I'm deep into the rehab of a 48 F1, and have just completed the install of a replacement cab back panel. The upper seam was the toughest part of the whole job, with a combination of spot welds and a door skin like hemmed seam. I've talked to a couple of rod builders that are very clear on not welding that seam to make it completely sealed. The seam needs to allow the cab to flex some, and a fully welded one would tend to eventually develop cracks. So ..... what kind of exterior seam sealer would be best?
I have the 3M seal sealer, and it does ok I've heard, but there is evidently an epoxy style sealer around that is better?? I cannot however find any info on the brand or where to get it. Or is there something even better than either the 3M or the epoxy material? Ford orignally used some kind of black body sealer, but it was applied on the inside. That seems a bit odd, but that was long ago, and the catalyzed stuff just wasn't around yet.

Thanks in advance for any advice.

RG in Spokane

 

I have to admit..,just about every 3M product I've ever used is good stuff, and they're " really " proud of the seam sealer...at over $50.00 a can!!..LoL!

Where do you expect to see cracks if fully welded? Have you posted on the paint/body forum? I wonder if they could answer you questions?
I just finished using the 3M seam sealer on my project and the epoxy primer adhesion to it was excellent...I tried peeling it off in an inconspicous place(...you didn't think I would tell you if I did a poor job did you...LoL!) I will add that 3M recommends using "their"...Special..3M seam sealer remover for clean-up...I used Brakeclean (0)..but I think the correct stuff would work better to help the stuff 'flow', when spreading in hard to get places, and might help slow down the set so you can work it better and longer.
Good Luck!

 

The rear corners of the Panel Truck roof are leaded and even they cracked after 60 yrs.
I was going over my panel when I first got it stop drilling all the little cracks, when I got to the rear I drilled one and got lead shavings.

 

Something pliable like 3M's product is likely to withstand the twisting of the body. They do sell it in caulk-tube size.

 

I use the sausage tube 3M stuff and it works great. It was about $20 for the tube but over $100 for the gun. You will want to do all your prep work to the cab right up to shooting the paint before putting the seam sealer on. 3M says to it should go on just before paint (allowing time to dry). I think the stuff I used was paint-able in 30min after applying.

Now you can weld up the seam if you plan on boxing the frame and doing up dated suspension. I will be boxing my frame front to back then adding plenty of cross members to STOP any chassis flex. I am running IFS and IRS so I will set the suspension to do all the work plus I am going very dark side with body mods and tight gaps.

Kevin
LFD Inc.

 

Any chance of getting a name or product number on the 3M stuff?

Thanks

 

The 3M stuff I have is:

3M Flexiclear Body Seam Sealer

Part # 051135 08405

The instructions say it can be applied to bare metal, bondo, or primer, and can be mixed with some paint to provide a colorized mixture to apply over paint.

Thanks everyone, by the way, for all the info. Looks like this stuff is the way to go. My local NAPA store got it for me. $12 per tube, and that's after a hefty discount.

 

I used a siliconized sealer I bought at the local hardware store. I used it about 15 years ago in the back seam on my F-2 and it's just as good as the day I painted it. I have to emphasize that the stuff I used said it was paintable. If it has silicone in it and doesn't say it's paintable don't even bring it near your truck! The smallest amount of silicone can ruin a paint job.