Heater channels are normally covered with carpeting and the first evidence of rot might be the fact that the windscreen stays permanently misted-up because no hot air is reaching it! It is possible to renew the heater channels without taking the body off the chassis, but this will mean fitting new belly pan gasket strips under the heater channel ends where they would almost certainly be damaged by the heat of.welding, and this usually spells water leaks at the end of the strips, which accelerates new rusting. Far better to remove the body and fit a complete belly gasket as already described, but if you cannot lift off the bodyshell, read on.
If the heater channels have rotted badly, then the floorpan edges will usually be found to have also rotted, so attend to these first.
The rear seat brace should be kept in position throughout. Cut through the old heater channel just ahead of the B post and behind the A post (take care not to cut into the floorpan edge), then part the welds to the flitch and the inner quarter panel. If the lower part of the flitch is also rotten, then cut this away, and weld in new steel after the new heater channels are in place. Cut the rear up to the lower inner wing flange.
Depending on whether the channel has been replaced before, you might also find weld between it and the flitch inner surface and bulkhead panels; this must be ground off, though in many such cases you will have to cut away the base of the flitch. Carefully cut around the bases of the A and B post. Remove the remaining sections of heater channel; if no welded joints remain then a (controlled) clout from a hammer will usually do the trick.
Bolt the new channel into position on the chassis assembly; a replacement length of belly pan gasket should have been obtained but not yet be fitted, because welding at the ends of the heater channels would burn it away! You may require an assistant to push the floor edges downwards as you push the heater channels into position. Then re-fit the door and check that the gaps are correct front and rear. Tack weld the bases of the A and B posts into position, remove the door, then knock down the inner quarter panel and seam weld this to the heater channel, and seam weld the flitch.
Undo the heater channel to floorpan bolts, push the floorpan edge downwards and try to work a new length of belly pan gasket into position.
If the heater channels have rotted badly, then the floorpan edges will usually be found to have also rotted, so attend to these first.
The rear seat brace should be kept in position throughout. Cut through the old heater channel just ahead of the B post and behind the A post (take care not to cut into the floorpan edge), then part the welds to the flitch and the inner quarter panel. If the lower part of the flitch is also rotten, then cut this away, and weld in new steel after the new heater channels are in place. Cut the rear up to the lower inner wing flange.
Depending on whether the channel has been replaced before, you might also find weld between it and the flitch inner surface and bulkhead panels; this must be ground off, though in many such cases you will have to cut away the base of the flitch. Carefully cut around the bases of the A and B post. Remove the remaining sections of heater channel; if no welded joints remain then a (controlled) clout from a hammer will usually do the trick.
Bolt the new channel into position on the chassis assembly; a replacement length of belly pan gasket should have been obtained but not yet be fitted, because welding at the ends of the heater channels would burn it away! You may require an assistant to push the floor edges downwards as you push the heater channels into position. Then re-fit the door and check that the gaps are correct front and rear. Tack weld the bases of the A and B posts into position, remove the door, then knock down the inner quarter panel and seam weld this to the heater channel, and seam weld the flitch.
Undo the heater channel to floorpan bolts, push the floorpan edge downwards and try to work a new length of belly pan gasket into position.
