Chassis failure on 1998 U 320

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Chassis failure on 1998 U 320

June 04, 2022, 06:33:08 am

There is visual evidence that the lower chords on each side on my MH chassis (1998 36 foot U320) have failed in tension. Previous to the discovery I heard two loud noises (like something large tipping over in the MH) while driving the unit home from storage. The sounds were about 5 minutes apart with the last noise occurring while I was entering my driveway (which does impart a torsion force on the coach). I was unable to determine the source of the loud sounds.

Later, while working on the MH in my driveway I discovered that the door on the water distribution bay just ahead of the engine battery bay could not be opened. I had to remove the door by removing the trim above the door and then unscrew the hinge at the top of the bay door. I was unable to adjust the door to make it close properly. There is no separation at the bulkhead.

The next day I noticed that the doors to the house battery bay and the adjacent storage bay were not opening easily and appeared to be misaligned. I returned the MH to storage without event nor having determined the reason for the problems.

It wasn't until tonight, while lying awake in bed and thinking about the issue that I put the noises and the observations together. I am pretty sure that the lower chords of the chassis frame that are below the wall and between the front and rear axles have failed in tension; most likely weld failures; probably an inital failure on one side that resulted in additional stress on the other side (as I entered the driveway) that caused a similar failure there. Closer inspection indicates that the passenger side failure is probably located between the water valve/water pump bay and the storage bay; and the driver side failure is probably located between the battery bay and the storage bay. I am sure that there is a vertical member in the frame and a welded joint at each location.

I know that this is a serious problem and I also know that it can be repaired, but I could use some counsel. To that end I have some questions. Has anyone else experienced a similar problem? And, if so, how did the repair go? Does anyone have a drawing of a chassis frame? The frame members are probably square tubing; maybe 1 1/2" square?

I will have to do some disassembly to expose the areas of concern which will include removing doors, slide outs and the cosmetic and functional covering of the joint areas. Once the failure in exposed it can be aligned, pulled together, re-welded and perhaps reinforced.

The failure might have been precipitated by a poor connection. A basic analysis of the frame suggests that there is probably compressive stress on the lower members when moving forward and only significant tensile stresses when hard braking or backing up. I use the retarder a lot which will cause tensile stress in all frame members ahead of the bulkhead because the front wheels are not braking.

Any comments or ideas are surely welcome.

Re: Chassis failure on 1998 U 320

Reply #1 – June 04, 2022, 06:57:52 am

Others will soon chime in on this one,any pictures will help us,what exactly do you mean by "chords",the nearest I can think of
for the cause of the door misalignment is bulkhead trouble,between the wheels and the chassis frame you have 8 air bags and
8 shocks and 10 torque rods,5 in front and 5 in back,one of those components may be the pop you heard.
When you can get underneath and check mounting points for those components and check ride height on a level surface.
Also check your ride height valves,one in front 2 in back.

Re: Chassis failure on 1998 U 320

Reply #2 – June 04, 2022, 08:29:37 am

Your last paragraph may hold true for a low cost cheaper unit but these Foretravels are built like tanks,they can withstand skidding and panic stops,your almost talking a design flaw and if that was the case they all would be doing it,and it would not have lasted this long,on your next post give us some history,mileage and what conditions driven in.

Re: Chassis failure on 1998 U 320

Reply #3 – June 04, 2022, 08:46:53 am

Quote from: John44 – June 04, 2022, 06:57:52 am

...what exactly do you mean by "chords"...

I think the OP is referring to whatever it is that connects the two ends of the coach together. He says there is no bulkhead separation (I assume he means at the rear bulkhead). I have always thought of the Foretravel construction as being a complex latticework of tubing in the middle, with the front and rear suspension/propulsion modules bolted on at the bulkheads. We know that the entire bottom floor structure between the bulkheads can be removed for rust repair. When the floor is removed, all that is left holding the two ends of the coach together is the the metal "cage" that forms the storage bays and the walls and the roof.

Re: Chassis failure on 1998 U 320

Reply #4 – June 04, 2022, 08:47:56 am

This is an unfortunate side effect of having a light rigid space saving "frame:" It's called the "Bulkhead Problem."

Chris Stump built his new frame out of steel at home, more recently, his name escapes me, built one out of aluminum -- because he could.

My basement rebuild

Re: Chassis failure on 1998 U 320

Reply #5 – June 04, 2022, 08:52:25 am

Quote from: GLV – June 04, 2022, 06:33:08 am

The failure might have been precipitated by a poor connection. A basic analysis of the frame suggests that there is probably compressive stress on the lower members when moving forward and only significant tensile stresses when hard braking or backing up. I use the retarder a lot which will cause tensile stress in all frame members ahead of the bulkhead because the front wheels are not braking.

