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FMC Chassis
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Duramaxer
Posted 2009-12-14 4:40 PM (#862)
Subject: FMC Chassis



Location: Oslo Norway
(84.49.209.102)

 

Dear friends

This is a posting that I felt like making as a response to the threads over at the yahoo group regarding sheer plating of the FMC Motorcoach. I rather post it here because I can use pictures on this forum.

I am no engineer, just a mechanic so all my work is based on the principle of repairing and improving as I go. What I’m writing here is not based on calculations and I can not prove any of it. But I have spent enough time cutting welding and grinding on #477 to have had time to think of the design, strengths, weaknesses and potential improvements on the 2900R structure. I hate to repair things more than once so I seldom repair anything without having a clue about the cause of why thing need to be repaired or modified.
My realty was the simple fact that I had a coach with rust damage and a sagging rear. And I believe they all do to some degree until proven wrong. I could have gone by the “easy” approach of just flicking on the rusted steel and adding sheer plates to the sides. I could have made that fix in a month. I have sheer plated my coach and I am glad I did. But sheer plating is just one piece to the puzzle.

The coach platform is different to most rv’s as we all know.  I have read some thoughts on the design but I do not think I have seen any explanation that I fully believe in yet. No one forgot to put a frame in to the design!

As so often there is a lot of focus on single parts of the structure the upper aluminum “cage” and the fiberglass skin are always the most popular subjects. Let’s leave out the fiberglass skin for now. The upper aluminum framework is obviously part of the “total frame structure”, as to what degree it is a part of carrying the engine weight I’m very uncertain.

I really believe there is a steel frame under the FMC or at least there is lot of steel framework. Some people must have missed the beams running from wheel to wheel on each side and the heavy cross member in front of the rear with the huge beams to the rear on each side of the engine. From these there are cross members out to where the aluminum structure is fixed.  If there is a section of the coach where you might say there is no frame that is up front. Exactly how the forces are distributed I do not know but I’m quite sure the engine is hanging from the steal beams and the aluminum structure just supports some of that weight if any at all.

 

This is where the left frame member is attatched to the crossmeber in front of the rear wheel. When welding in a new one I made a larger "patch" to make a stronger joint.

If we can just for a minute pretend that the steel under coach is something like a frame, then the two outer beams on each side is where it all starts. On the driver side this beam is placed “standing” and on the passenger side it is laying “flat” , both has the same rectangular dimension, this means the passenger side can carry less vertical forces than the drivers side. Also the passenger side has the door opening on the middle of the length so there is a huge “gap” where the upper structure is not supporting or distributing forces. Also there is no horizontal aluminum bar half way up right behind the passenger door for some reason. Take a look at the picture showing a naked coach under production. How much force could the aluminum framework possibly handle on the passenger side?
My approach to improve this on #477 was to weld a vertical flat bar on the inside of this member when changing it. This makes it stronger on vertical load still close to standard dimensions. Then I added an aluminum bar horizontal above the opening for the air conditioners. #477 also got heavier grade square tubing for the whole floor structure, heavy enough relief som of the outer side members and to distribute forces thru out the chassis like the flimsy original profiles never could. I beefed up the fixtures for the door frame and of course added the sheer plate. This area should have little to do with the rear sagging yet some and I believe it might affect the handling.

 

The blue illustrates where the sheer plate goes. The red is where I added vertical flat bar steel to improve vertical strenght of the existing frame..

 Further back the huge cross member in front of the rears is very much like the pivot point of the rear weight. I believe this must be the most critical part of the whole design. In that area you have both the rear weight and the suspension to deal with. Looks to me the engineers at FMC added a well dimensioned square tube. But I will keep an eye on everything attached to it. I welded on a square tube from side to side on the front of it and then welded my flooring structure on to this because I wanted to let the floor structure take some stress from the points on each side where this cross member is attached without fixing each tube straight on it.

