Towing Capacity 77 3/4 Ton 4X4

[Fraser Beatty]

Hey all, haven't been on the board in months, due to the fact I sold all of my trucks.

I'm now looking at getting another, a 77 Chevy K25. The truck has a 350 paired with a manual transmission, stock brakes, suspension, etc. etc. I was just wondering roughly what the "safe" towing capacity of this truck would be, assuming the trailer being pulled has working brakes. Would there be much of a difference in towing capacity in conventional hitch vs. gooseneck or fifth wheel?

Thanks for any help!

[bikes&bowties]

a gooseneck will help the truck handle way better than a receiver hitch style trailer. and working trailer brakes up safety by a lot. I cant say exact numbers but you should be in the gvwr area of 7500-9000 MAX... make sure you include trailer weight in that...

[Fraser Beatty]

For sure I'll include trailer weight. The load I'm thinking of towing is 4000lbs or less, so with 2000-2500lbs or so of trailer, I'll be within that estimate.

[78 Chevyrado]

This is out of my '78 Owners manual.

[lucjensen38]

Ok so that's the owners manual. So would my 1980 GMC c25 with a 4.8 liter 292 straaight 6/ auto trans( anyone know which one?) possibly pull that much? 12,000 pounds seems alot for that 6'er,even if its big. I know it feels like it has more balls than most 350s...torque wise anyway. Does anyone know if this 1980 C25 would have either a th350 or a th400?
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[78 Chevyrado]

It'll move it, otherwise it wouldn't have been available in a 3/4 ton truck. Its the brakes and springs that mainly decide how much weight you can haul. I've seen 1 ton trucks with utility bodies and 6 cylinders towing trailers. they're slow but they do get it done.

Don't know for sure behind a 6 cylinder, but I'm pretty sure 3/4 tons and up didnt ever come with th350's only 400's as as i know.

[lucjensen38]

Thank you for the input.. I haven't had many dealings with this old of a truck. I know our 3/4 ton chevys at work can pull 12k #s but they have 4L80Es and 6.0 V8s. The only dealings with anything newer than 93 is my grandpas old 78 sierra C10 farm truck, had a 350ci V8 and a TH350 trans. He pulled 4 grain wagons full every fall harvest with a 100 gallon diesel tank full in the back easy. Again,thank you. Maybe see ya round here again..
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[Number21]

Why is a K20 only rated at 6500 when a C20 is rated at 12000? I know the running gear adds some weight but not 5500lbs!

It's interesting that they list neither the engine nor the transmission when coming up with the weight rating...

[lucjensen38]

I would say mostly because of the transfer case...and maybe the fact that most were full time four wheel drive.. maybe. No expert but thinking mechanically..
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[Grease Monkey Kuztum]

Motors have nothing to do with how much weight a truck can HANDLE... The motor dictates how Fast you move that big of a load.... The GVWR ratings are for the trucks parts like frame rails, springs, axle assembly, brake size and overall ability of the CHASSIS taking the weight.... The motor doesnt really matter, you can have a small 4 banger with decent trq curve and right gearing and be able to tow 15k no sweat!!! Now will you be able to do 75mph up a 7 or 8% grade HELL NO but it will tow it lol....

The ratings are for the chassis as a wholes strength, they dont put the motor cuz it doesnt really matter.....

Hope this helps, I can go into it alot more detailed if needed and find the laws on gvwr ratings and things like that but you get the idea...

[Number21]

Originally Posted by Grease Monkey Kuztum

Motors have nothing to do with how much weight a truck can HANDLE... The motor dictates how Fast you move that big of a load.... The GVWR ratings are for the trucks parts like frame rails, springs, axle assembly, brake size and overall ability of the CHASSIS taking the weight.... The motor doesnt really matter, you can have a small 4 banger with decent trq curve and right gearing and be able to tow 15k no sweat!!! Now will you be able to do 75mph up a 7 or 8% grade HELL NO but it will tow it lol....

The ratings are for the chassis as a wholes strength, they dont put the motor cuz it doesnt really matter.....

Hope this helps, I can go into it alot more detailed if needed and find the laws on gvwr ratings and things like that but you get the idea...

So if I have a 454 K20 with the SM465 granny transmission, I can only tow half of what a I6 automatic C20 could tow? I don't think so. Engine and trans combo has a LOT to do with what a truck can tow.

