Towing?

[JPCY72]

Hey guys I just got a 72 k20 Im looking to tow with it I noticed that it had a GVWR of 7500 it has RPO codes for heavy springs front and rear. I also have the Eaton rear and 4.10 gears, it has the 350 th350 and thats it. Id like to tow a 2 or 3 horse trailer usually about 4k unloaded and 6-7k loaded.Thanks guys

[69halfton]

is it a hitch or a fifth wheel trailer?

if its a fifth wheel no problemo..

id be a little more carful about the standard trailer hitch..although its still very do-able.

heck, its a 3/4 Ton, thats what they are made to do

[69GMCLonghorn]

Agreed! Tow whatcha like! Just make dang sure it stays attached to the truck.

And of course, make sure the ol' brakes are in top condition! Get a trans temp gauge if you don't have one already. It's a small price to pay to save your tranny from grenading.

Send pics of it loaded up!!

[PanelDeland]

Tranny cooler, and maybe be sure it has a 4 core radiator.Do use a quality hitch.

[JPCY72]

thanks guys, what do you recomend for a hitch the one in the lmc catalog is only good for 5k I need at least 8k do I need a class 4? Also what would you do as far as motor trans combo as i may need to rebuild it sometime? so far i have an HEI dist and a performer manifold I also picked one of those Xtreme 4x4 cams, is 10-1 streetable towing? and what about stroker saya 383 I have a 400 rotating assembly that I can use soo many options and


Transmissions also?????
I thought about the 700r4 but it doesnt make sense since I cant use 4th towing and it almost always has some kind of load in it..... Im going to put 33s and a 4 inch lift and thats it I figure it should be good with the 410s.

Tell me what ya think..

['72customdeluxe]

If hauling all of the time I would stick with an old school trans since like you said, it won't be in overdrive. 10-1 compression would be good with an aftermarket cam and premium fuel. It would likely be more cost effective to use an aftermarket 383 crank than machining the 400 crank for a 350. And it's not internally balanced. A 383 with a smaller cam and 10-1 compression would make excellent torque.

[69halfton]

if your doing lots of towing, i would think about making the swap to a standard trans.

I like them better because once the clutch is out, have no fear of putting your foot right to the floor... im always a little nervous about automatics when towing for some reason.

A nice four speed truck tranny with a bull-low granny gear would be great for pulling away with a horse trailer in tow.

I have a 383 stroker in my truck and tow a circle track racecar around weighing about 6500 lbs total, and towing it with a shortbed halfton

not going to lie, the short wheel base and light duty truck makes it a handful, but from a power standpoint, i cant even tell the trailer is there. then it time to stop, thats a whole other story

[69halfton]

btw, the 383 is also a 10.5:1 motor.

[71swb4x4]

Trailer brakes, trailer brakes, trailer brakes.

[WorkinLonghorn]

Definately a tranny cooler in that climate. You're up at the max combined weight with that set-up.That TH350 could probably use a shift kit too.

Class 4 weight distributing hitch.

[El Jay]

Originally Posted by 71swb4x4

Trailer brakes, trailer brakes, trailer brakes.

Originally Posted by WorkinLonghorn

Definately a tranny cooler in that climate. You're up at the max combined weight with that set-up.That TH350 could probably use a shift kit too.

Class 4 weight distributing hitch.

^ X 2 ^ with these guys.

Since you said you'd like to tow a 2, or 3, horse trailer; that has me thinking you may not have the trailer yet.
If you don't, seriously consider a "goose neck" trailer so you can get the hitch directly of the rear axle.

WorkinLonghorn, izzat the Peterbilt from Duel in your avatar?

[69GMCLonghorn]

Originally Posted by 69halfton

if your doing lots of towing, i would think about making the swap to a standard trans.

I like them better because once the clutch is out, have no fear of putting your foot right to the floor... im always a little nervous about automatics when towing for some reason.

A nice four speed truck tranny with a bull-low granny gear would be great for pulling away with a horse trailer in tow.

