LOWER floor in 1975 MCI?

pixman · March 09, 2015, 04:18:25 AM

Hi there!
I'm working on a 1975 MCI Crusader conversion. I've pulled out the ramp from the driver's area and looked underneath. It LOOKS like it is all dead space under there with a steel frame that holds up the current floor.
Does anyone have any experience lowering a floor or can anyone give me advice on whether or not to attempt it?
I am a beginner at construction in general. It looks like I should be able to learn to use a cutting torch and cut the welds on the vertical steel supports that are used to raise the floor 4 inches.
Thank you for your advice(s).

JRandall · March 09, 2015, 08:24:34 AM

I know nothing about the structure of this bus...so I cannot address that. I am sure the gurus here on the board will do so. But, I can address the idea of your intended alteration. I was told that I couldn't shorten the frame of my 68 4 wheel drive...but I did, and 15 years later there are no issues. I was told I could not change my 4 door 56 chevy sedan into a two door...but I did and only someone who knows VIN numbers can tell it was ever a 4 door. I was told I could not graft an 80 El Camino front frame clip onto a 55 Ford F-100...but I did and to date, there are no appearing cracks and the power steering is straight and true and the disc brakes easily stop the stroker 350 that went with the clip. I was told that I could not shorten the longbed frame of my 92 chevy half-ton pickup onto a shortbed frame...but I did and it turned out perfect. SO listen to those who know about the structure, and don't listen to the naysayers.

Tony LEE · March 09, 2015, 08:53:20 AM

MCI has a monocoque construction which effectively means the whole structure is structural, even one of the layers of wall cladding on the inside walls under the windows.

Under that ramp is a return air duct covered by the plywood floor which isn't structural but it isn't very wide either and I doubt whether you would come up with a layout that would work using just that narrow bit with increased headroom.. I would say the steel sides of that duct and the tunnel beneath it ARE structural as is everything below floor level.

Stormcloud · March 09, 2015, 11:10:25 AM

I have an MCI-7 that should have similar construction. My new floor is over top of the existing floor, and maintains both the return airflow for the OTR heat and A/C, and doesn't tamper with the structural strength either.

The way I see it; these coaches were designed as over-the-road passenger and parcel/light freight transportation units.

If the design engineers had been able to increase the interior height of the baggage bays simply by removing some of the overhead structure, or lower the floor by removing same structure, thus lowering the entire vehicle by 4-6 inches, I think they would have done that. Extra room in a bay means extra profit$. Reduced overall height means less wind re$i$tance.

As for the tunnel, there is a tremendous amount of strength in a flat panel of steel formed into a long u-channel shape, and that tunnel is definitely gonna be structural. I wouldn't cut the floor structure out under any conditions.

Picture in your mind a fat dachshund....see the droop in the middle? Imagine what your coach would look like with a castering bogie mid-way between front and rear axles.

YMMV

Mark

bevans6 · March 09, 2015, 11:46:06 AM

My MC-5c doesn't have any tunnel space between the floor and bays, the cabin floor is the roof of the bay. I think he may be OK doing this, but I wouldn't say further until I looked at it with the cabin floor off.

Brian

pixman · March 09, 2015, 12:43:37 PM

Thanks for your input guys. I will be pulling out some panels to see what goes there. I have been afraid of what seems a momentous job of raising the roof. I'm 6'2" tall and want every free inch I can get.
®

TomC · March 09, 2015, 01:38:41 PM

MCI102C3 has 6'10" headroom. Would be my choice to convert now. I did a transit that has 6'10" headroom and is 102" wide. But-a transit is a bit of a challenge. Good Luck, TomC

Stormcloud · March 09, 2015, 07:42:31 PM

Roof raise isn't a monumental task, in the big scheme of things. I'm 6'4" and ended up with real comfortable headroom.
I think you would be happier with an 8" roof raise.

Mark

Dave5Cs · March 09, 2015, 09:36:06 PM

Brian unless someone before you took it out you do have a tunnel, but it is in the middle. Runs from behind driver area to back of rear bulkhead over the tranny. My 5C does. On the bottom it has removable panels. mine had electric and some air hoses in it and it cannot be remove. It is about 8 inches below floor, HTH

Dave5Cs

bevans6 · March 10, 2015, 03:52:28 AM

It has a sheet metal tunnel but it hangs down from the ceiling of the bay. It's not in a dead space above the bay ceiling and below the cabin floor. It sounds like the MC-8 in question has a double floor with about 3" between that has been used for plumbing or ducting in some way.

Brian

Dave5Cs · March 10, 2015, 07:07:57 AM

Interesting thanks for the clarification.
Dave

Jriddle · March 10, 2015, 07:27:08 AM

The rails in that area are structural.

IMO
John

Oonrahnjay · March 10, 2015, 04:05:13 PM

Quote from: Jriddle on March 10, 2015, 07:27:08 AM
The rails in that area are structural.
John

That pretty much answers it, doesn't it?

Jeremy · March 11, 2015, 08:33:36 AM

I went through exactly the same thought process with my bus of whether I could lower the floor rather than raising the roof. My bus isn't monocoque (so lowering the floor would be easier) but on the other hand the sidewalls are curved (so raising the roof is harder). But, after weighing-up all the pros-and-cons, I raised the roof.

Raising the roof seems like a big deal simply because you're dealing with such a physically big thing - but it's really quite a simple operation that just requires a hacksaw and welding in some new bits of box-section. On the other hand, lowering the floor is less scary, but much more fiddly and time-consuming I would suggest

Jeremy