Hi. New to this forum. Years ago I had a 69 Cutlass convertible and I sold it in 1992 and have been kicking myself ever since. Yesterday I picked up a 69 Cutlass convertible that needs total restoration. One question at the moment. Does anyone have a picture of the frame under the main body? I seem to remember that mine was fully boxed in and this car is partially open. I'm concerned that it is a frame from a hardtop. If it is, could it be reinforced or would it be ok to use as is? I think it may be very difficult to find a good convertible frame in my part of the world. Thanks in advance for any info.

 

Convertible frames are fully boxed from the front bumper to the rear axle. Only the rails behind the rear axle are C-channel. If yours is not fully boxed, it has been incorrectly replaced with a HT frame. The boxed frame uses the same outer rails, but has additional C-section parts welded to the side rails to make a complete box. Unfortunately, you can only get these from another convertible frame. No, simply boxing with flat plates like a street rod frame does not add the same stiffness, since the box cross section is much smaller. This photo shows the box reinforcement on the side rail. Note that the width of the side rail is about doubled.

 

Other than the obvious hard bend to create the C channel, how much is envolved to fabricate these sections?
I'm hoping one of the repro companies would come up with reproduction sections that would weld on the hardtop frame. I have 2 very clean extra frames from hardtop cars that can sell faster if these kits exists.
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They aren't a simple "C" channel. The top surface is contoured to clear the footwells. A portion of the inside surface is formed to provide a ledge for the crossmember. There's a formed section around the body mount holes.

 

Well that sucks. Just bought the car and just happened to notice the frame while taking a peek under. Car has new floor pan installed and new rockers. But will be near to impossible to find a convertible frame in this part of Canada. May just have to part the car out. Disappointed to say the least.

 

Vendors make kits to box a regular frame if you're not concerned about originality.

http://abcperformance.net/frame%20boxing%20kit.html

I'm sure there are others also.

My 66 frame is boxed to within 10-12 inches of the rear cross member from the factory. Not sure if a 69 goes that far but offering it up for clarity.

 

As I pointed out above, those kits do NOT provide near the increased section or stiffness increase of the factory reinforcements. The factory parts are much more complex than simple flat plates. These aftermarket parts are designed to reinforce frames under hardtops. Bending stiffness of a beam comes from the top and bottom flanges, not the sides. The factory reinforcements nearly double the area of the top and bottom flanges. These aftermarket plates add nothing in that area. They are a good way to add ballast, not bending stiffness. They DO marginally increase torsional stiffness, but again, not nearly as much as the factory designed parts.

 

there are Oldsmobile owners in Canada. Post adds in papers and online. Post on the parts wanted on CO. Post some pictures of the car.

 

It's just that convertibles ar far and few between and the chances of finding a good frame would be pretty slim. I'm in no rush though. I hadn't planned on starting work on the car until next winter so who knows, maybe something will pop up.

 

Up to 67, the frames were also boxed on convertibles and F35 HD frame cars behind the rear wheels, as Trip noted above. Not so 68-up. A more common source for the boxing parts would be a vista cruiser, although you would have to modify them as the wheelbase is 9" longer on a VC so the parts are too long. Another source would be an El Camino. You will need the tranny crossmember along with the donor parts. The frame has to be removed from the car in order to weld in the boxing parts correctly.

 

Just curious, (and I'm only asking if it's a good idea and safe) if your frame is good ( you will find that out when you lift off the body) could you buy the boxed sections from a original frame and have them welded to your frame. Not cut your frame apart, just add the supports to it? If so shipping what you need would be much easier and cheaper that shipping a whole frame. Not sure if welding on a frame weakens it.

 

These frames are mild steel, not heat treated. They are welded from the factory. Properly done welds will not weaken anything.

 

This kit is not like original either, but I think it looks closer to the stock c-channels than just a flat plate.

https://www.summitracing.com/parts/h...RcYaAqfw8P8HAQ

Thanks, Pete

 

Is a Vista Cruiser frame boxed the same as the convertible frame? Only longer?? If so this thread makes me ill. I tried to give away a good 70 Vista frame a couple years ago. Finally took it to the scrap yard. Ugggh....

 

Yup. ElCamino also.