How strong is the frame?

[72kool]

Ok so in my journey to make my truck my permanent daily, I'm looking into my towing needs. I came across this thread about a 4x4 swap http://67-72chevytrucks.com/vboard/s...d.php?t=659340

My understanding is that the C20 frame is stronger than a k20 frame? Someone posted a lot of specs from a manual and it says the C20 is 32% (I can't remember exact number) stronger than the k20. Is that correct, Or am I reading it wrong??

Reason I'm looking it up is I am looking into a gooseneck hitch, which will be challenging with the coil springs. But first I am looking into the strength of the frame. I see gooseneck and 5th wheels pulled with k20s on here alot but never a C20. Any insight would be appreciated

[Coley]

What are your towing needs?
-type of load?
-Max Weight?
-Towing Conditions? (mountains? long distance? city? ??)

...you don't need to swap frames in order to improve the trucks capability but remember, it won't change the tow capacity from a legal standpoint.

All good
Coley

[kwmech]

Not hard to get rid of the coils and convert to leaf

[72kool]

I'm not looking at swapping frames per say. I am looking into installing a gooseneck hitch. I can't find anywhere that somebody has a gooseneck on a C20. Only the k20 trucks. But I found that post that said C20 are stronger so I was curious if that was true. I will probably have to build my own hitch no matter what.

My towing needs are a two car gooseneck flatbed. It will be hauling Derby cars all over the state. I have a bumper pull single car trailer now. I know the truck can do it, i have pulled heavy loads before with it, just trying to figure out how to make a hitch for this truck. I have all the brakes updated, have the disc up front and it will have trailer brakes soon. Not worried about the capacity of towing, worried about how to get a gooseneck hitch installed that won't come off and kill someone.

[B. W.]

Back in the '80's I towed a gooseneck trailer all over Colorado with a '69 GMC C25. Had a BB, T400 & drum brakes. It went up the passes too slow & came down too Fast! All in all, it did a fine job & never talked back.

[72kool]

Fortunately I don't really have much for big inclines around here. Mostly flats with small hills. What hitch did you have? Any ideas on what to do for a hitch?

[special-K]

Show us that thyread. I never heard of C/20 frames being stronger than K/20. Why would GM do that? Maybe it was a C/20 Longhorn which sits on a 1t frame. Makes no sense at all for C/20 to be 1/3 stronger than K/20 which would be used in more harsh conditions. If you believe this is true, then why are you concerned?

[72kool]

The link is in the original post at the top. It says that according to the 1970 GM manual of engineering, that a C20 is 8% stiffer frame than a k20. I found that interesting.
Where it applies to me, I always saw large trailers being pulled by k20 trucks. I have never seen on this forum or web, a C20 pulling a 32' gooseneck. I started to wonder if it was because the frame was too weak. But according to the link provided above, my frame is stronger. My question in all of this was, is that statement true? Any reason not to pull. Gooseneck with a C20 coil spring truck? I've seen some c30 trucks , but hey, they are one tons so nobody thinks twice if it will handle it

[Mike C]

Frame strength doesn't have a whole lot to do with it IMO. Assuming 10% pin weight and 10,000 GVWR trailer you are only looking at 1000# in the bed.

What you should REALLY be worried about are brakes, cooling, transmission and tires.

And if you are looking at hauling more than 10,000# around all the time you should consider more truck.

[72kool]

Cooling is taken care of. It's all new system and has never had an issue overheating. If it gets warm while towing the bigger trailer, I'll upgrade to bigger radiator and electric fans. The transmission is decent, but will be changed also. Looking to do either a built 700r4 or possibly a 4l80e . Though a built 700r4 should be enough

[kwmech]

Originally Posted by 72kool

Cooling is taken care of. It's all new system and has never had an issue overheating. If it gets warm while towing the bigger trailer, I'll upgrade to bigger radiator and electric fans. The transmission is decent, but will be changed also. Looking to do either a built 700r4 or possibly a 4l80e . Though a built 700r4 should be enough

Just build a 4L80 for the towing. 700 won't last no matter how much money you put into it trying to make it as strong as a stock 4L80. Towing a gooseneck with 2 cars on it with a 700 is...well....

