Building a roof rack deck on a GMT800 Suburban Z-71

[rayra]

crossposted from my vehicle build topic


Today I started construction of the MkII Roof Deck. Still going with the 2 longitudinal halves, 'back boards', but for now with no handhold holes.
I am considering slightly notching their edges, so ropes or flat webbing could be tied around the boards and cinched to form handholds. The notches would keep the ropes / straps from slipping along the board.
I've chopped 1-1/4" off the tail end to preclude any interference with the factory Z71 rack's rear airfoil.
I've also extended the nose area quite a bit. +3" forward on the outer edges, right up to where the inner side of the rack side rail nose caps cruve inward. And +5" forward on the centerline. And changed the curvature of the front end to broaden / blunt the curve, put more material forward of the roof luggage rail ends, so I can better block the front gap with pipe foam insulation.
I also put a more pronounced slope on the leading edge.
I've also elected to go from 4 cross braces to 3, to change the layout to work better with my intended rooftop solar panel install. I'm fabricating new more rigid cross braces out of 3/4" square tubing.

Couple early fitment checks on the first piece. These are both the driver side front end. The front of the deck will now be less than 2" from the sunroof opening.

Here's a sneak peek of a coming attraction

The folding solar panel kit JUST fits the width of the deck / roof rack inner dimension. As it it was designed to do so. I intend to install a sort of picture frame mounting bracket, with a C-channel to trap the leading edge of the panel. And that C will have a sloped fairing to the front. The rear will be a sort of split C, with a piano hinge. You insert the panel into the front C-channel, set the trailing edge down and swing the rear bracket shut and use a pair of flush hood locks to latch the panel into place. Rubber gasketing to make a rattle-proof grip on the panel kit.

The pencil mark on the preceding pic is where the central brace will be. Ensuring the solar panel mounting frame will clear it.

I'm going with the same 'hammered finish black'. It held up very well in Socal heat and brutal sun. That is until I started going to a drive thru car wash. It lost it's gloss after 4-5 washes.

Hopefully the solid design and blocking the front end will eliminate the drone / moan at my preferred cruising speed.

Top side has been primed, priming the underside tonight, hoping to start paint tomorrow, after shaping the tubular steel cross braces.


12,203

 

[rayra]

Laid it on a little thick this morning, still tacky / soft. And unfortunately I elected to pain the top sides first. So I really can't flip them yet to paint the other sides.

That is again the Rustoleum 'Black' Hammered Finish paint, by the quart.

 

[jon_beer]

If I were you I'd consider making it out of Marine Ply or PVC sheet. I have been building everything for my Tacoma out of 1/2" PVC sheet from any big box store with 3 coats of bedliner on it. It holds up really well to daily abuse. I'm a contractor and built a platform in the cab behind the driver and passenger seats for my toolboxes. They are 30-40 lbs and dragging them over the bedlined PVC has resulted in no major scratches in over a year. Just putting it out there.

As a finish carpenter and someone who builds interior/exterior I find that sealing ply with spar urethane is great for interior finishes that must be waterproof but unless you could totally impregnate the ply with spar urethane you will always run the risk of delamination. You could seal the ply with a coat of resin epoxy, in the same way wooden boats are prepped for gel coating or paint. But at that point your deck boards might weigh substanstially more and the epoxy isnt cheap.

Check out the PVC sheet. If you find they are not stiff enough you could always cut a dado on the underside and JB weld in some aluminum flat stock or hardwood strips.

 

[thebmrust]

@rayra how has the MkII roof deck been working?

 

[rayra]

Not even on the vehicle right now. Had it off to make some foldign solar panel roof mount brackets and to make some 3/4" square tube braces instead of the flat strapping of Mk1. Got a wire feed welder and did some poor practice with it. And then got diverted on other things, vehicle repairs, remodeling projects.

Just spent the last 10 weeks turning a front yard planter into a brick patio.

But the Suburban roof deck is going back on pronto, weeks of 90-100F temps recently, many more weeks of such to come. Even if I have to re-use the flat strap mounts with the new deck boards. Gots to have some shade!

 

[thebmrust]

The reason I ask is that I might take on a similar project. Thank you for taking the lead on it. LOL

 

[rayra]

i'll hit you up when I get some highway time on the extended, handle-less, foam-dam-front MkII. I'll probably be putting it back on with the Mk1 strap brackets very soon. have another home improvement project to do before I can put more time on new brackets and solar

 

[rayra]

Major difference in MkII is I deleted all the handhold holes, extended the nose further forward and gave it a greater curve and leading edge.

