1982 GMC - What do I have? What can I tow?

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Autocar

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Mark
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1982
Truck Model
K25 VIN, but it's a 1 ton
Engine Size
350
I have a 1982 GMC K25 (VIN:1GTGK24M7CF714520), however, VIN code does not seem to match the truck. i.e. it is not 4WD and it also seems to be a 1 ton, possibly due to "camper package" per photo below of sticker in glove compartment. It is a dually, and brake parts align with 1 ton, not 3/4 ton. It has a 4 spd manual (creeper gear plus 3), a 12 bolt rear axle, and comfortable cruise speed is about 55-60, so gears are pretty low. It weighs about 5,700 lbs empty with a home-made flatbed. I've hauled 2+ tons without issue. Overall seems like a 1 ton, not 3/4 ton. Engine is 350ci. And if my 1 ton interpretation is accurate, can I "bumper" tow 10,000 lbs? Input is appreciated!
 

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SirRobyn0

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Truck Year
1984
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C20
Engine Size
305
I have a 1982 GMC K25 (VIN:1GTGK24M7CF714520), however, VIN code does not seem to match the truck. i.e. it is not 4WD and it also seems to be a 1 ton, possibly due to "camper package" per photo below of sticker in glove compartment. It is a dually, and brake parts align with 1 ton, not 3/4 ton. It has a 4 spd manual (creeper gear plus 3), a 12 bolt rear axle, and comfortable cruise speed is about 55-60, so gears are pretty low. It weighs about 5,700 lbs empty with a home-made flatbed. I've hauled 2+ tons without issue. Overall seems like a 1 ton, not 3/4 ton. Engine is 350ci. And if my 1 ton interpretation is accurate, can I "bumper" tow 10,000 lbs? Input is appreciated!
Does the vin code in the glove box match the one in the front windshied and the one on the D/S door or on the title? Start with all that. If the vin on the title doesn't match any of them you have a bigger problem. Also on the drivers door there should be a label with weight ratings. I'm not the best at figuring out what can be towed because it's not implicitly stated on the door sticker, but someone else with a better memory than mine for that stuff will come along I'm sure.

Also can you tow 10K and should you, and is it legal maybe different answers. Any idea what the rear end gearing is other than you think it's low? You really should find out before you attempt to tow.

Listen to Keith, he posted as I was typing. He knows what he's talking about.
 

Autocar

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1982
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K25 VIN, but it's a 1 ton
Engine Size
350
Thanks to all for your quick input and feedback. Later this week I'll triangulate on the VIN tags, stickers, etc and see if they match or don't for some reason. And I'll let you know!
Regarding rear end gearing, is there an easy way to know from the outside other than jacking it up and measuring driveshaft vs wheel rotation?
I bought the truck from my dad about 20 yrs ago, but it had been sitting at his place for some time and he didn't recall anything about the history of the truck, where he got it, etc.
Thanks again!
 

Markmx6

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C3500 dually
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454
I would not use the bumper to tow anything over about 3-4k lbs, but I am assuming you are using a frame receiver and using the term Bumper tow. Then you should be ok for that aspect for 10k lbs.
You also mentioned a 12 bolt axle. Should be 14, I don't believe there were 12 bolt dually axles.

This gets said a lot, but it's worth repeating. Your tow rating is more important for what you can control and stop more than it is for what you can get moving. It is also worth mentioning that when that truck was made speed limits were typically 55 on the highway. So towing a lot of weight over that speed is not what it was intended to do and may not be safe.
 

85K304SPD

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1985
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K30
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383
Please show us the truck that you are talking about. A few pictures would help everybody understand what you are talking about and maybe answer your questions.
I have a K30 SRW and it is rated at around 9-10 K towing capacity. I dont know if I would do it though.
 

Autocar

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K25 VIN, but it's a 1 ton
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350
Here are a couple of pics. And I'll check axle bolt count.....12 was from memory, so maybe I'm wrong.
Towing this much would be very infrequent, and never in a hurry. It's a frame mounted hitch, not bumper. If any more detailed pics would help just let me know and I'll get them. More to come!
 

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85K304SPD

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Nice looking truck. At least it is a dually one ton, for towing some weight. Maybe somebody changed the cab out some time in the past.
 

