Chopping the rear crossmember (1 Viewer)

[Lka1988]

Ok, so the time has come where I am officially sick of looking at the frame sticking out a mile and a half from the rear end.

I have a sawzall. I have access to a tube bender and gas MIG welder. I can get tube for cheap. So I'm gonna build a rear bumper (eventually).

First on the list of things that must go, though, is that rear crossmember.

1. What kind of issues am I looking at if I chop the crossmember without any support?
2. Will I need to brace the frame back there somehow when I actually chop it off?
3. Am I overthinking this and just need to do it?
4. How close can I get the cut to the rear body mount?

 

[donutfj80]

#1. None
#2. Only if your frame is tweeked
#3. Do it!!
#4. To the lip, or cut the lip and reweld

 

[greentruck]

Lka,
Random thoughts...

This is based on my thinking about this from looking at the different rear bumper options. I haven't made up my mind yet on how I'm going to proceed, except I will be buying, rather than building my bumper. I don't have the fabbing skills or tools many of you guys do, let alone a 25-year younger physique..

You can move the x-member in, so long as you tie things back together solidly. I would consider how the stock x-member is configured in designing its replacement.

If you're adding swingouts for spare tire, etc, then their mounting points have to be accommodated in some fashion. There are multiple ways to do this, which take up different depths of bumper space. If you're going for maximum departure angle and this doesn't matter, chop away, but you will lose these options without rebuilding the bumper later to get the room to squeeze them in.

I'm considering putting an aux fuel tank under the cargo area. Having been rear-ended in an FJ55, I can tell you that it was a very good thing -- except for my neck -- that this particular design feature of LandCruiser's was in place. The other guy was doing 35, totaled his car, and it was less than $500 damage to my 55. The stock tank is back there above the spare tire in the Pig. In the 80, the OEM tank's farther forward and even safer, but if you are thinking about putting an aux tank there -- and often a rear bumper is to move the spare out of the way to do just that -- then you might want to make sure you don't lose any protection the x-member gives you in designing its replacement.

Remember towing. No point in leaving low hanging fruit if you ever do plan to tow by designing in a receiver, etc up and out of the way. If you chop the x-member, I'm pretty sure that this will make mounting a typical aftermarket towbar problematic, so this may no longer be an option once you've cut the x-member.

 

[Tools R Us]

...
1. What kind of issues am I looking at if I chop the crossmember without any support?
2. Will I need to brace the frame back there somehow when I actually chop it off?
3. Am I overthinking this and just need to do it?
4. How close can I get the cut to the rear body mount?

I don't like driving mine with the bumper off. It wouldn't take much of a bump to bend the unsupported frame rails.

The 4x4Labs bumper chop is between the two rear receiver hitch bolt holes. This leaves two holes on each side, so the receiver hitch can be bolted on temporarily to provide support/protection. With the rear cross member off, the receiver hitch can be mounted upside down, providing more clearance in case wheeling happens before the bumper is done.

I would also leave the spare tire cross member on until the new bumper is done. This will help maintain frame rail spacing.

 

[Lka1988]

Lka,
Random thoughts...

This is based on my thinking about this from looking at the different rear bumper options. I haven't made up my mind yet on how I'm going to proceed, except I will be buying, rather than building my bumper. I don't have the fabbing skills or tools many of you guys do, let alone a 25-year younger physique..

You can move the x-member in, so long as you tie things back together solidly. I would consider how the stock x-member is configured in designing its replacement.

If you're adding swingouts for spare tire, etc, then their mounting points have to be accommodated in some fashion. There are multiple ways to do this, which take up different depths of bumper space. If you're going for maximum departure angle and this doesn't matter, chop away, but you will lose these options without rebuilding the bumper later to get the room to squeeze them in.

Remember towing. No point in leaving low hanging fruit if you ever do plan to tow by designing in a receiver, etc up and out of the way. If you chop the x-member, I'm pretty sure that this will make mounting a typical aftermarket towbar problematic, so this may no longer be an option once you've cut the x-member.

Gonna do it for max departure angle. I would like to do a swingout tire carrier, I've been mulling over different designs and mounts...

I will integrate a hitch receiver into the bumper, but I'm not sure how to do that. I won't be alone in this, though, so that shouldn't be a problem.

I don't like driving mine with the bumper off. It wouldn't take much of a bump to bend the unsupported frame rails.

I would also leave the spare tire cross member on until the new bumper is done. This will help maintain frame rail spacing.

Ok, my thoughts exactly, exspecially the one marked in red.... The spare tire x-member is already in place, I'm using it as a mount for my air tank.

 

[-Spike-]

I wouldn't do any surgery until you're ready to build the bumper. Ideas change.

 

[nicholas]

I think it was ?darwink? that actually integrated his factory hitch into a rear bumper and tire carrier. Search for "93 beater" or something like that to see it. It's a pretty slick design.

 

[Nay]

Just modify and weld a drawtite tucked up between the frame rails after you cut off the stock junk. Then build your tube bumper when ready. Will be strong as hell and completely functional for towing and extraction.

 

[-Spike-]

Nay's got a pretty sweet setup there.

 

[Lka1988]

I wouldn't do any surgery until you're ready to build the bumper. Ideas change.

Definitely.