Any comments or ideas are surely welcome.

The weight of the coach is carried by two bridge trusses running between the front and rear bulkheads from just below the windows to just above the storage bays. The box sections that make up the storage bays prevent the structure from twisting as did Galloping Gertie. You can remove the basement floor for repair and replacement. It's a once in a lifetime repair. I hope.

Re: Chassis failure on 1998 U 320

Reply #6 – June 04, 2022, 08:59:45 am

Quote from: GLV – June 04, 2022, 06:33:08 am

I have some questions. Has anyone else experienced a similar problem? And, if so, how did the repair go? Does anyone have a drawing of a chassis frame? The frame members are probably square tubing; maybe 1 1/2" square?

Scrolling down through the thread linked below will provide links to numerous photos taken during major floor reconstruction projects:

Major rear bulkhead troubles.

Re: Chassis failure on 1998 U 320

Reply #7 – June 04, 2022, 09:04:01 am

Think I'll wait until we get feedback from poster,may not even be close to a bulkhead problem.

Re: Chassis failure on 1998 U 320

Reply #8 – June 04, 2022, 09:29:28 am

Quote from: Old Toolmaker – June 04, 2022, 08:47:56 am

This is an unfortunate side effect of having a light rigid space saving "frame:" It's called the "Bulkhead Problem."

Chris Stump built his new frame out of steel at home, more recently, his name escapes me, built one out of aluminum -- because he could.

My basement rebuild

Basement Floor Bulkhead Repair Aluminum

Re: Chassis failure on 1998 U 320

Reply #9 – June 04, 2022, 09:32:46 am

Gary if in deed it has failed it probably was caused by corrosion. Repairs short of rebuild will be difficult. Best of luck
Scott

Re: Chassis failure on 1998 U 320

Reply #10 – June 04, 2022, 09:49:43 am

We REALLY need pictures to be of assistance.

The term "cord" is not one we are familiar with.

The good news is that many of us are quite familiar with the structure of your model coach.

If a problem posting pictures, there is a section in the "Forum Instruction Manual" to assist, or PM me.

Until we get more information, probably best that we don't speculate, as you could get a lot of mis-information as well as some good.

Brett/moderator

Re: Chassis failure on 1998 U 320

Reply #11 – June 04, 2022, 10:06:24 am

Got to go with Scott's analysis of the few facts known so far. Foretravel didn't do anyone any favors with the bridge design and worse with the implementation. The belly of the coach should have been made with easily removable panels for inspection and work. But, that's water under the bridge

. Next step is going to be to take the bottom covering off and see what is going on. If you can't make the repair yourself, I would find a small welding shop rather than a big RV facility. It's basic welding that a good journeyman welder will not have a problem with.

What is your level of knowledge of vehicles and are you or do you have the time and space to inspect it and or repair it? If you can pull the skin off the bottom, high resolution photos will help members advise the next steps you have to take.

Pierce

Re: Chassis failure on 1998 U 320

Reply #12 – June 04, 2022, 10:26:08 am

don't know how much foretravel experience you have, but if
there are other foretravel owners in your area, another set of
eyes on the problem might help.

Re: Chassis failure on 1998 U 320

Reply #13 – June 04, 2022, 12:16:38 pm

Quote from: Pierce & Gaylie Stewart – June 04, 2022, 10:06:24 am

Got to go with Scott's analysis of the few facts known so far. Foretravel didn't do anyone any favors with the bridge design and worse with the implementation. The belly of the coach should have been made with easily removable panels for inspection and work. But, that's water under the bridge . Next step is going to be to take the bottom covering off and see what is going on. If you can't make the repair yourself, I would find a small welding shop rather than a big RV facility. It's basic welding that a good journeyman welder will not have a problem with.

What is your level of knowledge of vehicles and are you or do you have the time and space to inspect it and or repair it? If you can pull the skin off the bottom, high resolution photos will help members advise the next steps you have to take.

Pierce

The key is to keep the inside structure dry. Proper corrosion control. They have a D- rating IMO. Is what it is. Still no better coach that I can afford IMO.
Scott

Re: Chassis failure on 1998 U 320

Reply #14 – June 04, 2022, 02:20:33 pm

Quote from: Pierce & Gaylie Stewart – June 04, 2022, 10:06:24 am

Got to go with Scott's analysis of the few facts known so far. Foretravel didn't do anyone any favors with the bridge design and worse with the implementation. The belly of the coach should have been made with easily removable panels for inspection and work. But, that's water under the bridge . Next step is going to be to take the bottom covering off and see what is going on. If you can't make the repair yourself, I would find a small welding shop rather than a big RV facility. It's basic welding that a good journeyman welder will not have a problem with.

