Towing Capacity 77 3/4 Ton 4X4

[MofoG23]

Originally Posted by 87 V20 Scottsdale

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?

Looking at various parts catalog's, yes, 7 was the max for 1976. That could be wrong, but if I wanted to buy replacement leafs, I can only find 5, 6 or 7 leaf packs for sale listed under a 1976 K20.

[Number21]

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

My point is that the published information from GM WITHOUT listing any drivetrain parts is completely worthless. My K20 has the same rear axle, brakes, and 350 engine, as my C30 rated at twice the towing load. It's only rated at 800lbs less GVW (8200 vs 9000) and that's about what the extra running gear weighs. So why can't I pull 12,000lbs with it, according to GM literature? Should be able to do at least 10k, if a 2WD of the same gearing/axle/engine can pull 12k.

Brakes really have little to do with it, as you're not supposed to tow anything over 1000lbs without trailer brakes.

[68 TT]

Originally Posted by MofoG23

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

I'm pretty close to that with nothing in the truck at all. It's got to be much higher than that in a K20 D44 vs. a K10 D44. My GVW is 8400 lbs with a base weight of 5200. Fully loaded it definitely sees more than 3500.

[lucjensen38]

I agree with the person about the frame/axle/brakes being the main towing factors. I have a 1980 C25 with a 292 I6/TH400 and a 14 bolt axles with 4.10s,feels lke it has a lot more power than my grandpas 1978 C15 with a 350TH350 and a 10 bolt with cruiser gearing. BUT motors do have a factor too. To little of an engine would be stressed all the time,and too big would be a huge energy waster.
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[MofoG23]

Originally Posted by 68 TT

I'm pretty close to that with nothing in the truck at all. It's got to be much higher than that in a K20 D44 vs. a K10 D44. My GVW is 8400 lbs with a base weight of 5200. Fully loaded it definitely sees more than 3500.

How many leafs do you have in the rear of your K20? Thanks!!!

[68 TT]

Originally Posted by MofoG23

How many leafs do you have in the rear of your K20? Thanks!!!

I didn't drive the truck to work today. I believe it is six plus the overload spring but I will have to take a look when I get home to know for sure. The only pic I have of the back end of the truck the spring area is hard to see.

I have had 3500 pounds of gravel in there and it only dropped the back end about four or five inches.

[MofoG23]

Thanks.

[68 TT]

Originally Posted by MofoG23

How many leafs do you have in the rear of your K20? Thanks!!!

Sorry it took so long to verify this.

My 78 K20 camper special has six full leaf springs plus one hefty overload spring.

[MofoG23]

Originally Posted by 68 TT

Sorry it took so long to verify this.

My 78 K20 camper special has six full leaf springs plus one hefty overload spring.

No problem - thank you for the picture!

That is the exact spring pack that is on my K20. Very strange that my K20 has the 7500GVW when it has the following equipment - all OEM from the factory - nothing was changed. Leaves me wondering what prevented it from getting the factory 8400GVW rating. Guess I'll never know...

7 rear leafs
3 front leafs
HD Brakes (larger rear drum)
14bolt FF rear axle
Dana 44 front axle
4:10 gears

[68 TT]

Originally Posted by MofoG23

No problem - thank you for the picture!

That is the exact spring pack that is on my K20. Very strange that my K20 has the 7500GVW when it has the following equipment - all OEM from the factory - nothing was changed. Leaves me wondering what prevented it from getting the factory 8400GVW rating. Guess I'll never know...

7 rear leafs
3 front leafs
HD Brakes (larger rear drum)
14bolt FF rear axle
Dana 44 front axle
4:10 gears

The guy who ordered your truck just didn't pay for the camper special or trailering special package to get the official heavier GVW is my bet.

I know the parts book says the master cylinder is different between the 7500 GVW and 8400 GVW trucks and they have different part numbers so it could be as simple as a valving difference in the brakes in your case since you have all the same equipment I have on mine. Probably puts more fluid to the rear wheels to compensate for the added load.