From this cross member and backwards there are three parts in the design. The two beams running backward on each side of the engine and tranny , the upper aluminum structure and the outer steel tubing on each side connecting the other two. I believe this is an important part of the structure and it easy to improve. I added all new steel tubing and then a stronger vertical steel plate on the inside all the way to make it stronger to vertical loads. I also beefed up all the steel to aluminum fixing points.

The light grey steel is the replacement for the original tubing and the darker stil is the heavier gauge plate.

The two rearward running beams on each side of the engine are carrying the load and those I will keep a close eye to. If I where to modify a coach to take a heavier stronger engine I would have looked into adding some strength to those.
In time I will change the crossmember in the rear that has the bracket for the original muffler on #477. And if I did not have one I would have added the heavy type bumper bracket because it is also holding things together back there

I do not want you guys to tear your coaches apart and do what I did, but I think all could benefit from trying to se a broader picture than only a sheer plate fix and take some of the woodo out of things. And if we wanted a traditional framed rv we should have bought one.
 

Kjetil

 

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Duramaxer
Posted 2009-12-14 7:13 PM (#863 - in reply to #862)
Subject: RE: FMC Chassis



Location: Oslo Norway
(84.49.209.102)

This is a rough picture showing more of how the framework layout is.

Ther red is the original. And the blue is the floorstructure of #477 by memory.

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Duramaxer
Posted 2009-12-26 3:20 PM (#872 - in reply to #862)
Subject: RE: FMC Chassis



Location: Oslo Norway
(84.49.216.40)

I have a few more pictures that might illustrate more aspects of the Fmc chassis.

I have had good feedback from other owners, and I will try to incorporate in to this posting some of the points made out.

This is the rolling chassis picture one more time. The large cross member (box) in front of the rear wheels is what connects the steel frame structure in the rear to the forward frame beams. Also this picture illustrates there is a lot of weight on those two narrow inside frame members running backwards on each side of the engine.

I know that the passenger side  frame member bowed on my coach. The members in the rear might bend or the cross member migh pivot (I have tried to illustrate with the arrows). In both cases you will have a sagging rear end. Lets say this occours, would the upper aluminum structure then be able to take up these forces, shear plated or not?

This pictures (above) showes the original aluminum sheet outside the fuel tank on #477. Clearly something is wrong.

Here (right) is a closeup of where the same thin aluminum plate is attached wherr the upper aluminum structure is fixed to the outer rear steel frame. Or should we say used to be attached. It is torn out from the pop rivets. Things where loose and they where moving around.

And I do not belive it is for one single reason but the combination of several. Pop riveting or fixing aluiminum directly to steel in any way, is seldom recomended I guess.

 

 

 

 

This picture (left) is taken from another coach inside the place where the fuel tank sits. This is exactly on the inside of the picture above.

 

 

 

 

 

 

I love the FMC Motorcoach, and this thread is just ment to help people undertand more about the structure and how several things might affect the rear end. Now do what ever makes you happy and if your coach is straight then you can just give it som attention to keep the rust from taking over. And you might want to check on those aluminum to steel fixing points.

Stay cool

Kjetil

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BigRabbitMan
Posted 2009-12-26 9:21 PM (#873 - in reply to #872)
Subject: Re: FMC Chassis



Location: Cottage Grove, OR
(71.142.254.210)
Kjetil,
Thank you for these detailed and well illustrated reviews of the FMC frame. It will help guide me at a future point.
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BigRabbitMan
Posted 2015-11-01 3:02 PM (#3141 - in reply to #862)
Subject: Re: FMC Chassis



Location: Cottage Grove, OR
(75.139.213.151)
byegorge

Posted 2015-10-30 1:11 PM (#3124 - in reply to #1311)
Subject: Re: The Dieselfication of Coach 1046 Quote Reply Alert Edit Delete

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25
Location: Olympia, Washington
(174.61.212.92) Len, Stephen:

I have read about 'shear plating' to stiffen the structure to better handle the weight of a Detroit diesel, is that a concern with the Duramax swap? Thanks.
-----
George Jensen
Coach 506
Olympia, Wa

