BMC, chop, wait, then weld???

[jbjones85]

I need to do a BMC on my ride to solve a minor rubbing issue. I know ideally I would cut and re-weld at the same time BUT is there a huge issue with doing the chop, waiting to make sure I don't need to do any additional trimming, then re-weld back in some supports? I do not plan to do any heavy wheeling during this time.

Thanks.

 

[JSparky]

I'm not an* engineer but I'd imagine you'd be weakening that mount substantially by not boxing it back in. I would just get it done all at once and not worry about it.

 

[wfo9]

No difference unless you are in an accident and even then all bets are off with it welded. Pointless to chop for 285s IMHO, but to each his own.

 

[JKLNHYD]

There should not be an issue with that. But you also probably don't need to go far to find an incline to flex the suspension and turn the wheels back and forth to make sure you took enough off. I wouldn't go on a road trip or hit the Rubicon Trail until the new metal is welded back in.

 

[Angelo]

I do not plan to do any heavy wheeling during this time.

I would just get it done all at once and not worry about it.

I second what [MENTION=96425]JSparky[/MENTION] said, get it done and have it done. The whole conversation is theoretical but you don't need to do heavy wheeling to bend or crack a weak frame mount. Would it crack or bend? Probably not, even if you decided to do some wheeling or ran over a pothole you didn't see coming at 60+ mph. The question is do you want to take a chance like that for something so relatively minor.

FWIW, the angle of the BMC will "max out" because of where the actual mount sits in relation to the steel covering that you'll be chopping. Relentless Fab makes a filler plate that gives you pretty good length guideline.

https://www.relentlessfabrication.c.../products/03-09-4runner-body-mount-chop-plate

And you probably know how to do everything already but Total Chaos has a great tutorial video on YouTube...

https://www.youtube.com/watch?v=0v2h6pBzIrs

Whether you use theirs or make your own don't forget to tack weld the plate rather than a continuous feed technique that can actually set the mount itself on fire. Some pretty unfortunate YouTube videos on that note. Good luck man.

 

[TeeDub21]

No difference unless you are in an accident and even then all bets are off with it welded. Pointless to chop for 285s IMHO, but to each his own.

Pointless unless your tires rub the body mount.

 

[Jetboy]

I would do it all at once. It's just easier to cut and make a template and weld back in all at once. If you're using a pre-made filler plate, you need it when you cut to get the pattern correct.

otherwise rust is the other issue. At least shoot with a weld through primer so you can weld it back up when you're ready.

Finally I used a piece of thin sheet metal to make a shroud to protect the rubber from the heat of the weld. That way you won't start a fire.

 

[83Mule]

The mount is High Strength Steel and cutting it beyond the rubber will not weaken it as it is more than heavily gusseted where it needs to be. The part you cut is the extension that protects for wheel intrusion in an offset crash. no need to weld it up just rustproof it.

 

[rochmpr]

To make welding easier, its best to loosen all of the body mount bolts, raise the body and remove the rubber mounts prior to welding. It also gives you more room to weld.

 

[jbjones85]

Thanks everyone, I am rubbing the BM with my wheel/tire combo and am planning to up size from the 285/70 to a 285/75 in the near future which will for sure require it so wanted to get ahead of that. i'll find a local shop and just get it all done at once.

 

[DannyLlama]

Have you done the fender mod? You can push back the fender a good .5 inches.

Like others said, does the benifit of 285 75 vs 285 70, outweigh the risk of more damage in an accident?

 

[jbjones85]

It's not rubbing the fender liner so i'm not sure doing anything with that is going to solve the rub on the BM.?

 

[DesertCanyons]

Body mount chop

The mount is High Strength Steel and cutting it beyond the rubber will not weaken it as it is more than heavily gusseted where it needs to be. The part you cut is the extension that protects for wheel intrusion in an offset crash. no need to weld it up just rustproof it.

After removing the front tire mud flaps yesterday most of my tire rub problems went away. I was looking at the body mount directly behind the front wheels. I have Falken AT3W LT 285/70R17 tires on 8.5" rims, which are at least as wide as what you may have in the same size tire. It only rubs in reverse when cranked all the way. Turning radius is so tight in reverse that not turning the wheel all the way is not going to limit your turning ability. I'd suggest you just not turn the wheel tightly in reverse and live with it if you're having the same experience.

The last point made by 83Mule is a pretty important one. Modern cars have crumple zones from the front bumper to the front firewall. The car can collapse like an accordion up to the firewall which absorbs the kinetic energy of a crash. Behind the firewall the cab should remain intact and protected from intrusion by the tires and collapse of the passenger compartment. In the event of an offset crash, or the collapse of one corner, you want that cab area protected. Don't become a statistic who gets severely injured in an accident. :croc:

 

[DannyLlama]

It's not rubbing the fender liner so i'm not sure doing anything with that is going to solve the rub on the BM.?

That's right.. removing the mudflap helped me the most. Just like [MENTION=115572]DesertCanyons[/MENTION] said

I simply view cutting into the frame in any capacity as a last ditch effort

 

[Runn4est]

It's not rubbing the fender liner so i'm not sure doing anything with that is going to solve the rub on the BM.?

What you should be doing first, especially if you're going to upsize again is UCAs. My 5th gen doesn't rub the BM or mudflap while running 4.3deg caster. Factory wheels, no spacers, so if your offset is different that might be a contributing factor.

 

[RedSled]

This is the passenger side on my 2017 SR5 P, i think the bmc came out great.

 

[jbjones85]

What you should be doing first, especially if you're going to upsize again is UCAs. My 5th gen doesn't rub the BM or mudflap while running 4.3deg caster. Factory wheels, no spacers, so if your offset is different that might be a contributing factor.

I am running UCS's (Icons), don't remember the caster angles. Stock tires wheels with 1.25 spacers. It is the spacers, without them no rubbing.