[Oilbrnr]

The C/K load ratings are different due to the load handling ability of the front suspension in a properly load leveled towing scenario. Has nothing to do with the TC or slightly heavier weight of a K series.

[rds]

I love how there are so many wrong ideals about towing. Chevy revised its tow rating in 1979 as follows.

C/K 10 blazer 6,000LBS
K 10 suburban 6,000
K10 pickup 6,500
K20 suburban 7,500
C10 andK20 pickup 8,000
C10 suburban 8,000
K30 pickup 9,000
C20suburban 9,500
C20 pickup 10,000
C30 pickup 12,000
As some one stated,brakes do not matter,because you are stupid if you tow over a 1000 lbs without trailer brakes. Not to mention in most states it is illegal to do so. But he is partially right. If anyone responding to this question knew all the fact,they would realize brakes on the tow vehicle does matter.Even though your trailer brakes stops the trailer,not your truck stopping the trailer,the rated tow capacity is based on if the trailer should lose all it brakes, the tow vehicle has to have enough stopping power to reasonably bring the truck and trailer to a stop,in a reasonable distance. Do we get it now???
The reason a C30 has a 12,000 tow rating an a k20 only has a 8,000 rating,is because the C30 has quite a bit larger brakes than a K20,even though the trucks are almost identical except for the front axle and transfer case,which does not weight 4,000 extra lbs!!! As someone already stated. So are we beginning to see the picture?The engine is not listed,because Chevy designed what ever combo got made,that the engine could pulled what they stated in the owners manual.
Again, the huge difference from 12,000, to 8,000 for almost the same truck, is due to the brakes. The tow ratings has direct correlation to the truck being able to somewhat bring the truck to a stop,IF YOU LOSE ALL TRAILER BRAKES.ARE WE CATCHING ON TO THE IDEAL OF THE RATINGS YET.
I hate to act like an a-hole,but it is irritating to read so many posting where the person has not ideal what they are talking about! All the truck have similar engine/drive trains/but huge different tow rating. Do we see yet?
Again, the C 20 is rated to haul 12,000, due to the fact that the truck can bring the truck and trailer to a stop SHOULD YOU LOSE ALL YOUR TRAILER BRAKES. If anyone think I am wrong,Please respond. I will acknowledge i am wrong if you show me.

[rds]

Hello, please read my answer. It is #37. It will help you see why the C20 has a bigger towing than the K20

[simonzelotes]

Slightly off topic here but sorta related...My neighbor and I both have mid 70's Camper Specials with lots of options with the main dif being his is a 4wd with a 350 and mine is 2wd w/ a 454...His big complaint is lack of pulling power in the Arizona mountains; mine pulls like crazy with no sweating but is not 4wd....My question is, was the 454 available in 4wd trucks?...To discourage him from getting any ideas about stealing my engine some night, I suggested to him that maybe the extra weight of a 454 was too cumbersome on the front wheel drive components...Anybody know for sure?...Thanks...

[MofoG23]

Originally Posted by rds

Hello, please read my answer. It is #37. It will help you see why the C20 has a bigger towing than the K20

Huh? Are you saying the C20 has WAY larger brakes than a K20 - which makes up 2,000 lbs of towing?

Also there is a difference between the C/K30 and C/K20 series....the frame. That would also contribute to the large difference in ratings. Also what is the difference in transfer cases between a K20 and a K30? My K20 has a NP205 from the factory - which is the same transfer case as a K30 from the same era.

[KMK454]

Originally Posted by 78 Chevyrado

This is out of my '78 Owners manual.

Am I reading this wrong, or can my three speed 305 78 C10 with a 3.07 rear can tow 8000lbs? I wish!

