposed to quote what some guy at the garage said? You're just going to confuse people with good sound engineering calculations. And they'll never believe you anyway.

Care to try to explain to these guys how the integrity of bolted joints is dependent on clamping force, not shear strength of the bolts? I've tried on several threads and now I'm just tired.

[Algoma]

If you are really concerned about the weak link then in my case it was the tow bar. Turning a corner in to a campground both legs broke, one being in compression the other in tension. Luckily the safety cables held so no serious damage This was the Blue Ox Aladdin (5,000 lb version) which has since been replaced by the new 7,000 lb Aladdin. The old version suffered from metal fatigue of the aluminum inside tube. So if anyone is still using the old version, be prepared.

[spider13]

I somehow lost my hitch pin on the way home this year.Not fun! $4000.00 damage to toad,tore both fenders off tow dolly,but all systems worked ,the saftey chains held the dolly to the coach and the straps and chains held the car on the dolly.It could have been so much worse.It was quite a ride getting it stopped.65 mph ,rt95 nth.mile mark20 Virginia.also destroyed DW 's bike that was on the back of the car.I learn something new every trip ,and don't take anything for granted.

[AFChap]

When I removed a10 yr old BlueOx baseplate in 2013 after it took a collision from the side, it had 4 bolts, 2 of which were broken, 1 of which had been broken for a very long time (rusted). The 4 bolts all ran parallel to the ground. New baseplate I put on slightly newer car of same model had 8 bolts, 4 parallel to the ground and 4 vertical.

[c5by55]

Couple of comments. I have installed 3 different base plates. All were Roadmaster as Roadmaster uses MORE and LARGER fasteners than Blue Ox. I can NOT comment on others, but each time that I look at the hardware and BOM, Roadmaster is the winner hands down.

I found some minor assembly issues and talked to Roadmaster Engineering and Development. I also was Chief Engineer for a Fastener Company many years ago. TIMES have changed with more digital equipment. The poster that commented on the Split Lock Washers is correct. I reached out to a Fastener Company and they said that Flat washers were the preferred locking device rather than the split lock washers. They also suggested a NORD dual glued locking washer, but that would cost prohibitive for any vendor.

Bottom line, the BEST advice that I can give and I am parroting Roadmaster, use Loctite RED and properly TORQUE the bolts. Had I been aware of the flat washer preference, I would have used them instead. The Grade 5 (3 marks on the head) bolts are more than adequate. BUT, I can tell you that the split lock washers with Loctite Red and the proper torque, NEVER, EVER gave me any issues on the first two baseplates. They were SOLID and never came loose or vibrated loose...and I DID periodically check them.

What has NOT been pointed out here is the need for securing (LOCKING) the various hitch pins used in the system. Again, I have the Roadmaster XL system. I have used the Falcon 2 for over 50K of towing. I had it rebuilt for around $150 last year and it had a LOT of life left PRIOR to the kit. I did clean it annually and lube it per Roadmaster.

I upgraded my TOAD and purchased the heavier Sterling 8K unit as my 2014 Yukon was approaching the 6K limit of the Falcon 2. I can NOT say enough good things about the overengineering of the Roadmaster.

On the Yukon, the competition used only the original factory bolts or perhaps the holes for the base plate. There were 2 per side and about 1/2". Roadmaster has an additional 5/8" bottom locking bolt (threaded into the base plate) and also a Booster or additional bracket that is bolted (1/2") to the frame below where the baseplates are located. It is SOLID. The Baseplate receiver tubes are WAY stronger than how the recovery tow hooks were attached.

Getting back to the PINS...I have locks on EVERY pin (draw bar included) that is used in the tow bar assembly....from the MH to the baseplates. Many members on the Bill D.'s Monacoers have reported that folks will pull out the hairpin clips, for FUN, when you are at a rest stop or leave the vehicle at places like a stopover or a Walmart parking lot. That is sadistic and MEAN.

My comments....others may differ....

[Jscott1000]

the hitch pin is a single point failure. They are plenty strong enough usually but things can and do fail. I only use locking hitch pins not because they are stronger but less likely to detach spontaneously or by sadistic vandals.

[SpringerPop]

Any thoughts on the use of a 5/8" grade-8 bolt with a split-lock washer between a nut and a pal-nut as a hitch pin?

Flat washers are used on both sides of the receiver, and the main nut is only finger-tightened against the bolt, and only really tightened against the split-washer and the pal-nut.

No hair-pin clips to be pulled, and the split-ring jams the two nuts sufficiently against loosening, either accidentally or maliciously.

Is the metallurgy appropriate?

Pop

[stroudwc]

Back to hitch pins I had the hair pin clip knocked out of the hitch after driving less than 20 miles on a gravel road years ago pulling a boat. I was lucky to catch it before the pin came out. I could see the mark on the hitch where a rock had hit it. I have used locking hitch pins on all hookups from that day on. I think many lost hitch pins are caused by road thrash knocking the hair pin clip out.

[sdagro]

I would like to extend this topic to include the "QUICK LINKS" used on the car end of the safety cables on the Roadmaster "All Terrain Falcon II". I was told by a very reputable machine shop that the QUICK LINK is the WEAKEST LINK!! Steve