Drop fuel tank

RVCuisineScene

RVCuisineScene

Active member
I need to drop the fuel tank to access the area under my van behind the drivers seat to mount a 3rd passenger seat to the frame, it looks fairly straight forward. Besides having minimal fuel in the tank is there anything I should be aware of before I attempt this project, I have a 2017 3500 4X4? All help is appreciated, thanks.
 
RVCuisineScene

RVCuisineScene

Active member
It's pretty straight forward. I dropped mine for a seat install and discussed it in this youtube video (see a couple of minutes into the video):
https://goo.gl/j2vgNC
Click to expand...
Excellent video, I've watched several of yours. You mention that there is no clearance between the fuel tank and floor for bolts is there room to put in a custom made 1/4" plate with bolts extending up thru the floor to bolt the seat to? Thanks
 
asimba2

asimba2

ourkaravan.com
RVCuisineScene said:
Excellent video, I've watched several of yours. You mention that there is no clearance between the fuel tank and floor for bolts is there room to put in a custom made 1/4" plate with bolts extending up thru the floor to bolt the seat to? Thanks
Click to expand...
There is some room but I'm not sure how much before you risk the head of the bolt rubbing on your tank and causing a leak over time. I'm using 3/16" plate with a nut welded in the steel, and I can confidently say the 3/8" it takes up is fine. Before you drop the tank I'd look around and see if you can gauge the available space before proceeding.
 
asimba2

asimba2

ourkaravan.com
Here's what I did...3/16" steel drilled and a nut was inserted into the hole, then welded in place. Final result was a low profile mount that sat within the floor corrugations. Because the nuts used were smaller than the original I doubled the fasteners, so there's two mounting points there where there was originally one.



The large nut you see further back is behind the fuel tank, so this modification was only done for that one location that sat above the fuel tank.

I discovered afterward that it did not need to be quite that low profile as there is some room in there, but it's not clear just how much.
 
RVCuisineScene

RVCuisineScene

Active member
Here's what I did...3/16" steel drilled and a nut was inserted into the hole, then welded in place. Final result was a low profile mount that sat within the floor corrugations. Because the nuts used were smaller than the original I doubled the fasteners, so there's two mounting points there where there was originally one.

https://farm3.staticflickr.com/2908/...93ef9b4d_c.jpg

The large nut you see further back is behind the fuel tank, so this modification was only done for that one location that sat above the fuel tank.

I discovered afterward that it did not need to be quite that low profile as there is some room in there, but it's not clear just how much
Click to expand...
.

Thanks for the picture, I'll probably go the route you did with the 3/16" plate placed in the upper floor corrugation so won't hang below interfering with the tank. As with most things like this what was going to be a "simple" job turns complex. Did you have to plug any of the fuel lines to prevent leaking and was there any issue running the engine after finished in terms of air in the fuel lines? Thanks
 
gltrimble

gltrimble

2017 170 4x4
Asimba2 is on track. I recall just pulling a rear vent line that is stuck into a crossmember. All other plumbing stays put if you just drop back half and support front half. I think there is 1-2 inches of space between tank and floor plenty for a nut and backing plate. Only one of my seat bolts landed under the fuel tank.


Sent from my iPhone using Tapatalk
 
asimba2

asimba2

ourkaravan.com
RVCuisineScene said:
.

As with most things like this what was going to be a "simple" job turns complex. Did you have to plug any of the fuel lines to prevent leaking and was there any issue running the engine after finished in terms of air in the fuel lines? Thanks
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"Simple job." Those words don't go together on my DIY projects. I did not plug any fuel lines and ended up with about a 1/2 cup of fuel spilled. Just make sure you put some plastic down because diesel fuel stains the asphalt. Van started right up without issue.
 
F

ForWorkAndPlay

2008 144 OBERAIGNER 4x4
I just did this aswell, I made mounts similar to Asimba2... I diconnected the fuel neck inside the filler door and did not have to disconnect any fuel lines, the tank lowered more than enough to access the mounts... one tip, drive until the tank is near empty to make the tank easier to handle.
 
A

aamert

Member
@asimba2 Thanks for the info.
I am also installing Transit Seats (2 seater and a single) in my 2009, similar to @gltrimble. A couple of questions for both of you:

1. I do not plan to weld anything, however, I am using Grade 8 (zinc coated) fasteners (bolt,split washer, flat washer) with factory Transit brackets. Any comments on that?