[DetroitDan]

[QUOTEMy point is that Brakes really have little to do with it, as you're not supposed to tow anything over 1000lbs without trailer brakes.[/QUOTE]

actually the law is 3000. states could conceivably lower the federal standards, so maybe its 1000 somewhere, I'm not sure, but fed is 3000 and thats the same as the states I am familiar with.

rds, I have long had an interest in this topic, and I for one appreciate any input from others, whether validated or not. However I have to say, the attitude that comes across in your posts is not appreciated. If you have verifiable information to offer that's great, if you just want to blast your opinions and flame everyone else, don't need it. Perhaps you'd like to tell us how it is that you know what you know; are you a former GM engineer, or a federal DOT enforcement officer? Or do you get your information off the internet like everyone else?

[DetroitDan]

I don't know what my 82 cab & chassis was rated for towing from the factory, but I know I have seen different numbers quoted at different times. Theres a lot of different info out there and it can't all be right. I have always noticed that they rate 2wds higher than 4wds, which I think must be a technical thing, because there's no physical reason a 4wd would tow less. FAGVWR is different between them, but without weight distributing you're only helping the front, not hurting it. Should be mentioned that shortbeds, longbeds and crewcabs are all going to have different capacities.

My truck has no big differences from a 78, so I'm sad to know my extra long chassis and dual rear wheels might only provide for 7000 lbs towing, but a 2wd single rear wheel half ton can tow 8000. Ha ha ha, yeah right.

I also happen to think that the motor does play a part. Sure, any little motor can get a rolling trailer moving, heck it's on wheels, but there should be some consideration given as to whether it can get it across an intersection before the light changes again, or if it can safely merge onto a highway without taking four miles to get up to speed. An I6 should have a lower GCVWR than a V8 or diesel. Maybe they didn't back in the 70s, but they weren't up to speed. The newer trucks do reflect different GCVWRs depending on engine, transmission and chassis configuration.

Lastly, I'm a little amused/annoyed by the new ratings war between the manufacturers, jsut keep blowing the numbers up every year. 11,300 for a Ford F150, 10,600 for a GM 1500. You need a commercial license to tow over 10,000 commercially, yet they're telling Joe Homeowner he can tow over 10 with his non-work truck. Maybe it's got to do with their artificially inflated horsepower ratings.

I've got an 11,000 gvwr camper I tow, and as soon as I get a new hitch on my 82 it will be towing it. Hope it pulls it okay, because I'd hate to have to go buy a new half ton to pull it. Or a 78 2wd.

[Jimmer]

There is a lot of mis information in this thread AND a bunch of nuggets that are good as well.

Engine size, axle ratio, trans, tires, all play a part in what the 'factory' 'says' it can tow.

The post above talks about how a 2wd can tow more than a 4wd....yeah...when the GCVW is a certain number...and a longer more optioned truck weighs more than a stripper 2wd standard cab....the 2wd has more room under the cap.

OK...here we go. From Chevy Truck Brochures

1977

c20/30 with the 454 can tow trailer 11,500 with axle ratios of 321, 373,410 or 456

k20 with the 400 tow 6500 with 410's

k30 with the 400 tow 7000 with 456's

Of course we all know that these are the GUIDELINES put out by the manufacturers.

[Jimmer]

Looks like the 454 was NOT avail in 77 in the 4wd trucks...that would be part of the reason for the lower tow rating. 400 was biggest shown as available.

[simonzelotes]

Jimmer, that 400 would be a smallblock, would it not?---Not like the 402 BB that came out in '71-'72...

[Jimmer]

Originally Posted by simonzelotes

Jimmer, that 400 would be a smallblock, would it not?---Not like the 402 BB that came out in '71-'72...

Correct small block 400. not a bored out 396.

[nekkidhillbilly]

that c20/30 on that list im could be the c20 crews only btw

[Jimmer]

Originally Posted by nekkidhillbilly

that c20/30 on that list im could be the c20 crews only btw

Nope.

The numbers I quoted are straight from the chevy trailering guide brochure1977. The info I put down for c20 and c30 are correct and specific to that model.

