Front Frame Rail Replacement Difficulty and Brand Options

[quagmire]

Good evening, all!  I've made a fair amount of progress on my 1974 Challenger resto in the last few months with the little free time I have.  This is my first go at body work as well, and I went off the deep end fast.  I have the firewall, cowl, floor pans, inner fenders, radiator support, outer hinge panels, splash panels, and all of the various front end brackets and reinforcement panels installed now.  Basically, the only things untouched at this point on the front end are the shock towers, frame rails, inner hinge panels, and A-pillars! I'm also installing the Level 2 reinforcement kit from USCT.  All of my before and after measurements are basically identical (nothing moved or shifted), and most of the side to side variation is actually a little lower than before.

On a side note: it's incredible how these rickety old buckets made it 45 years without falling apart!  The QC on the assembly was nonexistent on my car.  There are parts that had 2x as many spot welds as necessary, and then the same part on the other side would have all of the welds missing entirely.  The 1/8" steel shock tower support gusset on the LH side practically fell off after removing the inner fender and cowl brace!  All 5 or 6 giant spot welds had little/no penetration - the tower and gusset were rust free and solid.   

While my RH front rail looks great, there is some rot in the shock tower area of the LH rail.  I have not welded in the inner fender and brackets on that side yet.  How difficult is it to replace the frame rail given the car is fully stripped down?  I was thinking of welding in the remaining panels and reinforcement pieces with the exception of where they attach to the rail.  I'd think that with all of the new plug welded metal and reinforcement parts the car would have no chance of flexing if leveled out and all of the weight supported by the RH side, torsion bar crossmember and rockers, right?  After that, it'd just be a matter of drilling out the remaining welds tying it to the floor and crossmembers.  Does that approach make sense and seem safe?  Obviously, I'd measure everything humanly possible.

If I can avoid building a frame table that would be ideal.  I've also considered patching the rail, but I have OCD with patching a part of a car where I cannot definitively know how bad the rest of it is, especially on one as critical as a rail.  Also, I do not have the fab skills or tooling to make any patches more elaborate than a basic square or rectangle, so anything more than that and it is usually easier for me to replace vs. repair.  I do not want to do frame caps given the amount of work I'm already doing.  I want this done right and for it to last.

Also, what frame rail manufacturers are best?  I see offerings from AMD, Goodmark, and Dynacorn.  It sounds like they each have panels that are superior and some that are inferior to the others with no rhyme or reason, so I was hoping to get some insight from some people that have actually used them and had good results.  Thanks in advance!

[jimynick]

You're pretty much doing what I did to my 74. If you haven't put the front floor in yet, it's a LOT easier. I had the K frame in on mine and when I had the firewall and hinge pillars out, as well as the firewall, there were only a few more spot welds to cut to change the rail. I can't advise as to which re-pop rail to use as I was lucky enough to score a solid oem one. I just unbolted the K frame at the rail, slid the rail in and clamped it to the Tbar Xmember, put the bolts back through the K frame and that was that. Obviously, as you mentioned, measure, but if it's in place at the Kframe and also the Tbar Xmember and your widths are ok, then I'd say you were golden. Remember that there's TWO braces that go from the aprons to the rails and firewall and don't cut out and up the only ones you have- like I did. DOH! 

[70chall440]

It can be done without a frame table. You have already developed the skills necessary for the job, set it up, measure (several times), since you are only doing one side, make the LH side emulate the RH side. Do not jack or move the car once you start and make sure you measure the height from the floor as well. Look, guys have been doing this for a long time in garages without frame jigs and so can you. That said, you can also make up some wooded jigs to check your measurements. Another option is to weld some temporary locating bars to specific points on the good side that connect to specific points on the part you are replacing.

[quagmire]

Thanks for the info guys.  I feel more comfortable doing this job.  I do have the factory K-member that I can strip down and bolt up for reference.

I noticed the AMD rails come with shock towers.  Anybody know why?  Mine are solid with very little surface rust.  Part of my plan to ensure things stay aligned is to weld in the inner fender to the shock tower and other attachment points minus the rail flange so that I know the shock tower angle and positioning doesn't have any opportunity to change.  I may even weld a temporary brace between them just in case.

If I have to replace the shock tower due to some compatibility issue with the new rail that'll make this more complicated.

[jimynick]

In my opinion, AMD has the shock towers on because that foregoes the need to remove, reset and reweld them with the possibility of a screw up all along the way. If you look at the factory welds on same, you'll notice that the welders were mostly either drunk, stoned or just incompetent. If you go for the AMD rail, I'd put the whole thing in. I don't know what you're referring to when you say "minus the rail flange", but don't weld the aprons in until you've got the rail in and have done your measurements to make sure the apron is correctly positioned both fore and aft as well as heightwise. The aprons don't index on the firewall, so they can float and if they're put in in the wrong spot, you'll never get a hood to cowl fit, nor hood to fender fit, so measure three times and weld once, to bastardize an old carpenter's saying. This isn't like quadratic equations, just take your time and think three dimensionally and you'll be ok. 

