Tow Hitch for w123 300D - PeachParts Mercedes-Benz Forum

pdrayton · #1 01-28-2008, 07:57 AM

Thinking of putting a tow hitch on your Mercedes W123? Here's how I did it.

I've been looking for a tow hitch / tow bar setup for my 1984 300D for a while now. I got the hitch on yesterday and towed my almost 2000lb boat with it and nothing fell off, so that's a good start. It was a bit sluggish, but that is to be expected. I'm going to measure the tranny temperature after towing for a while and compare it to normal and see if there's any reason for concern.

I thought I'd share everything I learned so it's an easy road for someone who wants to add a tow bar to their baby.

Towing Specifications for Mercedes W123 300D 240D
First off, towing ratings / specifications for the mercedes W123 are 750KG (~1650lbs) unbraked, 1500KG (~3300lbs) braked, but only in Europe. Apparently if you use the same car in the USA you can't tow with it, according to Mercedes USA . There is some speculation as to why this is, but no-one really knows, at least not anyone I read from.

Tow Bar
After a lot of searching around, I found a towbar from Uhaul. It is made by Curt manufacturing curtmfg.com and is Uhaul part # 28033. This hitch is rated to tow up to 2000lbs and retails for $99.95 not including labor, so it's Class I -200lbs GVWR, 200lbs tongue weight. It attaches to the bumper and subframe. Takes 4 holes and about 30 minutes to put on, pretty easy actually. It's not a big Class II type hitch. I'll try get some photos up.

The wiring setup is easy, once you have it figured out! So here's it all figured out! First, you have to buy a 5 wire to 4 wire converter. It's a little plastic black box adapter available in a kit or by itself from Walmart or Advance Auto (probably other places, those are just the places I went to). Costs about $15 for the converter, or $23 for the kit, which you will need if you don't have any trailer wiring stuff. I had a connector left over that I used.

The wiring is actually very easy. The kit above comes with splicing stuff, so you don't have to cut any wires on your merc. All you have to do is take out the driver side plastic molding in the trunk - the interior plastic molding that covers the antenna electronics, etc. Once it is out, you can cut a stripe in the wiring that leads to the lights and access the wires that go to both sides of the rear lights. Then it is a simple process of matching the colors below to the colors of the merc wires. If you don't have an american merc, you might want to check the Haynes or Merc FSM for the correct colors, or use a multimeter to make sure you have the correct wires.

Towing wiring: Use 5 wire to 4 wire converter from walmart.
Wires: Black/White = Left
Black./Red = Stop light
Black/Green = Right
Gray/Black = Tail light

If there are any questions, or something I haven't covered, feel free to post.

Happy Towing

nhdoc · #2 01-28-2008, 08:10 AM

Since you live in a relatively flat part of the country you can probably get away with towing with a 300D but pulling a 2000# trailer up any kind of hill would surely put a strain on your transmission, especially a 20+ year old one. I'd probably say you should consider an extra cooler for it if you plan on towing frequently with it because that is really the greatest risk you run is overheating the fluid due to overloading it...but like I said it it mostly going to happen in hillier parts of the country I'd guess.

I guess it is a really good way to take a slow car and make it even slower. I'm glad I don't have to drive behind you

jkoebel · #3 01-28-2008, 08:17 AM

I've got a Class 1 fixed-receiver ball hitch on my car already from the previous owner, I'd love to tow a Scamp trailer behind my car but that is a good point, if I use it my transmission would probably die.

The thing already slips and flares badly 2-3 and 3-4...automatic.

pdrayton · #4 01-28-2008, 08:24 AM

Thanks for the advice.

Any idea what is an accceptable temperature range for the tranny? I have a digital laser thermometer wanting to be put to good use. There is a cooler on the car already (the stock one) is that not good enough?

I'm only going to be using it to tow my boat 2 miles to the boat ramp. Do you think the 15 seconds of pulling it out the water, up the ramp will be a problem? Also, I'll use it to tow my WVO sucker collection trailer. It weighs 1500lbs when TOTALLY full, which is not normally ever.

nhdoc · #5 01-28-2008, 08:43 AM

IIRC the "normal" operating temp for them is about 80C (180F±) but I am sure someone will correct me if I am wrong.

The stock cooler is OK for normal use. Heavy duty use like towing usually calls for a heavier duty tranny cooler and radiator. That is usually what a "towing package" consists of. Sometimes they also add a larger oil cooler too.

validius · #6 01-28-2008, 08:54 AM

The 300D is NOT a tow vehichle and should not be used as one. If you need to haul something around buy an old Ranger or S10!

pdrayton · #7 01-28-2008, 09:24 AM

Validius, thanks for the input.