I have a 383 stroker in my truck and tow a circle track racecar around weighing about 6500 lbs total, and towing it with a shortbed halfton

not going to lie, the short wheel base and light duty truck makes it a handful, but from a power standpoint, i cant even tell the trailer is there. then it time to stop, thats a whole other story

AH YEAH! Someone finally stepped up with same thought process that I have. How often do you hear about someone grenading a manual trans? Sure it happens, I know, but how often? If you have the option to go manual, DO IT! No freakin' trans coolers, no trans temp gauges, no shift kits, no stall speeds, etc... Just keep a good heavy duty clutch in it and GO! And plus, then you could opt for an NV4500 WITH OVERDRIVE and actually use it without fear of Murphy tapping you on the shoulder in the middle of nowhere.

[49gmc]

^agreed^

or the muncie sm465 (no overdrive)

[69GMCLonghorn]

I'm so tired of taching 3000 RPM on the highway... If I EVER have to put a tranny in my truck, it's going to be idling at 100 MPH!! I knew a guy with a mid 90's 454 Chevy dually with a 5 speed trans and a gear vendors. We had about 3 tons in the bed up a LONG onramp. He used about 8 of the 9 available gears and had power all the way up to 70 MPH without every getting above 3000 RPM. THAT is what I want!

[JPCY72]

Hey Guys,

I scored a 400 standard bore block and rotating assembly and new heads... I will install some new pistons 9.5-1 and new bearings. I cant decide what cam to use... comp has a 4x4 cam but the 268h is so close but has more lift and my buddie has it in his blazer with 308 gears and it does fine so im sure unless you guys think Im not over camming it, plus its a 400 so it can take more cam than a 350. As far as the trans its gonna need a shift kit and unless the truck really has 54000 miles which isnt out of the realm of possibilty cause it runs great just burns some oil. the trailer we dont have yet thats why I want to make sure i have the right stuff so if i happen to get a heavy trailer I dont have to worry.

[LilTruckMan'69]

I just picked up a C20 (350/Turbo400) for the same reason. Different load though. Car trailer & small 4x4 rig.



Thanks for posting the thread. I'll be watching.

[mrein3]

I find it funny that folks are saying you should switch to a manual trans for towing. I bought my truck with a three speed manual and use my truck mostly for towing my boat. One of the best things I did for my truck is to switch the 3-speed manual out in favor of a well built th350. The only reason I didn't go with a 700r4 is that while towing my boat I'd be using drive, not overdrive. I still may swap the th350 in favor of a 700r4 for the few times I do drive it on the freeway without my boat.

With 373 gears I'm just under 3000 rpms at 55mph.

I will admit the main reason for an auto in a boat towing rig is for when I'm at the boat ramp. I rebuilt the emergency brake before the auto switch but still feel a whole lot better about the truck in park and the brake on verses the truck in neutral with the brake on.

My mileage did suffer with the auto. I used to get up to 13 not towing, 10 towing. Now I get 11 not towing and 9.5 towing. A 700r4 with a lock-up converter should get closer to the numbers I was seeing before the swap.

For sure do the shift kit. I had my rebuilder install one in my th350. The shifts are nice and firm.

[JPCY72]

Also the reason I cant switch to a manual is the wife wont drive a stick and shes gonna be towing with it mostly. I used to drive a stick everyday I get tired of it and anyways I think a well built auto is much better and more consistent than my hand and foot are.

[mr48chev]

My truck is the two wheel drive equal to that truck and my uncle and cousin towed her horse trailer all over the northwest with it when she was the local rodeo queen.

I would for sure have the big four row radiator and an external trans cooler. You have the low range in the transfer if you need the extra grunt to pull out of a hole.
I tow my 21 ft sailboat with my truck and it handles it well.
I haven't weighed the boat and trailer but it think they are a bit over 4000 lbs.

I like the 383 idea or a 400 might be a good swap if the engine is tired.
I still have my original 4 bolt block and the plan for it is going to 383 with Vortec heads and performer and/or maybe going fi with it.
And as others said be and sure to use a well mounted top quality receiver type hitch.

[WorkinLonghorn]

The original GM Data Book recommends the auto trans for all "camper" applications and all towing. On the "Motor Home Chasssis" it is mandatory.
The maximum trailer weight for different engine/trans combo is listed as higher with the auto trans in all cases.

