Towing with a 305 V8?

Just got a package of 4 O2 bungs for this very purpose.^^^^^^^^ Hole saw and a welder, good to go

Like others said, check your SPID sheet (If present). I have an a '85 C10 that left the factory with a 305 mated mated to a 3 speed automatic th350. I also have an '84 K1500 that has the same engine but had a 700r4 from the factory.
If your SPID sheet is missing, look at the gear selector on the column. If the letter D has a box around it, its a 700r4, if not it's a TH350 (Note: some of these trucks have had transmission swaps and the owners didn't bother to change the gear selector indicators, if you suspect a transmission is not original, get under the truck, take a picture of the floor pan and use it as a reference. All GM Transmissions have slightly different floor pans.)

As for towing, the 305 is as useful as any other small block V8. As said by others, it's the rear end gearing that'll make or break you.

So the truck “looks” to be in great shape. Is it equally as reliable mechanically?
Using an antique truck and especially without much knowledge to keep it running is a recipe for disaster when relying on it for daily heavy duty use (yes that trailer is about all that truck would ever want to tow capably and comfortably even on its best day).
Possible? Sure.
But terrain, miles, frequency of use all factor in when you start a little small in the horseponies department and it’s an old truck to boot.
When I think Texas and mobile welder in the same sentence I think potentially hundreds of miles towing. Daily.

All depends on the truck. And if the truck is good, it will still be slow.

And good point. 305 or 350. 70s or 80s models doesn’t matter much. Both in stock form were/are more anemic on horsepower than anything made in the last 30 years.

We bought a 23' bumper pull travel trailer in '78, after Dad bought his '75 Sierra Classic. The people we bought it from had a '73 Burb with a 454 that they towed it with. We should have bought the Burb too, but couldn't swing 3 payments simultaneously. We towed this trailer a few times with the Sierra Classic, but the smogger 350 wouldn't do it with the AC on. We towed it a few more times with our '78 GMC Sierra Heavy Half, also a 350/QJ but without the smog stuff and cats That truck also got headers, duals and glasspacks.
It towed the trailer much better than the '75. We also had to move a bunch of old cars on short notice in spring of '88, and used the '81 Sierra with a 305 2 barrel(cause that was the truck that was running!). Was about a 12 mile round trip from one storage to the other one, and the Lil Brown Truck did it okay. Flat ground in central Texas, a few exits apart on I-10, and down a country road a little way. On hills it probably wouldn't have done as well. Trailer was a lightweight flatbed race car hauler, borrowed from a friend who was getting one of the cars. I think the heaviest cars were a '67 Riviera, a Chevelle station wagon, and a couple of fullsize Chevy 4 door sedans. Here again, different terrain or distance would've been different results.
For comparison, our '90 GMC R2500 Burb hauled several cars including a '77 big block C25 Burb, across town on a car hauler, no issues. That Burb had a TBI 350 with a TH400 and 4.10s in a 14 bolt SF rear axle. We regularly hauled a ton of stuff to swap meets and shows in that truck.

Yes but unfortunately the OP will find there is no plug on his pan. Those trans pans with drain plugs are available in the aftermarket only.
There's one on my truck....but only because I put it there!
It holds around 4 quarts worth. thanks for the add.

@Velder
Your pic looks like you just painted it, do you have a bumper/hitch for it?
What do you tow the trailer with now?
My suggestion was gonna be hook it up and see how she does.
Some might be totally satisfied towing with 1980s small small block smogger power, many will not be.
In general, it’s going to be a challenge to press a 40 year old truck into daily heavy work duty regardless of whether it’s anemic under the hood or not.
Guys like @SirRobyn0 are the exception, but he has several things going for him. Not the least of which is that he’s a certified mechanic, so diagnosis and repair come much easier and cheaper to him than someone who is still trying to figure out how to tell what gears it has.
Just trying to add some reality to this. Maybe save yourself some headaches and keep the nice old truck nice. Lots of $10k or less lowish mile GMT 400 HD and half ton trucks out there in good shape. (Gotta find them though. Ain’t like going to the car dealer and picking out your favorite and driving it home though.)
Low altitude and only a few little hills if you’re lucky enough to not live in the 90% of Texas that is board flat will help. But think about the days you’re gonna be headed home at night westbound with a 30mph head wind. How big of hurry you in? Those 80mph speed limits will leave you looking like an Amish buggy while the rest of the traffic flys by at 90mph.

