Modified Rear Bumper and Body Mounting on a Mk4 without Removing the Gas Tank
Modified Rear Bumper Mounting on a Mk4 without Removing the Gas Tank
I’ve been studying and thinking about this for a while now and finally got around to doing it; and it worked. Not as I had originally planned but this set up will work without removing the gas tank.
Note that I have converted from the standard size mounting of 7/16” to 1/2”. The only problem I really had was drilling out the Nudge Bar and Over-Riders to 1/2”. You’ve got to keep your bit cool or it will dull really quickly; and that’s hard to do when the drill is in one hand and you are trying to hold the part in the other hand and trying to spray the coolant with your third hand. I am using plain water as a coolant for the stainless steel.
I ran into a few other challenges but I’ll discuss those as I get to them.
I did some mock ups on the bench to make sure I could make this all work. I actually cut down a 3/4” wrench so I could get more turning radius on the final nut but it turned out I didn’t need to do that.
By studying other threads and ideas posted by others on this subject I decided to mount four coupling nuts both inside and below the trunk area in place of the standard bolts supplied with the bumpers. The challenge was to do this without removing the gas tank so I got some 1/2” x 1” and 1/2” x 3/4” button head bolts. I had already tried hex heads and they would not work but maybe the round head of the button head would allow a screw to fit in better. The hardest spot is the lower passenger mounting bolt. I did get the 1/2" x 3/4" to wiggle into that spot and 1/2" x 1” to fit into the other three spots to bolt into the coupling nuts. Note in the picture above the cut off Allen wrench. That was necessary to get to the lower passenger side button head bolt. Do realize that the Allen wrench is a little bit distorted where I cut it off, from the bend in the wrench, so you may have to clean up the hex a little with a file.
This is what I ended up doing. I’ll explain a few mounting challenges later. Note: I have added a nut for a lock nut on the nut against the body. This nut is not in the picture above this one.
Here I’m getting ready to measure and cut off the all thread to the proper length
All thread cut off and ready for Over-Rider mounting
The nuts are on to help clean up the threads once the rod is cut
Original threads cut out to 1/2" for all thread
Now the challenge is to get a nut over that all thread. I dropped eight nuts before I got one on
Here is how I finally did it. Still was hard to do.
Nice Job! Why did you convert to 1/2"? Availability of components? I know I have had some problems finding 7/16" components. An alternative to using the couplings and button head screws, that I am considering, would be to use 1/2" riv-nuts (can't locate 7/16" rid-nuts) inserted into the frame flanges. This might be a little more expensive but would make the removal and installation of the all-thread easier in the future. One problem there is that I believe the riv-nut would need to be shortened slightly to install in the lower flanges on each side without lowering the gas tank. I will provide photos if this is successful. David
You may be right JasonD. But, I'm thinking I'm going to be removing the body a few times during panel fitting, when time to paint, final assembly, later??? And lowering the tank is not exactly easy. The strap on the pass side is a real B.... Following the manual (I know, Don't follow the manual!), I have already riveted in the patch panel for the strap connection on the pass side. So, that means removing that and re-installing also.
Am I missing something? Looks nice but it seemsWTO me it is less work to just lower the tank?
Aww come on Jason....this is an MKIV tradition already...how to find a way to avoid dropping the tank AT ALL COSTS!!!
The funny thing is I did a nearly identical modification for my bumperette install and was very proud of myself that I didn't have to drop the tank, only to have a leak in my filler neck of the gas tank a few weeks later and I had to drop the tank the other day to fix that. So now I have some actual numbers to see if it was worth it to fabricate the modification:
Time to think up, order, modify and install the hardware to avoid dropping the tank: 4 hours.
Time to actually drop the tank: 15 minutes.
I'm still glad I did it though. Don't ask me why. Maybe it was the challenge.
Nice Job George!!!!
FFR 7386 MK IV Roadster
302 Block/347 Stroker/Mass-Flo/TKO 500/8.8 Moser Rear/Manual Brakes & Steering
Build Began 12/6/2010
First Start 11/18/2011
Go Kart 11/24/2011
Registered and on the Road 8/11/2012
Paint Winter-2012 at Metalmorphous
Picked up from Paint 4/6/2013. Awaiting graduation pics to make it official! My Build Project Website
thebicman - I do plan to use anti-seize as the components I'm using are all stainless steel. I will also use a nylock nut to hold the Over-Rider to the all thread. Lastly, I'll probably use blue Loc-Tite for the mounting of the coupler with the button head screws. Note there are two lock nuts to keep the other parts in place.
Dave O - I've tried to go back in time and think through why I changed to 1/2" and can only think that it was being done by others and at one time I was thinking about using turnbuckles and 7/16" was not available in that size.
RJM - I got the bumpers and over-riders during the 2011 FFR Open House.
Lowering the Tank
I don't understand several of you thinking the tank is easy to drop.
