Mercedes R320 CDI towing 31' '79 Excella

[Knuff]

Originally Posted by dkottum

Not sure what your point is. If the hitch connection produces road noise, then it is transmitted at the rear receiver connection. Honestly I've never heard any road noise difference hitched or unhitched.

But we should ask those with such a reinforcement; does this reinforcement produce more road noise?

Nope - not more noise. The reinforcement is benign with respect to vibration and noise.

[Knuff]

Originally Posted by rostam

I was talking about the super bowl game

There is a master certified Porsche/Audi technician in the forum that posted about issues with the hitch reinforcement before.

Reminds me that Audi/VW/Porsche are indeed a different platform compared to the Benz. Still, after towing 25K miles, there are no issues... Bummer with the Diesel scandal. I was hoping for the 5L Diesel Cayenne with 850 lbs of torque...

[dkottum]

Originally Posted by rostam

I was talking about the super bowl game

There is a master certified Porsche/Audi technician in the forum that posted about issues with the hitch reinforcement before.

Yes, a mechanic with credentials and experience which is useful but more of an opinion about hitch reinforcement, possibly related to his experience with Porsche/Audi suspension carriers. Read it because we want to know if such a tow vehicle is a good choice.

This sort of speculation is interesting but we need more than that. Can-Am (as well as others) has been doing this reinforcement on hundreds of such vehicles for years yet I can recall no reports of suspension damage on account of it.

Keeping an eye on our own unreinforced Ram 1500 receiver, I get the impression the long reinforcing arm would have plenty of leverage to steady the receiver without severe force on the suspension carrier. What is your towing experience telling you on the subject?

[jcl]

Originally Posted by rostam

I was talking about the super bowl game

There is a master certified Porsche/Audi technician in the forum that posted about issues with the hitch reinforcement before.

Perhaps there was more than one master Porsche technician posting on the topic of hitch reinforcements and the problems he had seen with them. The one I recall posted on a thread about tow ratings for the Touareg, and said he had seen every Porsche failure point, but didn't comment on hitch reinforcements. Also no specific posts on failures seen related to towing. Link below, post 14. Do you have another link? I am interested in problems documented after installing a brace, not the theory of why such a brace may cause noise transmission, which we have already discussed.

http://www.airforums.com/forums/f238...ml#post1666916

Jeff

[guskmg]

Re; Post #6. The hitch frame has to be attached to sheet metal in the uni-body vehicle's construction. In order to do this correctly you need to attach to as many points as possible with welds and nuts/bolts to spread the load out over the uni-body along the hitch frame. When hitched up there will be loads in both up and down directions on the front as well as the rear of the hitch frame (think a "T", "H", or box shaped hitch frames). In my case when the vehicle pitched up going over the tracks it overloaded the front of the hitch frame and the frame tore loose from the uni-body and almost snagged a track rail. Just prior to that, the hitch force was in the opposite going up over the RR track. Good sheet metal attachment procedures require bolt holes no closer than three bolt hole diameters. Probably the best thing to do would be to interspace short beads of weld in between the bolt and nuts. You could do it all with bolts/nuts only, but be sure and use many more than what seems necessary to spread out the load over the uni-body that will be encountered. Many aircraft fittings are attached this way. Remember the attaching area must be capable of supporting the load on a sustained basis including any stress that could possibly be encountered.
guskmg

[Andrew T]

29 years ago when we first fastened the front of the receiver to a rubber isolated suspension cradle we were really concerned. We did it thinking this won't work but lets just try it and see what happens. There was no affect at all on road noise or vibration, at least nothing detectable. Since then we have done this on a couple of thousand vehicles. We had one Hyundai SUV about 10 years ago that had a bit 0f a rumble afterwards but that is the only one.

I think due to the length of the receiver tube and the width of the stock receiver there is enough flex in the hitch to absorb the movement of the axle carrier. When the weight distribution is done up it actually takes a little pressure off of the bushings. We have not seen any accelerated wear of the bushings.

The great thing about the axle carrier is it distributes the downward force to 4 or 6 separated body points. Since we are fastening between the wheels as opposed to behind them on a live axle vehicle it makes a very strong installation.

The ones that concerned me more are vehicles like my Jag or Road Rulers Infinity where the Suspension Cradle is aluminum so far though not an issue on either after several years.

The R Class in the pictures on Page 1 is friend of ours and it never had any issues. They have replaced it with a newer one while they could still get one but have 110,000 miles on the old one.

I have driven several hundred miles with their 34 Classic and I have to say it is likely the best tow vehicle I have ever driven. Absolutely rock solid on the road but with a very nice ride at the same time.

