Opel GT Forum banner
1 - 16 of 16 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter · #1 ·
I need some help. Did Opel ever offer a trailer hitch as optional equipment? For the life of me I can't figure out why anyone would ever want to tow anything with a GT, but the reason I ask is that the '71 GT I just acquired was originally owned by the Buick dealer's wife and the underside of the hitch follows the contours of the car. I have looked online and can't find anything. I plan to remove it regardless, but if it was optional equipment I will hang on to the parts in case someone else needs them. Thank you in advance!
 

Attachments

·
Can Opeler
Joined
·
3,937 Posts
I installed a hitch just like the one in this thread. This thread and Gordos “Das Boot” thread helped me figure out how it goes on.

Here’s some photos for the next guy that gets one! This is a dealer option unit. There are a couple other threads on the forum with some helpful info if you google “Opel GT trailer hitch”

The original brochure for this part in the Buick Opel dealer options list claims 1000lb and 100lb tongue weight. That is also noted on the hitch itself.

Good enough for a bike rack, luggage shelf, or a small trailer.

I’ll probably use it for a bike rack!






 

·
Registered
Joined
·
2,129 Posts
I installed a hitch just like the one in this thread. This thread and Gordos “Das Boot” thread helped me figure out how it goes on.

Here’s some photos for the next guy that gets one! This is a dealer option unit. There are a couple other threads on the forum with some helpful info if you google “Opel GT trailer hitch”

The original brochure for this part in the Buick Opel dealer options list claims 1000lb and 100lb tongue weight. That is also noted on the hitch itself.

Good enough for a bike rack, luggage shelf, or a small trailer.

I’ll probably use it for a bike rack!






Very nice
 

·
Just Some Dude in Jersey
Joined
·
16,258 Posts
That style of rack attaches to the rear frame crossmember, which is also what the bumperettes attach to. No way would I suggest you try to pull that big car trailer. I added reinforcement struts, two on each side, that attach to the large round diameter shipping circular thingies, for extra strength.

For a trailer hitch mounted bike rack, the hitch should be strong enough, but I would attach your rack and mount a couple of bicycles on it, then get under the car and have someone pull back and forth on the rack/bike assemblage and observe the stress forces on the car. I also worked in bicycle shops and did biking for many years and used my GT to transport bikes every weekend for decades. Hitch tongue mounted bike racks apply enormous leverage stress to trailer hitches. On my long time GT I added two U bolts to just behind the vents above the rear window to give me a very secure place to attach straps going to the rack to eliminate back and forth flexing of my bike rack. If you have pop out windows you could loops a strap through them and to the rack to accomplish the same thing.

The oem hitch assembly is very strongly mounted to the front to rear main frame rails. If you could weld or bolt on metal bars from your hitch assembly to those front to rear frame rails, then you would truly have a super strong and secure hitch that would have very little chance of damaging the car AND you could even pull that car trailer!

:)
 

·
Can Opeler
Joined
·
3,937 Posts
I tested the stated 1000lbs capacity of the hitch today with my 1100lb trailer. It pulled fantastically well. The Opel has more than enough low end torque to tow comfortably and even back up an incline. It stopped fine from 50mph to 0mph, but you’d definitely need electric brakes going down mountains.

I don’t trust the hitch for long term towing or anything above city speeds without some strengthening. Putting some crossbars like Gordo did is a good idea. The factory tie down loops won’t add much strength though. You can bend those with your hands and they only have 2-3 spot welds holding them on. I may make mount there out of thicker steel plate though. The mounting through the bumperettes is the real problem with this set up. The under car mount is very strong, but the bumpers are the weak link no doubt.


 

·
Just Some Dude in Jersey
Joined
·
16,258 Posts
I just went out and took some pics of my reinforcement struts. I don't have the car on the lift so I had to lay down and take them from one foot away.

Okay, so I modded my hitch to not use the crossbar that attaches to the bumperetts. That crossbar is basically an anti-sway bar to prevent the tongue bar from pivoting right and left on it's attachment bolt to the main hitch bar under the car, plus it also adds some attachment strength to the car via where the bumperettes attach to the body. To compensate for the removal of the bumperette crossbar anti-sway function, I had 2 metal bars welded to the main crossbar tightly against where the tongue attaches and a 3rd metal bar welded to the tongue bar. In the pics I have the tongue removed:

436486


436487


436488



This sort of rack is attached to the rear right/left frame rail that connects to the ends of the main front-to-rear frame rails. That right/left frame rail is not very sturdy and was never designed to have a trailer hitch attached to it. The bumperettes are also attached to that right/left frame rail, so the entire hitch and trailer is solely depending on that frame rail's 50 year old welds to pull the trailer. This concern was voiced by a number of people when I installed my rack and I determined that it would be wise to add extra reinforcement to other parts of the car. These pics show the multiple turnbuckle struts I added to the shipping "loops" and then to the main hitch bar. There are 2 turnbuckles on each side of the main hitch crossbar: One big beefy one from Norbert and one wimpy one I had originally installed. These pics are just of the driver's side pair:


436491


436492


Sorry for the blurry pics, I can take better ones if needed.
 

