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HOW TO: Reinforce your Bulldog coupler by adding extra bolts.

John E Davies

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Here is a related thread, I thought this one should be spun off since folks might want to just add the parts to their existing coupler. .... https://olivertraveltrailers.com/topic/how-to-upgrade-the-bulldog-coupler-and-andersen-hitch-to-2-5-16/


And here is a thread about the hardware failure that prompted me to do this mod. There is a very good discussion there. ... https://olivertraveltrailers.com/topic/bulldog-coupler-complete-bolt-failure/


Here are the bolts I removed:




The  fundamental problem is that the couplers are fairly crudely formed. The sides are wider than the tongue, so when you torque down the nuts, the sides squeeze together to pinch the frame. This clamping force is what keeps the coupler from moving up and down when towing. The sides are not perfectly parallel. You can see that the failed bolt's washer was not contacting evenly - this puts a bending load on the head and nut. The right bolt has a slight bend from this misalignment, but it neither broke nor stretched, as you would expect from over torquing. I think I just had a bad bolt that was too brittle. I am pretty sure I did not over torque it.


Please NOTE that this bolt failed catastrophically with a BANG and it launched across the garage when I was retorquing it after the initial installation. It did not fail while driving down the highway. Though that is not impossible.


I decided to replace the bolts with Grade 5 which are more tolerant of bending loads like this. Bulldog support said that there were no issues with using the Grade 5 bolts, and that is what is recommended in their installation instructions. He also said that Grade 8 is fine, if you use the appropriate torque.


Grade 5 torque should be 55 ft lbs. Grade 8 should be 80 ft lbs (and this value is specified in the Oliver technical bulletin on Torques.) When installed with anti-seize, as I did , the torque should be reduced by 20%.


I chose this location so that there would be no need for spacers inside, and adding two extra bolts instead of one long one would add even more strength and safety factor. I added two 1/2-13x 1 3/4" Grade 5 bolts. I used Grade 8 nuts and washers since they are harder and do not compress as much, and they look nicer too. Also, the supply house did not have any in Grade 5 ;)




Remove the safety cables for better access. Unbolt the coupler. Tape it to prevent scratching.


Lay out the new hole locations. Center them between the existing holes and up 3/4" from the bottom edge. This location allows you to reach the nuts with a 3/4" open end wrench, even when the safety cables are installed.




Drill the new 1/2" holes. A drill press is very helpful but not mandatory. A bench and stout vice would work well too, or you could even do it sitting on the ground with the coupler installed.




Insert two new long Grade 5 bolts and place a jack stand under the coupler end and retract the trailer jack. You want the coupler loaded upward in the direction it wants to move. Drill the new holes in the tongue, using pilot holes to start. The new holes in the coupler act as precision guides.




Remove the coupler, clean it and the tongue to remove burrs and shavings. It is not prudent to leave steel savings jammed into aluminum, it will cause corrosion. Clean and paint the coupler. I like Dupli Color Brake Caliper Paint - it goes on beautifully and does not require a primer coat. Paint the tongue with a good metal primer. I  use Dupli Color Etching Primer which is specifically recommended for aluminum. (I primed the tongue just a month ago, so I touched up the scrapes with a Q Tip.)




Lay the coupler on the tongue. Reassemble the new long bolts with one washer under the head and two or more under the nut. This ensures that the nuts can't bottom out on the unthreaded shank and cause problems. Some early Olivers were delivered with too few washers.


With the coupler loaded vertically as before, install the two new short bolts. Use one washer under the head and one under the nut. Double check that the bolts are not too long, they must not hit each other when tight:




If you used anti seize compound, which I do recommend, torque to 45 ft lbs. Tighten the bolts alternately a little at a time, like doing wheel lug nuts.


If you do this "dry" torque to 55 ft lbs.


Cut off any excess threads, leaving 4 or 5 threads for the cap nuts, if you want to use them.






Install the pretty stainless cap nuts to conceal the cut end, to hide the rust and protect your shins from cuts.


Write down the torque on top of the coupler. Recheck the nuts for looseness after the next day of towing.


As an alternative, you could install a hardened hitch pin completely through the coupler lower holes. This would act as a safety pin in case a bolt should fail on a trip. You could probably tow your trailer to a shop to get it fixed rather than having to call AAA for a wrecker. I suggest a 5/8" set of holes and a 5/8" pin since that would give additional strength and you could even install a locking hitch pin, as a visual theft deterrent.




I asked Oliver Support if they would consider adding a third through hole with compression sleeve, like the other two. This would provide much more strength, but more importably it provides a safety factor if one should fail. It will be interesting to see what develops.


This shows that you can get access even when the cables are not removed:






John Davies


Spokane WA

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SOLD 07/23 "Mouse":  2017 Legacy Elite II Two Beds, Hull Number 218, See my HOW TO threads: https://olivertraveltrailers.com/topic/john-e-davies-how-to-threads-and-tech-articles-links/

Tow Vehicle: 2013 Land Cruiser 200, 32” LT tires, airbags, Safari snorkel, Maggiolina Grand Tour 360 Carbon RTT.

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  • 9 months later...
2 hours ago, bobholleron said:

Were you able to buy the Bulldog 2 5/16" Bulldog hitch with the two holes already drilled? The Bulldog hitches I'm looking at don't have any holes drilled in them.



No, you have to drill the extra holes.  I included pictures and info on how to do it - did you actually read this thread?

John Davies

Spokane WA

Edited by John E Davies

SOLD 07/23 "Mouse":  2017 Legacy Elite II Two Beds, Hull Number 218, See my HOW TO threads: https://olivertraveltrailers.com/topic/john-e-davies-how-to-threads-and-tech-articles-links/

Tow Vehicle: 2013 Land Cruiser 200, 32” LT tires, airbags, Safari snorkel, Maggiolina Grand Tour 360 Carbon RTT.

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I did not realize there were installation instructions following the parts info so, no, I did not read the whole thread. I did go back to see what I must have missed (a lot) and going forward I'll know to keep scrolling down and not assume I reached the end. I have the parts on order and hope to make the modification after we return from our next outing. I'll try the close fit 33/64" drill bit first and hope I get lucky. If not, I'll drill one or both sets of the holes out to 17/32" for a free fit unless you recommend something different. Great write-up for the install, especially if one reads it. 



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