Andrew T

[Silverleaf]

I pulled my 30'' with the ML variant of this engine and Andy's mods. The Hensley that Andy probably recommended helped immensely. There are a lot of naysayers out there, and it's true that the feel of this combo is different than a LWB truck, but IMO it is safe and viable. I wonder if you might exceed 7200 pounds loaded for full timing, so be careful of that. Wishing you safe and happy travels.

[jrswann]

I towed a 2013 FC 27' with the same engine in an ML350. Towing is fine. Problem is that you reach the maximum weight rating for the vehicle real fast. Not much room to carry extra stuff inthe vehicle.

[Road Ruler]

Originally Posted by Andrew T

29 years ago when we first fastened the front of the receiver to a rubber isolated suspension cradle we were really concerned. We did it thinking this won't work but lets just try it and see what happens. There was no affect at all on road noise or vibration, at least nothing detectable. Since then we have done this on a couple of thousand vehicles.

The ones that concerned me more are vehicles like my Jag or Road Rulers Infinity where the Suspension Cradle is aluminum so far though not an issue on either after several years.

Andrew T

Correct re our Infiniti. There is no transmitted road noise from Andy's mods or attachment points and after 200hrs of towing the aluminum suspension cradle is fine. The G35 is now 13 years old and has 255,000klm's on it.

PS.... just the other day we test drove a 2010 Jaguar XF sedan. Very nice V8 vehicle with lots of power.

[Tuco]

Originally Posted by Andrew T

29 years ago when we first fastened the front of the receiver to a rubber isolated suspension cradle we were really concerned. We did it thinking this won't work but lets just try it and see what happens. There was no affect at all on road noise or vibration, at least nothing detectable. Since then we have done this on a couple of thousand vehicles. We had one Hyundai SUV about 10 years ago that had a bit 0f a rumble afterwards but that is the only one.

I think due to the length of the receiver tube and the width of the stock receiver there is enough flex in the hitch to absorb the movement of the axle carrier. When the weight distribution is done up it actually takes a little pressure off of the bushings. We have not seen any accelerated wear of the bushings.

The great thing about the axle carrier is it distributes the downward force to 4 or 6 separated body points. Since we are fastening between the wheels as opposed to behind them on a live axle vehicle it makes a very strong installation.

The ones that concerned me more are vehicles like my Jag or Road Rulers Infinity where the Suspension Cradle is aluminum so far though not an issue on either after several years.

The R Class in the pictures on Page 1 is friend of ours and it never had any issues. They have replaced it with a newer one while they could still get one but have 110,000 miles on the old one.

I have driven several hundred miles with their 34 Classic and I have to say it is likely the best tow vehicle I have ever driven. Absolutely rock solid on the road but with a very nice ride at the same time.

Andrew T

29 years ago you knew that this was not the correct way to solve the problem. Yet for almost three decades you continued to do the same thing? All this talk about road noise would be moot if the reinforcement was attached to the uni-body and not the carrier. I don't understand why in all that time a proper engineering solution couldn't be found. "Because we have always done it that way" is not the answer. People are trusting and paying you to do it right.

[cameront120]

Originally Posted by Tuco

People are trusting and paying you to do it right.

And those same people have been trusting them for over 40 years. Andy must be doing something right.
What contributions to towing are are you making? If you can do it better, step up.

[Tuco]

Originally Posted by cameront120

And those same people have been trusting them for over 40 years. Andy must be doing something right.
What contributions to towing are are you making? If you can do it better, step up.

Been there and done that. I have already given two examples of how to tie the reinforcement to the uni-body with and without the carrier being involved. Both of them complete the reinforcement triangle. Please try and stay with the rest of us...thanks.

[PKI]

Noise and vibration are either transmitted or dampened depending on the mass and strength of a structure. Wonder if the large thickness of tube used to strengthen a hitch and the significant mass of most hitch structures might well dampen out the road noise transmission.

While it is easy to see up and down vertical loading of the suspension, it is hard to see an upward force from the front of the torque arm unless the trailer drops significantly lower than the tow vehicle or the WD preload is exceeded. But maybe it's just a blind spot in my logic. Retirement must turn off those brain cells. Pat

[PKI]

Originally Posted by Tuco

Been there and done that. I have already given two examples of how to tie the reinforcement to the uni-body with and without the carrier being involved. Both of them complete the reinforcement triangle. Please try and stay with the rest of us...thanks.

Tuco, are those two suggestions in another thread? I am only finding your suggestion to tie into the unibody in this thread. Trying to keep up. Pat

[Tuco]

Originally Posted by PKI

Tuco, are those two suggestions in another thread? I am only finding your suggestion to tie into the unibody in this thread. Trying to keep up. Pat

Yes they were.

http://www.airforums.com/forums/f463...-138296-5.html

Question, you are not running any reinforcement on your X5 correct?

Update: Interesting who posted right after my first suggestion...