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LCAC_Man

Posted 2015-10-30 6:45 PM (#3125 - in reply to #1311)
Subject: Re: The Dieselfication of Coach 1046 Quote Reply Alert Edit Delete

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Regular

2525
Location: Oceanside, CA
(172.10.134.245) The 8.2 is over 200lbs heavier than the Duramax, I'm also replacing the Onan 6.5kw with a Yanmar than is 115lbs lighter, and moving the battery forward. I don't think weight will drive structure changes.
Additional torque/power is another matter, while I'm still not sure it will be required, I'm going to make my new engine and transmission crossmembers more structurally significant portions of the frame, the original engine crossmember that incorporated the circular design to accommodate the exhaust couldn't have provided much if any additional frame rigidity.
-----
Len Barron
#1027 soon to be Duramaxed!

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andy1canada

Posted 2015-10-30 10:53 PM (#3126 - in reply to #1311)
Subject: Re: The Dieselfication of Coach 1046 Quote Reply Alert Edit Delete

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252525
Location: Victoria, BC. Canada
(108.180.117.65) Great observations Lenny! Can't wait to see what the outcome actually is. If we don't strive to make improvements - in spite of the prospect of failure - nothing will get better.
Please do keep us posted on your progress. It's people like you and Stephen and others who strive for improvement in what was originally a very good idea - that keep us all glued to our screens.

Terry
#846

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BigRabbitMan

Posted 2015-10-31 8:53 AM (#3127 - in reply to #1311)
Subject: Re: The Dieselfication of Coach 1046 Quote Reply Alert Edit Delete

Online


Extreme Veteran

500252525
Location: Cottage Grove, OR
(75.139.213.151) As I recall from memory (which is dangerous in my case!) the Detroit 8.2 weighs about 1400 pounds and the Cummins 5.9 about 1000-1100 pounds and the Duramax about 850 pounds and the 440 about 650-700 pounds. One problem with all of these numbers is getting them with the engine at the same state of "dress". The best comparison would be with them all fully dressed as they would be when installed in a vehicle with manifolds, generators, carbs, oil filter, etc. all installed. I haven't found those numbers as of yet. At this point, I leave that up to others. It would be good for the community if those numbers were found for those engines and any other engine under consideration with links to the source of the data so correct interpretations could be verified. Upgrading the transmission to an Allison also adds about 200 pounds to the mix.

But pound numbers are only part of the mix to be considered. Leverage is the other factor. A pound added to the transmission has half the leverage effect of a pound added out at the end of the frame. Due to the length of the Allison 1000 transmission, my engine is a couple of inches further back than the stock position of the 440. But the center of gravity of a V8 is further forward than the center of gravity of an inline six. I replaced the heavy brass radiator that was out at the end of the frame with a light early 2000's aluminum radiator. The 440 has a torque rating of about 350 ft.lbs. while the Duramax is rated at about 650 fl.lbs.. That is a factor to be considered, but it is a variable factor as torque is only generated as called upon by the fuel pedal. Weight is there 100% of the time including when parked!

In my and Len's case with the double overdrive transmission, we are able to retain the stock high ratio gearing between the drive shaft and the ground. That reduces the torque needed from the drive shaft/engine to achieve a given forward force as compared to diesel setups that have larger wheels and/or lower ratio differentials. All of this and more comes into play when making changes.

As to shear plating, I think that it adds to the stiffness of the body of the coach but if one looks at the structure of the frame members of the coach and how the body is attached to the frame in the rear and where the engine is attached, there is no direct support of the frame members that support the engine as a result of shear plating. So does shear plating solve a flexing issue or does it simply mask it? How much flexing of the engine support members is acceptable? As Len has noted, with and without the 440 causes things to flex. Some expected flex is designed into machines such as our coaches. How much is tolerable is the question! When I reattached the lower portion of the ladder to my coach, all of the bolt holes lined up. To me, that was a good sign that the frame members that support the bumper were in approximately the same position as they were originally. But, yes, that was a static measurement.