[Number21]

FWIW, the ratings in my 1979 manual are totally different than the ones listed above from '78. It shows 8000# for a C10 or a K20. K10 is 6500, C20 is 10,000, and C30 is 12,000. Still don't say anything about the engine, trans, or gear ratios.

My 1973 manual doesn't even give weight ratings, it basically says "check with your dealer".

It doesn't seem like Chevy did much testing relating to ACTUAL towing capacity in the 70s...

[MofoG23]

Originally Posted by Grease Monkey Kuztum

Motors have nothing to do with how much weight a truck can HANDLE... The motor dictates how Fast you move that big of a load.... The GVWR ratings are for the trucks parts like frame rails, springs, axle assembly, brake size and overall ability of the CHASSIS taking the weight.... The motor doesnt really matter, you can have a small 4 banger with decent trq curve and right gearing and be able to tow 15k no sweat!!! Now will you be able to do 75mph up a 7 or 8% grade HELL NO but it will tow it lol....

The ratings are for the chassis as a wholes strength, they dont put the motor cuz it doesnt really matter.....

Hope this helps, I can go into it alot more detailed if needed and find the laws on gvwr ratings and things like that but you get the idea...

What are the big differences between a C20 and a K20 other than a transfer case and some additional weight that would affect the payload or towing numbers?

I can understand some minor differences as it relates to towing/hauling numbers, but we are talking 5500 lbs difference....(that is the weight of another 3/4t truck!)

[78 Chevyrado]

Originally Posted by MofoG23

What are the big differences between a C20 and a K20 other than a transfer case and some additional weight that would affect the payload or towing numbers?

I can understand some minor differences as it relates to towing/hauling numbers, but we are talking 5500 lbs difference....(that is the weight of another 3/4t truck!)

I've always wondered that. like number21 said, it doesnt make sense. only differences rearlly are t-case and straight front axle with leaf springs.

I wonder what a 3/4 ton front axle is rated for. I do know a GM corporate 14 bolt FF is rated for 7,200lbs

[MofoG23]

I've seen numbers that show the Dana 44 rated up to ~3500 lbs. I'm assuming that is weight over the axle....

When towing, I'm not sure how that number would come into play since the front axle most likely will not see additional load if pulling in 2wd.

I guess I'm confused as well and would like to learn how they come up with towing and payload ratings.

[Grease Monkey Kuztum]

Originally Posted by Number21

So if I have a 454 K20 with the SM465 granny transmission, I can only tow half of what a I6 automatic C20 could tow? I don't think so. Engine and trans combo has a LOT to do with what a truck can tow.

Like I said motors make it easier to tow heavy and or up grades but you dont need a big motor to tow... lol Ill show you pics where my lil 2.3 ford ranger is pullin my powerstroke up a 7% grade.... Talk about a workout...

Big motors make it easier but any motor with the right gearing and a smart person can move a load....

[Grease Monkey Kuztum]

Brake size, Im not 100% sure what the differences in front brakes were compared between the trucks besides 2wd and 4wd obviously have different brakes and same with 44 vs 60 front axles 60 is gonna have bigger rotors atleast.....
axle or differential size is a huge factor on how much weight it takes before it shreds itself apart.... A 1 ton truck can look the same and one has a 10 bolt while other has 14 bolt obviously the 14 bolt will take more abuse... Usually they have bigger drums as well... the bigger the differential the more abuse it will take towing heavy.

the actual gauge of steel used on frame rails differs...
uhm theirs alot that can make small differences in load capacity... You can modify almost anything nowdays to make it do what you want, will it do it well is the question...

I Never said an i6 would out tow your big block so please dont put words in my mouth
The way I described it is if you have a big block in a half ton not meant for it and then a 1 ton truck with

[MofoG23]

Originally Posted by Grease Monkey Kuztum

Brake size, Im not 100% sure what the differences in front brakes were compared between the trucks besides 2wd and 4wd obviously have different brakes and same with 44 vs 60 front axles 60 is gonna have bigger rotors atleast.....
axle or differential size is a huge factor on how much weight it takes before it shreds itself apart.... A 1 ton truck can look the same and one has a 10 bolt while other has 14 bolt obviously the 14 bolt will take more abuse... Usually they have bigger drums as well... the bigger the differential the more abuse it will take towing heavy.

the actual gauge of steel used on frame rails differs...
uhm theirs alot that can make small differences in load capacity... You can modify almost anything nowdays to make it do what you want, will it do it well is the question...

