Technical: Repairing rust in boxbeams under doors

Another article from the B.O.C newsletter (Vol 1, number 3, March 1975).

This is perhaps the most bothersome area of rust, since a good repair is tricky. Although these beams do not hold the car together, they do hold the floor and seats as well as the door pillars (hinge post). This being by the way a “back-bone” frame, the weight is borne by the drive shaft tunnel.

These are offered only as suggestions, since each case of rust-out is different.

Where the outer skin below the rocker panels is rusted through.

MATERIALS: Hammer, flat tipped screw-driver and Philips with good points, 28 gauge or lighter galvanized sheet metal or aluminum (it does little work), “pop” rivets (or #7 x 1/2” sheet metal screws), 1/8” drill bits, roofing cement. With the front seat out.

1. Remove aluminum scuff-sills. Use Philips screw-driver and hammer to seat the screw driver into the screw heads, as well as to shock the screws loose from rust. 1960-61 – a very strong seal was used under scuff sills and they must be pried energetically.

2. Remove rocker panels. Take off chrome strips (Coupe and T.S.) with a screw driver and hammer, take out all screws – do not overlook the one just below the door hinge in the corner. The panel can be slipped off – note pads between panel and fenders. The same is done where they screw to the boxbeams


3. Check jack sockets, decide whether they are sound still. If not they can be reinforced with a 3” pipe driven between the sockets and the top of the beam (assuming rust has opened the beam along the bottom). The red lines shown above for the coupe run along the length of the beam. Those with welding facilities can weld braces between the top of the jack socket and the upper lip. For the Coupe, may be a rod between the two; a hole will have to be drilled through the rocker- panel support. If the inside beam is bad, the jack socket can be bolted to a plate of to the new beam, or you can do way better by forsaking the original system for a scissors jack.

4. Insert metal – a strip of about 8-10′ wide to cover from the upper lip to the floor with cut outs for jack sockets, if usable. Remove loose rust. It may be easier to cut the strip in half – do the back half first, then, seal with roofing cement along the upper lip, rivet of screw in (note a piece of the newsletter here was too hard to read and the OCR I’m using didn’t pick it up…)

Once the strip is fastened along the top, run roofing cement along the lower edge, fold strip over with jacks and a board, and fasten to the floor. A wider strip will be needed for the Coupe, if the (?) reinforcement has not rusted away. Do not fasten the strip fully to the floor if the inside part of the beam is rusted through, only tack it (see other post)

5. Remove any rust from behind fenders, sheet over any holes and coat with roofing cement. Water getting behind fenders through welting or access panel under front fenders will not drain, so those of you with solid beams and in wet areas be sure to forestall this by sealing particularly the rubber plug in the back of the wheel well.

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