What are you basing your statements that the 300D is not a tow vehicle on?

The information I have tending to make me think it's OK for under 1500KG is:

1. The tow ratings specified in Europe for the ostensibly the same car is 1500KG.

2. Others have done it and haven't had problems. One guy towed a trailer with furniture and stuff in it for about 1000 miles. Come to think of it, in all the posts I read, I didn't read anything from anyone saying they towed something and it damaged anything.

3. A number of american and European manufacturers make a trailer hitch specifically for this model, that is rated at 2000lbs.

If you have other information that negates this, please let us know. Otherwise, please state your opinions as such.

kerry · #8 01-28-2008, 09:41 AM

The Europeans pull 'caravans' all the time with the 300d. In fact the 300d in Europe would be considered a heavy towing vehicle. They pull caravans with the 200d's.
The cars came with factory hitches in Europe. If a 300d is not a tow vehicle, it's not a driving vehicle either.

Can someone elaborate on the differences in transmission heat production from driving a heavily loaded car and pulling a lightly loaded trailer? I've pulled a trailer over the Rockies with my 85 TD with a total load of around 2000lbs (as I recall--I wrote a thread on it). Most of the load was in the car but some in the trailer. No evidence of problems after having done it.

pdrayton · #9 01-28-2008, 03:47 PM

regarding the temperature of the TX, here's what I found from http://www.txchange.com/heatchrt.htm

"The effect is also cumulative. Short term exposure to high heat levels (or even prolonged exposure to moderate heat) can break down the oil to the point where even very short episodes of overheating will lead to failure."

mobetta · #10 01-29-2008, 01:07 AM

yeah, but that fancy graph isn't for mercedes trannies!!

I have towed a bit w/ my td, and no problems. finally upgraded my hitch to a curt receiver hitch recently. A cooler is not a bad idea. cheap insurance if you tow more than a few times a year.

keep fresh fluid in it, too.

charmalu · #11 01-29-2008, 02:23 AM

What`s the difference if you tow a trailer, or you have a car load
of fat girls

Charlie

300SDog · #12 01-29-2008, 05:17 AM

Weight distribution is the difference: carload of fat girls will not pull the vehicle off the road, say while breaking and cornering on steep mountain down slope.

4-spd 240D that I'd bought (and then never driven) off ebay few years ago came equipped with tow hitch. It was formerly owned by military family that probly did alot of towing from base to base. Left side axle was bad and under close inspection the tow hitch was mounted 3/8" off center. I'd be concerned about rear axles if y'all do alot of towing.

Maxbumpo · #13 01-29-2008, 07:25 AM

Quote:

Originally Posted by pdrayton

First off, towing ratings / specifications for the mercedes W123 are 750KG (~1650lbs) unbraked, 1500KG (~3300lbs) braked, but only in Europe. Apparently if you use the same car in the USA you can't tow with it, according to Mercedes USA . There is some speculation as to why this is, but no-one really knows, at least not anyone I read from.

In Europe, the hitches that are fitted have extensive bracing in the rear body channels and a massive cross piece under the rear bumper. I had an '85 300 TD Euro (non-turbo, 5 spd) that I fitted a Euro hitch, and I've also put one on my '87 300TD. Both were aftermarket but fit extremely well and are VERY solid. I bought both in Italy while on vacation (U.S. Customs was rather curious!). Neither one attaches to the bumper; all the attachment points are on the body.

I tow my sailboat, which on the trailer is about 2500 lbs.

Attached is diagram from the EPC which gives an idea of the bracing.

rg2098 · #14 01-29-2008, 06:45 PM

Quote:

Originally Posted by pdrayton

Towing Specifications for Mercedes W123 300D 240D
First off, towing ratings / specifications for the mercedes W123 are 750KG (~1650lbs) unbraked, 1500KG (~3300lbs) braked, but only in Europe. Apparently if you use the same car in the USA you can't tow with it, according to Mercedes USA . There is some speculation as to why this is, but no-one really knows, at least not anyone I read from.

They probably figure that all the extra weight from the american spec bumpers and burger-eating couch potatoes use up all that towing capacity....

pdrayton · #15 04-06-2008, 12:59 PM

Turns out there are 2 models of towbar from U-haul.

28033 (uhaul #) is a 1500lb, 100lb tongue weight towbar. It's not actually the one I got. Uhaul here is a little useless.

11711 (curt mfg's item#) is a 2000lb, 150 tongue towbar, and it is the one I have on my car.