Towing with a 305 V8?

[Velder]

Hello all, looking for some information on towing capacity.

I have an 85 C10, with a 305 V8, four barrel carb, automatic transmission, I think 5 speed.

The Truck belonged to my grandfather, He bought it new, and is completely stock with no mods.

The trailer I want to haul is my welding rig, a 12ft long cargo type trailer that weighs 2k pounds empty, and probably closer to 5k fully loaded. It is not a tall trailer so very little wind sail effect.

My question is will I be able to tow this with my truck? Is there any one out there who regularly hauls with a 305? everything I can find online seems to view it as a fairly weak motor not good for much. What do ya’ll think?

Any and all thoughts, opinions, or suggestions are greatly appreciated.

 

[fast 99]

Will just be low on power. Even a 350 towing 5k will be a slug. Might want to check gear ratio. Good idea to add a tranny cooler.

 

[Ricko1966]

I'll try to find a pic of the last big Azzz load I pulled with mine. Idk how many phones ago so it may take a minute.

 

[Big Ray]

I helped a buddy move his shop many years ago.
87 r10, 305, th350c, 2:73 rear
It sucked balls. Glad it was a 1 time deal
If this is going to be a regular thing I'd go at least with 3:73 gears. 4:10 would be better.
Gears do the work the 305 can't...

 

[Redfish]

@Velder if it's the stock transmission it is NOT a 5 speed. Probably a 4 speed auto, 700R4.

The right gears and the right mindset make the tow vehicle work. A man with realistic expectations and some common sense can do a lot with a 305. @SirRobyn0 has a very nice C20 that has a 305 and he tows whatever he wants to. He lives and tows in an area with higher elevations and steeper hills than I do.

If you want modern power, invest in a modern diesel. But a 5K load should not overwhelm a decently set up square body.

 

[Turbo4whl]

All the towing info will be in the vehicle owner's manual if you still have it. Yes the truck will tow the 5000 pounds, but you also should think about stopping the trailer too.

I would hope the trailer has electric (or surge) brakes. Need the proper electric brake controller in the truck to control the electric brakes.

Electric brakes are better for cost and maintenance, and better performance too. Surge brakes are best for boat trailers, but some regular trailers are built with them as well.

 

[75gmck25]

You need to verify the transmission, but it’s probably a 700R4 four speed. Then take a look at the rear axle ratio and tire height. Some of these trucks had a crazy high rear axle ratio (like 2.73) that sucks for towing. With a 700r4 the preferred ratio for towing would be about 3.91 or even 4.10.

If you tow anything over about 3500 lbs you should have trailer brakes. Otherwise when you hit the brakes hard you will have a 5000 lb trailer trying to push your truck forward, which often results in a jack knifed trailer. Its just simple kinetic energy doing its work.

And I assume you have a real Class 3 or 4 trailer hitch mounted on the frame? Bumper hitches might be labeled with a 5000 lb rating, but I would never try pulling that much with one.

 

[Ricko1966]

I'll try to find a pic of the last big Azzz load I pulled with mine. Idk how many phones ago so it may take a minute.

Couldn't find the pic I was looking for,are you towing 5000lbs daily or occasionally. My engine is stone stock 305 th350 and 3.73 gears. My trailer weighs 2000lbs empty and I occasionally will haul more than 5000lbs. I wouldn't win any races but the truck does it no problem.

 

[Rusty Nail]

My th oughts included servicing the transmission. Dude said add a cooler and that is also good advice.
Then I started to think that 305s are plenty strong and if you set the ignition timing correctly it oughta be a cake walk if you heed all that advice.
Don't forget rear differentials need service too.
Good luck!

 

[SquareRoot]

305 with a 5 speed?

 

[Velder]

Thank you all, that is a lot more response than I thought I would get.
I am not sure why I thought it was a 5 speed, you are right it is most likely a 4, but how do I tell?
@fast 99 I will definitely add a transmission cooler. How do I determine what gear ratio I have?
@Turbo4whl Yes my trailer has electric brakes, I just need to add the control module to the truck. I have the owners manual, but I don't remember anything about towing, but I will double check.
@Ricko1966 I am pleased to hear that yours will do it, could you tell me what type of terrain you pull in? I will be hauling this rig pretty much daily, I am trying to break out as an independent mobile welder, and I opted for the trailer rig because service trucks now cost upwards of $80k even used.
@75gmck25 the bumper pull was stamped 4,000 lbs so I built a new hitch setup for it. If I go for a 4.10 gear ratio, what will that do to my top speed? That maybe a stupid question, but I am still learning about engines so bear with me.
@Rusty Nail yes I need to set my timing, it will be the first thing I do after installing my new carb, before I try tuning. What servicing to the transmission would you recommend? When you say Rear differentials need service to, would you mind elaborating? I have had it flushed since inheriting it, but that is all.
@Redfish thank you for the encouragement, I know that it will never have the power of a true hauling truck, but those, like the service trucks, are beyond my financial ability at the moment.
Here are a few Pics of the truck and trailer in question.