I Never said an i6 would out tow your big block so please dont put words in my mouth
The way I described it is if you have a big block in a half ton not meant for it and then a 1 ton truck with

How about key differences between a C20 and a K20 (from the same year with equal equipment). Aside from a solid front axle (brakes are the same size, just different hub - C20 vs K20) and a transfer case - what allows for the increase of 5500lbs?

[Grease Monkey Kuztum]

Originally Posted by Number21

So if I have a 454 K20 with the SM465 granny transmission, I can only tow half of what a I6 automatic C20 could tow? I don't think so. Engine and trans combo has a LOT to do with what a truck can tow.

Did I say that NO I did not.... lets say you have a 1/2 ton with big block swapped into it with small axle... Hes trying to pull a 17k 5th wheel and he thinks hell be just fine, he punches it to drop a gear and go around a semi cuz hes got a big block hell be faster and BOOM the rear diff goes....

The guy that has the 1 ton & i6 may stay in the slow lane towing that 17k but ill bet he dont break stuff...

That was my point

[87 V20 Scottsdale]

I may be going out on a limb here but I'm guessing that the C20 was rated for 10k was so that GM could get around emissions laws at the time. I know that they offered two different GVW packages for K20's, and skirting the emissions laws was also part of the reason that they made the Big 10 and Heavy Half trucks. Just like Grease Monkey Kuztum said, it ain't about what kind of motor it has but the kind of springs, frame, and axles.

[Grease Monkey Kuztum]

Originally Posted by MofoG23

How about key differences between a C20 and a K20 (from the same year with equal equipment). Aside from a solid front axle (brakes are the same size, just different hub - C20 vs K20) and a transfer case - what allows for the increase of 5500lbs?

like the other guy said are you even sure those ratings are correct from what they were rating it with?
Makes ya not even want to be on this forum to learn more in the first place!!!

I dont know what the difference between a k20 and c20 would be if they were loaded the exact same except maybe the fact that gmc is more work truck people oriented and the chevy is a daily driver truck to the market place they have different load ratings for that??

IDK

[MofoG23]

Originally Posted by Grease Monkey Kuztum

like the other guy said are you even sure those ratings are correct from what they were rating it with?
Makes ya not even want to be on this forum to learn more in the first place!!!

I dont know what the difference between a k20 and c20 would be if they were loaded the exact same except maybe the fact that gmc is more work truck people oriented and the chevy is a daily driver truck to the market place they have different load ratings for that??

IDK

No one is attacking you.... Forums like this are here to ask questions and have discussions...thats all I see going on....

I was hoping you would go into more detail as quoted below...

Hope this helps, I can go into it alot more detailed if needed and find the laws on gvwr ratings and things like that but you get the idea...

BTW C20 is a 2wd 3/4ton and a K20 is a 4x4 3/4ton - not a GMC/Chevy difference.

[87 V20 Scottsdale]

I pulled this info from magazine articles at 73-87.com. In 1977 the K20 had three GVW options: 6800, 7500, and 8400. I couldn't find a C20 article from '77 so I used one from '79. It has four GVW choices: 6400, 7100, 7500, and 8200. the only vehicles I found that offered 10,000 GVW was the C/K30 with dual rear wheels.

[MofoG23]

I think that would be the payload you could haul (including the weight of the truck)?

The trailer towing ratings listed above would be different....what you can tow behind the truck.... I think that is what we are wondering.....

The payload ratings are fairly close, but why is the trailer towing ratings so different between the C20 and K20?

I've also been looking for spec's on what the key differences are between the 3 GVW ratings on the K20. My K20 has the heavy duty rear brakes, 7 rear leafs, 3 front leafs and the 14ff rear.... but is only rated for 7500 GVW - what is required for the 8400 GVW? I can't find anything on this spec either...

[87 V20 Scottsdale]

Originally Posted by MofoG23

I think that would be the payload you could haul (including the weight of the truck)?

The trailer towing ratings listed above would be different....what you can tow behind the truck.... I think that is what we are wondering.....

The payload ratings are fairly close, but why is the trailer towing ratings so different between the C20 and K20?

I've also been looking for spec's on what the key differences are between the 3 GVW ratings on the K20. My K20 has the heavy duty rear brakes, 7 rear leafs, 3 front leafs and the 14ff rear.... but is only rated for 7500 GVW - what is required for the 8400 GVW? I can't find anything on this spec either...

Right GVW is the payload including the weight of the truck. I forgot the thread was originally talking about trailering weight. Is seven leafs the largest spring pack available on K20's?