Rear frame rail repair/replace - options and opinions please

[Jamieg285]

Hi all.  I appreciate not all of you will have experience of 2nd gens, or serious structural repairs, but I'm looking for opinions on how to tackle my latest problem.

The drivers side rear frame rail is toast, from the rear bumper to just beyond the bumper brackets, most of what you see here:


I have been fortunate to find a decent used replacement, which is pretty much the same length as the aftermarket pieces, i.e. bumper to just past the shock mount.
This donor was cut out with the floor still attached to the rail - no spot welds have been cut.



I have spent ages looking at the task, but can't decide on the best way to deal with this, and I'm looking for opinions to help me decide the best way forward.


Firstly, should I remove the floor pan section from the donor and spot weld the rail to my floor, or should I leave it on and butt weld the donor floor to my floor?   My existing floor isn't too bad, but there are some areas that have been (badly) patched in the past, which the donor floor section would cover.


My second question is where to cut and join the rail.  I only need the first section, so could cut just past the drain hole (red line).  The downside of this is the trunk floor is in the way of the inner side, so I would need to cut that out to gain access.  Doing this doesn't bother me, it's just more work.

The alternative is to cut further back, beyond the dip in the trunk, where I would have access to all sides of the rail. This though would need to be an angled cut, as the access points on each side aren't in line. (green line). Downside to this option is there is more rail to remove and it gets more complicated as it gets near the wheel house panels.



I guess a third alternative would be to go even further and take out almost the whole rail, past the shock mount. This again is more work to get it out, but is does move the rail joint to a location with better access.  I have got a full inner wheel house panel to make use of, but don't plan on removing/replacing the whole panel.


One thing that I am wondering about, is where the main stresses would be, and if I want to put my welds there or not.

Any advice welcomed.

[Andy]

Wow, this car is turning into a Trigger's broom project good on you for keeping it up.

I would go for the first option on the basis of if the rest of the rail further on is in good shape, then just replace the knackered bits.

Also, does the green line cut mean you'll be welding in a new rail section with shock mounts on it? Can't quite tell from the photos. If so, this would take quite some work to get all the alignment sorted.

[Roadkill]

I'd remove the old floor pan attached to the rail first rather than try to butt-weld with it still in place.

Re. cutting the rail, the second & third options would be the more stressed areas, I'd guess . . . as Andy says, makes sense to remove as little as possible, providing what's existing is good.

[Jamieg285]

Quoting: Andy

Also, does the green line cut mean you'll be welding in a new rail section with shock mounts on it? Can't quite tell from the photos. If so, this would take quite some work to get all the alignment sorted.

The leaf spring mounts in the round tube at the back end of the rail (where it's currently rotten)

The bracket nearest the green line is the rear anti-roll bar mount.  The shock mounts outboard and up from this, you can make out the square edges of the space for it, just under the green line.


My current line of thinking, based on these and other comments on the 2nd gen forum, is to strip off the floor from the donor. Start cutting the old rail near the end and move back until I am happy the metal is solid, i.e. cut as close to the bumper as possible.  I think I will be able to butt weld the outer side of the rail and rear end to locate it, the cut out the floor above/around it to get access to finish the weld on the inner edge, and also allow me to weld it from the topside of the frame for added strength.

[Rob]

I cut the rear section and did mine.

http://www.mkb.cc/forum/index.php?action=vthread&forum=2&topic=11663
 
When I researched mine I found guys that drilled out all the spot welds instead of cutting the whole floor out.  

Just be sure to get some sort of datum before you start cutting the rail.