Cabover leaks - Would This Work

[fortytwo]

The current horror story thread detailing Coachman Leprechaun cabover leaks is unfortunately representative of very common class C events. Poor workmanship, combined with design incompetence are almost always present. After you own one locating, fixing, and keeping the leak fixed are difficult and often ugly.

There have been discussions of applying pickup bed liner material as a fix for pesky roof problems. Could that be a viable long term solution for the manufacturers inability to deliver leak free cabover units?

I discovered a Coachman class C I really like; no leaks yet; but the seam design is a leak waiting to happen. The selling dealer does not dispute my analysis, and said cabover seam leaks were a frequent problem with Coachman C's they get in trade. I can't consider trading until I identify a way to take the probability of cabover leaks away. I've been RV'ing almost 50 years and simply can't watch for em' and fix em' myself any more.

[ron_dittmer]

I frown upon motor home manufactures who still build their class-C's with seam work in the cab-over. Whatever their reasoning, I can't accept it. This is NOT an emerging market with all new ideas in road trip vacationing. There is a very long history with motor homes made poorly, resulting in leaks for new, used, and well used rigs. Any motor home manufacture still building rigs like this are inadvertently preying on the inexperienced.

I am not an advocate for government regulation, but there are a few areas in class-C motor homes where maybe some rules should be defined. This because the industry isn't doing an adequate job on it's own. Seamless fiberglass cab-overs (& roofs) and chassis stabilization/handling won't make or break but a few shady manufactures and a few prospective buyers. In short time there would be much safer and healthy mold free rigs for all.

You know how it goes....Eventually the tighter standard would become "The Norm" as does Electronic Stability Control and an array of airbags have today on cars and SUVs. If not, we'd still be getting 12 mpg on the highway in a 4-door sedan death trap without seat belts. It's an evolutionary process that I feel would be a good idea to get started in the previously mentioned areas with motor homes.

[super_camper]

Mocoondo wrote:

pnichols wrote:

Mocoondo wrote:
The cabover has to flex otherwise it would break right off the motorhome.

Sorry ... but I disagree ... at least with regards to up-down (vertical) flexing.

While this isn't the place for a lengthy discussion on materials elasticity and resilience, you should educate yourself on these subjects. All materials subject to stress and strain have to exhibit some degree of elasticity (ability to flex) and resilience (ability to flex without deforming) otherwise they will fracture due to overstress. My masters is in Aerospace Engineering and I am very familiar with these subjects. All properly designed solid vehicles will deform/flex when it receives energy, such as a bump in the road. Just because it may not be visible to your naked eye does not mean that it doesn't exist. The cabover of the average class C actually has a lot of built in flex by design. If it didn't, you would hit a bump and and there would be no place for the energy to dissipate to and the materials would deform and crack.

Compare the difference between, say, a porcelain tile and a wood 2x4. If you try to bend the porcelain tile, it will crack. Tile has a very high modulus and will basically not bend at all. A 2x4 has a relatively low modulus and will bend (deform) and then return to its original shape. The RV cabover is purposely built with materials that have a relatively low modulus. This allows it to flex up and down without failing or permanently deforming.

There is absolutely NO WAY modern day manufacturers design class C MH's with "built in flex by design". These things are designed the other way around which means flex is a result of the design and materials selection. Some manufacturers obviously do a better job than others.

[pnichols]

I'm well aware of all of what you say above ... within the conditions of when and where the various engineering principles apply. (Masters + in engineering fields, too ... FWIW.)

As much stiffness in Class C non-one-piece-walls/roofs design cabover areas is the name of the game if you're going to keep their interface points ("seams") from flexing relative to each other. You don't want seams flexing between themselves if you're going to keep sealants in them from being under unnecessary physical stress. You also don't want UV rays drying out and/or breaking down the chemistry of those sealants.