Mine is not, even with the car unfinished. I had to do some crazy shimming and cutting on the 3/4" square pipes that the tank is pulled up against. I would not want to go through that again, especially with the trunk aluminum finished. In addition, on an IRS car, the passenger side bolt and strap gets in the way of one of the frames cross members in the rear and it is a bear to fuss with. This is why I was driven to make this modification.
You also have to:
Disconnect the tank fill tube.
Disconnect the tank venting system.
Disconnect the fuel lines.
Disconnect the wiring to the fuel pump and fuel level sending unit.
What if the tank has gasoline in it?
With the set up I've detailed, I can change from the bumper and over-riders, to the over-rider only, to the quick jacks by simply changing the length of the all thread. In addition, as noted above, I can make small adjustments to the body to aid in alignment with the trunk lid. And of course, all this, without dropping the tank.
Two older threads documenting the trouble I had fitting my gas tank.
I didnt have to modify anything on my tank (MKIV) to get it to fit, but I did "adjust" the filler neck with a hammer to clear the 3/4 frame tube. To drop the tank I just used a floor jack, and a piece of wood. Removed the allen bolts on the rear of the straps and lowered it enough to get to the body bolts. Pretty easy after doing it two or three times.
I think that your rework is a great idea, and I would have done it if I could have gotten all the hardware in one trip to Lowes! But, my Lowes would not have all that stuff. Might be a good package deal for a vendor to put together.
#7619 MKIV IRS complete kit, non donor
351 tko 500
Delivered Nov 13, 2011
First start December 31, 2011
First gocart Jan 12 ,2012
picked up from painter 5/5/2012
Location: Blackberry Township, IL (west of Geneva)
I did something similar using this thread - but just for the lower rear passenger side so that I wouldn't have to remove the gas tank in order to install my rear bumper and overriders. I used 7/16" threaded rod, instead of 1/2", and was able to make is so that I can install it using the original threads in the overrider. Installation is as follows:
1) 7/16" x 1" bolt inserted through the chassis hole (no washer under the head)
2) washer and coupler attached to 7/16" x 1 bolt and tightened - just snug
3) thread the section of threaded rod into the socket on the overrider, then insert through the appropriate spacers, bumper, and body
4) add three nuts and the washer (washer with neoprene gasket to body) to the threaded rod inside the body
5) holding the overrider as close to the final positioning, thread the threaded rod out of the overrider and into the coupler (leaving 3/8" or so of threads sticking out of back side of overrider and bottoming the threaded rod out in the coupler
6) run the jamb nut down onto the coupler
7) slip a combination end wrench up between the gas tank and the chassis and turn the 7/16" x 1 bolt head to pull the overrider into final position, tightening the spacers against the bumper and the body
8) final adjustment is done by turning the other two nuts that are on the inside of the body on the threaded rod out against the body, using one for a jamb nut on the other
9) for final installation, I'll add some red loc-tite to make sure it all stays together.
Here's a shot of the installed assembly - no need for an external nut in the overrider!
And here it is installed:
Picked-up at FFR - 10/10/09
First start and go-kart - 9/19/12
"As smoke is blown away; so blow them away." Psalm 68:2
Hey GWL, thanks for documenting this!
Great mod, and it seemed to work well.
I mocked it up using some similar sized galvanized tubes (cheap and temporary), and once I'm comfortable that everything works as expected. I plan to order the expensive Finishline SS tubes and cut them to length.
I installed the trunk latch a week ago and completed the license plate mod last week, everything works GREAT, except that I noticed I cannot insert the key into the trunk latch, because the bumper is about 1/4" too close. I have a simple solution, since my sleeves are still temporary and I haven't cut the SS ones yet, I'll just make the SS sleeves 1/4" longer OR add a nut behind the SS sleeve and before the bumper.
Just wondering if anyone else ran into this issue?
Thanks Again! This was easier than I expected.
F5R #7446 Delivered 4/4/11, First start 9/29/12, First Go-Kart 11/17/12
Licensed 4/24/13!! Wahoo!
GWL, one other thing I would add to this mod, that is related.
For the latch pin bolt, I replaced the nut on the fuel tank side of the chassis plate, with a 10-24 Rivnut. It was a little tricky to open the hole up to accept the riv-nut (would recommend this before installing the body!). Installed the rivnut and shortened the sleeve just a little, but perfect fit now and I don't have to fight the little nut on the tank side now.
F5R #7446 Delivered 4/4/11, First start 9/29/12, First Go-Kart 11/17/12
Licensed 4/24/13!! Wahoo!
Just the other day, I read about the key interference. Someone posted that they had solved it by putting the trunk handle below the trunk opening and made a catch in the trunk lid, turning the whole thing upside down. This also solved the license plate interference.
I like your solution and hopefully you'll post pictures of what the bumpers look like a 'bit' further out when you get it done. Looks like I may have to use longer all thread and a longer sleeve. I'll figure it out when I get back to it again.
I just looked at my pictures and I may have enough thread to just add a few washers right behind the nudge bar.
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