Bottom line for me is that shear plating is a good thing as it stiffens the side panels of the coach, but it is not to be expected to materially support a diesel engine nor the torque it generates.


-----
Stephen Heinrichs
FMC Coach 1046
Cottage Grove, OR
Yep,I am here

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andy1canada

Posted 2015-10-31 9:33 AM (#3128 - in reply to #1311)
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252525
Location: Victoria, BC. Canada
(108.180.117.65) Very interesting Stephen.

Perhaps we might start a new thread focused on chassis capacity based on other owners real-world experiences and results with engine conversions?

Over the 8 or so years I've been involved with FMC's I have read occasional threads about issues with handling and measurable - if not visible - sagging in the butt-end of these things as a result. I think a new thread might be a good idea.

Frankly, I find it hard to swallow that FMC's motorhome was not overbuilt like most other stuff they made. One would imagine that those two primary aft frame members that carry the engine/trans load were stressed/engineered to handle at least twice the projected service weight. FMC tended to build stuff that way. Yet, we all know there were a few recalls on the coaches that, from what I can gather, were addressed.

So, anyone else think this would be a good thread to start? If so, I'd like to see info/results/observations on other projects of today & yesterday. If there were issues, how were they detected or measured? What are the original chassis specs that one can reference to see if theirs has moved any over the years or as a result of an engine swap? Tools and methodology: is a simple laser the way to go? what points beneath the coach can one easily reference? what signs on the exterior to look for? etc etc...

I remember one thread (IIRC) where a guy used a string pulled from one end of the coach to the other to determine if there was any frame/chassis deflection.

Wow! Way too much coffee this morning.

Feedback?

Terry
#846

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denshew

Posted 2015-10-31 11:52 AM (#3129 - in reply to #3128)
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1002525
Location: Canton, (Sixes) GA
(166.137.10.82) Mighty 890, 8.2/545, alum radiator weighs in at 16560 with fuel, propane & water tanks full, family (4) aboard, fully provisioned. Sheer plated. One or two finger steering when underway. Very slight bulge aft of passenger side door that has not changed in past 8.5 plus years. Would be good to get coach weighs with qualifying details. I am going to try to get it weighed with just fuel, propane water tanks full, no people or provisions. Scales at Red Oak II 2016?

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BigRabbitMan

Posted 2015-10-31 2:50 PM (#3130 - in reply to #1312)
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500252525
Location: Cottage Grove, OR
(75.139.213.151)




denshew - 2011-01-05 7:08 AM Stephen – WOW. You have done your homework so should be a great project. My mind is flooded with a hundred questions and suggestions but will just say good luck and wish I was there to lend a hand. Eat the elephant. Denny
Well Denny, we ate the elephant!!







-----
Stephen Heinrichs
FMC Coach 1046
Cottage Grove, OR
Yep,I am here

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BigRabbitMan

Posted 2015-10-31 3:46 PM (#3131 - in reply to #1311)
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500252525
Location: Cottage Grove, OR
(75.139.213.151) Here is weight information for 1046 prior to the conversion. At some point, I will weight the coach again and we will see what changed. I also did some ground to end of frame rail measurements immediately before and after removing the 440 and immediately before and after installing the Duramax. The information is below.

****************
FMC 1046 weights as of 4-8-2011 prior to Duramax conversion.

Current set up is Chrysler 440 with an Allison 545 transmission and Edelbrock MPI fuel injection. Stock radiator converted to 6 rows. A 120 pound internet antenna is centered on the roof near the front. The generator is an Onan Marquis 7000 (290lbs.)

At the time of weighing, the fresh water tanks were full (they are to the right of the centerline near front axel) and the waste tanks empty (they are to the left of the centerline in front of the rear wheel).

Also, to weigh the left side the coach was driven half on and half off the scales. There was a small difference in height so the coach was slightly tipped to the right which would cause a slight weight bias to the right that would not be there if everything was level. The right side weight was derived by subtracting the left side weights from the axel weights. It was a segmented scale so the axel and total weights are all actual scale weight and not calculated.