Cabover Class C areas do not have to "automatically" leak anymore than vehicle roofs leak - over the years. One has to know some very basic things to look for when buying a Class C as to what might keep any one particular Class C cabover setup from being future-leak prone. It doesn't take advanced, or any, educational degrees to figure out what might be required.

Ron Dittmer has posted plenty in these forums on some excellent basics to look for in RV roofs in general, and cabover roofs in particular, regarding what designs might or might not leak in the future with an RV.

My posts here in this discussion thread were merely to add some comments on sensible internal construction details that us buyers and OEM manufacturers should be keeping in mind if we want to buy, or they want to built in, a quality product strength-wise so as to help with seam-leak prevention. OEMs don't even need extensive engineering staffs to apply good old backyard savvy in getting their structures rigid enough on the road so they don't either crack from inadequate flexibility where it belongs or leak from too much flexibility in seam areas.

All In My Humble Mixed Background Opinion, of course.

[Mocoondo]

pnichols wrote:

Mocoondo wrote:
The cabover has to flex otherwise it would break right off the motorhome.

Sorry ... but I disagree ... at least with regards to up-down (vertical) flexing.

While this isn't the place for a lengthy discussion on materials elasticity and resilience, you should educate yourself on these subjects. All materials subject to stress and strain have to exhibit some degree of elasticity (ability to flex) and resilience (ability to flex without deforming) otherwise they will fracture due to overstress. My masters is in Aerospace Engineering and I am very familiar with these subjects. All properly designed solid vehicles will deform/flex when it receives energy, such as a bump in the road. Just because it may not be visible to your naked eye does not mean that it doesn't exist. The cabover of the average class C actually has a lot of built in flex by design. If it didn't, you would hit a bump and and there would be no place for the energy to dissipate to and the materials would deform and crack.

Compare the difference between, say, a porcelain tile and a wood 2x4. If you try to bend the porcelain tile, it will crack. Tile has a very high modulus and will basically not bend at all. A 2x4 has a relatively low modulus and will bend (deform) and then return to its original shape. The RV cabover is purposely built with materials that have a relatively low modulus. This allows it to flex up and down without failing or permanently deforming.

[hotbyte]

I would say the overhang section on a 5'er is very different. It is supported by frame that comes up to hold the king pin in place. A typical 5'er hitch is holding something like 25% of the full trailer weight.

If ours is bouncing/flexing, it is less movement than I can detect and still keep an eye on the road 🙂

[pnichols]

Mocoondo wrote:
The cabover has to flex otherwise it would break right off the motorhome.

Sorry ... but I disagree ... at least with regards to up-down (vertical) flexing.

A too-cheaply constructed Class C's cabover might flex more than it should but a properly designed Class C's cabover will have, and needs, almost the same amount of side-wall and roof-wall internal rectangular and triangular bracing as a 5th wheel's out-stretched front support section does.

Here's some - IMHO - things to consider:

Do truck camper cabover overhang sections break off?

Do truck camper cabover overhang sections need to rest on the cab roof?

Wood internal framing has no business being relied upon to support a Class C's cantilevered cabover (or a truck camper's) section. Metal internal roof/wall framing is the name of the game. Aluminum framing is probably adequate for supporting/bracing a Class C's cantilevered cabover section, but steel should be used for supporting/bracing a 5th wheel's front portion.

Overall cabover support/bracing strength is one reason we did not buy a Class C with a slide -> as internal wall stength needed for adequate cabover cantilever support is compromised when you have slides breaking up a Class C's internal wall integrity. The same thing can ultimately be said of 5th wheels with and without slides.

That earlier RV-vibration video in this thread shows the RV coach as (almost gently) only rolling and bouncing, not receiving sharp vertical jolts like the suspension system is absorbing in the video. Sharp vertical jolts are far more likely to loosen poorly designed and/or constructed wall material seals than rolling and bouncing motions.

