There have been a number of heater channel replacement queries recently but my "body off" and "no braces" seem to be making little impression. This may be because I usually respond to queries and my message may be getting lost in the confusion. So, I thought it might be better to lay out a more complete view of this procedure in the hope that it may make some sense and be of help to anyone who might wish to read on. It is still a fairly general account so I will clarify or expand wherever asked to do so.
First of all, I would like to state that I realise that there are a variety of 'local' limitations that will dictate how this job can actually be done. However, these "limitations" do not alter the fact that there is a proper way to do this and, if the correct procedure can be understood, it will assist and improve the quality of the job irrespective of the actual methods employed.
I have always advocated taking the body off and the general reasons why are:
1. You need to replace the seal.
2. You can't properly remove or fit the channels with the body on, without employing some improper methods - Like flexing or trimming panels.
3. More space to work and less frustration makes a better job
There is far too much concern over lining up the heater channel with the chassis bolt holes; this is not of primary importance. The main concern should be the door aperture (not the chassis bolts). If you get this part wrong, there is little you can do other than cut of the heater channel and start again. Not only do you have to obtain the correct gap between the A & B-pillars but you have to maintain the correct height and lateral positions. Remember that the outside face of the channel is also the 'seal joint' for the door and so must line up properly with the corresponding seal flanges on the A & B-pillars.
It is not necessary to weld everything together so that the door opens and shuts perfectly. Just as long as the dimensions are correct, the door can be made to fit later. At the factory, although the shell components were placed in a jig to get the correct shape for the door, it was impossible to actually maintain that shape once the jig was released. Invariably, what resulted was a slightly parallelogram door opening for a 'square' door. The shell was then 'jacked' one way and then another to 'make' it fit the door. Luckily, most of these procedures are not required when replacing the heater channels as the rest of the body has been 'shaped' at the factory so most, if not all, of the alignments will fall into place.
Don't use the Door as an alignment tool. It will just get in the way and add leverage to the A-pillar and, in the end, it won't do any better than a measuring tape.
Now the one that really seems to upset people is: Do not use braces to achieve or protect the correct body alignments. This may sound crazy but it is a practice that seems to have been brought about by either fear and/or the lack of understanding of how the bodyshell works. Remember that the body has already been assembled correctly at the factory, so it is not a case that removing one connecting panel will somehow cause the shell to reduce to a lump of unaligned jelly. The other thing to remember is that the body gets twisted and damaged throughout its life and this can affect the door alignments. If you then brace it all up, what you have done is simply fix in all those 'errors' and thrown away the chance to put it all back to original. Even if the body alignments are perfect, the actual installation of the braces can cause a distortion. As I have stated on numerous occasions, only brace the A & B-pillars if you think that channel may completely detach itself from one or the other pillar, while lifting the body off the chassis. Once it is set down on its working supports, remove the brace(s).
I hear people explain how you have to cross-brace (A-A etc) to maintain the correct dimensions, but this is entirely unnecessary. If your new heater channels are so badly made that they do not have the correct shape, then braces won't help you. The front section of the body is rigid all by itself, right down to the A-pillars (it was a subassembly at the factory) so they won't move against each other, The rear section too, is fairly rigid. All that is left to worry about is the alignment of the front section to the rear section. This is completely taken care of by the setting of the lower door gap (950-951mm) when you fit the heater channels. If after this the front is not straight with the back, then there is accident damage that has not been fully repaired. Either way, you have no choice but to set the doors gaps properly and there is nothing more that you can do that will make any difference.
All bar one of the heater channels available today are aftermarket and generally of low quality, the only genuine channel is made at VW Mexico, for the 69 and later models, and is probably the best ever produced. As with the VW Mexico product, heater channels should be supplied in two pieces; the upper part (which contains all the heater ducting etc) and the lower bottom plate. This makes it possible to fit the upper section according to the needs of the bodyshell and door aperture, without much concern for the alignments with the chassis. The bottom plate can then be fitted to ensure that match with the chassis. When heater channels are supplied as a complete unit, you can't be sure that the bolt holes will match. If you fit the channels so that the holes do align, then you may then have to compromise the fit along the door opening, rear quarter etc; it can be a difficult enough job without putting major obstacles in your way, too!
Once you have the complete channels fitted and before you reinstall the shell on the chassis, you can refit the doors. Chances are that they will not fit, so you then have to go through the door alignment procedures (another long winded topic). However, as long as you have fitted the channels so that the 950 to 951mm door gap exists, you will be able to get the doors to fit, just like new.
