300SD Trailer Hitch Receiver - Update - Page 2 - PeachParts Mercedes-Benz Forum

layback40 · #16 12-29-2009, 09:45 AM

Thanks for that link MaydayMike. It has good pics of them. I might get motivated and build one for my 124 wagon now. Just need 2 pieces of 3" angle, a yard of 3" RHS & the draw bar. Easy as!!

rcounts · #17 12-29-2009, 08:45 PM

The only problems I'd have with that Curt hitch are

1) It defeats the purpose of the bumper shocks (absorbing small impacts). A bump that would normally be soaked up harmlessly by the bumper shocks is going to push the rear panel in (where the hitch bolts to the lip). If the piece that bolts to the bumper weren't welded in solid and just had a square hole that surrounds the receiver tube - so that it could slide on the reciever tube and allow the bumper to move without damaging the panel behind it - I'd like it a lot better.

2) All the tongue weight and most of the pulling stress is on the two bolts through the bumper. I'd have to look at how thick the steel of the bumper is to be sure it is stout enough to handle that kind of weight and stress long term without warping or cracking.

300SD81 · #18 12-29-2009, 10:44 PM

Heres what I've come up with based on the design mentioned in the first post and this. There is no attachment to the bumper, so the shocks should still function, I'd imagine that if anyone rear ended me, the 2in receiver would puncture their bumper rather than cause any damage to the car.

The angle channels in the model are reversed, they would actually go OVER the bumper shocks with spacers, that way the bumper is not moved out. Everything is 1/4 steel. I'll probably add something like this as well.

Ordered the metal pieces already, so I should have this built in a week or 2.

rcounts · #19 12-30-2009, 12:50 AM

What did you use to do the modeling? Looks very clean.

My idea for my W123 coupe is to make the cross-bar fit between the mounting plates (rather than below them), so that the cross-bar is completely hidden up behind the bumper and the receiver tube will be the only thing hanging below the bumper. On the W123 shifting the bumper back 1/4" shouldn't create a noticeable appearance flaw, so I'll be bolting the mounting plates between the bumper shocks and the uniframe.

I also plan on welding a 1/4"x2" piece of bar stock to the bottom of the reciever tube and extending forward under the spare tire well. The forward end of the bar will have a plate that sits up against the bottom of the spare tire well, with some small reinforcing plates inside the tire well and bolts to sandwich the sheetmetal of the bottom of the spare tire well between the plate underneath and the smaller reinforcing plates inside.

Billybob · #20 12-30-2009, 01:57 AM

Quote:

Originally Posted by rcounts

The only problems I'd have with that Curt hitch are

2) All the tongue weight and most of the pulling stress is on the two bolts through the bumper. I'd have to look at how thick the steel of the bumper is to be sure it is stout enough to handle that kind of weight and stress long term without warping or cracking.

If I'm not mistaken the rear bumper on US 123 cars and up to 85 on US 126 cars is an aluminum extrusion. The real issue is not if it will allow you to pull some little trailer to the dump or some tin boat to the old fishing hole, most of the time that will not be very much of a problem. The problem comes when something unexpected and bad happens and you have to lock up the brakes or swerve to avoid some kid or old lady. When the bad thing happens and the hitch and its mounting points are subjected to stresses far and above what is exerted on them on the way to the dump with a month’s worth of household trash. When the bad thing occurs the hitch that is bolted to the aluminum bumper can be ripped free in the blink of an eye. The aluminum is much more likely to fracture and break than steel, hitches bolted through things like the thin single layer of sheet metal that forms the spare tire well will tear a chunk of sheet steel with them when the force of an 800 lb trailer moving 50 MPH in one direction is suddenly violently propelled in another direction because you had to slam on the brakes are swerve to avoid something and the weight your carrying in it shifts.

The measure of how appropriate a hitch design is should be will it withstand forces like that and keep the trailer and load connected to the car when something bad happens so that it doesn't come loose and fly into the oncoming lane of traffic killing the family in the minivan.

I have a close friend who had this exact thing happen to him when a landscraper’s trailer broke free breaking its mountings and the trailer with safety chains still attached to the hitch came across into his lane at about 40-50 MPH and destroyed his pickup with him and his wife in it. The guy who lost the trailer was trying to pass someone else and said he didn’t see he wasn’t far enough past the car he was passing, he started to move right and the guy he was cutting off laid on the horn, he swerved back left and the trailer started swinging!

The landscraper was underinsured and ended up loosing everything after being found negligent, my friend ended up with broken bones but his wife who came half way through the windshield is disabled and lost an eye!

300SD81 · #21 03-09-2010, 11:07 PM

Made some progress on this. Got everything but the receiver tube welded together. The angle channels I ordered were WAY thicker than expected, closer to 1/2in than 1/4... Had to get a local machine shop to cut it for me because my miter saw with cutting wheel couldn't do it. Weld penetration was crap because of the thickness, even though I V-cut the edges, but I welded it from both sides, so I bet its at least as strong as a good weld on 1/4" channels.

Need some advice on how to cut out the slots for the bumper mounts, I doubt I can use a jigsaw on the nearly 1/2" steel...

t walgamuth · #22 03-10-2010, 05:34 AM

1/2" thick? Yipes!

I would not carry a bicycle on a hitch bolted to my bumper. Those bumpers are noted for falling off with nothing on them at all.

The ones that bolt under the shocks are the only way to go, then a kicker going forward bolted to the front edge of the spare tire well is how the european hitch was on my old 220b which I used in europe to tow a 1300ish # travel trailer (which had full surge mechanical brakes).

300SD81 · #23 04-25-2010, 08:49 PM

Did some towing for the first time with this, no problems at all. Had that trailer on there for 1400 miles (700 empty, 700 loaded). I'll try to remember to take a picture of the hitch itself some time. Its built exactly like I posted above. Way too much tongue weight (about 500lbs) in the pic, but I couldn't really shift the engine around much.