Ok, while im still in the planning stages of my build, I was thinking about making my 1950 Pontiac either a convertible or maybe adding a Carson style top. So my question is.... IF I do this what do I need to do to strengthen the frame? Sent from my SM-N920P using The H.A.M.B. mobile app
i restored a 58 caddy convertible a few years ago and had a couple sedans for parts cars. the only difference in the frames, i remember, was the convertible had a 3/8" thick strips of steel welded on the bottom of the frame rails. i know it's not the same chassis as yours but i thought it might help you.
What's under your car should be a "C" channel frame with an "X" member (much stronger than what Chevy used in those years), my recommendation would be to box the frame and go on. As tb33anda3rd noted GM convertibles in that era had a thick metal strip welded to the bottom flanges of the frame, doubt it added much strength but it sure added a lot of weight. The big issue is to make sure the "B" pillar is stable so the doors will stay shut.
Hmmm. Not sure about the coupe, but my '51 wagon has an "X" member frame, like the converts. If indeed all Pontiacs had this style frame, you're fine to lop off the top, if not, proceed with caution. You'll find without the roof, the body will be so flexible the doors may not stay latched driving. Of note, my '48 Pontiac has no metal strip welded to the bottom of the frame, so I don't know about that. It's frame looks much like the wagon's. If the coupes and sedans didn't have the same frame as the wagons and converts, I'd make an X member if I were you to stiffen the chassis.
The frame does have sn X member, I thought about boxing the frame, but didnt know if i should also girder it or was that overkill. Sent from my SM-N920P using The H.A.M.B. mobile app
You're good to go. I did what you're thinking of doing to my '56 Caddy 20 years ago, it was fine. Cut 'er up...
i believe the reason for the big strip was to to stop any sag. when the frame tries to bend in the middle it has to stretch the strips. that makes it stronger. easy enough to add.
There are a lot of solutions, not all cars are the same. Both frame and body need reinforcement. Some made the convertible frame of thicker steel, some added bracing. Some 30s Chryslers added a frame about 1" or 2" thick between the body and frame. Bodies need extra strength in the cowl area to resist cowl shake, in the rocker panels, and door posts.
What kind of reinforcement should I add to the cowl, doorpost, rocker panel? I'm not sure how I would go about that. Sent from my SM-N920P using The H.A.M.B. mobile app
Thank you for all the replies so far guys, I appreciate the help. Sent from my cell phone when I shoulda been working using the H.A.M.B. mobile app
A friend has a 47 Olds convertible with X-member frame centre being a larger 'I' beam profile and NOT the normal open 'C' channel as in my 46 sedanette. The bottom connecting plate of the centre X is wider, presumably these all stop the inherent loss of torsional rigidity when you remove the roof. An OEM sedan frame needs strengthening to make it perform like a convertible frame.
Here's a pic of my frame before sandblasting. Sent from my cell phone when I shoulda been working using the H.A.M.B. mobile app
Years ago I had a 55 olds convertible and a 53 sedan,the X on the convertible was made of thicker metal then the one on the sedan and that was the only difference I could find.
My Caddy (originally a 4 door hardtop Sedan seville), I did nothing beyond cutting off the top, chopping the w/s 3", shortening the car 16", and making it a two door. ;-) I didn't have to brace the cowl, the door posts, nothing. I cut it in half, cut a chunk out, welded it back together, boom. Done. If your rockers are rusty, maybe make a 16 ga. inner rocker, which would serve to stiffen up the body.
I have, there was a nice thread here on the H.A.M.B. that's where the Carson top idea started from... the thread didn't give any info on if or how the frame should be stiffened though. Sent from my cell phone when I shoulda been working using the H.A.M.B. mobile app
I bet that looked sweet, I love Caddys. Do you have any pix? Sent from my cell phone when I shoulda been working using the H.A.M.B. mobile app
Thank you, i bookmarked that page Sent from my cell phone when I shoulda been working using the H.A.M.B. mobile app
Neither am I. These are typical places that the factory reinforced on convertibles to prevent cowl shake, doors popping open, bodies twisting up like a pretzel etc. Every car is different and every car maker had a different approach. If I were going to cut the roof off and make a convertible I would start by reinforcing the rocker panel area. One way to do this is take a piece of 1 1/2" square steel tubing that reaches from wheel well to wheel well, and weld on a few brackets to bolt it to the floor and into the reinforcing structure at the ends of the rockers. I did this on a rusty MGB and the difference in strength and rigidity was astonishing. Next would be the door posts. Examine some old 4 door hardtops and see how they were braced, they added to the door post so it looked like the root of a tree. You could duplicate this by getting a bent piece of heavy duty exhaust pipe, cutting it down and welding to the door post. Behind the seat you could add some extra cross bracing between the trunk and seat back. For the cowl I am not sure what to do. You would have to examine a convertible model similar to yours and see what they did. All this should be done BEFORE you cut the roof off. Once the roof is off the car can flop around and get all out of shape unless it is braced beforehand.
Brian I can't tell from your picture if you used the door from the 4 door or if you used a door from a 2 door. I checked your album and the only picture there is the one you posted above.
Uh, yeah ... i meant more pix...lol.... Seriously though, that looks beautiful [emoji4] Sent from my cell phone when I shoulda been working using the H.A.M.B. mobile app
I had a 50 Ford convertible that I bought to restore. Before handing over the cash I verified that it had the X frame with 3/8" thick strips welded to the frame, it did. I had read that Henry added these strips after experiencing problems with the 49.
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