What is your level of knowledge of vehicles and are you or do you have the time and space to inspect it and or repair it? If you can pull the skin off the bottom, high resolution photos will help members advise the next steps you have to take.

Pierce

Sounds a little like Monday morning quarterback to me. I thought there were a higher percentage of Foretravel's on the road than most other brands.

Re: Chassis failure on 1998 U 320

Reply #15 – June 04, 2022, 06:44:01 pm

I think you may find your failure at a venerable place that Foretravel later reinforced, and for many did the beefing up at no cost to owner.

In the rear, against the outside wall of the rear-most bay are two heavy duty vertical rear-facing frame members that were the weak link. Welds break. These two vertical pieces of steel are located about equally spaced from outside with about the same space between them. Reinforcing included welding new vertical frame pieces to the center facing side of each member. Several suspension parts are attached, probably causing the vertical frame members to want to bend rearward.

M11 coaches are heavier and produce more rotational torque than 8.3 engine and probably both have about the same frame.

There is no frame between front and rear axle structures on earlier coaches. The story is when slideouts were introduced around year 2000 Foretravel noticed the big hole in the side hurt their original no-frame design, so they hired a structural engineer who slowly added a frame that connected front and rear with different designs each of the earlier years after 2000.

Maybe other long time Foretravel owners who have had the parts reinforced may share their experience. Our C8.3 1997 did not have the reinforcement but later did find small cracks at the bottom side-to-side frame where the two vertical members attach.

BTW, whenever our streetside rear air bag leaked down, our curbside bay doors went out of line enough to interfere with smooth open and close by stressing the door latch.

Good luck with finding the source of the problem. Likely Rance in Xtreme Graphics would have experience with this frame problem.

Re: Chassis failure on 1998 U 320

Reply #16 – June 04, 2022, 08:02:46 pm

If this were an aircraft, the FAA would put our an AD notice for the problem along with a fix. The same for an automobile where the NHTSA would make a recall if necessary. With an RV, it's up to members of forums like this one to post problems like Gary has and then for members to respond with the experience that they have that may be helpful in securing a fix.

Our Foretravels are constantly changing ownership with new owners who, when something goes wrong, may have no idea what the problem is or how to fix it. So, call it Monday morning quarterbacking or what ever, but I don't believe in sweeping a potential problem under the carpet so will continue to add my two bits worth.

I thought Berry, in the above post, brought good insight into the way different years and engines may effect the structure and what was done to reinforce it. This is what the forum is for.

Pierce

Re: Chassis failure on 1998 U 320

Reply #17 – June 04, 2022, 08:17:30 pm

Thanks everyone for the comments. I visited the MH (back in storage about ten miles from my home) this afternoon and spent a few minutes studying the situation explained earlier. I am unable to find a visible break any where in the suspected area nor am I able to photograph anything that cannot be shared with a commentary.

Before the incident previously described all of the lower doors fit well and the gaps between the doors were uniform over the full height of the adjacent doors. Now some of the gaps are 1/4" wide measured at the top of the adjacent doors and 1/2" wide measured at the bottom of the doors. There is "0" clearance at the aft bottom edge of the water manifold door. I measured the width of the chassis openings at the top and bottom and found that the dimensions are the same. It doesn't make sense! Previously I could open adjacent doors and they did not touch when in the "up" position. Now, I cannot open adjacent doors at the same time because of interference.

There is no apparent problem fore-ward of the aft edge of the front wheel openings nor aft of the fore-ward rear wheel openings. The evidence suggests a problem in the bottom chord of the chassis frame that runs between the wheel openings (a chord is a tension or compression member in a truss). But, as I commented above, the measurements do not suggest elongation of the bottom chord.

?? I will perform a more rigorous inspection when time permits.

I found a schematic of the chassis construction on the front page of a "1998 Features and Specifications" catalog that I have in my possession. I attached a copy to help explain the suspected area (highlighted in yellow). I assume that the schematic is representative of the Unicoach chassis. It appears that there are two longitudinal members near the outside bottom edge of the frame and one about 18" inboard. I am positive that the most outboard member has not failed else it could be seen on examination of the bottom edge of the chassis beneath the doors, unless the frame broke but the plastic covering did not. Seems unlikely.