[PKI]

That was interesting reading. Thanks for the reminder. Pat

[jcl]

Originally Posted by Tuco

29 years ago you knew that this was not the correct way to solve the problem. Yet for almost three decades you continued to do the same thing? All this talk about road noise would be moot if the reinforcement was attached to the uni-body and not the carrier. I don't understand why in all that time a proper engineering solution couldn't be found. "Because we have always done it that way" is not the answer. People are trusting and paying you to do it right.

I disagree with your characterization that this is not the right way to solve the problem. 29 years ago the approach was tried, and there were initial concerns about noise transmission. Testing showed that it wasn't a problem. This is a valid approach, particularly considering the number of times this design of brace has been installed, and we can all learn from it.

All this talk about road noise appears to actually be moot given the occurrence of issues reported after installing many of these types of reinforcements.

You don't actually know what noise would be transmitted and perceived by occupants in the cabin (particularly the rear seats) with the receiver hitch solidly connected to the unibody right under the rear seats.

If you want a full engineering solution someone will need to do a frequency analysis of the components, and probably mount the rig on a shaker table for an extended test. A test could be designed that accelerates the vibration effects, to see what fails first. It is expensive. And all you may have to do to fix a problem if one is found is to add or subtract mass or otherwise tune the system to change the frequency response. You probably wouldn't ever find something better able to handle a vertical load than the vehicle subframe with its multiple encapsulated mounts.

Conversely, we could try and learn from how it has been done and conclude that the damping inherent in the design handles the vibration just fine, and the four or more subframe mounts collectively handle the torque from the single brace adequately.

Jeff

[Tuco]

Originally Posted by jcl

I disagree with your characterization that this is not the right way to solve the problem. 29 years ago the approach was tried, and there were initial concerns about noise transmission. Testing showed that it wasn't a problem. This is a valid approach, particularly considering the number of times this design of brace has been installed, and we can all learn from it.

All this talk about road noise appears to actually be moot given the occurrence of issues reported after installing many of these types of reinforcements.

You don't actually know what noise would be transmitted and perceived by occupants in the cabin (particularly the rear seats) with the receiver hitch solidly connected to the unibody right under the rear seats.

If you want a full engineering solution someone will need to do a frequency analysis of the components, and probably mount the rig on a shaker table for an extended test. A test could be designed that accelerates the vibration effects, to see what fails first. It is expensive. And all you may have to do to fix a problem if one is found is to add or subtract mass or otherwise tune the system to change the frequency response. You probably wouldn't ever find something better able to handle a vertical load than the vehicle subframe with its multiple encapsulated mounts.

Conversely, we could try and learn from how it has been done and conclude that the damping inherent in the design handles the vibration just fine, and the four or more subframe mounts collectively handle the torque from the single brace adequately.

Jeff

You have every right to disagree, but it does not make your point any more or less valid than mine. As usual you don't address my concerns but rather focus on the "noise issue". This is just more "Smoke and Mirrors" while falling back on the old and tired cliche "We've always done it this way".

The glaring design flaw is still there and has yet to be addressed. If the goal is to reinforce the hitch to handle more load and the forces applied by the WD setup, why are you attaching it to a component of the vehicle that moves independently of the uni-body and said hitch?

[jcl]

Originally Posted by Tuco

If the goal is to reinforce the hitch to handle more load and the forces applied by the WD setup, why are you attaching it to a component of the vehicle that moves independently of the uni-body and said hitch?

Because the force that matters at the front of the torque strut is vertical, not in other planes. There is no need to create a triangle or box.
Because the rear subframe is designed to handle loads far in excess of the load applied by the torque strut.
Because the subframe doesn't move freely, it is constrained by encapsulated mounts, at least on the models I have worked on. It is vibration isolated, not soft mounted.
Because the standard deflection of the receiver, as determined from reports of some owners who were not able to restore front axle loads without the torque strut, is greater than the amount of associated subframe vertical movement that takes place at the front of the torque strut.
Because it is widely reported to work well.
Because despite the potential for transmitting noise, it doesn't appear to do so.
Because the strongest part of the rear unibody is where the rear subframe is attached. This approach takes advantage of that.

it seems to be a "design flaw" in some people's minds, more than in reality.

Jeff

[rostam]

Jeff, please Google "BMW rear subframe failure". It seems several BMW sedans have had rear subframe failures in the years past, and that BMW settled a class action lawsuit with the owners. It seems the rear subframe is not as stout as you may think. Fixing the problem costs thousands of dollars.

To the OP: I suggest you buy a vehicle that can do the job right out of factory. If you want to stay with Mercedes, a 2011-2012 GL350 is a very good vehicle. Same engine and transmission as R, seats 7, and has a good hitch with tow package.