The Stovebolt Site Forums The Shop Area Paint and Body Shop Cab repair - on or off frame?

About to start some cab repairs on my '51 3100. Cowl, front floor panels, cab corners etc. The usual suspects.

I am a little confused as to whether it is preferable to do any repairs to the cab with it sitting on or off the frame.

Logic would seem to dictate that having the cab bolted down to the frame would seem to make more sense. The frame would hold it square and there shouldn't be any surprises when the cab is put back on the frame, after repairs have been completed. However, I am seeing a lot of people that tend to remove their cab and have it sitting on a dolly, or even nose down.

It would seem that access is a little better off the frame but if it at the expense of things being out of whack then not worth it.

Anyone got input on the preferred approach in this regard?

Thanks,
Paul

I did all of my repairs off the frame on a dolly and it seems that I did not have any alignment or fitment issues after everything was back together. I think a lot of people may point you to do it on the frame, which is probably better but like you said access might become an issue. If you do decide to do it off the frame Install some bracing in the door frames and an X brace between the corners to keep it square. Big plus to having it on a dolly is you can move it around, push it off to the side of shop when not working, roll it outside if it's nice out, etc. I guess the best of both would be to build a dolly with mounting points on it in their correct locations.

I'm planning on taking mine off and putting it on a rotisserie that I built from two engine stands. I'm old enough that I don't want to roll around on the ground any more than absolutely necessary. The rotisserie should give me good access at a convenient working height. I think it'll be easier to get proper alignment on the rotted away front cab mounts with it off the frame as well. It'll be either braced in multiple directions before the doors come off or reference dimensions taken and confirmed prior to welding in the patches so everything stays in alignment.

I built a roll around dolly that had the mounting holes exactly where they should have been, I had complete floor mounted on it when the old floor was cut out and replaced (after bracing). The whole cab was lifted then set down on new floor. Then he cab was transferred back to frame to double check figment then put back on dolly body work and paint. 🎩

It depends on how bad your rust is. If you have severe rust holes in the inner cowl, floor board, toe board, rocker panels, hinge pillars, and front cab supports, I would do it on the frame. Make sure to have rebuilt rear cab mount shackles, and new front cab mount pads, and adjust the cab to the frame per the Manual specs.

Thanks all.

I think I will do the initial repairs with the cab on the frame to ensure everything remains square. Inner/outer cowl, toe panels and front body mounts are all toast. Once I get the bulk of those done I will be more comfortable removing the cab, with some bracing in place. I can then rotate the cab to gain easy access to any other areas.

The good news is that there is a lot of good reference material out there for these repairs.

I agree with Carl.

If you're going to use the frame to keep it square, you will probably want to rebuild the cab mounts and get it all adjusted to spec prior to any repairs? Curious what others think about this.

Dave, totally agree. I have been searching online this past week or two to see how people are tackling cabs with rotted mounts and it seems the initial step is to get the cab oriented to the frame based upon FAM specs. Thankfully the FAM shows all measurements with respect to various points on the cab as well as the frame itself so it should be fairly straightforward.

I did see one example where someone used a 2x6 bolted to the firewall and then supported this at the correct height above the frame. I will instead set up an adjustable threaded support which will allow me to raise/lower the cab with respect to the frame to get it into specs and square. I will then tack it to the frame to keep it solid. I will then remove the floor/mounts and install new ones, checking that the frame/body combo have not shifted with respect to each other. I will do one side at a time to try to minimize issues.

Once floor/mounts are done it 'should' be clear sailing at least when concerned with the relationship between the cab and frame. I should be able to remove the previously added tacked in adjustable supports.

I can then attend to the cowl areas as normal. For these I will again do one at a time but the cab will now be bolted down to the frame via the newly installed floor/mounts.

If I think the adjustable support is something useful to others I will post some photos on here. Possibly a simple structure tacked to the cab at each front corner which incorporates a short 1/2 or 5/8 threaded rod, allowing it to be adjusted higher/lower with respect to the frame. I know the cab has slightly sagged at the driver's side front and so this will allow me to rotate the bar to raise it. If the cab is already at the right location at the rear which is likely, then I will only need to do this at the front.

Hopefully that all makes sense.

Makes sense to me. Would love to see pics as you get into it!

Dave, still early in my thoughts my this is the type of thing I am thinking of. Simple but effective. I might be able to simply bolt it to the firewall instead of a tack but time will tell. I will post what I end up doing.

The nut allows the cab to be raised/lowered with respect to the frame. If it isn't currently square I might add some lateral adjustment capabilities also.

Edit: the nut would be BELOW the attachment to the firewall.

Looks like you are on the right train of thought. Just take you time and plan out what you are going to do before hand. A well stocked beer fridge in the near vicinity helps along the way as well.