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[Rusty Nail]

Man that's a good lookin truck.

" flushing out" the differential should prove adequate. Transmissions require similar service but one must also remove the transmission pan in order to replace the filter inside The ONLY way to exchange the fluid inside of your Torque Converter is to attach it to a pump. The old fluid flushes out until it can be seen as clean. Perhaps a dealership would accommodate you, or a "quickie lube" place LIKE a Valvoline Instant Oil Change will offer a "transmission service", but make certain to say you'll want the old filter back to prevent being screwed.
Pick some reputable shop and ask around about it. Transmission fluid does not last 30 years and it sure as heck isn't, goin to take much towing to prove it.

Transmission service costs much, much less than a new transmission. After bad wear patterns start they can't be undone.

 

[Ricko1966]

Sir some things you need to notice,my truck has 3.73 gears and in my opinion to daily that rig you are going to need comparable gears. I'm on mostly flat land. The steeper the gears you go the more your milage drops as does your highway speed. I don't think your truck has the right combo to daily drive pulling 5k. If that were my intentions with that Truck I'd run less gear,a th400 or 4l80e and more engine a 350 at minimum. The bigger engine has more potential to make low end torque,which without steep gears you are going to need I tow occasionally not 5k daily. I also think using that truck as a daily pulling 5k is going to wear it out fast. And pulling a trailer daily would suk. I think I'd try looking for a g30 box truck, or a 1 ton diesel flat bed,to make a daily work horse welding rig out of. I found these 2 in seconds and I think either would be a better choice, better brakes,better suspension and no need to pull a trailer,scout around. Keep your Square as the nice truck that it is. The 6.2 box trucks get amazing gas milage,for as big and heavy as they are

 

[Ellie Niner]

@Velder - Check your SPID (the label inside the glove box); it will tell you what you've got for a transmission and final drive. Most of the mid 1980's "1/2 ton" trucks had stupid tall gearing by default... Usually a 700R4 and 2.73 for 2wd, and 3.08 in the 4wd. What will 4.10's behind a 700R4 do to your top speed? Absolutely nothing. You'll still be at around 2.87 in overdrive, though it'll be howling at highway speeds if you tow in direct (3rd gear), which I believe is what GM recommended.

I've had my '86 K10 for 22 years, and my initial plan to build a 327 to replace the 305 when it died, has gradually morphed into rebuilding the 305 and keeping it around instead... and the 305 just keeps on going. It's starting to get a bit tired, but keeps clocking in and doing the job, and can return poor fuel economy (as opposed to horrid) when you're cruising empty... say 14mpg. 15 or so under perfect conditions. It feels like it has slightly more beans than my 1975 GMC C25 with a 350.

I tow a wide body car trailer from time to time, which weighs about 2000lb empty, and add 3000-4000lb worth of car. Truck weighs ~4800lb. It's a stock K10 on 32's, with the usual 700R4 and 3.08 gears. I'm at around 2400' elevation and usually on level ground, and tow in town and up to about 65mph on the freeway. Loaded down, I have no problem getting rolling, even going uphill. It still pulls okay in 2nd gear, then power falls off once it shifts into 3rd. I'm able to cruise at 65mph fairly easily, though headwinds and hills are handled in 2nd gear with your foot pasted to the floor; I'm always able to keep up enough speed to not impede traffic.

tl;dr: it's not prime tow pig material, but does the job well enough that I'm not afraid to use it. The compromise is worth it to me to achieve better than 10-12mpg unladen. Your Mileage May Vary, or something like that?

-First photo is the trailer I usually pull, and the second one was a little piece of crap we borrowed one time to haul that '61 Lark parts car. Can't remember why.

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[Ricko1966]

@Rusty Nail and everyone else that believes clean transmission fluid is good preventative maintenance. I learned a long time ago to do a fluid and filter,while the pan is off install a pan with a drain plug ,or an add on drain plug to your pan. Now you can do a spill and fill on the transmission,do them often enough and you will have replaced 99 percent of the transmission fluid. Now you can do a spill at fill at every oil change and you will always have pretty good transmission fluid.