Cat scale, Dixon, CA

Left right
Front: 5,200 2,480 2720

Rear: 9,500 4,480 5,020

Total: 14,700 6,960 7,740


Frame rail height from ground before and after engine (440 w/Allison) removal:

Left Right

Before: 21” 20 ¼”

After: 21 3/8” 20 ¾”

Rise: 3/8” ½”

Frame rail height from ground before and after Duramax (w/Allison) installation.

Before 27 15/16 27 3/16

After 27 ¾ 27 1/8

Drop: 3/16 1/16 Note: Generator not yet reinstalled.

Note that the difference in rail height by approximately 6 inches was due to measuring to the bottom vs the top of the rail. Also overall coach height changed due to re-jacking/leveling the coach in the intervening time period.

****************

Hopefully this information will give others something to compare to. At such time as I am able to re-weigh the coach, the numbers will be posted.

Enjoy,

-----
Stephen Heinrichs
FMC Coach 1046
Cottage Grove, OR
Yep,I am here

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hemi354az

Posted 2015-10-31 5:05 PM (#3133 - in reply to #3124)
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Location: Scottsdale, Aridzona
(24.251.160.88) Please see Page 7 of "Discussions", Subject - FMC Chassis, messages #862, #863, and #872 by Duramaxer (Kjetil #477 Bergflødt).

All FMCers should review ALL of Duramaxers PHOTOS as he has rebuilt FMC #477 into the GOLD STANDARD that we all aspire.

There are many other PHOTOS of FMCs "without the skin" by others that are also worthwhile reviewing.

Bend(?) ON ! Lou #120


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Duramaxer

Posted 2015-10-31 5:08 PM (#3134 - in reply to #3128)
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Location: Oslo Norway
(84.213.37.196)
It's hardly a "tread" on the chassis as it got few comments and caused little discussion but this was some of my thoughts on the subject http://www.fmcowners.com/mbbs22/forums/thread-view.asp?tid=200&...

Sag on

Kjetil, #477









-----
http://www.fmcmotorcoach.com


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LCAC_Man

Posted 2015-10-31 6:54 PM (#3135 - in reply to #3129)
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2525
Location: Oceanside, CA
(172.10.134.245)
denshew - 2015-10-31 11:52 AM

Very slight bulge aft of passenger side door that has not changed in past 8.5 plus years.

Do any of them not have it? I've seen 5 in person, every one of them had that buldge (including mine with no engine in it).
-----
Len Barron
#1027 soon to be Duramaxed!

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byegorge

Posted 2015-10-31 9:33 PM (#3138 - in reply to #1311)
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Location: Olympia, Washington
(174.61.212.92) Is anything being done to increase the 'GVWR' beyond the stock 15,000 Lb. (10K rear & 5K front)? Maybe a better question would be how many 'Coaches' are currently being operated in an overloaded condition (ie: GVW in excess of 15,000 Lbs.)? I have yet to weigh #506 but I have no problem believing it will be in excess of 15,000 Lbs. fully loaded. How does one go about increasing the 'GVWR' of the Coach? What would need to be upgraded the tires, wheels, springs, bearings and/or frame structure? In a bone stock FMC what is the weakest link in the 'GVWR' equation?
-----
George Jensen
Coach 506
Olympia, Wa

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borrmann

Posted 2015-11-01 5:23 AM (#3139 - in reply to #3138)
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Location: Bluevale, Ontario
(24.138.185.30) Number 645 has a 5.9 Cummins and an Allison 2200, has been shear plated. Have scaled about 5 different times, full of fuel and fresh water and passengers. 15,000 lbs., 10,000 on the rear and 5,000 up front. Have never done individual wheel weights, would be interesting. Maybe at Red Oak. Frank.

