BONNET HINGE REPLACEMENT

Corrosion in the bonnet hinge plate joint leads to water ingress into the vehicle.

Water leakage here causes:

The top seam seal of the bonnet hinge acts as a gutter for disposal of water run off from the roof & windscreen. Stressing of the spot welds and the thin body metal around them occurs as the bonnet is opened & shut. Eventually movement occurs, due to the hinge center line spot weld fixing to the body & the soft factory sealant used. This leads to breakdown of the sealant bond between the hinge & body and subsequent water ingress and corrosion.

Replacement of the hinge and the body section in this area is required when rust or sealant failure becomes apparent.

To distribute and reduce the load on the spot welds, a hard setting sealant (such as POR paint) is recommended.

 

Leakage here causes hidden rust in the heat effected zone of the fixing spot welds, resulting in holes in the body's thin metal & can lead to rusting of the underlying steering column cross beam etc.

 

The result of water leakage build up in the Bottom Rail "Reservoir" is shown below.

The sidepanel/rail interface corrosion, seems to me, to suggest the source of rail rust came from the build up of water in the "reservoir" fed from the bonnet hinge mounting failure, rather than the rear crossbeam. Maybe a combination of the two was involved.

One convenient way of repairing the bonnet hinge problem is by using the "Furness" hinge unit assembly as shown opposite.

The "Furness" replacement, is an assembly of the bonnet hinge and a well made panel section of heavier metal than the original.

The panel fits neatly into the vent opening and only needs spot welding into place and sealing. The bottom section fits atop the firewall.

 

Procedure:

  • Cut out old hinge sealant.
  • Cut out old hinge spot welds, either by a thin bladed chisel or a spot weld drill.
  • Cut out top part of old panel section (leave the sides & a top side edge lip in place)
  • Drill out the spot welds holding the remainder of the panel to the firewall.
  • Align the unit with clamps & weld the new assembly using a portable spot welder.
  • Seal the ends of the assembly with Silver solder, take care to avoid distortion.
  • Seal the hinge grove by allowing multi layers of POR paint to seep thru it. (avoid normal flexible body sealants as unless the surfaces are bright clean metal and scrupulously clean)