Thank you to every one that has commented, lots of great info here.
Checked my SPID, (should have done that before posting) Yes my transmission is a 4 speed automatic, and my gear ratio is 2.73
@Grit dog You are correct, I have just repainted it, and that picture was just after putting the bed back on. so it didn't have it's bumpers on yet. I fabricated a hitch for it, so theoretically I could try it, BUT, right now I am having trouble with my quadrajet. on my first test drive after reassembling the whole thing, it would drive, but had no power, I literally had my foot to the floor, and could just barely make it up a small hill, belching black smoke. I think the choke was not opening? Any ways, I want to put a new carb in it, but how much more I spend on it depends on if it is capable of doing what I want it to.
And you are also right that I am a welder not a mechanic, I have done all the work on it myself, (apart from the flushing of the diff. and the trans.) but I just sort of learn about a topic as I go. And yes I foresee hundreds and hundreds of miles towing. looking for a lightly used late model truck is sort of my backup plan.

Here is where I am at;
I have already built my welding trailer, and need a reliable truck to haul it with. I decided to go with a trailer rig because it keeps all my equipment enclosed out of the elements, and allows me to have a lot more equipment on me than a service truck. I never thought of a box truck, wish I had now, but I have already built the trailer. I really don't mind pulling a trailer just need a vehicle to do so. So any way the truck has several mechanical issues that I have been addressing over the last few months. the original paint was peeling off all over, so I stripped it down and repainted at the same time. My grandmother would always run the cheapest fuel, and then it sat for about 5 years without running, so, rust in the fuel tanks, gunk in the carb.
I rebuilt the carb, and replaced both fuel tanks and all the fuel lines. like I said now she will run, but not well, I think it is just the Carb but I don't know for sure. She only has about 60k miles on her, so there shouldn't be to much wear?

@Ricko1966 Thank you for the idea of a box truck, that might prove to be the answer, what website did you pull those off? I have only looked on Craig's list. I assume one of those would pull a trailer with no problem?
I have had the transmission flushed, but if I do it again I will certainly add a pan with a drain plug.

What kind of distances/ speeds/ elevations/ are you anticipating for your work?

I don't think you are going to be very happy on the highway as you can't tow in OD. Maybe a 1000 pound trailer but much more than that you are relegated in 3rd/ 1:1 ratio. The 700r4 has a good steep 1st gear that should help you get going and you might get away with less rear gear for around town stuff.

Short term, you can do your work. Long term, need a different truck.

He said 2.73 and you can  hear the crowd groan. I know where this thread is headed next.
Good call Benny.
Dude don't tow in OD. You will have to keep the transmission in 3 when pulling the trailer or it will die. Or it will die. Or it will die.
You HAVE a reliable truck already, this is the journey to modify it to fit your needs. There is no reason to "keep it nice" in my opinion, it was built and designed for work. The needed modifications are attainable easily for well beneath the cost of a different truck...and you would get to be famous for driving around a bitchin classic that Noone will ever stop commenting on. It's beautiful.
Maybe you can think up a way to incorporate it into the business or logo, something will make itself evident. Ask your grandma for ideas and pay attention to your dreams. Keep a notepad next to the bed and write things down the MINUTE you wake up. Those thoughts are often VERY good ideas that become quickly lost forever.