[70chall440]

What he said plus I would add, lots and lots of mock up to make sure everything fits and aligns. To that point, you need to mock up about everything to ensure it all works. The plus side to this is that you will be able to get the front end better aligned and gapped than the factory ever even considered.

[quagmire]

Update:  Here's how I went about doing this.  I put the car on jack stands at various points and on the rockers on the LH front.  I measured, leveled, and measured countless times to ensure everything was level, plumb, and the frame to datum line measurements correct.

I never finished welding the new inner fender to the old rail and shock tower, so a dozen or so spot welds later and the old one is on the ground.  It actually came apart easily.

Before dropping the rail, I mocked up the entire front end and doors to ensure all of the body lines and parts fit up as they should.  As you may recall, I replaced the firewall, cowl, hinge panels, core support, inner fenders, all of the various weld on brackets and braces between them all, and a USCT core support and inner fender brace kit.  The fit is now better than it was from the factory!

I also did it this way to ensure everything goes back together correctly along with rechecking all of the other measurements.  I think having everything bolted up like that also helps ensure things do not shift easily since there is more rigidity up front.  Nothing moved from everything I measured....

After this, I'm moving back to do the rockers, which seem like they will be a real chore given how integral they are to the car.  Hoping to have that and the rear end work done by summer.

On an unrelated note, I despise the 1972+ side markers.  If I installed 1970 fenders and quarters, would they fit up with my 1974 grill and tail panel ok?  I don't want to make it a full 1970 clone, but would not be opposed to getting the 1970 side markers installed if I am already replacing the affected metal.

[redo1973]

Wow, nice job.  It must have been nerve racking doing a frame rail.  The most I did was the firewall/cowl and I spent hours measuring, setting reference points only to realize that I had forgotten to set reference point for the inner fenders and had to reinstall the entire front clip to be sure I had good gaps.  Congratulations on your success and thanks for taking the time to share the details. This is a cool project to watch develop.

[quagmire]

Wow, nice job.  It must have been nerve racking doing a frame rail.  The most I did was the firewall/cowl and I spent hours measuring, setting reference points only to realize that I had forgotten to set reference point for the inner fenders and had to reinstall the entire front clip to be sure I had good gaps.  Congratulations on your success and thanks for taking the time to share the details. This is a cool project to watch develop.

Thanks!  Honestly, if you can do the firewall, a front rail is cake, in my opinion.  It is sooo much harder to get solid references to line up the cowl and firewall since you can't reference a print or anything, and being complicated pieces with lots of bends and angles, mine didn't exactly fall into place.  My cowl especially had to be worked and drawn in over the firewall in a specific sequence to get everything where it needs to be.

We'll see how the replacement rail fits but I'm not expecting too much drama.

[70chall440]

Excellent job

[340challconvert]

Impressive work

[quagmire]

Ok, I've been busy with finals but wrapped up the rail and shock tower replacement a couple weeks ago.  Wasn't too hard. The car is now more in spec per frame measurements than it was before.

For any other body work newbies, I will say that there are a few differences with doing a heavy part like a rail vs a panel.  Firstly, unlike a 20ga panel, you cannot really massage or work these parts much at all.  I found that I had to rework the panels that attach to the rail to fit it instead of the other way around.  Luckily, most of it was minor work.  Attach the splash panel and bracket to the new rail first.  Otherwise, you will not be able to access the topside to weld the bracket without cutting the floor out.  The shock tower fitment was meh at best, but I was able to get it mounted to duplicate all factory measurements.  On a plus, it was much thicker than factory for some reason.

Use the K-Frame to help square up and install the rail!  You do not want to find out that those bolt holes were not quite 100% where they need to be AFTER welding in this thing!  It also makes a convenient jack point to get the rail into position.

Attached are some pics of the new rail and my installed USCT lower radiator support brace.  I'm moving onto the rockers next.

One question:  My side to side rail height (bottom of rail to floor) measurements are not identical (they never were).  How much is acceptable for side to side variance?  I know these cars had generous tolerances when new, but I'm not sure what is ok or what isn't.  I'm not planning replacing the other rail, but if needed, could have it pulled down to match the other 100%.  I'm just not sure if I should even bother since it's clearly not bent from damage or collision and may be normal. 

I measured about 3/8" to 1/2" difference in rail height from side to side - this also explains why my coil over on the RH front corner had to be cranked up more than the LH front, which is now dead on in spec.  I always wondered how that could be with all the weight on the left side.  Now I know!