I think that cabover leaks are primarily the result of too much flexing from inadequately designed/constructed internal wall framing, inadequately designed and/or poorly maintained outer wall material joints, front clearance lights not kept sealed around their bases, front facing cabover windows and their frames not being sealed using enough over-kill, and the cabover sections not being kept out of the sun and it's killing UV rays even though the rest of the RV may be outdoors. Our Class C is kept outdoors - but we intentionally park it with the front end under a large tree's shade so this part or the coach gets no sun.

Here's a photo of a 1969 Class C folks prior to us, and us, had for many years with nary a cabover leak, ever. It's cantilevered cabover section had air clearance between the undisturbed cab roof so it did not rely on support from the cab's steel roof. As best I can remember we never re-sealed anything on the roof or walls around the cabover part of the RV. Both the DW and myself and all the owners before us slept in the cabover section - so it was subjected to plenty of cantilevered weight every camping night. I believe that the RV was kept stored outdoors it's whole life, at least it was during our ownerhip years. However, we kept it's cabover section kindof parked away from the worst of the summmer sun. Also note that it's cabover section and whole roof were one-piece fiberglass:

[OldRadios]

NancyLong wrote:
Is there anyone out there that has had a C for several years and the cab-over did not leak?

2006 Tioga C with no leaks so far. Just noticed the rubber around the front window has separated at the seam so I will deal with that when the cover comes off. Not sure whether to just fill it or try to get a new replacement rubber and have the window reinstalled.

Edit: Tioga not Thor

[super_camper]

NancyLong wrote:
Is there anyone out there that has had a C for several years and the cab-over did not leak?

There is no doubt the ca-over on a C is susceptible to leaking but I believe the majority are due to a lack of maintenance and/or improper maintenance with the wrong materials etc.

Our 2006 MH is leak free

[Chopperbob]

My 2001 Tioga is leak free so far.
Bob

[bsinmich]

You have the primary reason I have a Class A. We had 2 Cs and another A prior to this. We entertain 8, feed 6, sleep 2.

[pnichols]

With regards to comparing a Class C's cabover overhang to that of a 5'er's leveraged oversupport portion:

According to diagrams on the Winnebago Website our Itasca Class C's cabover is supported by internal aluminum framing so there is no need for it to depend upon resting on the cab roof for actual support.

Looking at the diagrams, this internal framing looks like it is designed to support any weight in the cabover whether or not a cab is even under it - as the design should be. I see no difference in dead weight pushing down in a Class C cabover section versus a PU bed hitch pushing up on the "overhang" portion of a 5'er ... one is tending to be forced down and the other is tending to be forced up.

[Mocoondo]

ron.dittmer wrote:
It would be very interesting to see a new, used, and well used class C being tested like THIS. I wonder how much movement would be observed from the cantilevered cab-over bed.

To you with long overhangs on your C's, when hitting a bump in the road, do you see from the driver seat, your cab-over bed flexing?

All Class C's flex. New, used and well used. The cabover has to flex otherwise it would break right off the motorhome.

[ron_dittmer]

It would be very interesting to see a new, used, and well used class C being tested like THIS. I wonder how much movement would be observed from the cantilevered cab-over bed.

To you with long overhangs on your C's, when hitting a bump in the road, do you see from the driver seat, your cab-over bed flexing?

[tpi]

I live about 40 miles from Lazy Daze factory so that is what I bought. The design of the roof is nothing to write home about, it is flat thick aluminum and has a cabover seam with fiberglass cap. But the execution of build has been very good. I've had remarkably few problems. But the big deal for me is the factory is close- and given a problem I can bring their baby back to them for repairs. Which I suspect will be as good a bet as any because they built it.

[Mocoondo]

The real problem here is that owners do not maintain their roofs properly. Only when a leak actually occurs do people suddenly go into overdrive trying to fix it, but by then it is too late.

If you want your Class C roof to last and not leak, you need to be up there at regular intervals removing old sealant and resealing. If you are not on your roof twice a year going through the process, you are not properly maintaining your roof and *WILL* eventually have water damage.