If grandma liked cheap gas - read ethanol - that is easily remedied and sure as heck not a reason to inherent a car payment. Ethanol degrades rubber in time and that is what has happened to the truck and carburetor, that's all. It's no big deal and not a reason to stress. The rubber was 40 years old, you can get replacement PARTS much easier than a replacement TRUCK. It's easy.
We hold a world of knowledge in this website and it is crowdfunded by a huge group of really great folks that want to help you see the truck continue to suceed. Mostly because we like those trucks and they're fun to play with...

** We need more information about the carburetor ** (read pictures) and I guarantee there is already someone making plans to suggest for your 2.73s because im afraid they aren't compatible with your needs. At all.
2.73s and overdrive are built for grandmas and good gas mileage - brother it's goin down from here. Blow it off right now, the gas mileage?...it ain't never comin back.

And were off...

@Velder, if you have another vehicle to drive, send that Q jet off to get rebuilt by a known Q jet builder. Stay away from commercial Q jet rebuilds that are sold online and in big box stores. They are junk. If you need a carburetor now and can't wait for the Q jet to get rebuilt, the Edelbrock 1406 works quite well on a 305.

Velder said:

Thank you to every one that has commented, lots of great info here.
Checked my SPID, (should have done that before posting) Yes my transmission is a 4 speed automatic, and my gear ratio is 2.73
@Grit dog You are correct, I have just repainted it, and that picture was just after putting the bed back on. so it didn't have it's bumpers on yet. I fabricated a hitch for it, so theoretically I could try it, BUT, right now I am having trouble with my quadrajet. on my first test drive after reassembling the whole thing, it would drive, but had no power, I literally had my foot to the floor, and could just barely make it up a small hill, belching black smoke. I think the choke was not opening? Any ways, I want to put a new carb in it, but how much more I spend on it depends on if it is capable of doing what I want it to.
And you are also right that I am a welder not a mechanic, I have done all the work on it myself, (apart from the flushing of the diff. and the trans.) but I just sort of learn about a topic as I go. And yes I foresee hundreds and hundreds of miles towing. looking for a lightly used late model truck is sort of my backup plan.

Here is where I am at;
I have already built my welding trailer, and need a reliable truck to haul it with. I decided to go with a trailer rig because it keeps all my equipment enclosed out of the elements, and allows me to have a lot more equipment on me than a service truck. I never thought of a box truck, wish I had now, but I have already built the trailer. I really don't mind pulling a trailer just need a vehicle to do so. So any way the truck has several mechanical issues that I have been addressing over the last few months. the original paint was peeling off all over, so I stripped it down and repainted at the same time. My grandmother would always run the cheapest fuel, and then it sat for about 5 years without running, so, rust in the fuel tanks, gunk in the carb.
I rebuilt the carb, and replaced both fuel tanks and all the fuel lines. like I said now she will run, but not well, I think it is just the Carb but I don't know for sure. She only has about 60k miles on her, so there shouldn't be to much wear?

@Ricko1966 Thank you for the idea of a box truck, that might prove to be the answer, what website did you pull those off? I have only looked on Craig's list. I assume one of those would pull a trailer with no problem?
I have had the transmission flushed, but if I do it again I will certainly add a pan with a drain plug.

Click to expand...

I didn't go to a website I went to Google and typed in g30 box truck. Didn't try real hard and those popped up. Now realistically towing a trailer everyday,especially one that weighs as much as your truck is going to get old fast,I do it occasionally and not if it's raining,or snowing. And as for pulling a 5000lb trailer daily,I'd much rather use a C or G 30. Stronger everything and setup from the factory to pull the kind of weight you are talking about. If I was dead set on pulling that kind of weight daily I'd want a minimum of 3.73 gears ,and I'd make sure I had all the best brake components I could find,best,not cheapest. One more thing who decided your carburetor was the problem? That's always everyone's first go to,but have you checked engine Vacuum? If you have even just a decent size vacuum leak espe0cially with a properly set up q jet, or properly set up holley it's going to go pig rich,with a low vacuum signal the carburetor thinks you're floored so it' adds gas like you are floored.