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LCAC_Man

Posted 2015-11-01 5:44 AM (#3140 - in reply to #1311)
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2525
Location: Oceanside, CA
(172.10.134.245) Re-classifying a vehicles GVWR/GCWR is very difficult/impossible depending on what state you're trying to do it in.
From a practical standpoint, you really need to consider what elements drove the current GVWR. After looking at the existing suspension, brakes , chassis structure, tires, and drivetrain the weakest link in that chain is the transmission/driveshaft/parking brake system. I don't know of any applications where the 727 is rated beyond 15000lbs GVWR and I'm not sure how the FMC engineers got comfortable with using a slip driveshaft with only 1.375" 10spline shaft.
The parking/emergency brake must have been the minimum to meet DOT requirements at the time as it the same size as what was installed on my 4000lbs 75 Toyota Landcruiser FJ40 (previous vehicle).
The 140 series Rockwell differential is well below its max rating (I saw references to it being used in 24000lbs GVWR vehicles).
The tires are critical elements, but, most commercial tires in the 19.5" size fit the high weight ratings.
The suspension, while a little soft for higher weights can easily be stiffened with air bags.
The chassis construction is as good as/better than more modern coaches with high GVWR's, the 6" rectangle tube configuration in the drivetrain area is extremely strong.
I haven't spent any time really evaluating the drum brakes/brake surface area capacity, so, it is still something to consider. The duramax/allison is much more effective with engine/trans braking so a considerable amount of the load can be offset with them.

Edited by LCAC_Man 2015-11-01 6:02 AM

-----
Len Barron
#1027 soon to be Duramaxed!
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BigRabbitMan
Posted 2015-11-01 3:19 PM (#3143 - in reply to #862)
Subject: Re: FMC Chassis



Location: Cottage Grove, OR
(75.139.213.151)
The "Dieselfication of 1046" thread has evolved into a general discussion of the FMC chassis so I have copied the last series of posts and pasted them into the above post so that the discussion can continue here in what is a more appropriate thread as the initial posts by Duramaxer provide a good background for understanding the FMC chassis and for continuing the discussion of the chassis.
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byegorge
Posted 2015-11-01 5:57 PM (#3144 - in reply to #862)
Subject: Re: FMC Chassis


Location: Olympia, Washington
(174.61.212.92)
Thank you Stephen, looks like you kept busy for Halloween on your computer. Kjetil's post reminded me of the rust issue. Is 'Sagging Tail Syndrome' a function of added weight or a symptom of deteriorated frame strength due to rust damage? A weakened frame would also include the aluminium to steel attachment points. Did Jim ever report back on his rear suspension repair after it 'fell off'? Kjetil: I see from your before pictures your coach had severe rust issues when you got it. Any guesses as to how much strength was lost at that time compared to new? I think Lou has got it wrong your coach is way beyond any gold standard, platinum maybe keep up the good work.
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LCAC_Man
Posted 2015-11-02 7:04 AM (#3149 - in reply to #3144)
Subject: Re: FMC Chassis


Location: Oceanside, CA
(172.10.134.245)
byegorge - 2015-11-01 3:57 PM

Is 'Sagging Tail Syndrome' a function of added weight or a symptom of deteriorated frame strength due to rust damage?


I think that (after looking at) the overall design, that "STD" is probably just an age/fatigue symptom of the rear frame rails flexing for 40yrs; not much different than ships hulls with "hogging" and "sagging". Certainly rust would weaken and accelerate/exacerbate the sag, but, I bet there's not an FMC out there that doesn't have it to some extent (some very low mileage well cared for rigs maybe...but if you're not going to use them who cares..). I looked at the shear plating idea and it does have some merit, but, I don't think it's the only way to "skin the cat". I think that improving the connection from the aft frame rails to the large box tube structure would help, but, I believe the most effective would be to add structure at the rear wheel openings. Roll forming some large square tube to match the wheel well radius and then welding it in approx above the outboard tire, tying the forward box structure to the aft transverse tube structure. You'd want to lift the rear corners of the coach completely to relieve any of the sagging (put the new structure in pre-load)before welding in. I think this would give a tremendous boost to the rear frame section strength.
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Duramaxer
Posted 2015-11-02 5:17 PM (#3154 - in reply to #3149)
Subject: Re: FMC Chassis



