C-Notch strength

[BADAZ chevy guy]

I've been doing some reading on how to do a c-notch on my 1977 C10. I came across this article here on this forum. Worth reading. IMHO
http://67-72chevytrucks.com/vboard/s...d.php?t=457037

[low&slow]

Interesting. I've always tried thinking about that kind of stuff.

[chevyrestoguy]

It's interesting reading, but I think that it doesn't address or take into account that other things are attached to the frame in that area. Things like frame crossmembers, bed crossmembers, bumpers, etc. Each one of these items strengthens the entire assembly and takes up a degree of total stress. I also have to question the data that stated that the weld-in and bolt-in notches are 80% weaker than stock, when you have added .250" steel plate on the outside and underneath of the existing framerail. You have also added a .250 thick triangulated area at the notch. My '64 is originally a C-20, and my frame was double reinforced by the factory in this area before the notch was even added. I used the CPP bolt-in notch (.250 thick) and fully welded the perimeter. If you take into account the thickness of the original frame (.1875), plus the reinforcement (.1875), plus the thickness of the notch assembly (.250), you have a thickness of .625. (5/8ths of an inch). That's plenty strong, and that's not including the perimeter welding.

I could see the data being a concern if you have a leaf spring suspension, because the leverage between the ends of the spring is putting a strain on the frame at the center point between the two. On a coil spring suspension, the strain is at the forward attach point of the trailing arms and at the upper coil spring attach point, which are both forward of the c-notch.

I'm not coming down on the thread concerning frame strength, quite the opposite. I think it's a great thread with very interesting information that the OP put a lot of time and effort into. I'm just adding a little bit more insight and hoping to add a little more food for thought.

[SCOTI]

Originally Posted by chevyrestoguy

It's interesting reading, but I think that it doesn't address or take into account that other things are attached to the frame in that area. Things like frame crossmembers, bed crossmembers, bumpers, etc. Each one of these items strengthens the entire assembly and takes up a degree of total stress. I also have to question the data that stated that the weld-in and bolt-in notches are 80% weaker than stock, when you have added .250" steel plate on the outside and underneath of the existing framerail. You have also added a .250 thick triangulated area at the notch. My '64 is originally a C-20, and my frame was double reinforced by the factory in this area before the notch was even added. I used the CPP bolt-in notch (.250 thick) and fully welded the perimeter. If you take into account the thickness of the original frame (.1875), plus the reinforcement (.1875), plus the thickness of the notch assembly (.250), you have a thickness of .625. (5/8ths of an inch). That's plenty strong, and that's not including the perimeter welding.

I could see the data being a concern if you have a leaf spring suspension, because the leverage between the ends of the spring is putting a strain on the frame at the center point between the two. On a coil spring suspension, the strain is at the forward attach point of the trailing arms and at the upper coil spring attach point, which are both forward of the c-notch.

I'm not coming down on the thread concerning frame strength, quite the opposite. I think it's a great thread with very interesting information that the OP put a lot of time and effort into. I'm just adding a little bit more insight and hoping to add a little more food for thought.

The OP (of that linked thread) did the analysis on my behalf. He always indicated the numbers would not be 100% to eliminate any liability. He wasn't concerned so much w/me but when stuff on the internet starts getting spread. He used the same software that he did his work analysis with thus his liability concerns. There will be exceptions or slight variations but he knew what he was doing as I also ran the info by a structural engineer @ my work & the numbers he crunched w/o the software were relatively close.

You're correct on the truck-arm app vs the leaf spring app as far as the impact of loading on the frame itself structurally. That is the main reason I didn't do a leaf spring/flip-kit c-notch combo on my dually.

If I planned to do any extra capacity loads or towing & needed a c-notch, I would definitely do a CPP HD notch (3/8" thick IIRC) or Porterbuilts multi layer unit for T/A equipped trucks. I would also box the frame if possible.

I corrected my 64.
I tossed the c-notches I had bought for my dually & used Porterbuilts step notches welded in to maintain the max frame height possible since it's a HD truck. I'll prob remove the c-notches on my 90 & do small step notches too once my dually is up & going regularly.

[72MARIO]

I tow a 25' Airstream with my 1968 Suburban. I would love to get the back down a few more inches. But with the trailer hitch tongue weight I wouldn't C notch it.

After looking at the porter built step notches I am considering a step notch could have very close to the original strength. I would love to see a engineering article with some real numbers so I could get this truck level.