A decent square body pickup was out of my price range unless I got one that needed a LOT of work done to it. Being also familiar with the 400 platform as well as the square body trucks, I have been a member of GMT 400.com for almost 4 years now. Through that forum, I had been looking for a 2500/3500 pickup; the 1500 ones are too expensive and have a few known issues I'd rather not deal with. Last July I found a C3500 crew cab long bed, that has had a couple of problems I've gotten resolved. '97 with just over 120K on a Vortec 5.7 like my 400 Burb. Point being, it'll haul anything I ask it to, I'm not hauling big travel trailers, just an enclosed utility trailer or eventually a truck bed trailer and maybe a car hauler. These are old enough now, that they're distinctive too. I get lots of compliments on my truck, and a few months ago it won Truck of the Month.
If you can't resolve the issues with your square body truck, the 305 and its tall rear gears, a 400 might be the way to go. TBI 2500 with a 5.7 would probably haul your welding trailer rig well, and a Vortec 5.7 has 50 more HP to do it with.
I also agree with the others about checking for vacuum leaks and damaged lines. QJs are great carbs, but they need clean parts and good gaskets and seals like any other fuel delivery system. My Dad rebuilt several QJs on our older vehicles, with success, so it can be done if necessary. When they were new, that was the most precise carburetor out there.
So don't give up on your square...but there are other cool GM options w/o getting into big payments.

Tall gears kill 700r4s...along with heat.
I'd put a shift firming kit in while it's out. Eliminates the wear and heat caused by sloppy shifts. That, lower gears, (3:73 or4:10), and a 25k lb trans cooler and you'll be set. The 305 will tow until the cows come home...

@Bennyt Currently I am in Texas, so basically sea level and long distance, and ideally I would like to go at least 65mph. the speed limits here are usually 75 and most people drive 80+.
That being said, I am actually trying to relocate to Montana, so there could be mountain passes and such in my future. distance and speed are about the same. Most of my experience is in repair/fabrication, so I am anticipating lots of smaller jobs scattered around, rather than a few large new construction jobs.
@Rusty Nail, I love the idea of incorporating it into my logo, that would be really cool. I am definitely not opposed to swapping differential gears, or making some mods here and there. Any recommendations would be welcome. I read somewhere that putting in a larger intake manifold and bigger carb would boost HP. anyone know if that is true? How about different exhaust manifolds? De-smoging the engine? are these all things that only racers do?

As to the quadrajet, I am the only one who has diagnosed it as the problem, and I could be wrong. however I am reading between 20-25inHg with a vacuum gauge, and I have replaced pretty much every hose. On my test drive every thing seemed alright at first, then while climbing a small rise I was just crawling, had my foot to the floor, and was belching black smoke. pulled the air filter off, and it looked like the choke was closed. I have it set fairly light, and there is power to it. It would seem that it closed somewhere along the way? By the time I got back, the truck was Idling VERY rough. I planning on replacing the quad with a Holley for ease of tuning and so I can eliminate that as a source of trouble. I have completely torn down and re built the quad, chem-soak, very light soda blasting, installed brass bushings on the throttle shafts, new gaskets, new accelerator pump, left in the old ported-needle-seat 'cause I thought that would help with fuel delivery, (@Ricko1966 mentioned in another thread that the seat without windows could help with fuel drain-back issues but I didn't know that at the time) New needle, new float set to the specified height, Reassembled the whole thing put it back on, had a fuel leak around whatever that electronic solenoid thing is, took it back off, ended up putting a small amount of gasket maker on that edge and stopped the leak. I adjusted the Idle mixture screws for highest vacuum, and I set the fast and curb idle to to the recommended rpm (I added a aftermarket tach). She usually starts right up and idles smooth, but every once and awhile it will fire up, race a little shake and die, all about that fast.
I thought if I replaced with a Holley, then I could set the fuel level externally and tune the engine knowing that the carb is not the problem. Any thoughts on that?
Sorry to write a book on here but someone asked for more info didn't they?
Here are a few pictures of the quad, pre disassembly; I will try to get some after picture uploaded later.