·
Can Opeler
Joined
·
3,937 Posts
I just went out and took some pics of my reinforcement struts. I don't have the car on the lift so I had to lay down and take them from one foot away.

Okay, so I modded my hitch to not use the crossbar that attaches to the bumperetts. That crossbar is basically an anti-sway bar to prevent the tongue bar from pivoting right and left on it's attachment bolt to the main hitch bar under the car, plus it also adds some attachment strength to the car via where the bumperettes attach to the body. To compensate for the removal of the bumperette crossbar anti-sway function, I had 2 metal bars welded to the main crossbar tightly against where the tongue attaches and a 3rd metal bar welded to the tongue bar. In the pics I have the tongue removed:

View attachment 436486

View attachment 436487

View attachment 436488


This sort of rack is attached to the rear right/left frame rail that connects to the ends of the main front-to-rear frame rails. That right/left frame rail is not very sturdy and was never designed to have a trailer hitch attached to it. The bumperettes are also attached to that right/left frame rail, so the entire hitch and trailer is solely depending on that frame rail's 50 year old welds to pull the trailer. This concern was voiced by a number of people when I installed my rack and I determined that it would be wise to add extra reinforcement to other parts of the car. These pics show the multiple turnbuckle struts I added to the shipping "loops" and then to the main hitch bar. There are 2 turnbuckles on each side of the main hitch crossbar: One big beefy one from Norbert and one wimpy one I had originally installed. These pics are just of the driver's side pair:


View attachment 436491

View attachment 436492

Sorry for the blurry pics, I can take better ones if needed.
No those are good pics and very helpful. I have the same conclusion. I’m currently confident that the rear frame rail can handle 1000lbs, but the issue is repeated impact loads. The metal isn’t thick enough back there to handle that without eventually reaming out the mounting holes probably after 10k miles (or a handful of emergency stops) Once those mounting holes become elongated it’s game over and it will tear itself apart.

The engineer in me doesn’t think think your turnbuckles added any extra resistance unless you beefed up those tie down points better. I’ve broken them off before with a screwdriver and I’ve bent them by hand on two different GTs.

But the idea is solid and I will be copying it, but I’ll weld on a plate in their place there.

I like the metal bars by the tongue. That was a good idea as well.
 

·
Just Some Dude in Jersey
Joined
·
16,258 Posts
Yeah, my added struts probably don't add all that much strength. My main concern was to reduce flexing of the rear frame rail.

Probably the best solution is to somehow copy the oem hitch mounting concept and conjure up a way to run bars from the aftermarket hitch's main transverse hitch bar to the car's longitudinal frame rails. I don't have any pics of precisely where Opel mounted the hitch on them. Doing something like this, coupled with the aftermarket rack's mounting to the rear frame rail would make for a hitch assembly that's even stronger than the oem or aftermarket hitches.
 

·
Your Noble Friend ;-)
Joined
·
4,669 Posts
The metal isn’t thick enough back there to handle that without eventually reaming out the mounting holes probably after 10k miles (or a handful of emergency stops) Once those mounting holes become elongated it’s game over and it will tear itself apart.
If you are doing it this way, you did something wrong. A screw connection holds two parts together by the friction between the parts, caused by the force of the screw pressing them together. In a correctly designed screw connection, this friction needs to be higher than the shearing load, or the two parts move relative to each other and then, of cause, damage the screw. Not enough friction / clamping force? --> Add more screws.

Dieter
 

·
Can Opeler
Joined
·
3,937 Posts
If you are doing it this way, you did something wrong. A screw connection holds two parts together by the friction between the parts, caused by the force of the screw pressing them together. In a correctly designed screw connection, this friction needs to be higher than the shearing load, or the two parts move relative to each other and then, of cause, damage the screw. Not enough friction / clamping force? --> Add more screws.

Dieter
Well yes but also no. I didn’t design the connection. One m12 bolt will maintain the clamping pressure needed to maintain that friction for awhile, but not forever. Slippage is inevitable on a connection with this many cyclic loads above the connections probable endurance limit in multiple axes.
Adding another bolt would just make block shear more likely on the small mounting tab. It needs to be a welded connection or redesigned correctly.

Or I could just add a second support like Gordon and I are discussing so the m12 screw connections stay below their endurance limit.
 
1 - 16 of 16 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top