 

[Lka1988]

Just modify and weld a drawtite tucked up between the frame rails after you cut off the stock junk. Then build your tube bumper when ready. Will be strong as hell and completely functional for towing and extraction.

You got more pics of the process?

 

[CycloSteve]

Nay's design is a great minimalist one...I don't think you can do a better job than that for maximizing your departure angle.

 

[Ihasfip]

Nay's design is a great minimalist one...I don't think you can do a better job than that for maximizing your departure angle.

Look under the members rear bumper thread. Mine is in there.

D

 

[Lka1988]

So here is the idea I'm going for, but with some beefy recovery points, a higher hitch receiver, more supports, and two solid sections of tube instead of chopping out the middle (designed for a pickup-style license plate...).

And this is where I'm at. Minus the step plate.

 

[Nay]

You got more pics of the process?

I wish I did but forget the camera for the hitch project (see link below for quarter panel trimming for the high mounted tube bumper) - it's very intuitive once you start trying to fit the hitch between the rails by flipping it over so instead of the wings mounting under the frame with the hitch oriented beneath the rails in stock location it places the hitch between the rails (you can see in the pics that the safety chain mounts are now on top of the hitch instead of under).

We had to step on the hitch a bit to bend the wings down before welding because it was pointing slightly up, but that was easy and the goal was the weld the tube bumper to the very top of the hitch. This both provides additional leverage support to the hitch as well as triangulating support to the middle of the tube bumper.

But, basically all you do is cut down the mount wings until it sits flush up between the frame rails (and use some weight to bend it straight as needed with jacks under the wings against the frame) and then weld the s*** out of it both under the frame on the wings as well as to the inner frame rails.

At the end of world war three will be the frame of my 80 with that hitch between it. The hitch is the strength in my design - the tube itself was very vulnerable to a hit right in the middle, but now the basic assembly is bomb proof (you can always replace some tube if you mangle it.)

If you want to see my quarter panel trimming project, which is essential for a good tube bumper to get bracing back to the frame, with a lot of pics, here's a link:

https://forum.ih8mud.com/80-series-tech/202095-rear-quarter-panel-clearance-cutting-new-technique.html

 

[Lka1988]

I wish I did but forget the camera for the hitch project (see link below for quarter panel trimming for the high mounted tube bumper) - it's very intuitive once you start trying to fit the hitch between the rails by flipping it over so instead of the wings mounting under the frame with the hitch oriented beneath the rails in stock location it places the hitch between the rails (you can see in the pics that the safety chain mounts are now on top of the hitch instead of under).

We had to step on the hitch a bit to bend the wings down before welding because it was pointing slightly up, but that was easy and the goal was the weld the tube bumper to the very top of the hitch. This both provides additional leverage support to the hitch as well as triangulating support to the middle of the tube bumper.

But, basically all you do is cut down the mount wings until it sits flush up between the frame rails (and use some weight to bend it straight as needed with jacks under the wings against the frame) and then weld the **** out of it both under the frame on the wings as well as to the inner frame rails.

At the end of world war three will be the frame of my 80 with that hitch between it. The hitch is the strength in my design - the tube itself was very vulnerable to a hit right in the middle, but now the basic assembly is bomb proof (you can always replace some tube if you mangle it.)

If you want to see my quarter panel trimming project, which is essential for a good tube bumper to get bracing back to the frame, with a lot of pics, here's a link:

https://forum.ih8mud.com/80-series-...er-panel-clearance-cutting-new-technique.html

Hmm... I've been thinking about chopping the 1/4 panel wing things on mine, too. I couldn't remember who did it, though, until you brought up that thread.

Ok, so I'm really warming up to your design. I've got my old hitch receiver in the garage right now. I'd like to do some tube with it as well, kinda like the Taco bumper I posted above, since I REALLY like that design. Then I could chop the 1/4 wing things and tie the bumper ends into the frame...

Hey, I like this...

 

[Nay]

Hmm... I've been thinking about chopping the 1/4 panel wing things on mine, too. I couldn't remember who did it, though, until you brought up that thread.

Ok, so I'm really warming up to your design. I've got my old hitch receiver in the garage right now. I'd like to do some tube with it as well, kinda like the Taco bumper I posted above, since I REALLY like that design. Then I could chop the 1/4 wing things and tie the bumper ends into the frame...

Hey, I like this...

You have to chop the quarters if you want any strength on the wings of a tube bumper - you can't get a brace to the frame rails otherwise.

That project we did with the quarter panel "floors" has been the key - it is strong enough that I have hi-lifted off of the bumper wing in a bad stuck while crawling.

Keep it going

 

[Bikeman]

Just do it. I chopped 3.5" off the frame and made this. it has a brace to the frame rails, quarters unmolested. You'd have to have an 80 with 8"+ lift that has a traditional aftermarket bumper with a swing-out to have this departure angle:

 

[Lka1988]

Just do it. I chopped 3.5" off the frame and made this. it has a brace to the frame rails, quarters unmolested. You'd have to have an 80 with 8"+ lift that has a traditional aftermarket bumper with a swing-out to have this departure angle:

Hmm... That's close to my original idea...

But something has to be done with those 1/4 panels. They just look weird.

 

[snatchfj80]

very nice bumpers nay and bikeman, looking to do something very similar and was just wondering(to myself) if the hitch would mount upside down in the stock position, but nay answered my question in this thread, might have to do some cutting on my days off.