Like I said, a relatively brief account, but a start!
First of all, I would like to state that I realise that there are a variety of 'local' limitations that will dictate how this job can actually be done. However, these "limitations" do not alter the fact that there is a proper way to do this and, if the correct procedure can be understood, it will assist and improve the quality of the job irrespective of the actual methods employed.
I have always advocated taking the body off and the general reasons why are:
1. You need to replace the seal.
2. You can't properly remove or fit the channels with the body on, without employing some improper methods - Like flexing or trimming panels.
3. More space to work and less frustration makes a better job
There is far too much concern over lining up the heater channel with the chassis bolt holes; this is not of primary importance. The main concern should be the door aperture (not the chassis bolts). If you get this part wrong, there is little you can do other than cut of the heater channel and start again. Not only do you have to obtain the correct gap between the A & B-pillars but you have to maintain the correct height and lateral positions. Remember that the outside face of the channel is also the 'seal joint' for the door and so must line up properly with the corresponding seal flanges on the A & B-pillars.
It is not necessary to weld everything together so that the door opens and shuts perfectly. Just as long as the dimensions are correct, the door can be made to fit later. At the factory, although the shell components were placed in a jig to get the correct shape for the door, it was impossible to actually maintain that shape once the jig was released. Invariably, what resulted was a slightly parallelogram door opening for a 'square' door. The shell was then 'jacked' one way and then another to 'make' it fit the door. Luckily, most of these procedures are not required when replacing the heater channels as the rest of the body has been 'shaped' at the factory so most, if not all, of the alignments will fall into place.
Don't use the Door as an alignment tool. It will just get in the way and add leverage to the A-pillar and, in the end, it won't do any better than a measuring tape.
Now the one that really seems to upset people is: Do not use braces to achieve or protect the correct body alignments. This may sound crazy but it is a practice that seems to have been brought about by either fear and/or the lack of understanding of how the bodyshell works. Remember that the body has already been assembled correctly at the factory, so it is not a case that removing one connecting panel will somehow cause the shell to reduce to a lump of unaligned jelly. The other thing to remember is that the body gets twisted and damaged throughout its life and this can affect the door alignments. If you then brace it all up, what you have done is simply fix in all those 'errors' and thrown away the chance to put it all back to original. Even if the body alignments are perfect, the actual installation of the braces can cause a distortion. As I have stated on numerous occasions, only brace the A & B-pillars if you think that channel may completely detach itself from one or the other pillar, while lifting the body off the chassis. Once it is set down on its working supports, remove the brace(s).
I hear people explain how you have to cross-brace (A-A etc) to maintain the correct dimensions, but this is entirely unnecessary. If your new heater channels are so badly made that they do not have the correct shape, then braces won't help you. The front section of the body is rigid all by itself, right down to the A-pillars (it was a subassembly at the factory) so they won't move against each other, The rear section too, is fairly rigid. All that is left to worry about is the alignment of the front section to the rear section. This is completely taken care of by the setting of the lower door gap (950-951mm) when you fit the heater channels. If after this the front is not straight with the back, then there is accident damage that has not been fully repaired. Either way, you have no choice but to set the doors gaps properly and there is nothing more that you can do that will make any difference.
All bar one of the heater channels available today are aftermarket and generally of low quality, the only genuine channel is made at VW Mexico, for the 69 and later models, and is probably the best ever produced. As with the VW Mexico product, heater channels should be supplied in two pieces; the upper part (which contains all the heater ducting etc) and the lower bottom plate. This makes it possible to fit the upper section according to the needs of the bodyshell and door aperture, without much concern for the alignments with the chassis. The bottom plate can then be fitted to ensure that match with the chassis. When heater channels are supplied as a complete unit, you can't be sure that the bolt holes will match. If you fit the channels so that the holes do align, then you may then have to compromise the fit along the door opening, rear quarter etc; it can be a difficult enough job without putting major obstacles in your way, too!
Once you have the complete channels fitted and before you reinstall the shell on the chassis, you can refit the doors. Chances are that they will not fit, so you then have to go through the door alignment procedures (another long winded topic). However, as long as you have fitted the channels so that the 950 to 951mm door gap exists, you will be able to get the doors to fit, just like new.
Like I said, a relatively brief account, but a start!