Question about Rear Crossmember

[Remington]

It looks like, at some point, my car was rear-ended. This piece is smashed in and the rear crossmember is all bent up. I was in the process of replacing the trunk floor when I found this and realized the crossmember needed to be replaced. My question is what is the correct gap here once i get it straightened out? Should just hammer and dolly it out or build new pieces to hold the new crossmember?

I could go by the first spot weld at the top but since the old crossmember was so bent up I couldn't really compare the new metal with the old to make sure they were exactly the same size. I need some guidance here.

 

[mustang7173]

Hello Remington,

Here is the thread with the underbody chassis measurement that will help you realign the section you have pictured here.

http://www.7173mustangs.com/thread-chassis-dimension-questions?pid=247548&highlight=chassis+dimension#pid247548

Thanks,

mustang7173

 

[Mister 4x4]

Unfortunately, your picture is blocked through the proxy server at my work, but I'll check it out later this evening.

I'm a little confused by the use of the term "gaps," since the rear cross member welds directly to the rear frame rails, effectively closing the loop on the rear frame itself. The lower taillight panel welds to the rear cross member itself, and there are a pair of brackets that also butt up against the inside of the taillight panel for the rear bumper brackets to bolt into - not much in the way of "gaps" to contend with with these pieces. By not removing the quarters until the taillight panel, trunk pan, and rear cross member are replaced, the taillight panel should line right back up and fit into the area the original piece came from. Granted, mine was straight - albeit as rusty as the Titanic - but if the repair shop got the back end anywhere close to straight [despite the bent rear cross member] it should all fit right back in fairly well.

If your rear cross member has been compromised, rather than try to straighten it out (and possibly weaken it further) you might consider just getting a new one and replace it altogether.

https://www.npdlink.com/store/products/mustang_rear_floor_crossmember_repro_exact_fit-146898-484.html

If the rear frame rails themselves are also bent, there are replacements for those as well (which will become a much more involved repair, of course). If you choose to straighten out the ends of those instead, the rear cross member will help in establishing the side-to-side distance... obviously you'll want to center it on the vehicle as well to get it 'back to straight' if it's also tweaked one way or the other.

Hopefully, it was just superficial damage to the taillight panel and rear cross member, and the previous repair shop just tacked on a new taillight panel, bumper, valance, etc., thinking that nobody would really care about the rear cross member once the 'pretty stuff' was all back in-place. You might actually get away with just replacing the rear cross member (along with the rest of the sheet metal items you already planned on doing).

I hope I didn't go off on a completely different tangent, since I'm not able to see the pic at this time. I wouldn't want to give anyone the impression that I take this stuff lightly and am just hoping you get lucky with this repair or anything.

 

[Remington]

Unfortunately, your picture is blocked through the proxy server at my work, but I'll check it out later this evening.

I'm a little confused by the use of the term "gaps," since the rear cross member welds directly to the rear frame rails, effectively closing the loop on the rear frame itself. The lower taillight panel welds to the rear cross member itself, and there are a pair of brackets that also butt up against the inside of the taillight panel for the rear bumper brackets to bolt into - not much in the way of "gaps" to contend with with these pieces. By not removing the quarters until the taillight panel, trunk pan, and rear cross member are replaced, the taillight panel should line right back up and fit into the area the original piece came from. Granted, mine was straight - albeit as rusty as the Titanic - but if the repair shop got the back end anywhere close to straight [despite the bent rear cross member] it should all fit right back in fairly well.

If your rear cross member has been compromised, rather than try to straighten it out (and possibly weaken it further) you might consider just getting a new one and replace it altogether.

https://www.npdlink.com/store/products/mustang_rear_floor_crossmember_repro_exact_fit-146898-484.html

If the rear frame rails themselves are also bent, there are replacements for those as well (which will become a much more involved repair, of course). If you choose to straighten out the ends of those instead, the rear cross member will help in establishing the side-to-side distance... obviously you'll want to center it on the vehicle as well to get it 'back to straight' if it's also tweaked one way or the other.