2. The underside metal support that I am using, I plan to butt them edge to edge between framing underneath. Which means that the ends of the metal supports will land on the framing (like post 6 above). Does that compromise the framing by any means?
 
gltrimble

gltrimble

2017 170 4x4
aamert said:
@asimba2 Thanks for the info.
I am also installing Transit Seats (2 seater and a single) in my 2009, similar to @gltrimble. A couple of questions for both of you:

1. I do not plan to weld anything, however, I am using Grade 8 (zinc coated) fasteners (bolt,split washer, flat washer) with factory Transit brackets. Any comments on that?

2. The underside metal support that I am using, I plan to butt them edge to edge between framing underneath. Which means that the ends of the metal supports will land on the framing (like post 6 above). Does that compromise the framing by any means?
Click to expand...
Grade 5 bolts are more than adequate. Your proposal sounds plenty strong. My only concern would be what is holding the metal support in place should you want to remove the Transit floor brackets. That is why I tack welded the nuts and metal plate supports on the underside. Perhaps some construction adhesive would work.
 
A

aamert

Member
yes, I plan to use Sikaflex 252 to adhere the metal support to the underbody. Not sure if I can use the sikaflex to secure the nuts, but I will try.

Forgot to mention, I plan to apply POR-15 to both sides of the metal support (Have some leftover from the floor application).

gltrimble said:
Grade 5 bolts are more than adequate. Your proposal sounds plenty strong. My only concern would be what is holding the metal support in place should you want to remove the Transit floor brackets. That is why I tack welded the nuts and metal plate supports on the underside. Perhaps some construction adhesive would work.
Click to expand...
 
Kajtek1

Kajtek1

2015 3500 X long limo RV
I am late to the topic, but I bought Sprinter Limo, who had seats installed in Las Vegas.
The commercial installer used 1/2" heat-treated bolts with shims on the picture.
3/8" is too small from my estimate.

20200831_144013.jpg
 
OffroadHamster

OffroadHamster

Well-known member
If you are not going to be removing the seat, you can use a pan head carriage bolt welded to the backing plate and then use a nut on the inside. Down side is you have a stud sticking through the floor if you take the seat out.

Weigh your seat, assume worst case for passenger (I use 200lbs typically). Assume an FOS of N=2. Assume asymmetric loading of bolts in an accident (Number of bolts / 2) and 30g of deceleration. Size bolts accordingly. A 3/8 or 1/2" HS carriage bolt is rated to 150ksi. permissible working loads are 17,735lbs (P=S(Atensile) and 31,249lbs respectively.. With a 100lb seat your max load in a 30g accident is roughly 18K lbf. You want some factor of safety. Using 1/2" hardware with 4 bolts holding the seat down gives you and FOS of ~1.7 and has the additional built in safety of the asymmetric loading assumption.

If you have symmetric loading, a deceleration less than 30g (which is a GNARLY accident), 3/8" hardware is likely more than sufficient. 1/2" is appropriate overkill to without a doubt remove them from assignable cause of death. Because really, in a 30G accident, you are probably dead.
 
A

aamert

Member
OffroadHamster said:
If you are not going to be removing the seat, you can use a pan head carriage bolt welded to the backing plate and then use a nut on the inside. Down side is you have a stud sticking through the floor if you take the seat out.

Weigh your seat, assume worst case for passenger (I use 200lbs typically). Assume an FOS of N=2. Assume asymmetric loading of bolts in an accident (Number of bolts / 2) and 30g of deceleration. Size bolts accordingly. A 3/8 or 1/2" HS carriage bolt is rated to 150ksi. permissible working loads are 17,735lbs (P=S(Atensile) and 31,249lbs respectively.. With a 100lb seat your max load in a 30g accident is roughly 18K lbf. You want some factor of safety. Using 1/2" hardware with 4 bolts holding the seat down gives you and FOS of ~1.7 and has the additional built in safety of the asymmetric loading assumption.

If you have symmetric loading, a deceleration less than 30g (which is a GNARLY accident), 3/8" hardware is likely more than sufficient. 1/2" is appropriate overkill to without a doubt remove them from assignable cause of death. Because really, in a 30G accident, you are probably dead.
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Good Point. I am using 1/2 inch grade 8 bolts.

For the single-seat, I plan to use 2 bolts per bracket (4 for the seat), and that specific seat's rear mounting point is also secured to the brackets using a bolt.

For the double seat, I plan to use 3 bolts per bracket (6 for the seat). It is a heavy one !

One thing I don't see addressed anywhere is which direction the underside metal brackets be installed ; long ways going side to side or front to back. In the event of a crash, which direction proves to be better?
 
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OffroadHamster

OffroadHamster

Well-known member
Doesnt matter much. Brackets are to prevent tear out. Accidents happen in every which direction. No way to predict the vectors of a crash. Run them were most convenient to get the most surface area coverage and the best access to make sure they are appropriately torqued.
 
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