Bextreme04

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350-4bbl
The cab is from a 8600GVW K25. Single cab, single rear wheel. Looks like someone swapped the cab onto a C30 cab and chassis frame/running gear. You can see if it is a one ton by measuring the height of the frame C-channel. I think the 3/4 ton is 5-ish inches and the 1-ton is 6-ish inches tall. I'm not sure if all cab and chassis models were 1 ton or not.
 

SirRobyn0

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C20
Engine Size
305
The cab is from a 8600GVW K25. Single cab, single rear wheel. Looks like someone swapped the cab onto a C30 cab and chassis frame/running gear. You can see if it is a one ton by measuring the height of the frame C-channel. I think the 3/4 ton is 5-ish inches and the 1-ton is 6-ish inches tall. I'm not sure if all cab and chassis models were 1 ton or not.
Yes, if you want to be sure it's a one ton this would be an easy way to verify. You never know what might have gone on in the past. If it's got a 3/4 ton frame and someone swapped that axle in I personally do not think that would prevent it from being able to tow, 10K but it certainly would be good to know if the frame is lighter duty that you expect.

I always seem to say this and I haven't said it here yet. These trucks were made to work and they were very good at it back in the day. And they can still function well today if you set your expectations correctly. So yea depending on your rear end ratio you'll be topping out somewhere around 55 or 60mph. You will go up hills slower than newer rigs you'll see. You'll need to be more aware of the distance you need to stop and you'll absolutely have to have good trailer brakes, a nice modern brake controller that can sense stopping intensity is very helpful.

Probably 5 - 6 times per- year tow 6K - 7K trailer, loaded with feed, sometimes over mountain passes. My truck is a C20 with the 305 and 3.41 rear end, even with the higher gears I don't run much over 60MPH and some of the ridges in eastern Washington have me in first gear going 20 - 25 mph in the right lane with my hazard lights on. But she does it each and every time and never complains about the trip.

But you also have to keep in mind the law. While in most states you'll never be weighed if you are running over the registered weight limits of the truck and something bad happens whether it's your fault or not you can be in trouble for that. So it's really worth keeping in mind and trying to figure out the legal aspect, so if nothing less you are aware of it.
 

Bextreme04

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The VIN being for a K25 means you are only tow rated for 6k lbs or maybe even less. That being said... my 1980 K25 has the exact same drivetrain and brakes that could have come on a 1999 and earlier 1-ton truck that is rated for 10k lbs of towing or more. The only squarebody trucks I've seen with a higher tow rating than ~6k lbs are crew cabs or specific tow package equipped vehicles. I pretty regularly tow my 6400lb travel trailer with my truck and does just as well with it as my 2011 Suburban that is specifically set up for towing. Like Rob said, you might not be able to keep the same speeds as a modern truck on the hills, but it also shouldn't have much trouble.

Even at 6400lbs, the tongue weight will usually preclude being able to "bumper" tow. Anything over 500lbs is usually going to be a no-go and you will need 10-15% of the total trailer weight on the tongue for stability. 10k will almost certainly require a properly rated frame mounted receiver and a weight distribution hitch. Electronic brake control will also be a must. 10k is not very fun to tow with most modern vehicles TBH... it's gonna be super sucky in your rig.
 

Autocar

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K25 VIN, but it's a 1 ton
Engine Size
350
I know you've all been on the edge of your seats waiting for answers......and I am confident you were right.....someone swapped the cab at some point. VIN on cab door matches title, but there was no sticker in glove box. Rear end is 14 bolt, frame measures >7 inches, and a hint I should have paid attention to before......GMC grill, but dash has (Chevy) Cheyenne logo on it. So I'm confident it's a 1 ton chassis, and I assume from similar era, but I don't know what year for sure (any way to tell?). So I guess if I was ever stopped for being overloaded I'd have some explaining to do. Thanks for everyone's help and input!
 

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Dano500

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The cab is from a 8600GVW K25. Single cab, single rear wheel. Looks like someone swapped the cab onto a C30 cab and chassis frame/running gear. You can see if it is a one ton by measuring the height of the frame C-channel. I think the 3/4 ton is 5-ish inches and the 1-ton is 6-ish inches tall. I'm not sure if all cab and chassis models were 1 ton or not.
I hope it’s ok for me to ask more on this. So, what area of the frame do you measure to find out? I ask because in front of rear axle outer to outer measurement of frame is 6.5-ish, but from above rear axle to end of frame it is 4.75-ish.
 

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