I will re-write what the brochure states.

" The charts on these two pages pecify required trailering equipment (shown in red) and recommended available options (shown in blue) for both 1977 2 wheel drive and 4 wheel drive Chevy Pickups. standard and not required equipment is applicaible to both conventional fleetside and stepside models in either 6.5 or 8 foot box lengths."

To tow the max of 12K pounds...the brochure states you need the turbo 400 and a 454 big block WITH 456 gears. 4.10's get you a 10k trailer capacity and 3.73's 8500 lbs of GROSS TRAILER WEIGHT. this is again for both the c20 and c30.

Remember...the 454 was avail with the 2wd only...thus getting the higher tow capacity.

Now let's look at the crew cabs.

c20 and c30 with the 454 and 373's can tow 8000lbs. 4.10's gets you 9500 and 456's gets you 11,500. so there is a drop of 500 lbs by having the crew cab.

the k30 is listed at 5500 with 4.10's and 6500 with 4.56's. The biggest engine in the k30 was the 400 sb.

Funny to read back at some of the posts where is shows that a half ton can tow 8000 lbs....there is a reply that the straight 6 and 3.07 can do that? LOL. Remember to tow what CHEVY says is the max...you have to have the required equipment.

---this was posted from detroit dan---
"I don't know what my 82 cab & chassis was rated for towing from the factory, but I know I have seen different numbers quoted at different times. Theres a lot of different info out there and it can't all be right. I have always noticed that they rate 2wds higher than 4wds, which I think must be a technical thing, because there's no physical reason a 4wd would tow less. FAGVWR is different between them, but without weight distributing you're only helping the front, not hurting it. Should be mentioned that shortbeds, longbeds and crewcabs are all going to have different capacities.

My truck has no big differences from a 78, so I'm sad to know my extra long chassis and dual rear wheels might only provide for 7000 lbs towing, but a 2wd single rear wheel half ton can tow 8000. Ha ha ha, yeah right."


OK then...lets look at the ratings for a 77 cab and chassis dual rear wheel truck.

the c30 is rated to tow 13K with a 454 and 4.56's and the k30 is 11K.


Gotta love this line on the brochure. "Larger components may be ordered for special needs or applications." Humm. With that line...it could be possible to get a 454 in a 4wd?

[K20chevy]

Ok, so to me it mmakes sense that you have to have th right equipment to handle the load beeing towed. So engine, transmossion, T-case, axle, brakes and springs make up for that as well as the frame strength.

Could it be, that the 2WD trucks had more possible tow rating than the 4WD because of the lower CG?

Now another question: these trailer ratings are for a regular receiver hitch, not a goose neck, correct? so a gooseneck should add to that because the tongue weight on a receiver hitch is way lower that the weight that the gooseneck can put onto the coulper because it is right over the axle, just like a load in the bed, correct?

Right now I have a class V reciever hitch on my truck that is rated ad 12000 non WD and 15000 lbs WD. My truck is a 78 K20.. so it is rated lower than that from the factory. Originally the truck had a 350, 4 speed, 205, 4.11 gears and the 8400 lbs GVWR.

Since brakes, springs and drive train all play a role and I swapped my motor to a 500 HP L92, have a ZF 6-speed manual behind it (rated up to 26000 lbs GVWR), an ATLAS II t-case, a 14bolt FF van width rear axle with 4.88 gears and 2008 Dodge 3500 rear brakes, the front is a custom built Dynatrac D60 with 2008 F550 inner and outer C´s, knuckles and brakes and also 4.88 gears. So all of these components should really boost the towing capacity by a lot, correct? the only weak link remaining being the frame....

is there a way to get the truck rated for more due to the more HD parts added? Also how much more could you tow with a gooseneck over a regular receiver hitch?

there has got to be some formula that the OEM´s use to calculate the max tow rating (true rating, not the stuff they battle about in the advertizment)

Thank in advance!