Hopefully, it was just superficial damage to the taillight panel and rear cross member, and the previous repair shop just tacked on a new taillight panel, bumper, valance, etc., thinking that nobody would really care about the rear cross member once the 'pretty stuff' was all back in-place. You might actually get away with just replacing the rear cross member (along with the rest of the sheet metal items you already planned on doing).

I hope I didn't go off on a completely different tangent, since I'm not able to see the pic at this time. I wouldn't want to give anyone the impression that I take this stuff lightly and am just hoping you get lucky with this repair or anything.

I am definitely replacing the rear crossmember. Its about the little piece holding the crossmember to the frame that is bent out of place. You'd need to see the picture I guess.

 

[Mister 4x4]

I am definitely replacing the rear crossmember. Its about the little piece holding the crossmember to the frame that is bent out of place. You'd need to see the picture I guess.

Yeah, definitely - I'll admit it's been a day or two since I had mine apart. :whistling:

 

[judge]

I found these pictures on-line

 

[Mister 4x4]

I saw the pic last night, and from what I remember those are just the tabs on the ends of the frame rails... which looked like they were bent in toward the center, rather than outward as they are supposed to be.

These pics were made smaller to load quicker on the forums, but you should be able to make out how the ends of the frame rails are supposed to look before you weld on the new rear cross member. The rusty piece with the chain actually held up the front end of my gas tank - I re-purposed it as a brace by welding it to the frame rails to keep them aligned when I removed the old rear cross member and welded on the new one.



The new rear cross member is in-place. You can see the burn marks from where the rear frame rail tabs were welded to the inside of the new rear cross member.

This is most of what's left of the rear bumper mount that's welded onto the floor pan after it's in-place, and it lines up with the holes in the taillight panel. The flat tabs of the part hanging over the edge of the floor pan actually welds to the taillight panel itself.

After you [carefully] bend the tabs on the rear frame rails back into shape, test fit your new rear cross member and measure using the chassis diagram in the thread mustang7173 provided. Should get'cha where you need to be.

Hope this helps.

 

[Mister 4x4]

It looks like, at some point, my car was rear-ended. This piece is smashed in and the rear crossmember is all bent up. I was in the process of replacing the trunk floor when I found this and realized the crossmember needed to be replaced. My question is what is the correct gap here once i get it straightened out? Should just hammer and dolly it out or build new pieces to hold the new crossmember?

I could go by the first spot weld at the top but since the old crossmember was so bent up I couldn't really compare the new metal with the old to make sure they were exactly the same size. I need some guidance here.

OK - basically, that spot weld at the top

you mentioned looks like it's pretty well intact and where it should be - the rear cross member compressed when it was hit, which 'accordianed' the remaining frame rail extension. Is it similar on both sides, or just the passenger side (as shown in your pic)?

Mark the leading edge of the cross member on both sides (if it's similar on both sides), and remove the old cross member. If the driver side is undamaged, basically check the measurements to see if they're the same on both sides. Also, mark and duplicate what you see on the driver side onto the passenger side and see if it matches - if it does, you've got luck on your side.

Test fit the new cross member in the same position of the leading edge markings (clamp it down with some major vise-grips or similar). Then test fit your new taillight panel - it should pretty much line up with the quarter ends and quarter panels as well as be tight up against the backside of the cross member without any tweaking. I'm thinking it's going to line up.

If all of that matches up, then you should also be able to lay the new trunk pan in and have all the edges fall into place where they should go without any weird tweaking as well. Clamp that into place as well.

If the rear cross member comes up short (i.e. - there's a gap between the taillight panel and the rear cross member), you'll want to check the rear frame rails for additional compression by using the measurements from the chassis drawings. You should notice some wrinkles somewhere along the frame rails and/or at the torque box, if that's the case... along with some other places on the quarter panels themselves. I'm wagering that the frame rails are fine, and that the rear cross member took the energy of the collision (as it was supposed to). The smooshed frame rail ends were just a crappy repair job.

If it all lines up, then you should be able to carefully reshape the flanges on the end of the frame rails to fit up against the inside of the rear edge of the new rear cross member and weld it all back together. You might consider adding a layer of new sheet metal to each 'flange' to strengthen them and the joints as well.

I hope that all makes sense.

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