[69halfton]

The original GM Data Book recommends the auto trans for all "camper" applications and all towing. On the "Motor Home Chasssis" it is mandatory.
The maximum trailer weight for different engine/trans combo is listed as higher with the auto trans in all cases.

the reason for this is because factories have to take into account the pure idiots that drive their trucks and cars when new.

many people bought these trucks not knowing a thing about what goes on under the hood and in the drivetrain. the factories rated the autos for more trailer weight then standards because people were buying standard shift trucks, and then burning the clutch out of them in less than a year, simply because they didn't know how to properly tow with a standard transmission. also for pulling away on hills, it avoids rollback etc. The big wigs thought that the average idiot would be in more control of an automatic truck then a standard.

consider this...why is it that almost every simgle semi truck out there, even to this day, is built with a standard transmission? its not been until really the last 4 years that you have been able to find an automatic in a full size semi truck, and even then they are the ones that are spending most of their time in town. I would buy the guy a beer that finds a highway truck, on the highway, that runs trains down the interstate all day long with an automatic in it. they dont buy it because they wont last. nothing will last longer then a locked up clutch, and gear-to-gear contact all the way to the pavement.

[El Jay]

Originally Posted by 69halfton

the reason for this is because factories have to take into account the pure idiots that drive their trucks and cars when new.

many people bought these trucks not knowing a thing about what goes on under the hood and in the drivetrain. the factories rated the autos for more trailer weight then standards because people were buying standard shift trucks, and then burning the clutch out of them in less than a year, simply because they didn't know how to properly tow with a standard transmission. also for pulling away on hills, it avoids rollback etc. The big wigs thought that the average idiot would be in more control of an automatic truck then a standard.

consider this...why is it that almost every simgle semi truck out there, even to this day, is built with a standard transmission? its not been until really the last 4 years that you have been able to find an automatic in a full size semi truck, and even then they are the ones that are spending most of their time in town. I would buy the guy a beer that finds a highway truck, on the highway, that runs trains down the interstate all day long with an automatic in it. they dont buy it because they wont last. nothing will last longer then a locked up clutch, and gear-to-gear contact all the way to the pavement.

I'm not trying to hijack, or start an argument.
But perhaps it's a bit easier to keep a diesel engine up in its power band with a 9, 10, 13, or more speed transmission than it is with an automatic.
I do know some "rock haulers" that run autos in their 10 wheelers, and I've seen more than 1 quarry truck with an automatic in it.

[69GMCLonghorn]

The debate between auto and manual could and has gone on for years.

Manual: I feel you have more control. As prev stated, no shift kits, trans coolers, trans temp gauges, etc.

Auto: If you don't like the 3rd pedal, it's great. They are higher maintenance, especially if you work them. You have to keep the fluid/filter changed. Plus, as stated by others, start stashing away money for a cooler, shift kit, trans temp gauge, & who knows what else. Also, unless you manually downshift, you will typically go through brakes more frequently with an auto under a load.

Just some considerations to knock around.

[WorkinLonghorn]

Personally I like a manual with a deep 1st gear.If I'm on a steep incline with a large trailer behind me and traffic is stop and go,I think I'd rather have the torque multiplication of an auto trans torque converter.

[Mike C]

I'm with WorkinLonghorn, the granny gear 4 speed the way to go. At least on an older truck. I had a 70 GMC that was also a 7500 GVW equipped truck (max for the platform. Get a class IV receiver and possibly a load distribution hitch. Mine pulled 6000# quite well. I have had 2 other 70 3/4 ton GMC's and they were 6200 and 6600 GVWR respectively.) Mine was a 402/TH400 with 3.54 gears.

I can see how the above poster who swapped the 3 speed manual likes the auto better. The 1st gear of the 3 speed is the same as the 2nd of the SM465. And you really do need first with a load on an incline.

At the boat ramp, my Jimmy NEVER spins the tires using first gear to pull the boat out and 2 wheel drive. The truck would stall up and start to spin the tires on the ramp, leaving you stuck. I had to be hauled up the ramp with a strap a couple of times. Embarrasing. Another advantage to the manual trans is lower RPM on the highway compared to a non-lockup automatic. I bought all the parts to convert to the SM465, but sold the truck. With that said, htough. I REALLY like the Allison behind my Duramax.