Trailing arm crossmember support Q's

[Sherman Snouts]

Hello, everyone. I decided to cut my crossmember to allow compact exhaust routing. I've read the threads on this procedure, and there seems to be alot of stress about the structural integrity after this modification. I used the method of using a thick wooden board to act as a pilot to hold the saw steady (credit goes to whoever came up with this clever idea). And I see lots of people welding a thick pipe in the hole to support the crossmember. So my concerns are these:

My frame is already painted. I know, I should've researched these mods before going to final paint. But I am concerned about welding splatter and having to touch up the paint.

Is the support really neccessary? I'm sure it would'nt hurt to reinforce the crossmember, but that metal is pretty thick. And the crossmember is pretty stout.

And the real question: Has anyone ever seen one of these crossmember mods fail when no support is added? If so, I'd like to see where the failure point was, if pictures are available.

Thank you in advance! And I will post pictures ASAP.

LWB, static drop, no towing or hauling in mind. 3in hole saw.

[Xeen]

If you are worried about slag from the welding process, then use some green painters masking tape and heavy gauge aluminum foil and shield everything within range, cheap and effective.
IMO though you don't need to reinforce for a 3" hole, but it is advisable to do so for a 4" hole.

[Sherman Snouts]

Thank you for the reply, Xeen. I too feel that it shouldn't be an issue.

Here are the pics. I cut the hole pretty close to one of the factory holes. This is what worries me. No other opinions?

I believe this hole serves no purpose so either I fill it in or forget about it.

[67c10rustbuket]

I would not be concerned with reinforcing that little 3" hole. A 4 1/2" like mine sure but yours has plenty of wall around the hole. If you go 4 1/2" there is little vertical wall left and reinforcement is recommended. Looks good, nice job. I can't believe you hauled the frame in your truck bed though.

[Sherman Snouts]

Lol! I see that you took a look at my build thread. it was a white knuckled ride 30 miles home. But I made it. When I got home, I saw that the frame slipped about half a foot off the tailgate. Good thing my Walmart tie straps held!! Thanks for the input.

Has anyone seen one of these cross members fail? I'm interested to see what would happen. Cause when I'm blasting down these Texas back roads, that cross member will be in the back of my mind.

[67c10rustbuket]

Just a thought, The ECE crossmember does not have reinforcements. I decided next time I would rather buy this and swap out the stocker than risk the beating from my 1/2 drill hanging up and twisting my wrists into submission. My 2c

[Sherman Snouts]

I've looked into that. But always got confused because I have a long bed which requires a carrier bearing. Is it possible to switch to a one piece drive shaft? Or is there an option that has a carrier bearing mount? But after drilling out the holes, and busting up my knuckles a few times, I think I will enjoy the OE cross member for a while!

[Sherman Snouts]

Also, I'm starting to think about when the exhaust is run through the cross member, will the exhaust pipe contact the cross member when the engine is reved up? I'm worried that I could break the exhaust manifold if too much tension is applied as the motor tilts. 2 1/2 exhaust max.

[68C15]

mine has 4" holes and held up fine pulling a trailer with a 67C30 dump truck on it. Now, if you were drag racing it would be a different story

[Sherman Snouts]

What size exhaust are you running? I'm hoping with my 2.5 inch pipe running through a 3 inch hole, giving me a quarter inch all around, I'll have enough clearance to compensate for the engine tilting during a high rev. If need be, I could step down to a 2.25 exhaust. Any experience with this, y'all?

[67c10rustbuket]

Sounds pretty tight but might have some to do with your engine/trans mounting and exhaust hangars too. Are you using OE rubber mounts or poly mounts? I really cant say how much clearance you need. I have 2.5 exhaust through a 4" id pipe welded in and there's plenty of slop room. Using some hangars on the cross member may help keep it close to center like mike did here- http://67-72chevytrucks.com/vboard/s...354738&page=25. I plan to pretty much copy mikes hangars once I get done running the pipe on my truck.

[Sherman Snouts]

Those hangars look pretty impressive. I will have to do something like that. And I haven't gotten far enough in the build to look into it. I'm guessing I could secure the pipe right at the crossmember (like Mike) and let everything else flex. Maybe some tougher motor mounts could solve the problem as well.

[SierraMtns]

Originally Posted by Sherman Snouts

Thank you for the reply, Xeen. I too feel that it shouldn't be an issue.

Here are the pics. I cut the hole pretty close to one of the factory holes. This is what worries me. No other opinions?

I believe this hole serves no purpose so either I fill it in or forget about it.

Clever way to cut the holes.

[un4gvn!]

I cut 3 inch holes in my cross member and used 3 inch pipe. The hole is the hanger. I used the 6 inch long stainless steel flex hose coming off the 3 inch reducer from the Hooker headers for the engine flex when I jump on the gas. I've seen this set up on the manifolds with a down pipe also. Works great.

[un4gvn!]

Oh by the way. I only seen one fail. The guy cut a 3 1/2 inch hole real close to the trailing arm mounts. He told me at one time somebody pulled out in front of him and when he slammed on the brakes, the trailing arms came forward and bent the cross member where the mounts are riveted 3/4 of an inch. I've seen this cross member because I sold him a replacement.