I am considering having an X-Ray service (aided by the schematic) x-ray the most suspected areas of possible failure. I will keep the Forum updated when I discover the failure.

This information is to aid all in further consideration of the situation. Thanks again for your thoughtful comments.

Gary

Re: Chassis failure on 1998 U 320

Reply #18 – June 04, 2022, 09:11:33 pm

Bending and torsional loads in this area are controlled by the structure above the basement. Failed bolts or weld in the above structures would allow the sag and would sound as a pop at failure. Try looking at the area where the structures meet.

Re: Chassis failure on 1998 U 320

Reply #19 – June 05, 2022, 03:46:26 am

I attached two PDF files to this message. One shows how the gap between two of the compartment doors increases from about 1/4" at the top to about 1/2" at the bottom (previously the gap was constant from top to bottom). This is the only evidence of a problem that I have found so far. The problem exists on both sides of the coach. The other image shows the bulkhead (as I understand the definition) and shows no corrosion or bolt failure. No gap.

I purchased the unit in 2011 from" Motorhomes of Texas" after a personal inspection of the "bulkhead". There has been no change since then. The coach has about 120,000 thousand miles on it. I have no knowledge of the history of the coach before I purchased it other than I believe that there were two previous owners, the first in California and the second in Texas.

The coach has been stored in a closed garage when not in use since the purchase; the last three years in a heated garage. The climate where I live is very dry most of the year; less than 20% RH in the winter. We humidify our home to make it comfortable. The coach has had an easy time during our ownership. It is rarely driven off of paved roads, rarely above 65 miles per hour and rarely for more than 5 or 6 hours in a single day. The coach is kept clean and well serviced and we have had no suspension or chassis problems. However, as with all coaches, we have had some major expenses; new tires, replacement of the alternator, replacement of all of the batteries, replacement of the inter-cooler, replacement of the heater core and most recently a major repair to the radiator. The coach never left the garage for the 2 years prior to November of last year. Us old folk were intimidated by the COVID situation.

An aside. We were stir crazy so we took the coach to Glacier Park in early November of 2021. The weather was cold but no snow or clouds and lots of sunshine. We just stayed out of the shade and hiked and rode our trikes over frozen puddles in the sun . It was a most delightful 3 days.

I was surprised and shocked by the photos referred to by some of the commenters. I never would have imagined the possibility of the rust problem that some owners have discovered. It is hard to understand how such a problem would not have caused a catastrophic chassis failure before being discovered. It surely demonstrates that most of the strength in the coach is achieved by the coach shell, a large composite tubular structure (when combined with the floor) having relatively low stresses in its skin because of it's large size.

I will conduct a more thorough inspection (with tape measure and square in hand) some day this coming week. My inspection may lead to some disassembly.

Thanks for the continuing comments.

Gary

Re: Chassis failure on 1998 U 320

Reply #20 – June 05, 2022, 06:57:04 am

My coach build is 5359....I think I had better check my situation out too
Peter

Re: Chassis failure on 1998 U 320

Reply #21 – June 05, 2022, 08:33:30 am

Quote from: GLV – June 05, 2022, 03:46:26 am

I was surprised and shocked by the photos referred to by some of the commenters. I never would have imagined the possibility of the rust problem that some owners have discovered. It is hard to understand how such a problem would not have caused a catastrophic chassis failure before being discovered. It surely demonstrates that most of the strength in the coach is achieved by the coach shell, a large composite tubular structure (when combined with the floor) having relatively low stresses in its skin because of it's large size.

Gary

Gary, all of the weight is carried by the two trusses running between the bulkhead and from just below the side windows to just above the through bays. All the floor and bay structure does is keep the body from twisting. The front suspension and rear drive train are cantilevered off this main truss structure. If you think you can damage this meddle structure you need to see where Elliott took, what Elliott did to his Foretravel. And buy some of his socks. He's a good kid.

Re: Chassis failure on 1998 U 320

Reply #22 – June 05, 2022, 08:04:17 pm

Gary,it depends on the luck of the draw but if the coach has had work done at Foretravel they may have a record,worth a try.

Re: Chassis failure on 1998 U 320

Reply #23 – June 05, 2022, 08:23:57 pm

We go down sand washes like Elliot did and even through fields and on beaches and while it creaks and groans, we have had no trouble. Even used the front hooks to pull another 30 foot RV up and over an embankment. If it ever failed in any off road adventure, I would sell it in a second. Lots of big RVs go off road without a problem.

Pierce

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