[B. W.]

Originally Posted by 72kool

Fortunately I don't really have much for big inclines around here. Mostly flats with small hills. What hitch did you have? Any ideas on what to do for a hitch?

I don't remember, it was a fifth wheel type that sat in a cradle between two A frame uprights.

[jeffahart]

My insight is stolen from SS Tim post #20 in the following thread. It does seem that they build some flexibility into the K series for offroad flexibility, but you really need to look at the payload ratings. I would be more concerned with offroad tires than a K frame. Check out Tims numbers, they are interesting and a good reference.

http://67-72chevytrucks.com/vboard/s...d.php?t=463016


j

[toolboxchev]

I can tell you this, Standard C20 Longbed, leaf spring dana rear end will do a wet cord of oak no problem.

Doug Fir mostly seasoned I believe comes in at roughly 3,300 lbs.

Oak is considerably more.

I quickly added a set of HellWig Adjustable Progessive springs to the rears and never had an issue with a Cord 1/4 after that.

Original Drums (rebuilt) would stop me coming down the mountain. Oregon has some pretty big hills. Some fade but not smoking my foot on the pedal either.

Most people on here would agree the C20 frame looks much like a C10 frame. They are 2 completely different steels used in them.

[burnin oil]

Originally Posted by Mike C

Frame strength doesn't have a whole lot to do with it IMO. Assuming 10% pin weight and 10,000 GVWR trailer you are only looking at 1000# in the bed.

What you should REALLY be worried about are brakes, cooling, transmission and tires.

And if you are looking at hauling more than 10,000# around all the time you should consider more truck.

10% is bumper pull. GN should be closer to 25%

[Mike C]

Originally Posted by burnin oil

10% is bumper pull. GN should be closer to 25%

You are correct. 15%-25% Gooseneck pin weight on the truck.

But IMO, frame strength is the least important of all the things discussed in this thread concerning capability.

The first three are Brakes, brakes, brakes. Then tires. This is the safety aspect. Then follows cooling and transmission as they are durability items.

[jbarron]

Both of my C20's have gooseneck hitches in them.
They are both leaf spring trucks.
I looked at a 3rd one with the exact same setup, but didn't buy it.
Come to think of it I have not seen a C20 without a gooseneck hitch.

[davepl]

FWIW, I have the Longhorn frame which is C30 except for C20 front suspension bits, but the full C30 rails. It still is only rated for 7500 I think, if that!

[71blksuper4x4]

The C30 cab n chassis frames are even thicker and taller rails than the square body K30 frames.

[67 chevelle]

forget the 700 POS , 4L80 all the way

[Mike C]

Originally Posted by davepl

FWIW, I have the Longhorn frame which is C30 except for C20 front suspension bits, but the full C30 rails. It still is only rated for 7500 I think, if that!

My '70 C2500 Longhorn GMC parts truck was only rated at 6600#. That was with a 350 and a 4 speed. Not sure what other parts were needed to get the 7500# rating, but my C2500 '70 Sierra Grande 400/402 was rated at the max 7500#.

[burnin oil]

In all honesty the frame would be the least of my concerns. I have seen alot more bent or broken springs than frames. Usually the bent frames where due to someone hooking a logging chain to it when stuck and broken were from rust. So with that in mind I would just get a truck that can handle the weight and make sure the brakes are good to go. I am going out on a limb here and guessing that the truck will be loaded most of the time so unless you are driving 70+ all the time then an OD trans wouldnt even be needed. Let it rev and it will pull like a dream. The newer autos seem to shift alot better but a hunting transmission is annoying when pulling a load. I am old school and still prefer to run a clutch pedal on any hauling truck.