So 7mos since I fabricated the MkII deck and I still haven't got the new design 3/4" square tubing cross-braces / mounts fabricated and our recent ridiculous heatwave was quite enough. This morning I got out there at 0630 to wash the vehicle and dig out the old flat strap mounts to get the MkII deck up on the roof. Took about 3hrs for the install, it's a fiddly process. Had to enlarge a couple holes in the decks to get things lined up with the old brackets. Things got over 100F by 10am, started getting nauseous. So damned hot I should have split the install into two stages, mounting the brackets and do the decks tomorrow. But I got past the point of no return and had to press thru.
The decks lined up pretty well but were a snug fit. 2 coats of hammered finish paint adds a good bit of thickness, so be sure to factor that in your dimensions, as well as the thickness of the mounting tabs in your method. And once the two halves are wedge together it's a stone ********** to get them to slide past each other fore/aft. Had to pry up and reset the 2nd half a couple times to get it close enough. And some judicious whacks with a rubber mallet.
Take at least 3/16" off of each edge in your design width(s) to accommodate the primer and paint thickness.

I've gone from four crossbraces / mounts in Mk1 to just three in the Mk2. I kept the flat top strap on the foremost crossbrace as a safety device. I'll be going out this afternoon for a local test drive, maybe speeds up to 65mph. But I want to get some larger fender washers for the hold-down bolts. There's only 12 now, and I've lost track of the Mk1 washers. I want larger fender washers in place before I run this setup up to 80mph. I also have a laser thermometer to fart around with in the afternoon heat to compare the deck temp and the roof steel temp in its shade. That data to come.

Re-hanging the old flat crossbraces

http://www.rayra.net/imageshare/Suburban/subroofdeckmk2-020.jpg


Overall look at the installed deck, top safety strap and you can see how much closer the front end curve comes to the sunroof.

http://www.rayra.net/imageshare/Suburban/subroofdeckmk2-021.jpg


Shot from the front, leading edge

http://www.rayra.net/imageshare/Suburban/subroofdeckmk2-022.jpg


Side view of the deck and its shade. The end tabs of my cross braces have slots rather than holes, allowing for vertical adjustment of the deck. I put it all together loose where the crossbraces meet the factory roof rack rails. After the decks are tightened to the crossbraces, I use a towel-wrapped flat plank as a lever and pry up on the deck to make it flush with the underside of the roof rack rails, tightening the crossbrace mount nuts to hold it there. Makes a cleaner look from the ground.

http://www.rayra.net/imageshare/Suburban/subroofdeckmk2-023.jpg


And a closer look into the deep shade, blew out the brightness on this shot and still can't make out much of the details in the shade.

http://www.rayra.net/imageshare/Suburban/subroofdeckmk2-024.jpg


More to come, today and tomorrow. I'm starting off without the pipe insulation foam dam under the nose. I expect it will be needed, but want to experiment without it, first. I think the 'droning moan' that manifests above 65mph is a result of the flat deck and the fore to aft crown of the steel roof creating a narrowing in the middle, sorta like a ramjet. I think the air being compressed in the middle expanse then expanding out the back is producing the drone-moan. If the gap was tighter it would be a whistle. So ultimately I expect to dam the front with the foam.



eta Roof deck surface temp at 2pm, 170.5F
Vehicle roof in the deck shade, 144.5F
Side window glass, 122.5F
113F at Home Depot.

No discernible drone/moan at 55-70mph. Guess the (16) handle holes were the issue. Probably. Higher speed testing tomorrow, after I swap out the washers in the morning.

 

[rayra]

Got out there early again today and installed some broader 'fender' washers on the deck bolts. Then I took a whack at adding some R134 to my AC system, it's been blowing warm lately when stopped at red lights, particularly during these heat waves. Works fine rolling down the road, though.
So I bought the can of stuff with all the bells and whistles, oil, leak seal and detector, hose with pressure gauge. Just to find out I'd mounted my dual battery solenoid too close to the AC low pressure side fitting. Couldn't get the fat AC refill connector in there. So had to loosen and jigger things around enough to be able to do so. AC system pressure was down around 37psi, good zone goes to 45psi, riding at 44psi now and was blowing really cold in my driveway.

