The dreaded Unibody Repair...Trailing Arm (Stab.bar)

[sad-lumina-owner]

Some of you may have noticed my previous post in the engineering section here:

How can I repair (weld) a unibody rusted near rear stab-bars?

http://www.automotiveforums.com/vbul...d.php?t=920303

In that thread I proposed to deal with this rust problem quickly.

The first step of the treatment was hammering off all the loose rust and damaged steel, and then rasping and fixing and painting with rust-paint to stop all further damage.

The fact that one of the Trailing Arm brackets was 'loose' (that is capable of some motion) required immediate attention, and forced the priority of this project over everything else.

In fact, the rust had allowed the bracket to begin to detach from the unibody. This would also allow the horizontal position of the wheel to move out of alignment, resulting in worse handling and tire wear.

Again, the danger of say hitting some serious pothole or being hit by another vehicle could also result in additional dangers.

The first thing to do is to fix the bracket in its original position and prevent it from coming off or indeed having any play of motion at all relative to the body.

This was done by drilling up through the bracket (which conveniently has a hole apparently for this purpose) and into the car unibody through and under the rear seat.

First the back seat bottom must be removed (just two bolts):



Then a bolt is placed through the bracket from underneath.



On top we have a large washer followed by a lock washer (not visible) and smaller washer and nut. On top of that another lock washer and nut to lock everything down. (This part will endure vibrations from the rear wheel).

In fact, first I cut a strip of sheet steel about 2 1/2 inches wide and 8 inches long, which snugly fit inside the bracket. I drilled a hole in this to allow the bolt to pass through it, making a kind of sandwich which pins the bracket between the good flooring steel and the new piece below:



This strip was cut on an angle at each end to line up with its welding connections.

Here's a shot at the rear weld (welding in progress) from the view of the rear driver's side wheel well (wheel removed and well sawed out).

Here you can see all the bad steel has been cut out with a SawsAll. This is a hell of a job without a hoist. I used three jackstands and two jacks, (one rear wheel at a time removed). You learn to saw lying on a freezing concrete floor from just about every dangerous angle you can imagine. You absolutely MUST wear safety goggles while using the SawsAll at this close range. It throws tons of metal shards at high speed in your face in an unpredictable manner.



The shiney silver thing on right is the welding clamp ground.

The brake lines have been shielded with some ABS flexible piping in the background.

[sad-lumina-owner]

Note as well that (as usual) I have double-bagged the entire brake rotor/pad/calipers with green garbage bags during the entire process, of rasping with a drill and wire-wheel, sawing with the SawsAll, and welding with flux-core wire. You must keep the brake pads and rotors from contamination by bits of rust and metal shards, as well as spray from rust-treatment, primer, and rust-paint splash.

[sad-lumina-owner]

This process of bolting down with sheet steel plate solves the immediate safety issue regarding a loose Trailing Arm bracket. All play is removed and the trailing arm is rigid, and impossible to budge.

However, sawing out the rusted and damaged unibody sheet-steel creates a secondary problem (which was always there really), namely the weakened unibody/frame itself.

This could escalate into body warpage from overloading (fat passengers), or even doors no longer opening or closing properly.

So before too much mileage or rough driving is done, the steel has to be replaced with steel at least as good (or better even thicker) as the original.

We leave this to part II.

This involves carefully measuring and sawing new pieces of steel, choosing the seam positions etc. for good strength and durability.

In the end, the unibody will be more rigid (and heavier) than it was before. And stronger.

There is very little mileage penalty for adding some heavier steel plate here. The manufacture was using the bare minimum required.

One will immediately notice for instance that the Emergency Brake bracket is about 3 times as thick as the sheet steel everywhere else in this section of the car. This bracket will last about 20 years longer than the rest of the vehicle, which is ridiculous.

In fact, the bracket is the right thickness, and (as is apparent from the deterioration) the proper steel that should have been used for the Unibody Support Frame pieces (which we now have to replace).

The bracket is rusty but hardly needs replacing, and I just drilled a hole through it and remounted it closeby on the support Frame:

[sad-lumina-owner]

There is a three layer treatment of the exposed steel here:

(1) Rust Converter

(2) Rust Primer (light gray)

(3) John Deer Green Rust Paint.

The John Deer is amazing. Not only does it make for a great thick waterproof coating, but it lightens up the whole underside, so you can see what is going on under there at a glance. The principle is the same as painting a ceiling white to increase the available light in a room. It also contrasts with any rust, so you can see if there is further deterioration anywhere underneath the car, which might need attention.

And the quart of John Deer Rust paint is only $12. I used half on one side of the underside.

[ChrisinVT]

Do you have any pictures of this in it's final state?

[grandmasfreelumina]

thanks for the great advice and pics to save my lumina.
just nursing the rust along.
fyi someone posted some confusing comments about por15. por15 is designed to paint directly over rust ( just scrape off some of the major scale) and it does not require a topcoat. however it will change a different shade when exposed to uv rays. I put silver por15 on my white lumina and it turned to a gold color.