Location: Oslo Norway
(84.213.37.196)

LCAC
Adding "structure" at the wheel openings is part of the sheer plating approach.  There is no space for large square tubing but you would want to add to diagonals which becomes a,larger box structure the plate or plates are welded on. If you were to make a lager steel connection across the wheel openings you would have to make all new attachment point on the upper aluminum structure. 
Also the sheer plating on the driver side will go all the way up to the drivers door and on the passenger side up to the passenger door, this might be good too. If you are going to skin the cat in a different way, why don't you look into having the steel inner structure beefed up while you doing the diesel conversion, you are doing framework back there now anyway. 
 
I believe adding "preload" in thie rear wheel area will give same problems as the original configuration has because you will never be able to make the upper aluminum structure "follow" the lower steel frame.  I had a little bit of "negative sag" in #477 when doing the plating but that was more or less unintended and just because she was sitting on jack stands and had been so for a while. I would not know how to calculate or distribute any preload between the upper and the lower, and all upper structure attachment points had all been redone at that time. 
 
All you can do is make the rear of the coach as neutral, light and solid as practically possible.  Part from having a healthy front steering and suspension reducing the weight in the rear and moving what ever load possible forward this will be the best medicines for both the handling of the coach and the sagging issue. When driving my coach home from the fiberglass workshop with no genset, a stripped interior,  the sheer plating, a rigid new roof and repaired framework the coach was like a gigantic go-cart compared to before, even if my steering still was totally shot. This totally goes against my theory that some of the best handling FMC2900r's out there today are coaches with  heavy butts sitting way deep in their add-on rubber springs, but that is for a another thread. 
 

Travel light - travel straight and fast.
 
Kjetil, #477
 
 
 
 
 
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LCAC_Man
Posted 2015-11-02 8:41 PM (#3156 - in reply to #3154)
Subject: Re: FMC Chassis


Location: Oceanside, CA
(172.10.134.245)
Duramaxer - 2015-11-02 3:17 PM

 There is no space for large square tubing but you would want to add to diagonals which becomes a,larger box structure the plate or plates are welded on. If you were to make a lager steel connection across the wheel openings you would have to make all new attachment point on the upper aluminum structure.  If you are going to skin the cat in a different way, why don't you look into having the steel inner structure beefed up while you doing the diesel conversion, you are doing framework back there now anyway. 
 
I believe adding "preload" in thie rear wheel area will give same problems as the original configuration has because you will never be able to make the upper aluminum structure "follow" the lower steel frame.

I think you could make room in the wheel opening, if you rolled it to the same radius and notched the wheel well I think you tuck a couple 2" square tube sections (welded together to make 4" wide), there would be some protrusion to the wheel well but there's room to give there. Since it is all new structure placed for rigidity I wouldn't try to tie it to the aluminum superstructure at all.
I think almost all the movement is coming right at the connection point of the aft frame rails to that box structure. They did a poor job with that joint design and didn't do much to load spread, at least 2" of the 6" tube is hanging below the box structure completely un-utilized.
I doubt those 6"x3" rectangular tubes are bowing much at all, tube of those dimensions is incredibly rigid.A better job gusseting that connection would probably yield some good results. Anything to spread that rear section weight across a larger portion of the box structure would be helpful.
Totally agree that any weight that can be reduced back aft will do wonders.
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andy1canada
Posted 2015-11-01 6:43 PM (#3146 - in reply to #862)
Subject: Re: FMC Chassis


Location: Victoria, BC. Canada
(108.180.117.65)
Ha-ha! By-George you've done it again! Now we've got 'STD's AND 'STS' as it relates to our beloved old coaches.

Let's see... okay here we go: 'BES' = Blown Engine Syndrome.

I digress. Next?

Terry
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