The solenoid mounting mistake
http://www.rayra.net/imageshare/Suburban/sub AC low pressure.jpg

Pics of the washers installed and some views of the installed deck. Soon to come is a deck-mounted folding solar panel kit
http://www.rayra.net/imageshare/Suburban/subroofdeckmk2-025.jpg
http://www.rayra.net/imageshare/Suburban/subroofdeckmk2-026.jpg
http://www.rayra.net/imageshare/Suburban/subroofdeckmk2-027.jpg

High-speed highway test later today. And repeating the temperature tests.


eta little 20mi jaunt up the Grapevine. AC performing well. No drone/moan at speeds up to 85mph. Some buffeting turbulence noise emanating from the back half area. That was both with the sunroof open and without. No real difference in total noise level, any reduction at the back when opened was cancelled out by increase in buffeting noise with the sunroof tilted up.
Probably do a road test next week with the foam insert at the front, to see what effects that has. I'll call the drone/moan noise solved for now.

eta2
fresh temps, l-r are steel roof above windshield, steel roof in the deck shade, offside passenger window. outside temps are ~104F locally right now

Painted plywood roof deck was 150F, concrete sidewalk in the sun 135F, 90F in the shaded slab in the garage.

Time to go screw off er work on the pool.

 

[rayra]

Another view of the Suburban's roof deck, while we were on the house roof early yesterday morning -

 

[rayra]

More fiddling with the MkII roof deck. I went ahead with my foam / pipe insulation front air dam idea. I used two diameters of closed cell pipe insulation, smaller nestled inside the larger. I left the larger open / unglued and wedged the bundle in under the leading lip of the deck, leaving the glue edge of the exposed portion of the larger outer layer in a position to attach to the front edge of my roof deck. The inner core and the bottom of the outer made for about 1-1/2" of foam wedged under the forward edge of the deck. I then fine-tuned the position of the leading edge of the foam to the deck and stripped out the protective plastic from the adhesive and pressed things together as hard as I could. two days in the hot sun and some local driving and things are still where I put them. We shall see what time and sustained high speed driving do to the whole thing.
The way I extended the front end of the MkII deck, this wad of foam should be up against the front ends of the protruding luggage rails in the vehicle roof. THat should keep the foam from being shoved deep under by wind pressure at speed. The outermost ends will probably fold back in, though. Taller gap, less squeeze pressure, no rails to back the ends. Setting soem sort of rod as a core might stop that. Something like those plastic re-bar looking plant stakes, or something with similar flex.

 

[s.e.charles]

where do y'alls go you need to be 85 mph? or is this just in "test-mode"?

being retired, I got no where to go and all day to get there, so i'm just curious I guess.

 

[rayra]

Sometimes I'm in a hurry. And one good thing about the southwest is outside of massive cities, the roads can be pretty wide open.
And since I'm in an area prone to natural disasters and riots of various flavors, I like to know in advance how my vehicle and equipment can handle higher than normal speeds.
I'm not building this rig just for idle vacations.

 

[Hillbilly Heaven]

Evidently he hasn't driven thru Atlanta or Charlotte. 85 is minimum to keep up with traffic flow.

 

[rayra]

welp, the foam nose has vanished, I know not where or when. Must have been on a recent night highway run, as I'm usually looking in my mirrors as much as I am forward (see the above references to 'speeding') and I think I would have noticed if it came off in the daytime.

I think when I finally get around to a 'MkIII' version, it will be with anodized aluminum plate and have rigid 3/4" square tubing crossbraces. But the braces will be inverted so that the aluminum plate is flush with the top of the side rails. But I'll probably never get around to that due to the expense and it conflicts with my solar panel roof mounting plan. The current recessed height of the decking will help hide the presence of my solar panel mount from people on the ground. With a flush top plate the solar mount would be totally apparent.

I'm still using the flat strap cross braces and I am getting some flexing in the outer ends, outboard of the top deck fasteners. Only noticeable as a banging noise if I hit some hard road bumps. I might be drilling thru the deck and straps closer to side rails and tap the strap so some more fasteners can be added to defeat the flex.
And I've looked and there really isn't room for a rigid tube cross brace under the middle position, there's too much fore-aft arch in the roof, not enough clearance. Would still work at the front and rear, though.